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!
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.
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.
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.
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.
In Central Europe most interior plastering and exterior rendering uses fibreglass mesh embedded in a flexible adhesive, then topped with a flexible silicon render. It leaves a more textured finish than finishing plaster, but is less prone to cracking.
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
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.
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.
As a German, I have never seen 3 inch aircrete blocks used on house walls! We use them to build a “none carrying wall “ to build a shower cabin. Or to build cabinets. We use 12 inch blocks to build houses. They don’t crack. And on top, we do not use any hand mixed sand & cement mix. That’s completely wrong! We use the thin bed clue you get from the building supply store.
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.
When I did a house refurb and extension, everyone told me that aircrete blocks were the way forward. "Great insulation and just as strong". I got a few and tried simple things like hammering in a nail and inserting a screw, just as if I was hanging a picture or fixing some cupboards. They just fell out. I banned my builder from using them.
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.
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.
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.
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.
I use Stowell Fibotherms, look like a concrete block but uses pea pumice. Lightweight, no cracking, dabs stick and get you a decent fixing to them. No brainer 👍.
We are in the process of buying a new build, from a well known developer, was invited to view at point of roof completion, the party wall has exactly this problem, 2 cracks from roof truss all the way down to ground floor concrete base at either end of the wall, property now delayed whilst they get a team in to fix with steel inserts and resin, I’m shocked they could make such a mistake on a large development!
In Australia in the 80s rooftilers used to put bondcrete in the bedding mix, the ridges would then crack down the guts, because there was no room for movement
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.
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 .
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.
@@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.
The mason that put up the inner walls in my garrage could have used several of those tips back in 1976. And they are only 50mm thick, so I dare not hang anything on them.
I came to the conclusion many years after that; as a custom home bricklaying contractor... that 3 things are for certain. Hard Labor = moving each brick for the layer to lay & each shovel of mortar for the bricklayer to spread. Glorified Hard Labor = Picking up & adjusting each brick to be leveled & plumbed after moving those cubic yards of mortar with a mere trowel for them to be suspended forever in that leveled & plumbed state. The total Gloried Hard Labor of it all combined = ''There's no building material that has been touched and adjusted by the human hand than that of the lowly brick or stone.'' -William Gilpin 71021
Thanks for the video! So good! Would you do the same if you were making an aircrete dome with a fiberglass mesh? Those seem to be popping up everywhere. Curious if you could add it to a weird shape like that. Or if that would mess with the integrity of the structure.
So, who came up with the magic 6 meter number and what is the reasoning for that specific distance? Cracks are from movement but finding the root cause can quickly become complex, especially when combining dissimilar materials.
Im a bricklayer and this is exactly what I know to be true. But I’m from Australia and our crack joints (expansion joints as they are called down under) are 4 metres maximum.
Good info, I am just about to do my walls that have a concrete skin 100 mm thick and aircrete 400 mm behind that. There is 3.0 metres between columns . Was designed for half metre earth pour walls originally. Thanks for your info.
I'm planning an AAC facade/wall and wondered about using the panels or like one commenter asked, the interlocking block. Any info on those would really be appreciated! Great video!
I don't disagree with anything here, but would add that allowing the blocks from getting wet onsite before laying (they are very porous) or not allowing them to cool fully after the kiln are other causes of AAC block cracking. If I can help it I specify aggregate concrete blocks as they are more resilient - the cavity insulation can be upgraded to compensate for the reduced R value.
by Aircrete do you mean Aerated Autoclaved Concrete, i.e. AAC? if so, your joints have too much mortar and you need hollow core & Ublocks filled with concrete & Rebar . I used thinset mortar on walls that were 28 ft tall and 48 ft x 80 ft. there are no cracks even after earthquakes. i did follow HEBEL's instructions to the letter. the structures has a lot of rebar. there is a dual lintel band made of Ublock & 2 pieces of #5 rebar. there is verticle or horizontal rebar every 10 ft or lwss. all windows or doors are surounded on the sides by cored block filled with 5500 psi concrete & #5 rebar and by U Blocks above. the problem is Labor thinks they know more than engineers and don't do what they are told. I find this to be a common problem; all to often i here "Oh you don't have to do it that way ; we never do". we will soon solve the labor problem with robots.
When people say stuff like 6 parts sand 1 part lime 1 part cement. How do you work that out. So how much is 1 part? Is it a spade full? A cup full? A bucket full?
Aircrete, never heard that name before. We usually name it "cellular concrete" or "gas concrete", or by the brandname Ytong. But I guess it's all the same.
Aircrete is the generic name for these blocks in the U.K. A point to bore people with is that the cement slurry is aerated by throwing in a handful of zinc filings. If you want more air pockets in the mix you increase the number of filings. I am not sure how Ytong are made but they are different.
Hi Roy The lintel above the window transfers the load to the side and it travels down each side of the window. When it reaches the bottom of the window it starts to transfer back but it only manages to do that in a diagonal which leaves the centre of the widow with no load. This means it can move easily and forms a natural break point. By putting in a few courses of bed joint reinforcement you are effectively tying the two loaded ends together.
Hi Dirk Back in the day the breeze block was made from cement and flyash from power stations and air was forced through the mix. These aircrete blocks produce their closed cell pockets of air by a chemical reaction between zinc filings and the cement so no air is forced through. No breeze.
Is there a way to make the movement joint the same color as the mortar? Also, how difficulty is it to make the movement joint follow the existing mortar joints, as in go back and forth like a zipper or start in the upper corner and stair step down to the bottom?
Possibly if the mortar was mixed properly with properly gauged mortar as said in this vid , food for thought the Romans then ourselves didn't have modern cement in their construction! The fruits of their labour using line mortar still with us ! Downside, lime mortar mixing done properly is a time consuming process, that cannot be rushed.
If you have any knowlege of victorian french drains around the basement level. I would love your input. I am scooping the "gravel" out of it now, barely a brick wide. a gully broke when a drainage company smashed out the u bend and flooded the french drain about 30 years ago. that side of her house is 3-4 foot deep, that gravel is thick nasty slime rat madness laying on the walls. Maybe something for a pod cast. I can't find nothing on the internet regarding UK freanch drains etc. Anyhows, the wifes calling me about sliding wall ties.
Just don’t use them - end of!! Increase your cavity width to give you the same U-value and use standard concrete blocks! These aerated blocks are cheap shit, the crack crack and crumble and also cannot get a proper strong mechanical fixing into them! Should never have been given load bearing classification IMO!
@@iansheppard6735 But can you find a proof mathematically for your magnetism theory ? My comment is based upon Moment Distribution , the mathematics of which I understood once upon a time , in a far off world , when I believed in the power of the force OB1.
