I had some builders put down self leveling compound in the kitchen. The units were due to be fitted, so I asked them to do it, even though it is an easy job, to make sure it was done properly. Now the floor has large cracks. In one area, about 1m across, there are cracks radiating out from one spot, and the compound rocks when pressed, so areas have come away from the screed floor. Was it put down wrongly or is this usual? Will this be an issue when laying floor tiles (porcelain, 60mm by 60cm)?

Reading around it is clear it was put down wrongly. Only part of the floor is affected, about 1m by 1m and then only parts are clearly not bonded to the concrete below. Also there are areas where it went wrinkly, and now when you walk on them, the wrinkles break, exposing a grey layer below.

I will talk with the builder. I wonder about levering out the pieces that are not sticking, and bonding them down with a strong adhesive? It sounds like a bodge, but would it work?

No mate, that won't work.

Why don't you ask the builders to sort it?

Thanks. I will, but it shouldn't have happened.

Agreed it shouldn't have happened but the last thing you want to do is muck about with it. Leave the bad work exactly how the builders left it then they won't be able to level portion of the blame your way. If they're any good, they won't quibble. Sounds like they just knocked the muck up wrong or spread it too thin.

Yeah, good point, I've left it as is. It is only part of the floor that is bad, about 1m square. I think they are decent builders, and will make good.

the builders will rake out the affected area, prime and re latex to feather in, not a big problem

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Natural stone specialists mosaic, porcelain and ceramics

I was hoping that was the fix. I should have done it myself, but I was concerned about the sealing and assumed they would do that as needed.

They patched it a few days ago, and now the patch has cracked. This time the compound does not seem to have come away from the floor. Hohum. I guess it will have to be patched again?

I have been told by the builder that although the floor is cracked it is okay. I inspected it today and there are certainly areas that sound hollow when tapped i.e. no adhesion to the concrete floor. This all sounds a bit crap to me, and he is fobbing me off with excuses for a bad job. I think I might prise off loose bits, apply PVA, then apply more SLC. My belief is that the SLC cracked because it dried too quickly. As it dries, the volume reduces, and it has to spread out. If it dries to quickly, it cannot spread properly, stresses build up, and it cracks. The cracks appeared over a few days. And I guess if I walk on it more will appear. Using PVA on the concrete will seal it, allowing the SLC to dry slowly. Can anyone confirm if I am correct, and if they think the cracking is unacceptable?

No, do not use PVA to prime. Use a proper primer such as mapei primer G (screwfix sell it, its cheap)

I would take up ALL the hollow, loose parts of the SLC without delay.

what is the substrate made of? is it solid with no deflection? If that is the weak point then whatever you put down will crack so that will need resolving.

yes, sounds like the screed is absorbing the water content too quickly, are there hot water pipes in the affected area? prime and knock the slc up stronger ( less water ) make sure the slc is flexible and can be laid up to a thickness of 50mm which is pretty std these days.

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Natural stone specialists mosaic, porcelain and ceramics

Thanks. I'll ask the bathroom fitter if he would be comfortable tiling on the floor, and I expect he will say no. That will help back up my statement to the builder that the job is unsatisfactory, and then I will repair it.

FWIW the bathroom fitter said it might be okay, but it is not worth the risk.