What's the Best Mix for Perfect Rendering?
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- เผยแพร่เมื่อ 11 ม.ค. 2018
- Roger helps you get the perfect ratio for your rendering mix.
So, what's the best mix for rendering?
It all depends on what you're rendering on to.
The golden rule is you never make the mix stronger than the material that you're going on to. For example, lightweight concrete block that's 3.6kN, so we don't want a really strong mix for this because if the wall moves, which it will as you always get some expansion and contraction as the seasons change, you don't want the render to be the thing that stops the wall from moving otherwise the render will crack. If you've ever wondered why render cracks, often this is a reason. Also if you put too much cement in the render it shrinks back and it will crack. People don't always believe that, lots of people do a 3:1 mix and say it's nice and strong but that won't stop it from cracking because there's no real tensile strength in it so there's no point putting too much cement in.
Why lime helps make the best mix for rendering
Instead, we make a 6:1:1, which is six parts of sand, one part of cement and one part of hydrated lime. The sand must be plastering sand or rendering sand, not building sand - do not use building sand for rendering because it shrinks and cracks. Sometimes you can add some building sand to the mix for the base coat, but it shouldn't be your primary sand. It's important not to put more than one part lime to one part cement because hydrated lime won't set on its own, you need the cement to help it set. But the lime does give the mix body and make it creamy and gives it a certain amount of elasticity so that if the building moves the render will go with it a bit and if you do get a crack the lime in the mix will move into the crack and re-calcify to some extent. In a way it is self curing and self-rendering. A lot of renderers don't use it and prefer to use plastisier which puts lots of bubbles into the mix which is a good thing but the lime is better as we demonstrate in this video.
Roger also discusses the best weather for rendering.
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#rendering #homeimprovement #diy
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This makes my impending job achievable. Thank you.
Too many young builders get caught in the 'brand new transit van and nagging wife for a bigger house' brigade and before they know it they're working 7 days a week and ripping everyone off so they can take their spoilt kids on a dull tour of Disney Land, because their wife thinks they'll like them more. Well here's a message to busy builders everywhere - forget Disney land and a dull pile of plastic presents: buy your kids some second hand books to read as this'll give them the best life imaginable, then work 4 days a week so you can spend time with your family as opposed to throwing sh*t on walls all day while listening to talk sport and talking about talk sport.
Great vid BTW and what a lovely guy. Shows there's a lot of intelligent and articulate builders out there who live a meaningful life and aim to help others. Got some render patches to fix now but I think 5:1 and plasticiser for me.
forbidden forest I don’t know anything about render ratios but you’ve summed up today’s lame mentality perfectly there mate.
we got maybe 5 years left of civilization. A job=wage slave
Well said
Lol so true. But you forgot the VW transporter van thats for work but been lowered and got alloy wheels. And the Fiamma awning on the side that they have never used. Haha
you know nothing john snow
Love the Hawk over the head trick, I used the same with labourers and apprentices for mixing mud for bricklaying. Saved me giving them a clip for making a sloppy batch and they soon learned that if it fell off the trowel over their head, they got it wrong.
This guy explains in detail better than some lecturers I’ve sat across from
excellent information delivered appropriately with no fluff, thank you very much.
Probably the best rendering video I have seen thanks for the tips
Another great video, Roger. I have an extension to render, built with high-density, concrete blocks. Mercifully, most of it is glazed but I can see that your advice will make all the difference to the job. I recently completed an en-suite bathroom and your videos were a huge help. Your presentation skills are top notch. Thank you so much for all the help and advice. Truly appreciated.
Great detail, superbly presented. Thanks
Wow, after about half a century of doing it my way I have finally found an expert who explains it all so well. I can only say thanks Roger and luckily (?) I have nearly always done any mortar jobs with a 3:1:1 mixture (so I think I am not too far out).
Here in Italy, they are all very vague on the proportions to use but I once contacted the cement company and asked them what they use in a typical 'ready to use' mortar and they told me Sand 71%, Cement 13%, Lime (calce) 16% at the time, which is about a 5:1:1 ratio.
Love it Roger! This is the video where my SkillBuilder journey began back in lockdown 😂
Well done Roger, great tutorial. Cheers
Roger, thank you. You're informative, knowledgable, and entertaining too. I enjoyed and learned from your additional info regarding temperature - living here in a pretty hot climate. Brilliant video production too I should add; not too many, but just Goldilocks effects and editing. I'm about to look up your other Skill Builder videos. Hope you're well mate.
Just seen a few of these video's. Excellent. I mean, really excellent.
I like some washed river sand along with some yellow in my scratch coat.
3 : river
2 : yellow
1 : cement
1 : Lime ( or plasticiser, water proofer)
Top coat
5 : yellow
1 : river ( washed & graded)
1 : cement
1 : Lime ( plasticiser/ waterproofer)
Not everyone puts water proofer in the top coat but it works for me.
43 years down the line and no problems yet.
Must say though.Give me a Hydraulic Lime/ River Sand render any day of the week.Beautiful to use, rubs up a treat and looks terrific.
Each to their own I say!!
Just what Ive been looking for!!
Hi Roger when I was very young as you do we used to just Lime(except cement and sand) for rendering, but it was different than Lime you show on video.
Usually we putted into the hole Lime and mixed it with water and left for few day to get proper consistency and when it becomes like butter we add into every mix and it was brilliant stuff for rendering.
Same we used for bricklaying, just a bit less than for rendering.
Very useful information...simple and comprehensive..
I'm in the construction industry pal and always looking to learn more and progress, I don't comment on videos often but 2 minutes in and iv already learned somethimg new, thanks for the info mate and keep up the good work ! 👏
Again half way through the vid and iv learned so much, its hard to come by an old school guy like urself that's willing to share the vast amount of knowledge you have as easy as you you do... I'll be subscribing for sure pal... thanks for the info boss 👍 😎
Very helpful Roger thanks.
What a great tutorial. Nice one.
Great video. Really informative for the DIY'er like myself.
Nice video mate very explanatory.
I’m learning of you and I appreciate it really
brillant video mate.
Thank you sir, a very big help for me.
Very helpful, thanks!
Excellent explanations!
Thank you Roger
Thank you for your advice
I’m starting to build a fish pond this summer and want a render finish
I’m using the same block as in this video 👍
I love information when it is given rich yet still lends itself to being understood. Great video and explanation, it was easy to watch. 🙂
brilliant video
Good vid roger, thanks
Great video really helped me out!!!
Thanks That's the information I needed
Good video, thanks!
Nice, thanks 🤘
ACTUAL EXPERT....a rare thing nowdays.
and appreciated.
Yes most on sites these days havnt got a clue
Love it! I've always had problems keeping the muck on the wall, maybe, finally, I'll be able to do it right.
Start small.
Great vid👍🏽
Good honest advice
Great video - this will be very useful for me, as a DIY person/occasional user of building materials. Shame about the negative comments, but as usual the people posting them have no videos of their own (I checked), so until they put up videos showcasing their expertise, their coments are worthless.
Thanks Howard, glad to see you're enjoying SB
Hey Roger, i knew nothing about rendering and followed your mix and application advise exactly,, I was happy wwith the first half wall i did, and after doing 4 half walls my results were almost professional...........thanks so much!!. P.S I remembered a trick from 4 decades ago an amateur plasterer/stucco guy told me; add a capful of dishwashing detergent to the mixture............it makes the render light and fluffy. Too much makes it too light and fluffy though, but it was a very useful tip!
I'm not an expert by any means but I believe washing up liquid / detergent acts as a plasticiser - experts correct me if I'm wrong
I love your channel Roger thanks so much
As I have retrain to become a plumber late in life I've just gained so much from your channel particularly
A friend of mine rendered a concrete block wall for us, he used 60% building sand & 40% washed plastering sand in a 4 to 1 mix, was done ions ago, still perfect, he's been a spread for the last 50 years or so. He didn't use corner beads either, did it freehand, loveley job.
yes a lot of plasterers will chuck in a bit of building sand to make the mix more workable.
Often it can shrink and crack. The other problem is that building sand often has tiny pebbles in it which are a problem in the top coat.
Great tip about lime in render, I specify and see so many 1:3 as standard, in books too! Stay safe guv
Hegrewt
Great video.
Good one, thanks
Cheers Roger, thanks for the good vids and advice. Building a Pizza oven so needed a bit of info on the render and top coat for the support structure and oven itself. Got a bit of lime also so we are all go. I made fine care not to follow up any of the tosspot replies you have received. Not too many vids from them I see.
Cheers
I have always intended to build an outdoor pizza oven come bar-b-cue but never got round to it. I did some sketches with my son when he was 12 years old and it was going to be our project. He is 32 now.
Very interesting TY
Best quality job
I've got a house that's been rendered on to concrete blocks and I've had quite a few long cracks I've had to chop the cracks out and patch them and this time I used plastering sand cement and lime I've been a plasterer for 16 years and the first thing I was taught when floating and rendering was the mix it's important to always put lime in the mix never use building sand I've always done a 5:1:1 mix I hardly render these days but it's fact to much cement and the wrong sand will make your render crack in time
thanks mate! Top tips before my DIY disaster
Roger’s the man 👍🏻
Roger seems like such a top bloke!
😛😛😛😛
in the early 80s i used 1-4 and was criticised for it ? still smile about it now
good tip man
Thank you Roger and i`ll take your advices next week down to new zealand. I did read all comments and i still have some days to think about it - what is the "right" mixture between all the opinions.... , and if i don`t fail and my buddy didn`t kill me after our work, well, i`ll give you my feedback. And one thing we do know about it, the sand should not be salty. Anyway, thanx man.
Good quality video.
Boss I worked for always used buckets to measure sand and cement with - not shovels. This way the mixes are always accurate ratios and the same even colour throughout the job. This also went for mixing brick mortar. Buckets seem cumbersome but you get used to using them. There is an art to using the mixer - keeping it clean and not having stuff stuck on the inside and affecting the next mix. All the best. ...And look after your backs too! (...or you will be sorry... Ha Ha)
Thanks Val, good advice and buckets are the way but hardly anyone has the time, rush, rush.
Correct as a big shovel the lad was using would have made that about 8-1
my Dad had me use a small shovel on the sand and big one on the dust.
Gauge is good for any colour mix
Actually, i find buckets are quicker, i never thought that they would be till i started to use them for consistency... it does depend slightly on your mixers location to the sand if it will be quicker... ... but i find its alot quicker to fill 3 buckets level, and only go to the mixer 3 times than shovel and count 12 times over to the mixer.
less chance of error in counting shovels/better consistency/cleaner site/and can be alot quicker if sand is not close to mixer.
Val Caino Great advice, username and comment!
I've always used bucket's more accurate mix
Good job
Merci pour explication 🙏☺️
Thanks!
Thank you so much for helping us to carry on the work.
legend.
Bravo.
At last a video that tells straight away what and why and how much. Brilliant!
Given your body some blood as well 😉
I live in Iraq and we use bricks mainly to build our homes I agree with you my contractor has advised me the rendering in winter because cement crazy about water loves hydration.
Best utilize the local material....Iraq....best bricks for 4 thousand years.. the blue and gold bricks of the Ishtar Gate....is something to behold. ;-)
What's with all the hate? 1 part
Hydrated Lime, 1 part Type GP Grey Cement and 6 parts sand by volume seems to be standard here in Oz.
SHARP sand....mostly called Sydney sand here....very important detail....and they DON'T use a lot of lime here...impe.
I agree with you Roger, I use a 280 liters cement mixer 6 buckets of sharp sand, 1 bucket of cement and one and an half of lime, plaster like you said doesn't need to be bomb or scratch proof, and if the wall is nice and strait use as little plaster as you can because using a lot is a waste of time and material.
I personally go any less than 4-1 on a scratch unless the masonry was very soft.
So many different opinions on the mix ratio. i am now confused and i want to render a low limestone garden bed
well don you . very helpfull . great explanation .top man
Glad it helped
Thanks Roger, informative video. Not sure about the parting comment. You will survive lol
Nice video, you'll always get people slagging you off in the comments saying they've got a better way of doing things. I've done a few videos on my channel and get a few negative comments, I don't mind constructive criticism but I don't like people having a go just for the sake of it. Keep up the good work!!
Thanks Sam. I really don't mind plasterers having a go and encouraging their mates to take a pop. All the comments, good and bad, help the channel. The important thing for me is that people have watched this video and gone on to have a go themselves and a lot of them have been surprised just how easy it is to make a decent job of a small extension or garden wall.
Simple and straightforward explanation, thank you. One question, with the base coat of 6 parts sand, 1 part cement and some plasticiser, do I add waterproofer as well?
no
Your great ;)
So are you saying sand, cement and plasticiser for scratch and sand cement and lime (no plasticiser) for top coat? Cheers
65 years ago when I began to serve my time one of the first things I was told as a right hander,always work from left to right. You usually can spot a plasterer by how he uses his hardboard and TROWEL,it's never called a float. A float is made from straight grain wood(yellow pine if possible).
i think you are a top guy Roger
For the scratch, you say 6 parts Sand 1 part cement and “a bit of plasticizer”. How much is a bit and what would would be the ratio or part ?
How do you measure the amount of sand you need to buy? What's the coverage?
You are a fantastic help Roger.
Do you ever consider using a hydraulic lime as an additional binder to your sharp sand based mix?
I always find my void ratio in a sand ( its a simple process)
Sharp sand will generally have enough void to acomadate 1 binder to 2.5 or 3 units of aggregate.
6:1:1 is therefore a very good mix.
Although my work is mainly brickwork the mix rule is generally the same.
What are your thoughts on scud coats on celcon type blocks 1st?
6:1:1 still a good mix for old red brick walls that need rendering?
Great video - given me the confidence to try patching the broken render myself, save a fortune and feel smug! Thanks!
We hose the walls down soaking wet in summer down in Oz , he’s right it stops the cracks & also gos off slower.
I've been plastering all my adult life and agree with everything said here. Only recommendation is that you use should really measure the mix /ratio accurately using a bucket or similar as just using shovels , especially if you have a novice labourer, can go waaaay out.
I once had to do a repair job for a builder which had some serious cracking. So I called a consultant who put me into touch with an industrial chemist. I then worked on using plaster without lime and rendering or even mortar without lime. The industrial chemist stated. We consider lime to be no good. I thought okay. It was the best thing I even did.
So what I'm saying if you use lime then you make the strength of the mortar according to the strength of the substance you are putting it on. Exactly what you mentioned.
However, with the product I use you can mix whatever strength you like to a certain extent.
And I think there are many factors to take into consideration.
I use what is called a latex rubberised synthetic emulsion system.
If you render onto old bricks which were laid without cement then you will get surface retention. So you will see a certain amount of cracking as the compression is very low opposed to bricks laid with cement in the mortar.
Without lime I can wash my tools without wearing rubber gloves. Also if some material splashes in my eyes I don't need to race to the water to get the mortar or plaster mixed with lime put. Lime is highly corrosive so if it gets on aluminium it anodises. Although cement had alkaline and can sometimes leave a mark on specially coated windows glass. I found that out with a client when some mortar got in behind covered up windows.
This is partly due to cement manufacturers cutting costs and leaving out gypsum which in the last we had better cement than from recent times.
I'm not sure about U.K. Because I'm from Australia.
I think of you use plasticisers then perhaps also use some bonding agent. I use an addicrete add mixture which is a plant based material which also is a water proofer.
That combined with the rubbberised emulsion system really makes a great mix and you will never go back using lime. Trust me. It also has a stronger finish and reduces efflorescence. Anyway great video.
There is a lot to consider here. I think you might be talking about SBR but I am not sure. Can you send some product details so we can look at the spec? It would be great to develop this discussion.
Skill Builder thanks for the reply. Check out calmarc chemicals based not far from where I live. The product I'm talking about is screedbond. It is rather expensive and I have had many discussions with Jeffrey consulting his products and working with the plaster so give it trowel slide.
Here is the link. www.calmarc.com/
Plaster I worked with Jeffrey and there are only a few of us in the whole state that worked out the method to use this product. Thankfully I listened to plasterers from UK who stated get the plaster on, trowel it smooth and let it go hard before giving final trowel. The product gets very hard and does not draw fat so making a small batch to fill in voids achieves a more desirable finish.
Also I use a fine spray to spread the material.
www.calmarc.com/gypsum-plaster-finishes.html
Screedbond www.calmarc.com/adhesives.html
In this screedbond is a data sheet within.
Jeffrey stated the screedbond can be used to make tile adhesive mixed with cement.
I have also patched timber at 2/1 sand cement ratio with screedbond 50/ 50.
I recently did a cement dado 50%'water 50%'screedbond. It hasn't cracked yet so I will keep an eye on it. The cement mortar wasn't too strong either. That's what I was amazed with. It's like throwing the rule book away.
Mind you the lime industries don't like it.
Cheers. Keep up your great video. Yourself and Robin Specialists in your field.
Oh the cement dado I mixed I made one mix 2.8 fine .3mm silica sand to 1 cement also adding addicrete p. The second mix I made 2.5 /1 all 50/50 water screedbond. I found the 2.8 to one better mix. Normally cement dado is 1 cement 1 lime and 1.5 sand. You get lots of cracking.
I did a small screed on top of smooth concrete upon advice from Jeffrey. Since the results were rather pleasing I decided to do the mix of cement dado. I plan to actually polish with a wet concrete polisher.
Great video! If I took the old render off our garden wall, could I just put new render on, or would it all need repointing first? It's not awful under the render, but the points could be redone. Would the render kill two birds with one stone?
Don't point it. The more dents there are for the render to hang onto the better.
Can you use this method to build a outdoors fireplace ?
Always used 5-1 on render and weaker on stonework.also I prefer more of holm sand mix as it floats up really nice.
your talking tomuch
Exactly the info I needed Roger, thanks yet again. I think the BBC should create a DIY competition series like Bake Off or Sewing Bee and let you be the chief judge !! :O)
That idea was tried 30 years ago on a BBC pilot show I did with Phillip Schofield. It was called The Practically Useful Show quickly dubbed The Practically Useless Show. It was supposed to combine good information with fun but the people taking part badly wanted to win and that killed the fun element stone dead.
@@SkillBuilder That's interesting Roger. I've always felt that you were good 'TV' and surprised we've not seen you on the telly in some way. I've always been a serious DIY'er and last year retired, so can now properly get into those incomplete projects. I'm currently reroofing our place under a 'tin hat' temporary roof that was put up last week. I've discovered that the chimney pots need resetting, hence why I'm here but I assume that I need plastering/rendering sand which is not currently available down her in Eastbourne. Roger, could I use sharp sand for this purpose please? Could I perhaps use a pre mix render ?
Hi mate
I have an garage to render over lbc heaters, what is the best primer to use before scratch coat or is enough just to water down the wall?
Cheers
What is the differecne between building sand and plastering sand? Which one is finer?
What is the purpose of render? What are the properties of render that make it fit for that purpose?
Have a question so iam going to block up a door and window on my extension with breeze blocks what blocks should .I use and will I have to have a different rendering mix for this area to the solid brick area
Top bloke Roger
Cheers Roger, spot on forgive the pun !
😂
Thanks for a great video. I am doing a small shed and need to do the inside wall. I bought sand and cement. Question is do you need plasticiser. Is it essential or we can do without it ?
It will make it easier to spread but it is not essential. Just the smallest squirt of washing up liquid will do on an inside wall.
Never spotted lime in Wickes, not that I was ever looking for it.
crazygeorgelincoln they sell em in Tescos next to the lemons
Do I always need scratch and finish coat. I've got a 4m run of plinth about 20cm tall 10-15mm thick and an gonna use some Rendagrip. I normally do two coats but fancy trying it with one coat. Your thoughts?
Hydrated lime DOES set. Used it at 1:2 with sharp sand for flintwork. Still good 2 decades later.
Also used it for render and plaster.
I am not a scientist but I think what you have there is a natural pozzolan in the sand.
The addition of pozzolan to any lime mortar (hydraulic or non-hydraulic) will modify its characteristics. Pozzolanic materials can combine with uncarbonated lime (calcium hydroxide) to form stable compounds, thus reducing the risk of early leaching or frost damage and increasing the potential durability of the mortar.
I did an experiment years ago - made a filler out of normal hydrate (not NHL) and water - carbonated (set) hard.
Sand from my pit has no clay content, so no pozzalanic inclusion.
A lime company around here were trying to say that all lime historically was NHL - which it wasnt as it was all from burnt chalk - so not NHL. But, inclusion in aggregates and ash from lime kiln would have a pozzalnic effect, but not even as much as an NHL 2 from clay rich limestone.
Try a 1:2 hydrate and sand mortar - 2 days and its very much done on initial set ..... carbonation much longer thereafter.
Even Historic England are ok with the use of hydrate now (although they say 1:3, not realising that this was historic mix of quicklime and aggregate - once quicklime slakes, it can double in proportion, hence l use a 1:2)
But, in essence, no pozzolan needed for a normal hydrated bag lime.