Concrete screed floor problems. Tilers won't tile it!

[SmileItsSunny]

Hi, we have just had an extension built. Whilst waiting for the screed to dry, we noticed it was dusty. Now, however nearly 4 months later (took forever to dry!) it is crumbling in patches and falling apart near the edges. DH has repaired the large cracks, and pulled out a lump of concrete that is clearly not to the thickness detailed in our plans.

Tiler has come and said he cannot guarantee his work on such a poor surface.

Builder says it is crumbling w either because we dried it out too fast, or too much heavy foot traffic!

Builder is talking total rubbish. He has got this mix wrong hence the concrete is failing. (Thank God it is not a tower block). Try and get the builder back because his work is not up to an acceptable standard. If he refuses, get another builder in. More expense, but what you have is useless so it has to be fixed one way or another. You might be able to hack out the failing bits, put replacement in and then use a self levelling compound to give a level surface for the tiler. However another builder would be able to tell you if any of the concrete is worth saving. Hopefully some of it will be.

thank you so much for your response. It is great to have reassurance. He has said he will come round to explain to us, but not communicated since DH advised what time he would be available.

we also have underfloor heating within this concrete, I'd hate to have to install that again watch Dh install it

how does the builder say you dried it off too fast? Did you turn off his sprinkler, or pull away the polythene sheet he had put down, or bring in dehumidifiers with 48 hours?

Or did you trample about on it in clogs in the first 24 hours?

I'd say the builder is chancing his arm. Your tiler has a point though.

We had large porcelain tiles laid on top of self levelling compound. I didn't know it wasn't actually completely self levelling, and the tiler said nothing, but did a beautiful job laying the floors. After about 5 years though, the tiles started to crack, and we couldn't find anyone willing just to replace the cracked tiles (though I understand why). It was a huge area - almost 100msq and also had underfloor heating. The people who bought the house after us gave up, and put engineered wood over the whole thing.

PigletJohn there was no sprinkler or polythene sheet. We did borrow and use a dehumidifier but not for at least a month.

PigletJohn there was no sprinkler or polythene sheet. We did borrow and use a dehumidifier but not for at least a month.

we may have walked on it... eventually we had a temp kitchen installed so obviously used it.

Sheila Oh no! That is exactly what we want to avoid!

I didn't really think there was a sprinkler, it is not usually done in houses although industrially, it is one of the ways of achieving good strength and hardness. Concrete needs to be kept wet for a couple of weeks to cure to reasonable strength, so a sheet of polythene is quite common. I really had in mind, what did he claim you did to interfere with the cure? And was there anything he warned you not to do?

You didn't turn on the underfloor heating, did you?

No, no underfloor heating fit 14 weeks. No mention was made of keeping it wet.
We used the back door, into the area, took shoes off, and carried on into the rest of the house. Temp kitchen was installed, I.e. cupboards with plug in electric hob balanced on top. Also washing machine, sitting on a pallet. To be fair, the area of worst damage is where the most foot traffic happened to be.

*for, not fit

he had a heater on in the room to dry the plaster, but we stopped using that quite quickly.

Then we have not yet heard evidence to support his allegation that you did something to make it dry too fast.

Thin latex levelling screed (poured out of buckets) hardens quite fast. Actual concrete needs two weeks to gain good strength and hardness.

we haven't got to the latex layer yet :-(

PigletJohn does that depend on the thickness of screed though?

If you mean concrete, the chemical reactions that cause it to harden depend on it staying wet. The longer it is EET, the harder and stronger it gets. Underground concrete, that never dries out, can be exceptionally strong and hard, for example sewers and even round fenceposts. The rate of hardening gets slower and slower but never stops. E.g. (examples not accurate) after 2 days it might achieve 25% hardness, after another 4 days it might achieve an extra 12%, after another 8 days it might achieve another 6%.

Curing is not the same as drying. Drying happens faster with thin concrete, curing doesn't.

Two weeks is generally considered to give good strength.

Once it has dried, it stops hardening and will not start again.

There are some special cements that harden very fast, e.g. for use underwater. They get much hotter, as the chemical reaction is speeded up, and crack more.

"Wet" not "EET"

It really should have had something over it to keep it damp - hessian or some other damp material.

I'd get him back in again to redo it.

the builder is coming back today to 'explain' to DH what needs doing. I can't wait to hear his explanation for the thickness of the screed, let alone anything else! Will keep you posted.