Great video, thanks. I'm planning on making a mess of my house this summer in Sweden as it needs re-rendering. I think the previous owner had the local kindergartan do it 5 years ago and it's dropping off the brick in chunks. I figured I'll do it myself because at least if I screw it up I can call it art (and it'll be cheaper to re-do it). The last quote I got for the place was around £10K (two storey house about 12m x 6m - 3 sides need doing) and these days I have more time than money. TH-cam is a godsend. Thanks again.
Better than I thought it would. I did the side that was in the worst condition in May. Took a week and half to get all of the old plaster off. The bricks weren't in the best condition so I re-pointed a lot of the wall to strengthen it. The harl coat was fun. It took a while, and a few covered cats, to get the technique down. I could hear the neighbours grumbling amongst themselves wondering what the hell I was doing. I got pretty accurate by about halfway through the wall. The scratch coat was good practice with the trowel. My home made scratcher took a bit of adjustment to get all the nails the same length. I then put a fine coat on top which looks great when the sun is directly on it, or if it's in shade (looks brilliant in the dark), but looks like the surface of the moon when the sun is shining straight across the surface, so it'll need another fine skim coat (I think I'll need to use a darby this time, hopefully the lime will stick as well as the layers that are on now do - maybe a light harl coat first to provide a key). Anyway, that'll happen in August. After spending the whole of May working on the wall, I'd had enough, and my trowelling arm was knackered - literally became too painful to apply the lime. So a fresh attack in month. And thanks to MikeWyeAssociates for your videos. Turned a complete novice into an amateur (I've had quite a lot of compliments on the wall when the sun is in the right place :-)
It's taken me 5 tries to answer your post! Karma? Anyways, good on you for getting it done. I've had those visually obvious learning curves myself. Right now I'm trying to see if I can cover a cinder block retaining wall. Wish me luck.
Good luck. Half the job is plucking up the courage to get stuck in. I'm sure it'll look fantastic once you're done (and you can't go wrong when you have Robert Plant as your teacher :-)
Thank you very much for the video. I plaster a fair bit with cement and modern plasters and use lime mortar for stonemasonry and brickwork and this is a good example of rendering with lime mortar.
Unfortunately we don't have a video showing the mixing process but if you have specific questions relating to this you can email us at sales@mikewye.co.uk Regards, Ryan @ Mike Wye
Great video. I need my house lime rendered as it currently got 3 different render finishes. I guess each wall could be broken down into sections to make it easier but the final coat would need to be applied in one go across the entire wall? Am I right in my thinking there or could the final coat also be broken down into smaller sections?
Hi Pete, the backing coats could absolutely be applied in sections. The float coat would be better applied on each face in one hit to avoid visible joins, if you have downpipes then these can be used to hide these.
I couldn't make out what you said about the additive to the mixture at the beginning. Could you tell me what that is that you said was made in Cornwall?
+Kevin Wixson The additive is generically known as a pozzolan which is a clay additive sometimes used in lime render and plaster coats in order to achieve a slight hydraulic set. We tend to add it in where we want to improve the resilience to frost and adverse weather conditions, or where the wall is damp. The pozzolan from Cornwall me mention is Metastar. Unfortunately this clip is a few years old now and Metastar is no longer produced. We supply a similar metakaolin called Argical, from France. Other materials can act as a pozzolan with varying results, such as brick dust, ash and GBFS.
Mike Wye hi, love your videos. I have 180m2 of external Hydraulic Lime render to do on a Grade II. The architect has spec'd for no hair in any of the coats, I think he's just copy and pasted the method from Wikipedia or something! Please tell me what the gauges of the coats you use are and also which ones you add hair to. Many thank!
Great video, thanks. Would this same process apply to a chalk cob wall? This is what I have in Hampshire and it needs rendering so I'm thinking of using this video as a model.
Hi there, Professor, thanks for your comment. This is purely a training/demonstration wall we built at our premises many years ago, and it had no DPC. You are correct to identify this as a potential issue in "real World" work, where we would always be conscious of such features and avoiding the creation of moisture bridges. Good observation 👍
Hello wanted to ask, in your opinion is possible to use cement (for better setting) with hydrated lime and sand (0,5:1:5 ratio) for rendering a brick wall layed with lime mortar, as it is quite difficult to find hydraulic lime in our region? Or even small amounts of cement will trap moisture, make wall unbreathable and ruin the bricks? Kind regards
Hello. A 6:1:1 mix (sand:cement:hydrated lime) is a relatively common mix in the UK but we still consider this to be a weak concrete mix rather than a lime mix. I understand that it may be difficult to source hydraulic lime or lime putty where you are, so a mix like this will be a better option if you have no other option. Despite some information out there, concrete mixes do offer some breathability and have hygroscopic properties than can help to wick moisture away from the fabric of the building - it's just much lower than lime by comparison. As a general rule, the stronger the mix the less vapour permeable it will be. So choosing a weaker mix is always best. It is also possible to "re-hydrate" a hydrated lime by soaking it and creating a putty. However this putty as a binder is generally considered inferior to a fully matured lime putty and definitely not comparable to a hydraulic lime. If you do have to use a mix containing cement and are concerned about breathability, then the use of a breathable paint finish will help the render to work as efficiently as possible. Our recommendation would be a silicate paint which can be applied to both lime renders and cement renders, and is highly breathable and durable. I hope this helps.
Hi Sam, the video refers to "Metastar" which is a pozzolan we used to supply. This has now been superseded by Argical M1000 - details here: www.mikewye.co.uk/product/argical-pozzolan/
Thanks for the video I have a question for you my neighbor today was putting this product on their Garden Wall I thought it was paint at first but they told me it was lime it was very white in color and very watery they were applying it with a broom but there was not any residue really left on the broom after some time it dried to a hardness and it was very white I'm living in a different country so I'm not exactly sure but I was wondering if you've ever heard of something like this I saw the powder online they call lime powder I'm going to ask the neighbor but I'm thinking to buy some because if I can just mix it with water without having to add any sand that would be a lot easier for me to do on that way I can use it on my own wall
Thanks for your comment. It sound like your neighbour was applying a limewash or "sheltercoat" to the wall. Limewash is a suspension of lime in water, and sheltercoats are often similar perhaps with the addition of some finer stone dust/powder. Our limewash is a mix of lime putty with water, which we have found to be robust and reliable over the years.
@@MikeWyeLtd I appreciate the reply it's been a few days and we had some rain come through I noticed for the most part it's still in place but some of it did wash away. We don't get a lot of rain here in the summertime but I think eventually I'll just use regular outdoor paint on my garden wall. someday.
I have a solid wall house Devon Cornwall border and we are experiencing damp issues I believe it's been rendered with cement and painted with modern paint. The inside has been painted with vinyl silk I can pick the paint off its about 3 mm thick do I need to remove all of this and lime render both sides with lime wash outside and distemper inside any advice would be much appreciated Thank you
Hi, it sounds like there has been water getting behind the render possibly through some cracks in the render. It is then very hard for the moisture to escape again through the cement and paint layers. If you were to re-render in a lime mortar this should greatly reduce any damp issues that you are having. It would be good to wait for better weather, uncover the wall and let it dry before re-rendering.
TO reinforce what Mike is saying about permeability of lime versus cement - the Romans discovered cement and valued it because it sets underwater. Lime does not. So if you want a material to trap and hold moisture - damp, use cement.
Hydraulic lime sets by hydrolysis whereas non-hydraulic lime sets by carbonation. The hydraulic lime can set underwater, that's because hydrolysis is a reaction caused by water. The non-hydraulic lime needs air to carbonate and thus set.
The Romans would never put cermet onto cob because they understood that cob needs to breath. Lime finishes on the other hand and is very compatible with cob. Never put cement or advice putting it onto cob the Romans knew better.
Hi, thanks for this video, it's a great starting point. I'm wanting to build walls with chalk cob/block, and knowing that it's quite susceptible to the elements have been thinking about how I should coat it. Can old render be repurposed? Is a silicate paint finish detrimental to re-use? Is it environmentally friendly? Though here's hoping a render would last long enough for me not to worry about it.
Hello, Lime render can be repurposed into an aggregate but you would then have to add more lime as a binder. I don't think the silicate paint would have any detrimental effect on this aggregate. They are environmentally friendly in production.
@@MikeWyeLtd many thanks for the reply. First time I've heard about the silicate paints. I quite liked the idea of lime washes, but was worried that they wouldn't or wouldn't much fend off the rain. Will investigate more into the silicate paints.
@@mrdespondency6598 Lime washes normally contain a small amount of linseed oil for water repellency but silicate paints seem to shed more water than they absorb
@@MikeWyeLtd how breathable is linseed in/on lime? I see it's used on earthen floors. Spoke to my Mum yesterday and some cowboys had been around to 'waterproof' her house. Her brick wall was south facing and I can't imagine had any problems drying out. I now have horrible thoughts that she will have a non-breathable wall. But as with lots of Mums/people, there was no telling her.
@@mrdespondency6598 It's a very small percentage of the limewash so still allows for vapour permeability. If the have 'tanked' the wall of your mum's house, it is normally only the bottom few feet. I wouldn't worry too much.
If you had to render the front of a whole house I'd imagine it is hard to do the full area in one? If you have to do sections at a time are there issues where the sections join? Should you start from the bottom or the top?
With the backing coats doing sections isn't an issue. When it comes to the float coat ideally you want to finish in one but it would require more than one plasterer. If this isn't possible then use the natural breaks in the building for example the window line, then it makes the join less obvious. Always start from the top so as not to drop stuff on completed work. I hope this helps.
Hi. Great video thanks. I've got some patching up to do after removing some rotten wooden fake beams on the external walls of my house. I'm pretty sure the original render is lime. So I want to patch up using lime render. The existing render appears to be only one coat and quite thin it varies between 5 and 15mm! Is it ok to do just one coat. Thinking of using nhl 3.5 mixed with sand at 3:1. Would like some advice. Thanks Rich
Hi Rich. It's not uncommon to find thinner render coats of lime and of course you'll be limited to a single coat where the areas are as thin as 5-10 mm. There's generally a reference to repair like-for-like, but natural hydraulic lime does have some properties not too dissimilar from sand cement but would be beneficial in other ways. Therefore using an NHL3.5 mix would probably be a safe bet any way. If however you're dealing with a traditional putty lime or similar then it would be better to try and repair using a similar mix. If you're unsure what you're dealing with you can always send us a small sample in the post and we'll take a look at it for you. Kind regards, Ryan @ Mike Wye
@@MikeWyeLtd Hi Ryan. Thanks for the reply. It's good to know I can get some sound advice on this. I would definitely like to send a sample to be certain of the material that was first used. Is your address on the web site? I was thinking of nhl 3.5 with plastering sand because I've read that it is similar to apply as sand and cement render. I'm not a plasterer by trade but I'm competent enough to get sand/cement render on the wall and get a decent finish. Is it acceptable to prime with sbr on brick when using lime or does this defeat the object of letting the wall breath?
Hi Rich. Don't prime with sbr. It will undo any benefit of using lime but will also slow curing times and possibly case the lime render to slump/delaminate and/or fail. The brick needs to take a harl coat first (as shown in the video) to provide a mechanical and chemical key for the thicker render coat(s). You can use a thinned down NHL mix for this if preferred or we do supply a premixed product used specifically for this. Our address for sending the sample is on the website but here it is any way: Mike Wye & Associates Ltd, Buckland Filleigh Sawmills, Buckland Filleigh, Devon EX21 5RN. Regards, Ryan.
Hi Mike - My sandstone house has cement render all over one side. It's mostly in good condition, but at ground level some large bits have fallen off. Could you recommend the best approach for this?
Hi Michael. In an ideal world you'd want to replace the cement render with a lime render over the whole elevation. However we understand the disruption and cost this can incur and therefore try to take a practical view on making good. There's always a danger of cracking or differential movement at junctions - particularly where you would be running a lime render into a concrete render. Therefore it may be wise to pick a lime render for the lower levels that is more closely matched to the properties of the existing sand/cement mix. I would suggest an NHL 3.5 render at the lower levels where the render has failed that should blend in better aesthetically but encourage better moisture management at the bottom of the wall. I hope this helps. Regards, Ryan @ Mike Wye
This is an example of a render on cob (essentially compressed and dried sub-soils, clay, aggregate and fibres) so the roof is absolutely needed! The principles are the same for lime rendering on solid masonry. Lime render will last for decades once cured and if applied correctly. However, we would never suggest a lime render is left bare and recommend protective coatings of limewash or silicate masonry paint.
Deri Brown - Thanks for the feedback. Yes, the process is essentially the same if using natural hydraulic lime (although we personally prefer the use of putty lime onto soft substrates such as the cob shown here). If you’re using NHL mixes on solid masonry then we advise a slightly weaker float coat than the scratch coat (2.5:1 sand:NHL for the scratch, followed by 3:1 for the float). I hope this helps.
If i drive nails in this one , or remove a bit while putting in my electrical conduits, will the plaster around hold? Or will it come off from one edge and then all at once successively? I'm also having some trouble with the way it powders, what must i do to control the powdering of the plaster?
If you're having to put fixings in to the wall then placing masking tape over the plaster can prevent cracking. Chasing out for conduit can be tricky but can be filled again with a suitable lime mix once the conduit is in place. There's not much that can be done to control powdering of older plasters unfortunately aside from trying to dampen down with water to try and minimise dust.
hi Mike!, thanks a lot for share with us your knowledge, i have some question Mike: is this an adobe wall?, i listen that is very common what the adobe wall dont accept any material even lime plaster, what do you think about this? right now i am looking for what kind of material will use on my house, thanks again!
Hi Zakura. We don't have much experience of adobe but I believe building with cob has some similarities. Cob is a blend of sub-soil, clay and fibres which is either applied as a mass, or dried and used in the form of blocks and bricks. Original cob would have often contained animal dung and other waste materials due to the soil being trampled and mixed by farm animals. We use the harl coat to create a physical and chemical bond on to the cob before applying thicker render coats. If the surface of the cob/adobe is very smooth then it may be advisable to try and create an improved key before applying the harl coat. I hope this helps.
Thank you for your kind comment, Sumant. We are aiming to add more instructional videos over the coming months and will endeavour to put something together on the application of a silicate masonry paint. Watch this space!.............
I got here by watching Peter Ward's videos about damp walls. He keeps showing how cement over the top of bricks and rock traps moisture in the wall. And he seems to always describe a, "lime render" as the solution. Why is a lime render so much better than cement for not trapping moisture in the wall? I thought cement was porous too.
Hi Dantama. Thanks for leaving a comment. You're not wrong in your assumption that cement is porous, but it's ability to manage moisture through diffusion is much lower than lime by comparison. As a general rule, as you increase strength, you decrease vapour permeability. Both lime and cement are hygroscopic (ability to absorb moisture). However the ability of cement to release moisture when drying out is lower than lime and this could therefore could be problematic in dealing with higher levels of moisture in a solid, non-cavity wall. So despite some advice and popular belief - cement is breathable to an extent. One of the other, and often more significant contributing factors, is the use of modern, relatively impervious paints over the top of cement renders. This can have the effect of shrink-wrapping the render and further restricting the movement of moisture. It does go beyond this, and there are further cases for the use of lime over cement on traditional, solid wall constructed properties, but I hope this helps to give a general reply to your comment.
Hi Ben. Sorry for the delay in replying to you. A pozzolan (pronounced pots-so-lan) is an additive that reacts with lime and water to bring about a hydraulic set. The addition of a pozzolan (Argical M1000 is our preferred product/brand) is generally recommended for external works where lime putty mixes are vulnerable to frost - even if carrying out work earlier in the year. I hope this helps.
Sylvain Richard Would you care to elaborate? We’ve been applying lime plasters and renders for significantly longer than 10 years and have yet to experience our work falling apart! We’re confident that you’ll find the methods shown in our videos are widely accepted as standard practice for traditional lime work but it would be interesting to read why you think otherwise. Happy to discuss on here if you can support your statement.
Mike Wye Hello, I’m a french stone masson and I use to learn that the second and third coating should be projected. The air between the coat ‘ll be chased. I’m very surprised you didn’t do that way cause obviously you have a great technique that you show in the first coating. Excuse me if I had offensed you. Lime is a great product and you seem to be very conscientious. I’ve seen a lot of wall whith the third coat whore are falling, and I seen masson doing bad job too... perhaps they were not so conscientious than you with the first and second coating...
Sylvain Richard we’re not offended at all. It’s interesting to hear the knowledge and experience of others - even if it differs from our own. We’ve completed many successful projects in the 25 years we’ve been in business using the techniques seen in this video. Lime certainly needs a conscientious approach and we take pride in our work and ensure that the same understanding and sympathetic approach is passed to others in our guidance and training. I’d be interested to see examples of the techniques you’re familiar with and how they differ from our own - do you have examples on TH-cam or a website link?
@@ps7462 Projecting coats means that you "throw the plaster onto the surface"... At the start they propeply applied the precoat by "hurling it against the wall" as they said...
These days, and for ease, we use a pre-mixed hydraulic lime blend called Consolidation Mortar by Secil. 5 litres of water per 25 kg bag gives the perfect consistency. If you want to mix your own from NHL 3.5 mix then we suggest 2.5 parts sharp to 1 part NHL by volume with an excess of water to get it to the ‘porridge-like’ consistency you see here.
Stick with a 2.5:1 mix for the scratch coat followed by a slightly thinner and weaker float coat at 3:1. It’s a rough guide as the mix strength can sometimes vary depending on the substrate and brand of NHL you’re using (some brands in the same grade of NHL can be very different in strength than others). I hope this helps
As a general rule, add hair or fibres if you’re applying a render/plaster coat more that 10 mm thick (although hair/fibres in the scratch coat can help to minimise shrinkage and improve flexibility irrespective of thickness)
@@MikeWyeLtd sorry to jump on this thread, but I've just bought an old schist building in Portugal. The bottom parts of the external walls are rock and it's been heightened over time with the hollow red bricks. Some has already been rendered/ painted, some not. There are clear signs of dampness so ideally I'd like to remove the current render/plaster/paint and redo using lime render, lime plaster and lime wash! As I'm completely new to this, I'm getting very easily confused about the mixes etc. The first coat is scratch coat and is 2.5 parts sand to one part lime. If there are some places needing more of this thickness than others (different sized stones) how much hair is required to add this mix? and then for the float coat is 3 sand to 1 lime. Again, how much hair? Which coat has additives? WHat additives? I'm really struggling to hear with my terrible laptop speakers! Any help much appreciated!
Thanks for taking the time to leave a comment. Whilst it's possible to use a straight edge when rendering some traditional buildings, it's also not possible on many others. The straight lines and sharp corners you may be used to on modern buildings do not exist on most traditional properties up until the Georgian and Victorian eras. Therefore anyone with some understanding and desire to maintain when renovating and repairing older buildings will generally not consider using a straight edge (even if it is possible). It's something known in the trade as 'character'.
what happen to your hand if didn't wash off lime ? is it just like cement mix that didn't wash away ? my heel became crack after cementing... ya.. painful crack, cement sucks all moisture from my feet.. is it the same with lime ?
Found these instructions on a website; Rendering (Internal & External): Render with a mix of sand, cement and lime should be applied in two coats using the procedures defined within BS EN 13914-1 :2005 to a total thickness of 14mm. A 3mm skim coat of finishing plaster of can be added once the render is fully cured. The scratch coat should be a mix of 1 part lime: 1 part cement: 5 parts clean well-graded sharp sand and the second or float coat should be a mix of 1 part lime: 1 part cement: 6 parts clean well-graded sharp sand. The scratch coat should be 7mm and the second or float coat should be 7mm. To lessen incidence of cracking, it is best to mix the lime and sand a day or more before use. Cement can then be added at the time of rendering. The work should be of two coats of render and if required, a third coat of finishing plaster. The purpose of the 7mm scratch coat is to stiffen up the lath and to provide rough and absorbent, backing for subsequent coats. Work this scratch coat well into the mesh. Each 7mm coat of render should be allowed to dry for a period of not less than seven, preferably ten days, longer if possible. Cracking may occur if shorter time is allowed between coats. It is important that the render coats are allowed to cure correctly over the 7 to 10 day period with the render dampened as required. If the scratch coat has not fully cured, slumping of the render can result. Before applying the second or float coat, carefully drill or scratch out a small area into an area behind the mesh, within the membrane stud, to confirm that it is fully cured. The surface will cure quite quickly but the area behind the mesh must be fully cured also. In warm periods the render should be protected from excessive drying out by covering with damp hessian sheets with plastic sheeting over. Dampened down the scratch coat before application of the float coat. A smooth finish is not recommended. Expansion joints should be trowelled in through the render to the membrane. These joints must be filled with a suitable flexible polymer-based sealant. Expanded metal angle beads and stop beads can be fixed where appropriate using dabs of the same material mixed as for the scratch coat. Natural Hydraulic Lime (Internally & Externally): NHL (Natural Hydraulic Lime) 3.5 should be used to a combined depth of 20mm with a 10mm scratch coat and a 10mm second or float coat. The mix ratio is 2.5 parts sand to 1 part NHL 3.5 mixed as per manufacturers instructions. The 10mm scratch coat is pushed firmly into the membrane mesh. Check the application the day after and rub out any cracks. The surface should be thoroughly scratched without breaking the surface of the mesh. The scratch coat has to be left for a minimum of 7 days to set. It should be protected from draughts and extremes of temperature. Before applying the second or float coat, carefully drill or scratch out a small area into an area behind the mesh, within the membrane stud, to confirm that it is set and reasonably hard. The surface will cure quite quickly but the area behind the mesh that has to be set. The second coat is the float coat and is applied then ruled off to flatten the wall surface. The mix ratio is 2.5 parts sand to 1 part NHL 3.5 mixed as per manufacturers instructions. The scratch coat has to be dampened down before application of the float coat. The work has to be protected and tended as for the scratch coat. The second coat is floated or trowelled as the finished coat.
Thanks for leaving a comment. However, I urge anyone reading this not to go down this route unless you're happy to be applying a concrete render/plaster to your property. A 6:1:1 or 5:1:1 mix is a concrete mix - not a lime mix. This will result in a hard, brittle and significantly less breathable render/plaster than the lime systems we are demonstrating here. The lime element in this mix is a hydrated lime which is included as a plasticiser. Such a mix does offer improved vapour permeability compared to a 1:3 mix of cement:sand by comparison, but is still very low compared to the putty lime mix shown in our video. The natural hydraulic lime snippet you're left in your comment is okay, but we generally reserve hydraulic lime mixes for strength works and very exposed situations (such as floor screeds or the rebuilding of a chimney). External renders using NHL3.5 may be considered fine in some situations but consideration should be taken regarding the type of property you are working on (such as age, exposure, substrate). Older buildings and softer substrates will need sympathetic materials that can accommodate subtle movement over time; you won't get this with a harder, more brittle renders/plasters such as the ones mentioned in your comment. Building materials such as cob (a mixture of dried, compressed sub-soils, aggregate and natural fibres) will need highly permeable coatings to encourage moisture to move away from the substrate. If this can't happen you could be risking serious structural damage further down the line. I could go on, but hopefully this gives you a better understanding of the decision making needed for the careful selection of the correct materials for the job. We're not anti-cement but, like many construction materials, they should only be used for suitable applications. It's use on traditional buildings is generally not one! Regards, Ryan @ Mike Wye
@@MikeWyeLtd Adding hydrated to a cement mix has a pore filling quality making it less breathable not more. Its specified for strength not workablility even though it does have that effect.
lame duck - I notice you haven't said where you first saw your "instructions". But Mike Wye's traditional lime methods bear no relation to the cement mixtures you write about. Deliberately so. Cement and concrete are an absolute menace on old and traditional houses. I hope no-one has taken any notice of what you wrote.
This is an ancient system and with todays labor prices i cant see how anyone can afford this type of repair.
Highly skilled.
Thank you
GRT to watch a video of someone making this look easy....
One of the best tutorial videos .
Thanks for sharing your knowledge.
Blessings and more Blessings
Thank you very much Charles.
Unbelievably skilful work.A pleasure to watch
Great video, thanks. I'm planning on making a mess of my house this summer in Sweden as it needs re-rendering. I think the previous owner had the local kindergartan do it 5 years ago and it's dropping off the brick in chunks. I figured I'll do it myself because at least if I screw it up I can call it art (and it'll be cheaper to re-do it). The last quote I got for the place was around £10K (two storey house about 12m x 6m - 3 sides need doing) and these days I have more time than money. TH-cam is a godsend. Thanks again.
How is your "mess" going? Have you covered the neighbor's cat yet? :)
Better than I thought it would. I did the side that was in the worst condition in May. Took a week and half to get all of the old plaster off. The bricks weren't in the best condition so I re-pointed a lot of the wall to strengthen it. The harl coat was fun. It took a while, and a few covered cats, to get the technique down. I could hear the neighbours grumbling amongst themselves wondering what the hell I was doing. I got pretty accurate by about halfway through the wall. The scratch coat was good practice with the trowel. My home made scratcher took a bit of adjustment to get all the nails the same length. I then put a fine coat on top which looks great when the sun is directly on it, or if it's in shade (looks brilliant in the dark), but looks like the surface of the moon when the sun is shining straight across the surface, so it'll need another fine skim coat (I think I'll need to use a darby this time, hopefully the lime will stick as well as the layers that are on now do - maybe a light harl coat first to provide a key).
Anyway, that'll happen in August. After spending the whole of May working on the wall, I'd had enough, and my trowelling arm was knackered - literally became too painful to apply the lime. So a fresh attack in month.
And thanks to MikeWyeAssociates for your videos. Turned a complete novice into an amateur (I've had quite a lot of compliments on the wall when the sun is in the right place :-)
It's taken me 5 tries to answer your post! Karma? Anyways, good on you for getting it done. I've had those visually obvious learning curves myself. Right now I'm trying to see if I can cover a cinder block retaining wall. Wish me luck.
Good luck. Half the job is plucking up the courage to get stuck in. I'm sure it'll look fantastic once you're done (and you can't go wrong when you have Robert Plant as your teacher :-)
How did it go?
Thank you very much for the video. I plaster a fair bit with cement and modern plasters and use lime mortar for stonemasonry and brickwork and this is a good example of rendering with lime mortar.
Hi Michael, thank you for taking the time to comment and for the kind words.
@@MikeWyeLtd I'm usually fairly critical but I recognise skilled workers and you lads know your stuff
Brilliant video, thank you for sharing your knowledge. Perfection in motion!
Thank you, sir! This video was so useful that i can not describe!
Just wondering whether there is a video on mixing up the mortar and an explanation about hair etc?
Unfortunately we don't have a video showing the mixing process but if you have specific questions relating to this you can email us at sales@mikewye.co.uk
Regards, Ryan @ Mike Wye
Great video. I need my house lime rendered as it currently got 3 different render finishes.
I guess each wall could be broken down into sections to make it easier but the final coat would need to be applied in one go across the entire wall? Am I right in my thinking there or could the final coat also be broken down into smaller sections?
Hi Pete, the backing coats could absolutely be applied in sections. The float coat would be better applied on each face in one hit to avoid visible joins, if you have downpipes then these can be used to hide these.
@@MikeWyeLtd brilliant thank you very much
Wd this work as an exterior finish in very hot climates ? Ie Thailand
Hi Will, Yes it is absolutely suitable in hot climates
Man robert plant has had a long and varied career.
Nice video! Regarding the harling coat mix, after adding more water and whisking how long do you leave the mix to set? Cheers.
Once the harling mix is prepared it can be applied straight away and tends to dry in 24-48 hours
I couldn't make out what you said about the additive to the mixture at the beginning. Could you tell me what that is that you said was made in Cornwall?
+Kevin Wixson The additive is generically known as a pozzolan which is a clay additive sometimes used in lime render and plaster coats in order to achieve a slight hydraulic set. We tend to add it in where we want to improve the resilience to frost and adverse weather conditions, or where the wall is damp.
The pozzolan from Cornwall me mention is Metastar. Unfortunately this clip is a few years old now and Metastar is no longer produced. We supply a similar metakaolin called Argical, from France.
Other materials can act as a pozzolan with varying results, such as brick dust, ash and GBFS.
Mike Wye hi, love your videos. I have 180m2 of external Hydraulic Lime render to do on a Grade II. The architect has spec'd for no hair in any of the coats, I think he's just copy and pasted the method from Wikipedia or something! Please tell me what the gauges of the coats you use are and also which ones you add hair to. Many thank!
Mike Wye... Also I'd be interested in purchasing the additive you mentioned for curing 👍
If you going to render do you have to repoint a rubble stone wall
Hi Max, it would always be better to repoint before applying a render
What are you mixing, lime and sand with hair?
Great video, thanks. Would this same process apply to a chalk cob wall? This is what I have in Hampshire and it needs rendering so I'm thinking of using this video as a model.
Hi, yes, it would be exactly the same approach.
@@MikeWyeLtd Thank you. I'd like to attend your lime rendering course sometime.
Do you have to rule off lime like normal render before floating
Hi Chaz, you can rule off the same with lime, it just wasn't necessary in this video
Has the dpc not been bridged on that wall?
Hi there, Professor, thanks for your comment. This is purely a training/demonstration wall we built at our premises many years ago, and it had no DPC. You are correct to identify this as a potential issue in "real World" work, where we would always be conscious of such features and avoiding the creation of moisture bridges. Good observation 👍
great video, what is the mix in the top coat?
Hi! It's a mix of lime putty and washed sharp sand sand 3:1
Hi,thanks for the reply. It's to same mix as the scratch coat?
Would you recommend adding some finer sand into the top coat for a finer finish? Thanks
Hello wanted to ask, in your opinion is possible to use cement (for better setting) with hydrated lime and sand (0,5:1:5 ratio) for rendering a brick wall layed with lime mortar, as it is quite difficult to find hydraulic lime in our region?
Or even small amounts of cement will trap moisture, make wall unbreathable and ruin the bricks?
Kind regards
Hello. A 6:1:1 mix (sand:cement:hydrated lime) is a relatively common mix in the UK but we still consider this to be a weak concrete mix rather than a lime mix.
I understand that it may be difficult to source hydraulic lime or lime putty where you are, so a mix like this will be a better option if you have no other option.
Despite some information out there, concrete mixes do offer some breathability and have hygroscopic properties than can help to wick moisture away from the fabric of the building - it's just much lower than lime by comparison.
As a general rule, the stronger the mix the less vapour permeable it will be. So choosing a weaker mix is always best.
It is also possible to "re-hydrate" a hydrated lime by soaking it and creating a putty. However this putty as a binder is generally considered inferior to a fully matured lime putty and definitely not comparable to a hydraulic lime.
If you do have to use a mix containing cement and are concerned about breathability, then the use of a breathable paint finish will help the render to work as efficiently as possible. Our recommendation would be a silicate paint which can be applied to both lime renders and cement renders, and is highly breathable and durable.
I hope this helps.
What is the name of the additive I can't quite make it out. Something mega star lol. Great video.
Hi Sam, the video refers to "Metastar" which is a pozzolan we used to supply. This has now been superseded by Argical M1000 - details here: www.mikewye.co.uk/product/argical-pozzolan/
Thanks for the video I have a question for you my neighbor today was putting this product on their Garden Wall I thought it was paint at first but they told me it was lime it was very white in color and very watery they were applying it with a broom but there was not any residue really left on the broom after some time it dried to a hardness and it was very white I'm living in a different country so I'm not exactly sure but I was wondering if you've ever heard of something like this I saw the powder online they call lime powder I'm going to ask the neighbor but I'm thinking to buy some because if I can just mix it with water without having to add any sand that would be a lot easier for me to do on that way I can use it on my own wall
Thanks for your comment. It sound like your neighbour was applying a limewash or "sheltercoat" to the wall. Limewash is a suspension of lime in water, and sheltercoats are often similar perhaps with the addition of some finer stone dust/powder. Our limewash is a mix of lime putty with water, which we have found to be robust and reliable over the years.
@@MikeWyeLtd I appreciate the reply it's been a few days and we had some rain come through I noticed for the most part it's still in place but some of it did wash away. We don't get a lot of rain here in the summertime but I think eventually I'll just use regular outdoor paint on my garden wall. someday.
We are about to do this on our old house. May I know what is the mortar mixture here (ratios and so..)?
The Lime mortars are 3 parts washed sharp sand to one part lime putty by volume. A pozzolan is also added at around 8 parts mortar to one pozzolan
@@MikeWyeLtd Thank you!
I have a solid wall house Devon Cornwall border and we are experiencing damp issues I believe it's been rendered with cement and painted with modern paint. The inside has been painted with vinyl silk I can pick the paint off its about 3 mm thick do I need to remove all of this and lime render both sides with lime wash outside and distemper inside any advice would be much appreciated
Thank you
Hi, it sounds like there has been water getting behind the render possibly through some cracks in the render. It is then very hard for the moisture to escape again through the cement and paint layers. If you were to re-render in a lime mortar this should greatly reduce any damp issues that you are having. It would be good to wait for better weather, uncover the wall and let it dry before re-rendering.
TO reinforce what Mike is saying about permeability of lime versus cement - the Romans discovered cement and valued it because it sets underwater. Lime does not. So if you want a material to trap and hold moisture - damp, use cement.
Hydraulic lime sets by hydrolysis whereas non-hydraulic lime sets by carbonation. The hydraulic lime can set underwater, that's because hydrolysis is a reaction caused by water. The non-hydraulic lime needs air to carbonate and thus set.
The Romans would never put cermet onto cob because they understood that cob needs to breath. Lime finishes on the other hand and is very compatible with cob. Never put cement or advice putting it onto cob the Romans knew better.
Hi, thanks for this video, it's a great starting point. I'm wanting to build walls with chalk cob/block, and knowing that it's quite susceptible to the elements have been thinking about how I should coat it. Can old render be repurposed? Is a silicate paint finish detrimental to re-use? Is it environmentally friendly? Though here's hoping a render would last long enough for me not to worry about it.
Hello,
Lime render can be repurposed into an aggregate but you would then have to add more lime as a binder. I don't think the silicate paint would have any detrimental effect on this aggregate. They are environmentally friendly in production.
@@MikeWyeLtd many thanks for the reply. First time I've heard about the silicate paints. I quite liked the idea of lime washes, but was worried that they wouldn't or wouldn't much fend off the rain. Will investigate more into the silicate paints.
@@mrdespondency6598 Lime washes normally contain a small amount of linseed oil for water repellency but silicate paints seem to shed more water than they absorb
@@MikeWyeLtd how breathable is linseed in/on lime? I see it's used on earthen floors. Spoke to my Mum yesterday and some cowboys had been around to 'waterproof' her house. Her brick wall was south facing and I can't imagine had any problems drying out. I now have horrible thoughts that she will have a non-breathable wall. But as with lots of Mums/people, there was no telling her.
@@mrdespondency6598 It's a very small percentage of the limewash so still allows for vapour permeability. If the have 'tanked' the wall of your mum's house, it is normally only the bottom few feet. I wouldn't worry too much.
If you had to render the front of a whole house I'd imagine it is hard to do the full area in one? If you have to do sections at a time are there issues where the sections join? Should you start from the bottom or the top?
With the backing coats doing sections isn't an issue. When it comes to the float coat ideally you want to finish in one but it would require more than one plasterer. If this isn't possible then use the natural breaks in the building for example the window line, then it makes the join less obvious. Always start from the top so as not to drop stuff on completed work. I hope this helps.
Thanks for the info, it sounds like I would be best to bring a friend if I attend one of your courses!
Hi. Great video thanks.
I've got some patching up to do after removing some rotten wooden fake beams on the external walls of my house. I'm pretty sure the original render is lime. So I want to patch up using lime render. The existing render appears to be only one coat and quite thin it varies between 5 and 15mm! Is it ok to do just one coat. Thinking of using nhl 3.5 mixed with sand at 3:1. Would like some advice. Thanks Rich
Hi Rich. It's not uncommon to find thinner render coats of lime and of course you'll be limited to a single coat where the areas are as thin as 5-10 mm. There's generally a reference to repair like-for-like, but natural hydraulic lime does have some properties not too dissimilar from sand cement but would be beneficial in other ways. Therefore using an NHL3.5 mix would probably be a safe bet any way. If however you're dealing with a traditional putty lime or similar then it would be better to try and repair using a similar mix. If you're unsure what you're dealing with you can always send us a small sample in the post and we'll take a look at it for you. Kind regards, Ryan @ Mike Wye
@@MikeWyeLtd Hi Ryan. Thanks for the reply. It's good to know I can get some sound advice on this. I would definitely like to send a sample to be certain of the material that was first used. Is your address on the web site?
I was thinking of nhl 3.5 with plastering sand because I've read that it is similar to apply as sand and cement render. I'm not a plasterer by trade but I'm competent enough to get sand/cement render on the wall and get a decent finish. Is it acceptable to prime with sbr on brick when using lime or does this defeat the object of letting the wall breath?
Hi Rich. Don't prime with sbr. It will undo any benefit of using lime but will also slow curing times and possibly case the lime render to slump/delaminate and/or fail. The brick needs to take a harl coat first (as shown in the video) to provide a mechanical and chemical key for the thicker render coat(s). You can use a thinned down NHL mix for this if preferred or we do supply a premixed product used specifically for this. Our address for sending the sample is on the website but here it is any way: Mike Wye & Associates Ltd, Buckland Filleigh Sawmills, Buckland Filleigh, Devon EX21 5RN. Regards, Ryan.
@@MikeWyeLtd Thanks Ryan. I'll stick a sample in the post today, and put the lid back on the sbr!! Many thanks.
Hi Mike - My sandstone house has cement render all over one side. It's mostly in good condition, but at ground level some large bits have fallen off. Could you recommend the best approach for this?
Hi Michael. In an ideal world you'd want to replace the cement render with a lime render over the whole elevation. However we understand the disruption and cost this can incur and therefore try to take a practical view on making good.
There's always a danger of cracking or differential movement at junctions - particularly where you would be running a lime render into a concrete render. Therefore it may be wise to pick a lime render for the lower levels that is more closely matched to the properties of the existing sand/cement mix.
I would suggest an NHL 3.5 render at the lower levels where the render has failed that should blend in better aesthetically but encourage better moisture management at the bottom of the wall.
I hope this helps. Regards, Ryan @ Mike Wye
@@MikeWyeLtd Thanks Mike - very helpful. I may even remove the bottom foot all round and replace it with lime render.
perpendicular, always perpendicular
Is the roof needed? How long will the plaster hold up in the weather?
This is an example of a render on cob (essentially compressed and dried sub-soils, clay, aggregate and fibres) so the roof is absolutely needed! The principles are the same for lime rendering on solid masonry. Lime render will last for decades once cured and if applied correctly. However, we would never suggest a lime render is left bare and recommend protective coatings of limewash or silicate masonry paint.
@@MikeWyeLtd So are you saying that even a lime wash alone isn't enough protection?
@@Jim-K-Baker A limewash is adequate protection for a lime render externally but is less durable and protective than a silicate paint by comparison.
Will a silicate paint allow the cob to breathe?
@@Jim-K-Baker Yes, the silicate paint is highly breathable with an SD value of 0.01.
Great video. Thanks a lot!
Brilliant video... render porn!
YOU BOYS. ....GOOD SHIT. MANY THANKS.
DBM. ENGLAND.
Top vid. Would you use exactly the same process if using nhl3.5 mix?
Deri Brown - Thanks for the feedback. Yes, the process is essentially the same if using natural hydraulic lime (although we personally prefer the use of putty lime onto soft substrates such as the cob shown here).
If you’re using NHL mixes on solid masonry then we advise a slightly weaker float coat than the scratch coat (2.5:1 sand:NHL for the scratch, followed by 3:1 for the float).
I hope this helps.
Mike Wye thanks. I have a job where I have hacked all the s&c render away on a stone property and a nhl3.5 render has been specced to go back on.
Deri Brown - Drop us an email sales@mikewye.co.uk or call if you want to talk it through 01409 281644. Ryan
If i drive nails in this one , or remove a bit while putting in my electrical conduits, will the plaster around hold? Or will it come off from one edge and then all at once successively? I'm also having some trouble with the way it powders, what must i do to control the powdering of the plaster?
If you're having to put fixings in to the wall then placing masking tape over the plaster can prevent cracking. Chasing out for conduit can be tricky but can be filled again with a suitable lime mix once the conduit is in place. There's not much that can be done to control powdering of older plasters unfortunately aside from trying to dampen down with water to try and minimise dust.
Good work , my brother
hi Mike!, thanks a lot for share with us your knowledge, i have some question Mike: is this an adobe wall?, i listen that is very common what the adobe wall dont accept any material even lime plaster, what do you think about this?
right now i am looking for what kind of material will use on my house, thanks again!
Hi Zakura. We don't have much experience of adobe but I believe building with cob has some similarities. Cob is a blend of sub-soil, clay and fibres which is either applied as a mass, or dried and used in the form of blocks and bricks. Original cob would have often contained animal dung and other waste materials due to the soil being trampled and mixed by farm animals.
We use the harl coat to create a physical and chemical bond on to the cob before applying thicker render coats.
If the surface of the cob/adobe is very smooth then it may be advisable to try and create an improved key before applying the harl coat.
I hope this helps.
Mike: thanks alot!
greetings from Mexico
That's how it's done!
Proper job!
Thank you so much for your videos. I was wondering, is this a demo wall or a real job?
Hi Lisa, it's a training wall. Part of our setup for our practical courses:
www.mikewye.co.uk/product-category/training-courses/
Old school out of a barrow niiice 😂😂
Thank you for this very informative video.Please keep them coming.Is there any chance of doing a mineral oil/potassium silicate exterior?Thanks again.
Thank you for your kind comment, Sumant. We are aiming to add more instructional videos over the coming months and will endeavour to put something together on the application of a silicate masonry paint. Watch this space!.............
I got here by watching Peter Ward's videos about damp walls. He keeps showing how cement over the top of bricks and rock traps moisture in the wall. And he seems to always describe a, "lime render" as the solution. Why is a lime render so much better than cement for not trapping moisture in the wall? I thought cement was porous too.
Hi Dantama. Thanks for leaving a comment.
You're not wrong in your assumption that cement is porous, but it's ability to manage moisture through diffusion is much lower than lime by comparison.
As a general rule, as you increase strength, you decrease vapour permeability. Both lime and cement are hygroscopic (ability to absorb moisture). However the ability of cement to release moisture when drying out is lower than lime and this could therefore could be problematic in dealing with higher levels of moisture in a solid, non-cavity wall.
So despite some advice and popular belief - cement is breathable to an extent.
One of the other, and often more significant contributing factors, is the use of modern, relatively impervious paints over the top of cement renders. This can have the effect of shrink-wrapping the render and further restricting the movement of moisture.
It does go beyond this, and there are further cases for the use of lime over cement on traditional, solid wall constructed properties, but I hope this helps to give a general reply to your comment.
@@MikeWyeLtd Way helpful. You explained it in a way that is totally understandable. Thanks.
Love this vidoe
What is plotslane please ?
Hi Ben. Sorry for the delay in replying to you.
A pozzolan (pronounced pots-so-lan) is an additive that reacts with lime and water to bring about a hydraulic set.
The addition of a pozzolan (Argical M1000 is our preferred product/brand) is generally recommended for external works where lime putty mixes are vulnerable to frost - even if carrying out work earlier in the year.
I hope this helps.
No projecting coats ? 50% chance that in ten years all will fall apart. I think.
Sylvain Richard Would you care to elaborate? We’ve been applying lime plasters and renders for significantly longer than 10 years and have yet to experience our work falling apart!
We’re confident that you’ll find the methods shown in our videos are widely accepted as standard practice for traditional lime work but it would be interesting to read why you think otherwise.
Happy to discuss on here if you can support your statement.
Mike Wye Hello, I’m a french stone masson and I use to learn that the second and third coating should be projected. The air between the coat ‘ll be chased. I’m very surprised you didn’t do that way cause obviously you have a great technique that you show in the first coating. Excuse me if I had offensed you. Lime is a great product and you seem to be very conscientious. I’ve seen a lot of wall whith the third coat whore are falling, and I seen masson doing bad job too... perhaps they were not so conscientious than you with the first and second coating...
Sylvain Richard we’re not offended at all. It’s interesting to hear the knowledge and experience of others - even if it differs from our own. We’ve completed many successful projects in the 25 years we’ve been in business using the techniques seen in this video. Lime certainly needs a conscientious approach and we take pride in our work and ensure that the same understanding and sympathetic approach is passed to others in our guidance and training.
I’d be interested to see examples of the techniques you’re familiar with and how they differ from our own - do you have examples on TH-cam or a website link?
What are projecting coats?
@@ps7462 Projecting coats means that you "throw the plaster onto the surface"...
At the start they propeply applied the precoat by "hurling it against the wall" as they said...
What ratio is the harl mix you you are using???? If using nhl 3.5
These days, and for ease, we use a pre-mixed hydraulic lime blend called Consolidation Mortar by Secil. 5 litres of water per 25 kg bag gives the perfect consistency.
If you want to mix your own from NHL 3.5 mix then we suggest 2.5 parts sharp to 1 part NHL by volume with an excess of water to get it to the ‘porridge-like’ consistency you see here.
Stick with a 2.5:1 mix for the scratch coat followed by a slightly thinner and weaker float coat at 3:1.
It’s a rough guide as the mix strength can sometimes vary depending on the substrate and brand of NHL you’re using (some brands in the same grade of NHL can be very different in strength than others).
I hope this helps
No, two and a half parts sharp sand to one part lime for the scratch coat. Correct for the float coat. Sorry for the confusion. Ryan
As a general rule, add hair or fibres if you’re applying a render/plaster coat more that 10 mm thick (although hair/fibres in the scratch coat can help to minimise shrinkage and improve flexibility irrespective of thickness)
@@MikeWyeLtd sorry to jump on this thread, but I've just bought an old schist building in Portugal. The bottom parts of the external walls are rock and it's been heightened over time with the hollow red bricks. Some has already been rendered/ painted, some not. There are clear signs of dampness so ideally I'd like to remove the current render/plaster/paint and redo using lime render, lime plaster and lime wash! As I'm completely new to this, I'm getting very easily confused about the mixes etc. The first coat is scratch coat and is 2.5 parts sand to one part lime. If there are some places needing more of this thickness than others (different sized stones) how much hair is required to add this mix? and then for the float coat is 3 sand to 1 lime. Again, how much hair? Which coat has additives? WHat additives? I'm really struggling to hear with my terrible laptop speakers! Any help much appreciated!
you can level it with a sponge. ever heard of a straight edge or a Darby
Thanks for taking the time to leave a comment. Whilst it's possible to use a straight edge when rendering some traditional buildings, it's also not possible on many others.
The straight lines and sharp corners you may be used to on modern buildings do not exist on most traditional properties up until the Georgian and Victorian eras.
Therefore anyone with some understanding and desire to maintain when renovating and repairing older buildings will generally not consider using a straight edge (even if it is possible).
It's something known in the trade as 'character'.
@@MikeWyeLtd I must agree free hand as such is the correct way, the eye, our true master.
He does exactly that near the end of the video.
Just keep that lime off your hands!!. I had to pay to learn fella,! Lol,😂😂
what happen to your hand if didn't wash off lime ? is it just like cement mix that didn't wash away ? my heel became crack after cementing... ya.. painful crack, cement sucks all moisture from my feet.. is it the same with lime ?
Found these instructions on a website;
Rendering (Internal & External):
Render with a mix of sand, cement and lime should be applied in two coats using the procedures defined within BS EN 13914-1 :2005 to a total thickness of 14mm.
A 3mm skim coat of finishing plaster of can be added once the render is fully cured. The scratch coat should be a mix of 1 part lime: 1 part cement: 5 parts clean well-graded sharp sand and the second or float coat should be a mix of 1 part lime: 1 part cement: 6 parts clean well-graded sharp sand. The scratch coat should be 7mm and the second or float coat should be 7mm.
To lessen incidence of cracking, it is best to mix the lime and sand a day or more before use. Cement can then be added at the time of rendering. The work should be of two coats of render and if required, a third coat of finishing plaster. The purpose of the 7mm scratch coat is to stiffen up the lath and to provide rough and absorbent, backing for subsequent coats. Work this scratch coat well into the mesh.
Each 7mm coat of render should be allowed to dry for a period of not less than seven, preferably ten days, longer if possible. Cracking may occur if shorter time is allowed between coats.
It is important that the render coats are allowed to cure correctly over the 7 to 10 day period with the render dampened as required. If the scratch coat has not fully cured, slumping of the render can result.
Before applying the second or float coat, carefully drill or scratch out a small area into an area behind the mesh, within the membrane stud, to confirm that it is fully cured. The surface will cure quite quickly but the area behind the mesh must be fully cured also.
In warm periods the render should be protected from excessive drying out by covering with damp hessian sheets with plastic sheeting over. Dampened down the scratch coat before application of the float coat. A smooth finish is not recommended.
Expansion joints should be trowelled in through the render to the membrane. These joints must be filled with a suitable flexible polymer-based sealant.
Expanded metal angle beads and stop beads can be fixed where appropriate using dabs of the same material mixed as for the scratch coat.
Natural Hydraulic Lime (Internally & Externally):
NHL (Natural Hydraulic Lime) 3.5 should be used to a combined depth of 20mm with a 10mm scratch coat and a 10mm second or float coat. The mix ratio is 2.5 parts sand to 1 part NHL 3.5 mixed as per manufacturers instructions.
The 10mm scratch coat is pushed firmly into the membrane mesh. Check the application the day after and rub out any cracks. The surface should be thoroughly scratched without breaking the surface of the mesh.
The scratch coat has to be left for a minimum of 7 days to set. It should be protected from draughts and extremes of temperature. Before applying the second or float coat, carefully drill or scratch out a small area into an area behind the mesh, within the membrane stud, to confirm that it is set and reasonably hard. The surface will cure quite quickly but the area behind the mesh that has to be set.
The second coat is the float coat and is applied then ruled off to flatten the wall surface. The mix ratio is 2.5 parts sand to 1 part NHL 3.5 mixed as per manufacturers instructions. The scratch coat has to be dampened down before application of the float coat.
The work has to be protected and tended as for the scratch coat. The second coat is floated or trowelled as the finished coat.
Thanks for leaving a comment. However, I urge anyone reading this not to go down this route unless you're happy to be applying a concrete render/plaster to your property.
A 6:1:1 or 5:1:1 mix is a concrete mix - not a lime mix. This will result in a hard, brittle and significantly less breathable render/plaster than the lime systems we are demonstrating here.
The lime element in this mix is a hydrated lime which is included as a plasticiser. Such a mix does offer improved vapour permeability compared to a 1:3 mix of cement:sand by comparison, but is still very low compared to the putty lime mix shown in our video.
The natural hydraulic lime snippet you're left in your comment is okay, but we generally reserve hydraulic lime mixes for strength works and very exposed situations (such as floor screeds or the rebuilding of a chimney). External renders using NHL3.5 may be considered fine in some situations but consideration should be taken regarding the type of property you are working on (such as age, exposure, substrate). Older buildings and softer substrates will need sympathetic materials that can accommodate subtle movement over time; you won't get this with a harder, more brittle renders/plasters such as the ones mentioned in your comment.
Building materials such as cob (a mixture of dried, compressed sub-soils, aggregate and natural fibres) will need highly permeable coatings to encourage moisture to move away from the substrate. If this can't happen you could be risking serious structural damage further down the line.
I could go on, but hopefully this gives you a better understanding of the decision making needed for the careful selection of the correct materials for the job. We're not anti-cement but, like many construction materials, they should only be used for suitable applications. It's use on traditional buildings is generally not one!
Regards, Ryan @ Mike Wye
@@MikeWyeLtd Adding hydrated to a cement mix has a pore filling quality making it less breathable not more. Its specified for strength not workablility even though it does have that effect.
lame duck - I notice you haven't said where you first saw your "instructions". But Mike Wye's traditional lime methods bear no relation to the cement mixtures you write about. Deliberately so. Cement and concrete are an absolute menace on old and traditional houses. I hope no-one has taken any notice of what you wrote.
do i need to harl on a stone wall or can i just point and 2 coat it?
Although it is possible to just two coat, we always recommend a harling coat to provide a better key.
@@MikeWyeLtd ty