Problems with new floor screed

18 Jun 2005
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United Kingdom
I have replaced an old concrete floor using a builder as at my age I couldn't face all the physical work. The floor is about 13m square and was a thin layer of concrete over what looked like old lime mortar on top of rubble. This was dug out and the new floor has a DPM, about 4" of concrete, and a top screed of over 2".

The builder started to lay ceramic tiles, but it is clear that the screed is not level enough. There are high spots and a dip which is about 15mm deep. The screed also seems very crumbly, and you can scrape grooves in it with a finger nail.

I feel that the tiles should be taken up, and the floor re-leveled. Can anyone give me some quick advice before the builder arrives tomorrow morning?

Just how strong should a screed be? Should they be this crumbly?

If the floor is leveled with self-leveling compound will it (and the crumbly screed) be strong enough for the tiles?
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Difficult questions to answer without seeing the actual job and unreasonable to ask us to quantify someone elses work in this way, I will do my best to give objective comments, but discuss this with your builder, don't approach this using my reply as ammunition.

A sand/cement screed is not designed to have any sort of abrasive resistance whatsoever, and technically it takes 5 weeks for this to dry fully before any tiling should be done.

The screed should be flat, 15mm tolerance is appalling and should be dealt with. Building standards for tiling preparation should be +/- 3mm.

A self levelling screed will sort this out and should be used.

I can't comment ont he consistency of the screed without seeing it myself.
Thanks Mudster,

No, I won't use it as ammunition. I just wanted to get it clear in my own mind what I should expect from a screed. I think the hollow was the result of adding more screed to fill in a dip as the screed was layed, but it didn't bond properly and crumbled away.

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