Crack in garage wall

[Alan]

Hi,

My grandfathers detached garage has been built for a couple of months now but a vertical hairline crack has formed on the interior wall going from the second thermalite block up to the ceiling. The garage is double skinned with four inch blocks on the outside and four inch thermalite blocks on the inside. The garage is rendered but I can't see any visible cracking externally in the render. I'm assuming that, at the moment, it's just the thermalites that have cracked but I am (as he is) concerned.

What is likely to have happened for them to have cracked? The whole garage is built on a raft foundation with reinforced steel, as the ground it's on is a bit soft. Extra attention and expense was spent on the foundation to stop it doing this sort of thing! Is the best thing to simply keep an eye on it? The builder is coming to look at it soon but I want my grandfather to be pre-prepared.

Thanks

Alan

[BigWallop]

Some movement is natural, but it shouldn't do any harm to check with the builder again. If the crack is opening at a steady rate, then it shows that something is wrong, but if it is just natural settlement, then it's expected. The drying and temperature changes can also cause shrinkage on buildings, and these are normally designed in to the build right at the start. So they too are nothing to worry about.

Keep an eye on it and make sure that it isn't opening at a continuous rate. If it's still the same way in a month or two, then it's all down to natural shrinkage and settlement.

[riccip]

Sounds like it's been built properly. After two months it's probably just general drying out and initial settlement that's caused it. Personally I'd be most surprised if hairline cracks didn't appear. Think of the weight of the roof bearing down on the blocks. It's the price we pay these days for using s**te to build walls. Internal cracks are quite the norm in new houses, as are sagging lintels & ill-fitting doors/windows. Keep an eye on it but don't worry unless the cracks become gaping.

riccip

[Alan]

Thanks for the advice, I'll keep an eye on it. I guess I'm surprised to see that sort of crack in a new build, especially the blocks cracking..and I gather blocks crack all the way through when they go. Fingers crossed eh?!

Alan

[Andrew Gabriel]

Very common with airated concrete blocks. They expand and contract as they get wet or dry. Often they aren't very dry when laid, and dry out afterwards. The mortar between them tends to be much stronger in compression than the blocks are in tension, so each block cracks through the middle as it shrinks, or manages to pull away from the mortar at one side. It seems to be the norm.

[--s-p-o-n-i-x--]

Thje best way to do this is to attach a glass microscope slide across the crack, with a blob of araldite at each end.

If the glass cracks, it is proof the crack is widening and the two bits of wall are going in different directions.

sponix