Had a builder put a floating floor down and I refused to tile on it and said that I wanted it screeded. The builder rang the plasterer to do the screed and he said can you leave the celotex insulation down and I will screed over that. I'm not happy that this is going to be a secure surface either as the celotex isn't fixed to the substrate. The plasterer said that he's done it loads of times and it will be fine. It sounds to me that he's trying to make it easier for himself by not laying as much screed but I don't know enough about screeding to be sure. Has anyone else heard of this method before? The room is 9m2 and it will be a sand/cement screed. Cheers Ross

I thought all new build was the same process?

Sub base, DMP then 100mm insulation and then screed. Ss long as the screed is thick enough then the weight should hld it down. Im prepared to be wrong though as construction isnt my bag at all.

Yes laying the screed direct onto insulation is standard practise for a floating floor.

A standard sand/cement screed would need to be laid at a minimum depth of 65mm for a domestic property. If modified screed is used you can get down to 55mm.

i don't like celotex it can soak -up water!! i would use Styrofoam but as above is standard

Originally Posted by FlexiDry

Yes laying the screed direct onto insulation is standard practise for a floating floor.

A standard sand/cement screed would need to be laid at a minimum depth of 65mm for a domestic property. If modified screed is used you can get down to 55mm.

British Standard (8204:1) says minimum 65mm for domestic floating sand:cement screed. The standard does not differentiate between non modified and modified sand cement screeds so that should be treated the same e.g. You would have to use a proprietary material and step outside of the standards to go below this depth. That can clearly be risky.

Thanks all for advice.

Interesting about celotex soaking up water as i always see it sored outside on a variety of building sites