Why Are Aircrete Blocks Cracking Up So Often?

[@harveysmith100]

As a fifty five year old bricklayer this lack of basic knowledge drives me nuts. We used to have Clerk of the Works on sites monitoring the standard of work and materials used. They got rid of them and the problems like cracking started. Instead of asking the tradesmen what was happening the college boys thought they knew best and started coming up with all these solutions, expansion joints, stainless steel rail tracks etc. These new ideas actually weaken the wall in a secondary way. Roger was correct when he said, you shouldn't use a mortar stronger than the material you are using. Any building older than a hundred years ago had no cement whatsoever, it was all lime sand mortar with no cracking problems. Most modern problems are the engineers being obsessed with strength, "Strength is better so make the mortar stronger." No, that is the cause of most of the problems. Go look at a terrace row of Victorian houses, nine inch solid walls a street long, not a single crack from one end of the street to the other. Go look at huge Georgian houses, no cracks. Go look at huge Roman buildings that have stood for two thousand years, no cracks. But of course, we need to make our mortar stronger and add reinforcement to it. Is it me?

[@FlamesOfThought]

Couldn't agree more. Top comment

[@harveysmith100]

@@FlamesOfThought Thanks Jack. We just know

[@thertis580]

Was a subby 40yrs. You're spot on. I would add that every sand has different characteristics when mixed. And a simplistic specified formulation of 5:1 or 6:1 etc always catches the college learnt guys out. It's practical application that determines a mix.

[@harveysmith100]

@@thertis580 I agree, gone are the days when you could walk into a builders merchant and ask them what soft sand they have. Now theY say, it's just builders sand. How I long for a bag of Runfold or Westerham. (The local sand quarries when I was a lad)

[@trevorleggett1777]

@@harveysmith100 dont forget to add,every render coat,is weaker than the last one applied. As you head to the finish coat

[@memyself7413]

I love these “Skill Builder” videos, and the way that Roger explains things is a breath of fresh air and easily understood.

[@handymanr4729]

Something about the old pom builders thats just so straighforward, no knocking around - Pure and simple. Not like those americans blah blah bah

[@branwensloper8197]

This is so interesting, expecially in light of the widespread aircrete issue recently announced in 100s of UK schools and municipal buildings.

[@SkillBuilder]

More to come on that subject is a couple of days time

[@davebell4917]

There's a couple of differences in the naming, but these blocks look to avoid the worst risks of the RAAC story in Britain. What I know of that scares me is the long panels and beams. These blockwork walls are under compression loads. The RAAC beams and panels, supported at the ends, get a tension load at the lower side. The descriptions I have seen include other problems, associated with the reinforcement, which I don't see any sign of here. But this video showed a couple of details that could be easily missed - the strength of the mortar and the expansion joints. The RAAC failure mode seems nasty - less warning time than we were promised for an ICBM attack.

[@whirled_peas]

@@davebell4917 just on the face of it, anything-crete under tension is simply bad engineering, end of.

[@ziggarillo]

That is an RAAC issue, not aircrete. Different stuff used very differently

[@richardcapey-wade8191]

Spot on Roger, doing exactly that on my extension, doing it all myself as didn't trust any brickies at work (I'm a carpenter) Only one guy ever used lime before ,when he was an apprentice, they don't seem to learn much, as a proper bricklayer is a skilled and comprehensive trade when you get into it, but as most trades nowadays it's watered down to a basic craft for speed etc needed to get that off the chest, cheers

[@Carl-yu6uw]

Same here - building my extension for that very reason. Asked the mortar question yesterday to a bricky in screwfix who replied they use exact same mortar on both skins, concretes and aircrete.

[@jamieroberts6904]

Lime is the way forward

[@scottnever8732]

Sorry richard for your experience but I do agree, the need for so called tradesmen/bricklayers was so high they invented an NVQ. worst thing that ever happened to my industry. passing people within 6 weeks for a job that took at least 3 years to learn with intensive training . Blokes that I learnt from were on a 7 year apprenticeship

[@johnclements6614]

@@scottnever8732 There are too many things that only come up now and again to be taught in 6 weeks. People also do not remember everything they are taught first time. You get decent craftsmen if they do a year in the classroom then a couple day release. then they get to be on different sites and see different things and problems.

[@rob-123]

@@scottnever8732 NVQ? Not Very Qualified...

[@lelandcarlson1668]

A skilled tradesman is invaluable. I'm always amazed at how many details go into a trade like masonry or carpentry. Great video!

[@Cruner62]

I'm not a bricklayer but I am a qualified engineer so when I built my own home I read up on this in detail and consulted my inspector. We decided upon using a 5/1/1 mix for the mortar one was lime. We also looked at where to put an expansion joint in a 12m front wall facing the sun. There were four windows in the ground and first floor ( Brick faced and 7n 140 mm light concrete block internal) in the 22 years there has been no cracks inside or out. We did fit bison Hollow core planks 8m single span that also helps to prevent movement of the inner leaf by absorbing the heat and cold expansion/contraction with underfloor heating to maintain a consistent temperature level., also we kept the windows on both levels 1.2 m from the corners to avoid stresses there Hope this helps.

[@JehuMcSpooran]

Dad made the brickie use lime in the mortar with our first house that we built back in 87. None of the brickwork has cracked even though other parts of the house had moved. I don't know what the ratio was but it has lasted.

[@brettarmstrong4040]

So so so refreshing to listen to someone who has knowledge from experience and not someone talking about what they did last Tuesday for ten minutes and two minutes on what you clicked on, based on what they think from watching someone else doing it on KZbin Job well done and a job done well!!!

[@TheSnekkerShow]

This was eye-opening and helpful. I never thought about the consequences of mortar being too strong.

[@richardross7219]

Very interesting. Many years ago as a teenager, I mixed mortar for my old man when he was laying block. That built up my muscles fast. We used lime in the mortar. I became an Army Combat Engineer and a Civil Engineer. I avoided using bricks and blocks because I found that there was too much inconsistency with our masonary work in my area. Very good video. Good Luck, Rick

[@ivornotion6624]

Feel like I am repeating the praise levelled at Roger from the many comments below but without the effort Roger puts into these videos the world is a poorer place. 'What we do in life echos in eternity' -

[@SkillBuilder]

Thank you Ivor.

[@Aaron-gl8cm]

Movement joints for blockwork are approx 6m in any straight run and 3m from a corner. This can extend to around 9 and 4.5m if you use bed joint reinforcement. It's closer to the corner as it's a point of high restraint. I say "approx" as if you were to put a joint after say 7m it won't definitely crack it will just have a higher chance of cracking. Roger, you hit the nail on the head with the mortar.

[@zeez9053]

Way impressed what a total clear and concise video with everthing gone through and fully explained 👍🤘

[@UberAlphaSirus]

Yhea, I am absolutly allergic to wet trades and ground works. So it's a nice head up on stuff I don't/won't get involved in. I can't knock this lot to be fair. Sometimes there is a a bit of a fuck up, but you have to piss with what you got at the end of the day.

[@hectorheath9742]

Bollocks, he says the weight of a JCB and he'll have meant an RSJ. Re cracks he's saying the cracks will be in the mortar if the mortar mix is 'right'. How is that better? And Nm (Newtonmeter) is not a unit of pressure, and 3.5 Newtons is like 4 apples of weight so that can't be right either. He mentions reinforcing mesh in the mortar; he should have said the first coat of plaster. The aerated blocks in my extension are riddled with cracks..bottom line ..aerated blocks are a crap building product.

[@UberAlphaSirus]

@@hectorheath9742 The problem is you think you know, but have no idea.

[@hectorheath9742]

@@UberAlphaSirus Oh really, Sirus? You've gotta defend your comment with a reason or reasons. Tell me what's wrong with my accurate review of this shabby vid. But you'd better read the rest of the comments first.

[@UberAlphaSirus]

@@hectorheath9742 I told you already. "The problem is you think you know, but have no idea." I read everything you and others said before. What do you want me to do? I can't un thick you.

[@OttoTheWeim]

Here I am watching a British man talking about mortar and air Crete with no general usage for this information aside from personal knowledge. Great presentation and now I can maintain a conversation about the subject with my mates that are in construction.

[@metropolitandream]

OUTSTANDING explanations. It pays to attend to these details if you want a lower maintenance home. Super helpful info.

[@FSM925]

I love how the way he demonstrates it moving “in and out” at 1:34

[@OB-LA]

I liked the presenter right off, he just sounds and looks like a journeyman, expert builder.

[@markhaynes6410]

Didn't he do well kids?! Only the slightest glint in the eye when the background noise started 😂😂😂 Great little video though, informative as ever.

[@allanmcintosh3347]

The mortar doesn’t hold the blocks together, it holds them apart. Grin.

[@SkillBuilder]

could something not do both? double grin.

[@SirGregory]

[grin] I like the use of plain English emojis. [wink+thumbs-up]

[@doordye6503]

Say what..

[@FelonyVideos]

He's right, you know. Most masonry is very strong in compression, but useless in tension. That is why a shifting foundation always yields cracks, and never smushes the grout out of the joints, and you never see bricks crushed.

[@paulhunt8743]

that's why they used lime it accommodates for movement lime is a softer mix that cement

[@ML6103]

Regarding the mortar not being stronger than the brick. This now makes sense why the 'hebel' blocks produced in Australia have their own specific mortar. Very good to know and thanks for the video

[@ksptm4]

It’s like you knew about the potential RAAC issues before they were made public knowledge. It’s a pity that those in power and authority do not consult skilled and experiences engineers such as yourself. Love your channel, as an electrical engineer, I still find it fascinating and your delivery of information is on point. Absolute professional and fantastic educator. Wish you all the success with the channel

[@ericconnor8419]

This is aircrete, the bubbles come from aiding aluminium powder. RAAC is made in an autoclave and has reinforcing (giant pressure cooker) It stands for Reinforced autoclaved aerated concrete

[@golfhacker9051]

Precise, well worded, simply explained and no unnecessary drible.

[@rauldemoura2417]

Very useful tips. I especially liked the tips about the different mortar mixes for block and brick. I never knew that! Of course, I’m no concrete or brick laying expert. Thanks!

[@FlamesOfThought]

Thank you and I hope you are alright and in good health Rodger - you're a treasure in the trade

[@habsom1406]

Fascinating! Would never have thought you can have too strong a mortar but hey you live and learn, thanks Roger! Good job I'm not a builder ha! Really clear and well presented video, top class production.

[@mmpod70]

Very well explained - you should lecture Specification writers and Building Designers - best explanation I have heard in 30 years Cheers keep up the good work.

[@terrymontague7946]

Many thanks for such a clear explanation. I now understand why the block walls inside my internal garage have cracks in them. The house is around 25 years old with dot and dab hiding most problems but not in my garage.

[@MrMatiDi]

Amazing - the quality of these tips and advice can put many a college to shame. Good job

[@EireFirst2024]

I only saw this on a new (ish) build,googled it - found the video, result = explanation / relief.. Nice 1 Roger 😅

[@XstaticState69]

Aircrete blocks cracking is nothing new! I used to do up to 10 site inspections a week on self-build houses, housing estates and apartment blocks back in the 1980's and 1990's, sometimes the blocks would have serious cracking even before building completion! This is the reason, why I have never specified aircrete, or lightweight blocks on any of my projects! Chartered Architect.

[@Mariazellerbahn]

My house was built by Redrow in 1997. Lots of these celcon lightweight blocks visible in the loft, a lot of them cracked and I noticed whilst being built that the upstairs floor joists are are laid on these blocks where I would have put a wooden flat bearer to spread the weight. I have also noticed that the celcon blocks have also been used underground in the main foundations.

[@nc3826]

thx for sharing your years of practical experience, detailing what to do to help prevent Aircrete Block cracks.... and a few good tips for working with any cementitious block... But your main point is hire trades people who have a pride in their work, and will not cut corners.... Since knowing what to do vs doing it are 2 different matters... But even then you need other people such as the general contractor or ourselves spot checking its done to specs.. Check it 2x (or 100x) times and cut once is good general rule....

[@bisthebuilder7305]

6:1 mortar and EML every second course everywhere. I have used this method for the last twenty years and it works. I pay £6 for a 20m roll of EML, this covers approx 18m2 blockwork, works out at 33p per m2. It's a no brainer to me. As you said Roger the brickies don't like the tramline reinforcement but the EML is easier to use.

[@bimble7240]

What is EML?

[@SkillBuilder]

Do you use stainless?

[@SkillBuilder]

Expanded metal lath.

[@ljens8485]

This fella is outstanding.

[@thescouselander5531]

Very interesting. I was always worried about these blocks in my old house - drilling into them was like drilling into fresh air and they generally seemed extremely weak.

[@neroc1]

another excellent video, ive been told to keep the block dry as well , thanks for sharing your knowledge.

[@SkillBuilder]

Yes it helps to keep them dry but that is not always easy to do.

[@simoncooper8272]

The problem is typically inherent with a wrong strength mix! The mortar joints need to be at least 10% less strength than the material being laid,

[@carolegreen8701]

In warm conditions these blocks absorb the moisture out of the mortar as it is spread .Always soak the blocks when laying .Bigger cavity and clinker blocks preferred choice .

[@dlorien7306]

I'm laying my first blocks & they soak out the mortar moisture wicked fast in 32 C (90 F) temps. But my block mfr does *not* recommend pre-soaking. So, 2 questions... Are you talking about aerated or autoclaved aerated (or both) and what is your pre-soak rexommendation based on?

[@markanderson6969]

We've all known about the mortar being to strong for years but nothing changes especially on new build with silo muck, same old story quantity over qaulity

[@MrB3ngy]

Agree silo muck is used for concrete/thermo lite/ and the many different bricks used on site. Whether there engineering brick or soft stocks. That’s why these new houses have massive shrinkage cracks when the thrown up in the depths of winter.

[@terrytytula]

Really enjoyed the video, don't know anything about brick laying. I just replaced the vinyl on my house, and had to follow the same rule about allowing movement, in my case to prevent buckling and distortion.

[@workdevice7808]

Wow! Excellent presentation and superb information. Thank you!

[@simonharper4199]

i was told many years ago by a long retired foreman who went to see Celcon blocks being made ( from one massive block and the wavy lines in the blocks are the marks of the saw teeth that have cut them up) that the manufacturers specified laying 100mm expanded metal lath into every third horizontal course . Goes to say that ive never seen it done.

[@SkillBuilder]

That is true

[@BlueBeeMCMLXI]

Thanks, Roger, that opened my thick head up. You have saved me a lot of bother. Good man!

[@MrEtonmess]

Excellent video. Sounds like a ‘wonder block’ which creates more problems than it solves. I drive past the 100+ year old terraces and wonder how far we have come. Fast fashion, fast food, fast houses?

[@Lou.B]

Great video! Fascinating and very knowledgeable, Roger! Thank You!

[@topflightmechanic8692]

I don't even work in the construction industry but that video explanation was well done

[@rickygray222]

Those aircrete always make me nervous, they’ve got the consistency of a wotsit

[@gbwildlifeuk8269]

A wotsit? I dont know what is it?

[@800Viffer]

AKA a "What's it"

[@FlamesOfThought]

@Bercilak de hautdesert a puffy air-filled one

[@EzeePosseTV]

Wotsit! What a Whopping Whoosh!

[@romanszefler7479]

Hmmm.... ? Looks like that's a trade of personality BEING NERVOUS. Just do something even if its wrong

[@darrellbrown8977]

Just a couple of things !! 1. Most sites use silos now that are 6/7 to 1 ratio 2. What’s the point in a movement joint on the blocks if u are dot and dabbing over it?? 3. When u use a movement joint u have to use more wall ties! Every course vertical up both sides!! It’s literally going to do the same thing! 4. Better using train track 5. It’s all down to how materials are stored and kept! Sites should be setting up with a tin roof over all bricks and blocks keeping the rain and damp from getting to them! 6. Better kept materials = better work = better houses = better trade simple as that.

[@spanishpeaches2930]

Used thin joint on my extension and used reinforcement every couple of layers. Used monocouche rendering on the outside on the blockwork. Much better, and a better finish.

[@miastory247]

totally impressed by your tech knowledge! wow! I am thinking now of using fiberglass more. however I will keep your video filed for reference and try to follow caution as much as possible.

[@sarwarn2107]

As a structural engineer, we normally provide expansion joints to the external leaf and contraction joints to the inner leaf for traditional masonry wall. For the brickwork this need to be every continues 9m of wall or less and the blockwork is every continues 6m of wall or less but from the corners its good practise to provide at half of that distance due to high stresses from thermal expansion and higher induced wind load at the corners.

[@murraymadness4674]

I also thought lightweight concrete was a great way to save time, mortaring blocks of them vs pouring a tilt-up wall seems backwards! Anyway great video, concise no nonsense

[@petemoring67]

Roger Bisby & Common Sense ..... Always in the same room together :-)

[@PBG762]

aircrete was design as filler material for partition/non weigh bearing walls. supposed to be put inside rigid cadre that takes the load- key word rigid. So steel/wood frame = no go. Should go under concrete frame-post and beam, even that will give you crack at joints, so best option drywall/mesh-fiber glass of chicken wire over.

[@mattphillips9107]

Lol this is now a scandal 2 years after you posted this. Nobody listens!

[@jwatkins5155]

No... You're talking about RAAC this is a different material

[@katabrontes]

Hi Roger, it's the same here in France. Sadly you often see stone walls repaired or repainted with cement instead of lime mortar. Trouble ahead I am sure. Mike

[@WideCuriosity]

Interesting. Thanks. But what would also be useful is precise details on how to fix walls both internal & external where a previous owner's builders have already messed this exact thing up. (And how to find a builder both capable of understanding the required job and not deciding that crack fixing is too small a job to bother with, so not submitting a quote.)

[@lightning9279]

Roger, well done. Straight to the point with the facts. 👍

[@jinron24]

I've noticed here in the states that building construction has taken a turn for the worse, materials are sub-standard, workmanship is atrocious and a general lack of pride in what's been constructed. Back in the day we had trade school education in regular high school, now all that is gone. I don't know if you see this where you are or that maybe it's a touchy subject to comment on!

[@AmityPost]

The more houses fall down, the more new ones you get paid to build.

[@AmityPost]

It's common sense to me when you see castles from the 1500's still standing and luxury apartments from the 80's collapsing and killing people. If we still built our buildings like they did in the dark ages, they would all still be here and most builders would be out of a job.

[@metagen77]

@@AmityPost Take a look at the heating bill of a castle and you will wish the ceiling had collapsed on your head instead.

[@alext8828]

Best teacher in the world.

[@akesha4138]

Thank you for educating the uninformed, enjoy learning about this topic.

[@petergambier]

Thanks Roger, sound advise thanks. Lime spread here, I don't like to see expansion joints or use angle-bead on corners but I can see why they are necessary. At the start of the pandemic I built a 7 meter, half-round, rubble stone & old brick lime putty mortar wall without a concrete base and no expansion joints about 4 foot high, 3 stones wide with a stone & mortar infill to hold the end of my veg garden in. Finished in 3 days (lots of big stones) and about a year later big cracks suddenly appeared right from top to the bottom in 3 or 4 places almost where the expansion joints would have been. From the end of the wall to the first crack was about 2m.

[@klingonwarrior1206]

He knows what he is talking about, he should be a minister for buildings for our country.👍👍

[@Casual_Comment]

More likely to be filled by the secretary of state for sports and media

[@richardgraham2303]

Excellent mate spot on 👍🏴󠁧󠁢󠁳󠁣󠁴󠁿cheers

[@eamonhannon1103]

Excellent advice Roger !

[@californiadreamin8423]

The same principle described here, applies to brickwork, particularly pointing. Too strong a mortar could lead to shrinkage cracking of the joints and even brick fracturing, particularly on soft dry brickwork....a good soaking helps to give good brick mortar adhesion. In restoration work on really old brick, a lime sand mortar, no cement, may be required. A controlled small amount of cement may be added to help the mortar “go off” a little quicker, but there is a lot to be said for avoiding too quick a build, to allow the brickwork time to settle under its own weight. I don’t know if the Brick Development Association still exists but 40 years ago I found their data sheets very informative when I worked for a small civil structural consulting engineering practice.

[@SkillBuilder]

Yes the BDA is still around but is largely a marketing arm rather than a research body. I agree with what you say but fast track has made lime mortar uneconomic.

[@SigurdVolsunga]

Research has found you shouldn't add any cement to lime mortars, they work best when they are just the lime. Any pre WW1 house is probably built with lime mortar, and any repairs on it should only be done in lime, using cement will cause brick damage and dampness.

[@hondacr250hrc4]

I wouldn't buy a new build older houses are solid

[@jeremyscott6641]

I always like knowing if it stood for 25 years and still looks good the problem you will fined are usually just cosmetics.

[@MindBodySoulOk]

Are yall writing with an English accent? I'm reading and it sounds like an English accent.

[@TheRainHarvester]

Leaded pipes, asbestos, aluminum wiring, roots in septic...But the wood is tight grained! :-)

[@davidjames666]

@@TheRainHarvester aluminum wiring was an experiment in new home construction 20 or 30 years ago. it was short lived as the resistance caused the wires to heat up and burn the house down.

[@robertaylor9218]

Yes and no. Survivorship bias, the houses that stand the test of time were better built, the poorly built one's aren't encountered and easily forgotten.

[@martinlouden9005]

Cracking bit of advice there Roger!

[@p2as33]

Another interesting video, you explain these things really well.

[@SkillBuilder]

Thank you very much!

[@travisklein6831]

Lovely Malcolm McDowell “A Clockwork Orange” tribute at 1:35 complete with in-out hand gesture and authentic accent.

[@aileenjohnson1508]

Smashing video did not realise how important mixes were when dealing with different tasks, I amgoing your and build a small seating area which will be inside a breeze block walled area, and hopefully render so this video has been sooooo helpful thank you

[@michaelharrison9340]

Bed reinforcement (such as by BRC) is available, laid typically in alternate the bed joints to allow the movement joints to be spaced further apart or even omitted.

[@mpdavis731]

And I thought this was about laughing blocks - still, enjoyed it and subbed. Thanks!

[@espats9212]

That’s why we use either glue or mortar of 1mm in Europe, both for cracking and to not loose the insulation properties

[@SkillBuilder]

I have used thin joint adhesive and still have cracks. I think it is due to the moisture in the blocks. They shrink as they dry and the glue holds them too tight. Answer dry blocks

[@greymase]

Thanks, Harvey. This was SO incredibly helpful. I have watched hundreds of aircrete evangelist videos, and none have addressed this. QUESTION: Does using something like basalt fiber in the concrete with which the bricks are made abate this problem as well?

[@m4inline]

We use Ytong a lot where i live. With that stuff you afe supposed to use their recommended mortar and no more than 3mm thick. That looks like a ton more mortar there than they use here

[@UberAlphaSirus]

How do those sliding ties work again? Lol

[@mistervelux]

🤣🤣🤣🤣

[@andyphillips7437]

kzbin.info/www/bejne/j2e7l3pmi7SHndk

[@SalomonX88]

1:41 my Mrs was looking at my phone and I had headphones on 😳

[@TheOriginal_BigMac]

I swear I could hear porno music in the background

[@m4inline]

I am gonna make that into a looping gif and send it to the mrs

[@edmundhodgson2572]

We used to render/skim these 40 years ago, I was taught to drench them first. I wouldn,t dream of rendering these now!

[@nickcollins1289]

Brilliant channel. Full of useful information

[@SkillBuilder]

Much appreciated!

[@johncoppock3823]

Thanks Roger for great video, loads explained. Have seen new builds (not particularly big) where expansion joint hidden behind drain pipes at corners. That alarmed me that the gable then does not appear restrained properly (unless there are some hidden straps or clever ties). Suppose the roof timbers though might have more restraint straps and perhaps the floors also to keep it all together.

[@carlreed1000]

How about a follow up video detailing what to do if the cracks have already occurred ?. It has happened on my build possibly due to strong mortar. cheers

[@SkillBuilder]

good idea

[@johnclements6614]

@@Benzknees It is more likely to be thermal movement of the blocks. Most of the curing will take place within a month of manufacture.

[@johnclements6614]

@@Benzknees If the cracks are not moving once they are formed it is more likely to be the moisture content of the blocks. when they dry they shrink. Curing of concrete is related to strength gain. Most of the strength gain, when the cement bonds with the water, takes place in the first week. You are unlikely to be laying blocks that were made last week but you are likely to be laying blocks that have been out in the rain. You can also get a reaction between CO2 and concrete in the long term but that is different to the hydration of the cement due to its bonding with water.

[@johnclements6614]

n@@Benzknees You state "not subjected to chemical changes". Curing is a chemical process. Also "one offs appearing on dry, inside block walls". When the building was under construction the blockwork was subject to the rain. Not everybody covers up the blocks and bricks when they are on the pallet. Wet blocks expand. As you state it is now dry, because there is a roof etc, so they contract. And "not subjected to wide temperature changes". What temperature do you think blocks left out on site in the winter will cool down too, you could be using them at 5C. Then the weather improves and you get a new delivery and you start laying them at 15C. Completed houses can be subject to temperature change. Most people heat their house to about 21C so the inner skin may get up to 20C (ignoring sunny walls). If a house is unheated, maybe unoccupied, it will cool down. There are more causes to expansion and contraction of blocks than curing. If you think that curing is the only problem you can not protect yourself against other causes.

[@johnclements6614]

@@Benzknees A chemical reaction results in a chemical change. Why do you think thermal crack would close up especially in lightweight block. For a crack to to close up it has to be unobstructed. Yes you have said you were looking at cracks 2 years after walls were constructed. 2 years after 90% the curing has taken place but you rule out any other cause.

[@glenr834]

Such a legend Rog!

[@martinroberts5577]

I learnt something today. Thanks Roger and the Skill Builder team.

[@StuMas]

As good as your advice may be, it still wouldn't be enough to prevent the UK from cracking up!

[@normbograham]

Every profession is facing the same crisis, there is someone willing to do it cheaper. Not better, but cheaper. Thus, things get progressively worse.

[@zmirc]

Agreed. A very bad trend

[@bluevanmani]

I know what your saying roger but we only use fibrelite blocks now and just upgrade the insulation batts no problem with cracking.just looks crap if you see any cracks worries the life out of the clients😄

[@mikepeters9887]

This is excellent - very thorough!

[@SoundAssault]

Great video - I learnt a lot there. Thanks Roger! 👍🏻

[@magicdaveable]

I build with aircrete poured in steel stud boxes 6.3 cm (16") x 37.8 (96") x 1.6 (4") cm thick. The void is filled with a layer of hardware cloth then the aircrete is poured to fill the box. The panels weigh approx. 36.6 kilos. When set they are easy as pie to stand in steel stud channels and tie together to construct walls. 1.6 cm (4") thick aircrete walls are incredibly strong and extremely well insulated.

[@barry-cq4xg]

Great stuff. It is always good to learn the correct method and not the quick bodge to finish the job, get paid and move on to the next (bodge).

[@chadcooper7348]

Really appreciate this video! Question: What are your thoughts regarding AAC blocks that are interlocking? And, the mortarless stacking of blocks (expect for first run of blocks on slab or cmu block stem walls) in which closed cell foam is applied instead?

[@johnboughton7451]

Extension at 35A I loved that series of videos featuring a very young Robin Clevet

[@dissonantiacognitiva7438]

The aircrete blocks require something along the lines of glass fibres in the mix, hemp shiv or other similar products

[@utube1818]

I am amazed they get away with a "stronger" mortar mix. I would have thought if management could save half a penny by making you use a weaker mix they would be all over you.

[@SkillBuilder]

Management? this is building sites we are talking about

[@Clark-Mills]

Thanks!

[@SkillBuilder]

Thank you Clark it is welcome.

[@workinalday4351]

I've never seen these as a material I would use for Building structural, just for Insulation. I've made some fire proof stove applications and I've always used the fiberglass fluff that you can get at most mason supply. Works great' no cracks, the stuff floats it's essentially explosion resistant as well apparently. Yea good stuff. I don't think I would ever trust it to take the place of concrete in a building though.

[@Dave5843-d9m]

I rendered my concrete blocks with Tyrolean cement. Spattered on a first coat and allowed to cure. Then sprayed a second coat which was wood floated while wet. I planned on a third spatter coat but the smooth finish was so nice I left it smooth. That was in the mid 1980s and the wall still looks great.

[@tinytonymaloney7832]

I did my own render indoors as the plasterer was to busy and it saved him time so he just did the pink coat. He told me his preferred mix which was 5 and 1 plus 1 of lime which puzzled me, he said it allows for slight movement. Anyway I did as he said. I cheated and used battens upright to get straight and level. I was thrilled when he came to pink up and commented on a nice neat job I had made. Did take me a few days though but I ain't a spread. Hearing his positive comment on my handiwork was quite rewarding. That was 7 years ago now and no cracks yet,. Would like to know why spreads leave a gap between the finished floor and bottom of plaster, I think it's a damp thing but it can't be that simple. Good vid that one 👍👍👍👍

[@kc8485]

It's sort of a way of stopping damp (from a floor spill) bridging but more importantly it stops the trowel picking up bits of grit into the skim coat that would 'drag' through the finish coat..It's also a time saver ;-)

[@jacannon9147]

Pure laziness, not coating low enough Finished screed isn't laid til after plastering normally, so no need to skim too low Scudding exterior walls is a great job prior to plastering Messy but creates a fantastic bond

[@cooking.with.rob.official]

Bloody brilliant 👌🏼🏴󠁧󠁢󠁳󠁣󠁴󠁿👍🏼

[@bobf1290]

Everything he said was bang on 👌

[@pinarellolimoncello]

Roger, you're a man after my own heart, brilliant video, what is it with the building trade that so many people carry on like absolute donkeys thinking they know better than the set standard or that its ok to constantly deviate and divert from professional standards. I'm not even a brick layer but I've still been to the library to get a book on brick laying, was written by some engineers or phd bloke, he was even suggesting mortar ratios as weak as 9 sand 1 cement 1 lime and don't forget volume isn't the same as weight. Look at the cladding crisis, billions of pounds worth of damage, law suits and death, all caused by donkeys that refuse to learn, understand or work to professional standards. I have a saying I say to my son, wise man absorbs knowledge like sponge absorbs water. It's up to everyone to act a bit more like a sponge to absorb not just knowledge but other peoples advice in order to improve build quality and prevent damage and disasters. How about a video on the golden mean 1-1.61, how many builders know about that, would create much prettier houses than just lego houses. Keep up the good work .

[@SkillBuilder]

Great comment. I think many builders have a pride in not learning things which is perverse. Not many people even look at instructions and consider it a sign of weakness to seek advice. I have seen aircrete manufacturers recommend a 1.1.8 and I have tried it. It makes a very weak mix that can be diifcult to work with but a lot depends on the sand.

[@pinarellolimoncello]

@@SkillBuilder I do agree that does it seem quite a weak mix but like you pointed out too strong a mix increases chances of cracks from reduced flexibility. Getting back to donkey syndrome, we all know what causes it, 'pride', bravado, nobody wants to look like a twat. I was out cycling yesterday, ran into a bloke who's chain was jammed, I said do you want a hand, no no, was on the phone to his wife, I said are you sure , he said , no all fine, maybe he didn't want to trouble me either. I thought bollocks to the pleasantries, he'll be waiting there for ages , jumped off my bike and yanked the chain out for him, we were both on the way within minutes enjoying a sunny day again, that is how simple things should be. Anyway, brilliant videos you do, is really nice to hear someone increasing knowledge, educating people and driving up standards without being bureaucratic.