Why Has This Lintel Cracked?
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- เผยแพร่เมื่อ 28 ส.ค. 2024
- 📪 Ask Skill Builder: skill-builder.u...
Roger looks at a problem with a concrete lintel.
Here's the message from Ryan:
Hi, so about 6 months ago, I had this arch open extended.
For the last three months, the lintel below the wall has been cracking.
The wall on the left has not cracked at all.
The wall that is cracking is on the side of the house against a main road.
I wondered if this is a problem, if this lintel must be replaced or if it can be repaired with something like a helical bar or studs through the lintel into the wall above it.
Thanks,
Ryan
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I am not a builder just a basic DIYer but I am really enjoying these short videos on problem investigations. Keep them coming please.
I'm an engineer and we have a saying at work "if it looks right then it probably is". That lintel doesn't look right. It's the wrong product for the job.
Hi Roger, love the video.
I have some experience with this type of situation. One thing that's often overlooked when designing or choosing a beam is how it will deflect (bend) when underload (installed). When doing a job like this its not just a case of assessing the beams capacity to take the load (dead and imposed loads) but also how much it will bend and sag over time as the load is applied. There are British standards that are used to assess beam deflection and if it will cause cracking to plaster or any final surface finishes. An added complication in this case is when lintels are installed in this scenario there is likely to be a small gap above the lintel and the brickwork above it. Meaning over time the brickwork will sag and start to fully bear on the lintel and cause it to deflect. If the beam deflection hasn't been taken into account when selecting lintel size then you will see a crack.
This link gives a guide for steel, principles are very similar: th-cam.com/video/brC9JEKqV7M/w-d-xo.html
Bang on Roger, “Wrong Lintel, wrong guys”, succinct & straight to the heart of the matter. Should have been steels, no argument.
For a non-Engineer you explained it very well. When doing stress calculations on a beam like this the inherent 'strength' of the beam determines the load it can carry. By straining the metal bar and letting concrete set around it, the inherent strength of the beam is increased, It is pre-loaded (= pre-stressed). It contains energy, strain energy. This can be compared to your van. Its static weight that pre-load the spring with twisting energy in the spring. When you go over a pothole the wheel is pushed downwards by this release of strain energy stored in the spring. Without this the van would lurch into the pot hole. Same thing with continuous railway lines. These are stretched and welded at the same time. When the sun heats them up the stored tensile strain energy absorbs the energy of thermal expansion and so they don't buckle. Strain energy stored in toughened glass makes it shatter into small pieces.
The upwards curve of the lintel is encouraged because concrete is very strong in compression. For the beam to sag it has to go through the mid-position which is resisted by the compressive strength of the concrete on the upper surface. Building the lintel into 'wet' brickwork adds to the compressive resistance on the upper surface. With the upward bend the additional bricks would all have to compress for the beam to pass the mid-point. Built in 'dry' then there is a built-in fault line above the lintel that can move a bit more than if it were all done wet and set at the same time. There is however an ultimate load in all of this. The weight of bricks above will ultimately exceeds the benefit of their compressive strength, its going to sag.
The wet brickwork does not add to the compressive resistance of the concrete it increases the compression in the concrete. Wet brickwork does not act as a beam. Built in 'dry' the lintel would be nominally arched upwards. Crack should not appear above lintel if properly installed.
@@lenb9037 Len, you are correct. My (and Roger's) use of the term 'wet' refers to the laying up of courses of brickwork using wet mortar on top of the pre-cast (dry) lintel. If something like SBR is used there would be a good bond to the lintel and once dried out, the effective depth and strength on the cast lintel would be increased due to the homogenuity of the now dried out mortar. For the lintel to go through it's 'arched up' posture would require this new brickwork above the lintel to compress. It will do so eventually, but only after it has provided addition load-bearing capacity to the lintel. I agree with your last sentence, but we all agree that this is what this post was all about, the lintel was not installed correctly. I'm not as convinced as you that a 'dry' installation would ever me good in this instance, but I'm an engineer, not a builder!
@@whitefields5595 Design for 'dry' brickwork would be normal for this application in an existing wall and the packing above the lintel and below the 'dry' brickwork would be installed as tight as possible to restrict any gap perhaps with an expanding grout admixture. I personally would not consider SBR in structural calculations although there may be some nominal/minimal assistance. Just to clarify I am a structural engineer (retired) not a builder!
It would be interesting to find out whether the lintel may have been installed upside down and if so whether re-installation took place to correct it.
Well said “you never stop learning”, unfortunately some individuals never start. 😂
In 35 years I’ve never heard of a plank lintel 😳. The fact that there is a full pike/ gable above that room means that wall is load bearing.
My guess is that the left hand one is in correctly and the right hand side is maybe upside down? Meaning the pre stressed camber is pushing down instead of up .
On openings that big steels every time 🧱🤙🏽💪🏽
Steve
They call them plank lintels in the South of England but we are as thick as two short............planks down here
@@SkillBuilder 😆😆🧱👍🏽
Not all gable walls are load bearing, only older ones with purlin roofs. Modern ones with trusses aren't.
@@lksf9820 surely the gable is a load in itself , that’s a lot of heavy bricks above as in a “ load “
@@SteveAndAlexBuild Then It's just a wall. 'Load bearing' means it's carrying something other than itself.
The change of loading onto the central pier to support the gable wall may mean the foundation are not sufficient for the increased loading. When it was a full length wall the loadings would have been spread evenly along the foundations now they are concentrated onto the lintel bearing points and then through the piers to the foundations, point loading.
I used 150mm for a much shorter opening non-load-bearing wall. 75mm doesn't look reliable enough for me 😅
I think when you build it as one the cement and brickwork above will set as one solid object to the lintel. When you try to introduce a new lintel under neath old brickwork it just won’t form as one solid object. I reckon they might have the Lintel upside down. Having followed many structural drawings I’ve never installed a lintel of 65mm (assuming it’s uk) with that span. It would normally be a a UB or a double UB bolted together.
I think you are right (again),
@@SkillBuilder wish my missis thought the same 🙄😆
1st thing I said in my head was the lintel is upside down, I would only use a lintel like that above a patio door with no more than 3 courses of brick on top otherwise its a steel all the way even a box section would be better pre stressed concrete lintels have their uses but i don't think that is one of them
Yes the thin beam and brickwork effectively form a compound beam from new. But replace the beam and use a beam designed as if the whole lot above constitutes the load, plus using acros during the process, of course!
@@johnf3326 so effectively the new beam would be calculated as a separate entity.
Spot on Roger, as soon as I saw that, I could see that the incorrect lintle was used.. Steel would be the way to go..
Didn't even realise you could get those lintels in that length. It won't even support its own weight over that span. I wouldn't be surprised if the bricks above are supporting themselves and the cracks have occurred where the lintel has sagged away from them under its own weight
You can see there is one acrow prop supporting the middle of the lintel before it's plastered in. That would suggest to me that maybe instead of fitting the lintel and installing brick work above, or dry packing with mortar they may have tried to wind the beam up to the underside of the existing brickwork. If I were installing a lintel or a steel beam I would form a pocket or shoulder using a padstone (are there any padstones?) and sit the ends of the beam/lintel on that. Sometimes you can't do it that first and might need to build the padstone up to the bottom of lintel/beam, in which case there should be a prop at one or both ends while the mortar is setting.
Did he have a structural engineer's calculation? Were building control involved at all?
If there is gable end brickwork above that would be classed as a load bearing wall, even it wasn't supporting joists or purlins, it is supporting the weight of the masonry above!
Never seen a "beam " like that before. Only time I've seen a flat lintel is above a short apan like a window opening. There's no strength in that. That added wih probable inverted installation could account for the drop or sag. Get the builders back in. Give them cups of tea and plenty water for their horses.
That scarf is certainly 'entertaining' Roger! 👍😎
He's wearing it to cover his concrete wrinkles.
cant afford to run his heat pump 😅
Hab Som
It is called a snood and it is from Keyfix.
Those 65mm lintels should have 2 courses of Engineering bricks above with ex-met reinforcement in the bed joints, built in one go as you said Rog so in effect it becomes a 225mm deep solid unit
You're right about the compression of concrete lintel. They have to be built in wet so the weight of the bricks pushes down against the upward force of the rods.
The opposite effect is with those thin metal lintels you have to support them with timber until they go off.
Even if the beam is correct for the span it should never have an acrow jacking it up in the centre. If this needs to be done to squeeze the mortar between the lintel and bricks above it should be done at each end. This takes out any bowing which may take place once the mortar is set and the props removed. It looks in the pics that the lintel has settled in the middle causing the cracking and can probably be packed and repointed assuming the lintel is correct for the span and there’s no underlying structural issues.
Shows how important it is to now protect unsuspecting customers and regulate the industry to prevent any upstart calling themselves a builder imo.
Looking at the picture it looks like it was a garage that's been converted. Hence the roof above. Either Way you can only remove two thirds of a supporting wall . This looks like more has been removed. The cracking has occurred because the builder has pushed the lintel up in the middle with an acro prop when bedding it in . Hence it's dropped back to its neutral state . Just cut out and repoint with a finger trowel.
I’ve recently removed a load bearing wall to form a open kitchen diner, used a RSJ and no cracking at all.
Usually in a prestressed lintel the top of the beam is the rough bit. Also the stressed rebar would be in the bottom of the concrete with about 50mm of cover. Concrete is strong in compression and weak in tension. Hence the bottom of the beam would be in tension if the load was great and the rebar here was not prestressed. In this way you can get away with a smaller beam. But at 75mm you could only have rebar right down the middle so prestressing would not have as significant effect
I put in a concrete lintel just like that. About same length. But mine was 150mm tall and only held up 5-6 course of brick which the rafters didn't sit on anyway.
I'm not sure if I set it in correctly but hopefully over did it on inherent strength side.
Roger your channel is one of the best. I don’t comment on these types of platforms often, but I want to offer that this may be an interior wall, (ie not likey but possible for sure, we cannot see the layout but I may be wrong and it is indeed under a gable- the drawing is not a shop drawing nor blueprint) and I’m wondering if it’s a combination of poorly installed finishes in conjunction with the issues that you already mentioned in the video. We have that problem with drywall stress cracks at corner bead when it’s not installed correctly and when there’s movement in the walls.
If this is the case, the cracking would’ve been caused after the finishes (ie in my country, drywall/plaster, trims, paint) installation by any additional work done above the are or by dynamic loads above the lintels.
In addition to poor design, the execution of finish installation can contribute (though not “cause”) these types of issues.
Thanks for all you do! Kudos!
You are correct Roger about the courses of brickwork above the lintel being required in order to form an arching effect. The manufacture normally stipulates the minimum number of courses required for the sectional size of lintel, this could be something like 3,5 or 7 courses. Your are meant to lay the lintels with the rough side up and just like rendering you should give your brickwork and lintel a wet down first with something like a garden pump up pesticide sprayer to control the suction much like in rendering with a scratch coat or priming. Also best to pack in structural non shrink grout between the existing brickwork and lintels. Think of the brickwork and lintel combination being like the section size of timber, the deeper the beam of the brickwork and lintel the greater it can span. It acts much like a floor joists versus a ceiling joist or a common rafter vs a hip rafter. Also the brickwork either side of the lintel matters, en castre is the engineering term if I am not mistaken, this resists the deflection/bending moment of the beam.
The bearings on those lintels look rubbish, it honestly looks terrible. Normally building control want a minimum of 150mm bearing if a lintel is retro fitted. Also on some sort of Padstone. That looked like a load of cement just parged in. Also like Roger said, it would have been steels not a shite concrete lintel.
Where is the building inspector. They have to be involved on structural work. They would not have allowed a prestressed lintol in that situation surely.
My thoughts exactly, needs an SE and a building control application, that needs sorting ASAP
I believe the interlocking of the bricks above the linetel is called the cordobelling effect(bricks lock together preventing collapse.
It is exactly as you describe and that is what you are seeing here in the images. The lintel has sagged and isn't having any contact with the 'self supporting' brickwork above it. They need to strip the lot back and make certain the lintel isn't fitted upside down then at the very least install wedging packers between the lintel and brickwork and point the whole joint full with sand/cement mix. The size of the seating nibs at either end may also be too small as it stands.
The wall below the eaves/ceiling level should definitely be described as load bearing if there is a brick wall above.
All lintels of this type with brickwork above must be designed for the weight of a triangular brickwork area directly above in accordance with the relevant standards (which assumes the brickwork above the triangle will arch and support itself). In this case the depth of brickwork above the lintels at either end may not be sufficient to conform with the relevant standard (i.e. insufficient to arch properly above the nominal triangle) due to the gable shape and a more liberal loading should be adopted for the lintel design.
If its a fair face or fire spec lintel they have a top and bottom and are usually marked, but rule of thumb is to position the reinforced steel rods towards the bottom away from load thus eliminating sag.
I’m surprised that got past the Building Control inspector. It wouldn’t have got passed by my local Council.
It would be nice to see the brick work above to see if there is any cracks
Like someone said its not the UK? It would be steels with UK regs and that pillar looks ropey too, would probably be a steel too in UK. As it stands it probably won't crack more so just fill it if its definitely got no loading but I'd want a structural engineer to have a look.
Bringing new build quality to old build property.
it was nice to hear you on BBC radio 2 yesterday!
Thank you,, it was difficult because I was on site and had to ask everyone to stop working to keep the noise down, it puit me under a bit of pressure.
Nice JINGLE😂
The reason prestressed lintels tend to arch upwards should be because stressed reinforcement is placed below centre and the off-set results in an upward bending tendency. Could it be possible that they have installed this lintel upside down? That would greatly reduce the strength of the lintel, not necessarily catastrophically if it is not heavily loaded, but it could account for the cracking. As an ex- structural engineer, albeit with limited experience, that was my first thought.
Your description of tensioned wire reinforcement placement is absolutely correct. I spent some years working for a concrete fabrication company who made all types of concrete lintels and this as you describe is exactly how the moulds and reinforcement were set up before pouring.
@@howardosborne8647 When I was working as a structural engineer my job was to do the design calculations for reinforced and pre-stressed concrete beams, columns and slabs. I did not do this for long - hence my stating I'd had little experience - but the principle I described I know is correct. I guess I had enough experience to know that the basic principles haven't changed but, just to date my knowledge, I did my calculations on a slide rule.
As you said Roger prestressed lintels are supposed to have 6 courses over and anything over a metre is supposed to have a 150mm bearing that looks like 100mm also there's often a way up to them too I took one out of the garage door opening on a townhouse Ashford that had a crack in the middle when we got it out there was an arrow on the front pointing down, it had been layed upside down 9" deep with one rebar in at the bottom
Isn't the rebar supposed to be at the bottom?
@@SkillBuilder yes I didn’t make it clear, the lintel had one piece of steel at the bottom with an arrow pointing upwards but it was layed upside down with the arrow pointing down
A 9" x 6" concrete lintel for that span is a must, a single course lintel is bound to sag
Marginal depth pads atop that pillar as well.
The point of building the brickwork on top of the concrete lintel is that the bricks "hold the end of the lintels down" and also the mortar ties lintel and the bricks together. If you just squeeze the lintel under the existing brickwork you support the ends of the lintel on the bricks at the ends and the lintel doesn't really support anything (the bricks will "float" above it, even if there is no gap) - sooner or later you get this "triangle" above it because those are the bricks it was supposed to support.
In this case I assume the lintel was soo long (and maybe upside down) and sagged on its own weight even without the bricks pushing down on it. Assuming the lintel could have supported the bricks above - if you laid the bricks on top of the lintel, they would have bent the lintel a little, but because everything would have "sagged together" you don't get a crack anywhere.
0:43 you can see the electrical panel - that looks like a USA panel, that might explain some of the points and issues and techniques used.
Could be S.A
The span is way too long for any notable load for a prestressed concrete lintel of that depth to provide structural support. I’d never design one for a span over about 1.6/1.8m.
Roger, did you ask the guy to send the structural calculations? Does he have any?
Excellent roger..
Easier to install upside-down since any bow won't hit the bricks above it!
You look like a Radio 2 presenter sitting there all wired up 😂
Are there any left?
There’s not a lot of bearing by the looks of it either roger, can’t believe that was knocked out without a strong boy in sight 😬😬
Don’t stress out too much as it is that tiny pilar in the middle that failed 😅
thats not in the uk looks like south africa
South Africa’s tends to have better building standards.
they put the pre stressed side arc facing down
that was my thought too. I have used dozens of these, and there is always an arc. Not sure of what they are bedded on either, from the photos looks like excessive mortar, but I could be wrong?
You could maybe educate me Roger, but thats a hell of a span for a 75MM lintel init?, just asking
They sell that lintel so it must work under the right conditions
Composite Vs non-composite are the 2 types. One needs bricks above it, the other can take direct load.
continuous wall ? how is that not load bearing?
Issues like this is why we use structural engineers. Above our pay grade to understand why it's not enough to take the load 😅
Simple rule in sizing: If it looks right it is right and vice versa
Ugh get rsj's in there ASAP!
from what I can tell from the pics i would say it is load bearing, but would need to see more to say for sure. but either way you need to get somebody to look at it properly and im guessing rip it all out an put steels in.
On my extension( single story) I used a steel that accomodated the block and brick over the door and window.Very little load on it but under building notice it should and would be capable in the future of supporting a second storey above if that was ever done not that I will but in the future someone may.Much like the footings I built it on.Able to support another storey easily.To be fair UK building regs are as good if not better than any in the world structually.I prefer to over engineer any job than under engineer.
I’m not a builder but I would want a structural engineer to see that before any works done , I would hazard a guess this was done let’s say on the cheap.
I think pretty much everything is covered in the comments. Brickwork really needs to be built over them as you go and fully propped until it has cured. There is plenty of room to use 150mm lintels or steels. I certainly wouldn't consider using such a lintel on this span retrospectively.
It seems a very odd choice, I would assume the length would make a steel the optimum choice.
I tend to assume when space isn't a premium you don't want it to feel marginal.
This is a mystery Roger, there is an inside on this side of the wall and an outside of the wall. So, basically, there is no brick work in the middle of this home. Is there? Curious, because you are awesome, but maybe the pictures are just misleading.
So if it has a set of bricks on the top, presumably as they are rigidly connected, they become part of the beam and are in compression? Hence why you can get away with the plank sizing.
looks like the lintel is not sitting on enough brick! Not a reason for it to crack though. Can only see cracking in the plaster work! Could the lintel be Ok behind the plaster?
I'm not sure why they didn't use steel box lintels...you can get them made to just about any dimensions and you can offer them to the upper coarse because you're allowed to pad the ends. 🤷♂
Did they go through building control? Did they use an engineers design? Or was this the builders idea?
I suspect the latter. Which may cause an issue when they try to sell the place. Any search by a surveyor will show the work was never signed off and it'll need retro inspection.
If they went through building control and an engineer, the install must be wrong. Maybe it wasn't packed well.
But my feeling is that they should have used RSJ's. I cant see how it's a non load bearing wall with that gable above.
And that supporting pier don't look sufficient, it should maybe have been a steel post bolted to the RSJ's.
Lintel not strong enough or packed properly under brickwork above ?
when I did building work with concrete lintels or even steels in this way I would tress the lintels by hammering wedges between the centre brick and lintel or beams so it took the load, basically taking the slack out of the lintel or beam
What were your wedges made from?
@@lksf9820cheese I believe. Bloody expensive these days though.
@@ricos1497 Wenslydale then, Dairylea would be no good here.
@@lksf9820 chisels or a bit of steel, it doesn't matter of the material at it can be removed after pointing up, there are many ways to put a lintel under a bit of stress,
Should have put a steel in on pad stones job done
How’s that been passed by building control ?
Imagine that the pre stressed lintel was installed upside down?
The bow pointing downward???
Surely a gable end wall is a load? Too much flex on a lintel that thickness with the span. When built in from the beginning the cement bonds to the lintel making it far stronger …
First thing is this sort of structural work needs building reg's approval and if you do that you'll need structural calculations for the lintels. A structural engineer would specify a steel for this job, single course pre-stressed concrete lintels are generally just for small spans and standard/light loads.
It really is worth the extra expense of doing it with BR approval as not only will you sleep easier and have no problems but when you come to sell the house you can run into big legal issues with the solicitor costing you much more than the few hundred it would have cost you to do it properly.
? how did building control pass this? Bearing is too short and as stated should be a steel or load bearing lintel.
I do not like the look of any of that, it does not look safe. Have they plastered directly onto the concrete lintel? the same coving is visible in the before and after. At 1:18 The original plaster on the brick seems to be flush with the side of the lintel.
This hasn't been seen by building control or a structural engineer, it is not safe, you need to get some props under this soon as possible, is the concrete floor beneath the central peer capable of holding the weight.
Those 75mm precast lintels are non load bearing!!!!
One rule of thumb for rc is beam depth in inches = beam span in feet. That beam may have been installed on its side….
Exactly 👍🏼 - and maybe a bit more given the load that it’s supporting above. It’s only a matter of time before the whole house comes down.
Do the concrete lintels not have a top and bottom? How can the manufacturers determine in which direction they will bow? Is it by placing the rods offset within the concrete? 🤔
some do some don't. In a plank lintel the rods are in the middle and you look at the bow.
@@SkillBuilder Thanks. Just can't understand how, if the rods are in the middle the direction of bow can be controlled? Surely each rod could be working against the others? 🙂
What did you mean by "equalised"?
Obviously does not have Building Control consent either ! If it collapses someone will be up in front of the judge for manslaughter charges. I can’t emphasise the need to get professional help with building alterations
I can't see how that is not load bearing, looks like they need to prop asap and get some steels in there
these concrete lintels are OK for a single door opening but the span of that opening is far too much for the capacity of the lintel and it has just over deflected. The builder has not consulted a structural engineer and just taken a guess at using that lintel. I suspect that he has not made a building regulation submission. The lintel is carrying load - the masonry above - so it IS load bearing. I am wondering if he thinks it is not load bearing that he doesn't need to make a build regs submission. As you rightly suggest Roger there should be steel beams going in for that span.
Hi… we have a cracked lintel in an old Victorian house. I can send you pictures. We have insurance coming to look at it but thought would we would as your advice.
yes please www.skill-builder.uk/send
Not surprised that has cracked. All the loading from the gable end brickwork is now transferred through that tiny central column into the foundation. The two side walls will be under increased stress too. I'll bet they didn't check that whatever was underneath was capable of dealing with the increased load. In fact I'd wager that whichever shaven monkeys did the work didn't check anything much.
Just a question (driffting somewhat) What became of Roger and Rob Clevett ??, thought they were big pals.
Robin is focusing on building the 'Robin Clevett' brand.
I'm no builder but that sht don't look safe I'd go and get some acros supports sharpish as that sht looks like it could drop any time soon.
A non load bearing wall would terminate within the floor/ceiling joist
Old brickwork is always loose, so it was going to fail,
The beam is upside down 💯 the force is wanting to push down centrally
I would have got a structural engineer to look at the job to calculate the opening for the correct lintel of steel.
I think he needs to get a structural engineer in for a look in case it is load bearing. Not convinced he's clear enough about that. Would have thought best practice would be two steels, and depending on the load possibly a column.
Very rarely use concrete lintles in anything other than windows or doorways. never on opening that size! definatly should have been steel. would have thought building control would have pulled that
Just a guess. Could have been installed upside down, Then the acro has forced the lintel straight and now removed is bowing down again.
I cant find the emoji for a builder sucking through his teeth
Wrong lintel type and insufficient end bearing. Lintel used is a composite lintel which takes up deflection as you build above it and when mortar sets it can arch and work with lintel. If brickwork above this lintel then they have removed a load bearing wall which requires Building Regulations approval. Think only answer is to start again with a designed solution. The central pier design may also need to be considered depending on loads it is required to support.
👍👍👍 Thanks.
Blimey, where do you start? So much that is wrong. I always work on a lintel being able to distribute a triangular load across its length - relying on the arching effects of the masonry. You get to a certain span and load when a normal lintel will not work and you have to use an engineer designed steel (be that a UB, UC , back to back channels etc). It doesn’t stop there though as the supporting masonry also needs checking out. As a rule of thumb take the reaction as the area of bearing required. Work on the beam covering 2/3 of the length to adequate spread the load. Then do a proper check! Of course you then rely on the builder installing the new beam properly. I have seen too many examples where dry pack between the steel and existing has not been used or if it has the load relaxed before the dry pack has set. This reminds me of that and the only way to correct this is to almost start again: support the masonry above and jack it back into position, pack the resultant gap, wait then relax the supports. But if the ‘lintel’ is not good enough you have to start again and quickly!
The opening is too long for the lintel and the brickwork above is causing deflection of the lintel. If it’s single story then a concrete lintel is fine but the lintel needs to be strong enough for the size of the opening. God knows how it was signed off by building control and would like to know who did the structural calculations 😂
There was no building control or calculations done, that's the answer to that.