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Carpets, Lino & Flooring

How long before I can place floor tiles onto a new concrete screed of 100mm depth?

Anonymous user 09/03/2024 - 2.45 PM

How long should I wait before I can place floor tiles onto a new concrete screed of 100mm depth? The 100mm concrete screed has been laid atop celotex insulation onto which underfloor heating pipes are clipped. Beneath the celotex layer is a concrete layer atop compacted type 1 hardcore and rubble. The screed has been down and drying for 5 weeks now. The floor tiles are uncalibrated natural stone slate and will be laid onto Ditra matting. The Ditra will be fixed with rapid flexible adhesive and the uncalibrated slate tiles fixed using thick bed flexible adhesive.

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2 Answers

j ward joint sealing specialists ltd

Rating: 5 out of 5

Reading

Robert, you do not need to lay Ditra on to a screed floor this is mainly for wooden floors, also you do not need to lay flexi adhesive again thats for wooden floors, but there is nothing to say you can not. I would use either PFT rapid set or use Super fibre flex, there are so many different types to use but i would def check first on the correct adhesive to use for stone slate. Check aswell does the slate need sealing before and after you lay the tiles. Its normall 1 " drying time to ever 1 week, A little hint, turn underfloor heating on firts for week or so, because otherwise once turned on and tiles are laid you could crack screed and tiles so double check first, thank jason

Answered5 December 2016

Mcculloch Builders & Joinery

Rating: 4 out of 5

Selby

Hi Robert, i gather you are using Ditra 25 matting as a DPM (damproof membrane) ? I havn't used Ditra yet, i use F.Ball produts and their DPM (F77) in liquid form allows you to proceed with fixing tiles on a concrete slab with a RH reading (relative humidity) of 98%. To measure the RH requires an expensive hygrometer or protimeter but as a rule of thumb a 100mm concrete slab dries out at approx 25mm per 4 weeks (not per week as previous post) and usually takes 6 weeks to get to 75% which according to British Standards is safe to lay flooring. As above, you can see it would only take a week or so for a slab to dry to 98%, where it would be safe to lay an F.Ball DPM and lay tiles the following day. As an experienced estimate i would say your slab will be at @ 80%. What i don't know is when it is safe to lay the Ditra so call them and ask. As it is a DPM i assume you could lay it straight away and most definately at 80% and lay tiles immediately. More importantly, you will have a layer of Laitance on your concrete. Has it been removed ???? If not it will need taking off as Ditra matting is bonded to it and it will fail. A levelling screed on top of laitance will also fail. It absolutely "has" to be removed.. It's correct to use flexible adhesive for both Ditra and Tiles Hope this helps

Answered14 December 2016