Floor Screed

[Mr M]

I have solid floor in the Kitchen/Diner in a 1900's terrace house which I am refurbishing. The existing floor is out of level, sloping by about 45mm over its length from front to back. The floor had timber floorboards laid directly onto the original concrete and the floorboards have now been removed.

I would like to lay a screed over the existing concrete to bring the floor back level. The screed will therefore be approx 20mm thick at its thinnest point (the thickness of the floorboards which have been removed), increasing to about 65 at its thickest point. The floor will eventually have laminate flooring laid over it.

What mix of screed should I use?

 

[Notch7]

I have solid floor in the Kitchen/Diner in a 1900's terrace house which I am refurbishing. The existing floor is out of level, sloping by about 45mm over its length from front to back. The floor had timber floorboards laid directly onto the original concrete and the floorboards have now been removed.

I would like to lay a screed over the existing concrete to bring the floor back level. The screed will therefore be approx 20mm thick at its thinnest point (the thickness of the floorboards which have been removed), increasing to about 65 at its thickest point. The floor will eventually have laminate flooring laid over it.

What mix of screed should I use?

Tricky, it wont be that easy to make a new screed bond to an old concrete floor. The minimum thickness for bonded screed is 25mm. Typically unbonded screeds need a minimum of 50mm.

I wonder if the existing floor has a dpm? If its pretty old, then unlikely, in which you need a dpm beforr the screed making it an unbonded screed.

A proper job would be gunning up the existing oversite and lowering so you can insulate the floor before laying 65mm screed.

There are specialist screeds that can be laid quite thin, but they are pumped liquid screeds, not diy. I csnt see the point as it would cost a lot to achieve an uninsulated floor.

If you dig up floor, you fall under building regs......strictly speaking

 

[^woody^]

If you used SBR as a primer, and in the mix you can screed down to nothing.

But SBR in a screed mix makes it very difficult to use.

So the thing to do is either lay an SBR mix slurry to the thinner areas first, or work with two mixes and lay the thin areas first with a slightly wetter SBR mix, and then lay the thicker areas with a normal drier screed mix.

Be prepared to need to use some self leveler on the wet mix areas as you won't get the finish. And use fibres in the mix to prevent cracking.

 

[Notch7]

If you used SBR as a primer, and in the mix you can screed down to nothing.

But SBR in a screed mix makes it very difficult to use.

So the thing to do is either lay an SBR mix slurry to the thinner areas first, or work with two mixes and lay the thin areas first with a slightly wetter SBR mix, and then lay the thicker areas with a normal drier screed mix.

Be prepared to need to use some self leveler on the wet mix areas as you won't get the finish. And use fibres in the mix to prevent cracking.

Thats interesting, I never knew that!

 

[Doggit]

As there were floorboards down, it suggest the floor was dry, but you could play safe and paint a liquid DPM on the floor, throw some dry sharp sand on it before it dries, and then put down a latex self leveller in stages. I'd then use 10mm SPX insulation boards or 6mm fibreboard before laying the laminate, or engineered wood floor if funds allow - much warmer than laminate.

 

[^woody^]

Thats interesting, I never knew that!

*Disclaimer. Woody accepts no liability for the results if bad.

*If good, he accepts the glory.

I use this principle a lot with render or fine kiln dried sand to feather floors or paths in. If you use too much cement though, the top will skin and flake, as the SBR makes it go off really quick.