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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Building Questions >> Wall Crack https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1486125035 Message started by TrevorP on Feb 3^rd, 2017, 12:30pm

Title: Wall Crack
Post by TrevorP on Feb 3^rd, 2017, 12:30pm

Just removed wallpaper from room we are decorating, and found quite a few cracks. A couple am quite concerned about, these are fairly large and did not notice with wallpaper on (only been in this house for 9 months)
I have chip plaster away and found the crack is though and in the thermolite internal wall, see pics.
Is this a concern? do I need a structural eng[album]TrevorP&1486123982[/album] to look .at.
The house is a 60s build, and all internals are thermolie block and under and top coat plaster.
What should I do, as I think this is not the only one in the house, do thermolite crumble and fall apart.
There are no external cracks in brickwork.
Any advice much appreciated
Trev

Title: Re: Wall Crack
Post by stuart45 on Feb 3^rd, 2017, 8:03pm

Thermalite and other AAC blocks often suffer from shrinkage cracking as they dry out. It's not really a serious problem.

Title: Re: Wall Crack
Post by TrevorP on Feb 3^rd, 2017, 8:12pm

Thank, bit of a relief, should I bridge the crack with a mesh type matl before re-plastering, after chipping out?

Title: Re: Wall Crack
Post by stuart45 on Feb 3^rd, 2017, 8:25pm

You can do.

Title: Re: Wall Crack
Post by woodsmith on Feb 4^th, 2017, 8:28am

Are there any cracks in the external walls?

Title: Re: Wall Crack
Post by TrevorP on Feb 4^th, 2017, 10:47am

No, have checked and re-checked and there are none. As said this is not the only room with a crack through to and including internal block work, but no external cracking.
That's why I asked the question about thermolite being so very soft, breakable, to me as an ex engineer I would have never used such "weak" blocks that crack so easily, but I know you builders will disagree.
Was also thinking if it would be advisable to open these cracks a bit and try and get some cement in for strength, what do you think?
Trev

Title: Re: Wall Crack
Post by woodsmith on Feb 5^th, 2017, 8:19am

It's not normally the relatively soft blocks that are at fault but the mortar used by the brickie. Thermolite needs a weak mortar but as your cracks are going through the blocks it looks like they used the same mix they would use for bricks, a common mistake unfortunately. I don't think there would be much point trying to rake out the cracks although adding mesh would help. If the problem is not too bad it may be better to paper the entire wall; there are some lining papers available which are designed to hide this sort of problem; B&Q sell one and it does work if the cracks are relatively minor. If the cracks are too bad to paper over, then it would probably be best to dry line the wall with plasterboard.

Title: Re: Wall Crack
Post by TrevorP on Feb 5^th, 2017, 9:51am

I totally agree about the mortar used, as when I chased out for an additionally socket found it to be as hard as nails.
As the cracks in the blocks are cracks and not gaps will use a mess cover and re-plaster, then maybe a skim coat. We have considered dry lining so if as a last resort will go with it.
Thanks for quick replays and advise.
Cheers
Trev

Title: Re: Wall Crack
Post by stuart45 on Feb 5^th, 2017, 10:34am

It's not being a soft block that's the real problem as harder concrete blockwork can also crack.
Blocks when made are initially wet, so as they dry in the wall it shrinks.
Clay bricks are usually the opposite being dry from the kiln so the external walls tend to expand with moisture.
Newly made blocks tend to be wetter and cause more problems, although using something like a 1/2/9 OPC/lime/sand mix can help.
The advantage of an AAC block is that it's lighter, easy to cut and has better thermal qualities although some builders now prefer other types of block.

Title: Re: Wall Crack
Post by Natedog on Feb 5^th, 2017, 10:18pm

if it's had paper over it for 9 months, and the paper hasn't cracked too, that would suggest that it has stopped moving

Title: Re: Wall Crack
Post by TrevorP on Feb 7^th, 2017, 8:51pm

Yes I think you are right, it has stopped moving, as paper had no cracks at all. Now chased out cracks and most seem to follow the motor line, with a couple with hairline crack through the block.
So am fairly confident now once re-plastered shouldn't get more.
Trev