why did my self levelling compound crack?

Doglover88

bought 2 bags of self levelling compound to level off a florr before laying laminate, had a friend come round (who's a builder) to level it off. 4 days on cracks have started to appear? and if you tread on them you hear it start to crack more! Any ideas? Need some ammo and a bit of knowledge for wen i call him back round
cheers
glen

paul_h

Sounds like the floor was porous and it has drawn the moisture out of the levelling compound before it went off. Was it a bare newish concrete floor?

The floor should have been sealed first with a PVA solution, e.g. Unibond, diluted about 5:1 with water.

If its coming away from the floor below, the only thing you can do now is hack it up and start again...

plumb1_2

paul_h wrote:

Sounds like the floor was porous and it has drawn the moisture out of the levelling compound before it went off. Was it a bare newish concrete floor?

The floor should have been sealed first with a PVA solution, e.g. Unibond, diluted about 5:1 with water.

Agree with the above,also always best to put 2 thin layers,rather than 1 thick 1

Doglover88

cheers guys
Paul it went down on top of old tiles, think they are marley tiles? been thereforever and its quite a level floor! we PVA'd it beforehand but he said a mix of 50% water 50% PVA could this be the reason? Also it had a 500w light on it (builders one on a tripod) might it of dried out too quickly?
glen

paul_h

If the tiles were old, then they'd be pretty well sealed by now... and a 1:1 mix of PVA would make sure...

Was the sealer dry before putting down the compound? Were the tiles firmly attached to the floor below, with no movement? Also, plumb1 could be right - might have been but on too thick?

JanCee

Exactly the same thing happened to us when we were installing our new kitchen. Our very experienced builder couldn't understand what had happened but when the floor tiler saw it he said it could have been too much water in the levelling compound, or the quality of the product in the first place. The tiler would only use a product by Bal(i think that was what it was called). Anyway when he dug it out and redid it the floor was perfect.

Doglover88

thanks again people, Paul no it wasnt dry before he puored on the levelling compund, he PVA'd it and poured the compund on about 10 mins later? Should it of been left to dry?
The compound come from wickes and of the 3 coats he put down, first was quite think (he smoothed it out with a trowel), next coat was little more runny and last one was very wet, and he did them all on the same night, should each coat/level of been left to dry?
Was doing it as a favour perhaps he just wanted to get it done and off to the pub?
Thanks again

paul_h

glenbat wrote:

thanks again people, Paul no it wasnt dry before he puored on the levelling compund, he PVA'd it and poured the compund on about 10 mins later? Should it of been left to dry?
The compound come from wickes and of the 3 coats he put down, first was quite think (he smoothed it out with a trowel), next coat was little more runny and last one was very wet, and he did them all on the same night, should each coat/level of been left to dry?
Was doing it as a favour perhaps he just wanted to get it done and off to the pub?
Thanks again

It's possible that the high strength of the PVA mix and the fact that it was wet may have affected it - normally you're OK as soon as it's touch dry. If the surface was old tiles, which were probably already well sealed with age, it would take quite a while to dry... At that strength he's probably used it as a bonding agent rather than a sealer, to ensure adhesion of the compound.

Other than that, method sounds OK - you're OK to put the next layer of compound on as soon as the one below has gone off - i.e. solid to the touch, but still 'wet'.

Doglover88

Thanks Paul

He did say it was put down to ensure the compound had something to stick too, and the 1st layer of compound was VERY thick, probably 10mm in places as it was applied more like a plaster as there was a nasty slope where an old wall had been. Im guessing he should of built it up with several shallower loads instead of 2 thick ones

micko2602

Self-levelling compuond is not too good at large deviations so that could be a factor, but it does sound like it has been a problem with the original surface. Definately worth letting the PVA go off to make sure you get a good seal.

JanCee

glenbat wrote:

The compound come from wickes and of the 3 coats he put down, first was quite think (he smoothed it out with a trowel), next coat was little more runny and last one was very wet, and he did them all on the same night, should each coat/level of been left to dry?
Was doing it as a favour perhaps he just wanted to get it done and off to the pub?
Thanks again

When my floor went down the surface underneath was bone dry but because the builder hadn't got it level the first time I think he made the compound too runny to ensure it levelled off. The tiler thought that this was the problem too and it does sound similar to your case.