Help!: porcelain on Weyrock Protect

[biker mike]

Hi, I have to install 600x600 porcelain on to a chipboard floor with underfloor heating. The chipboard is 2400x600x18 tongued and grooved Weyrock Protect bonded and screwed to the joists(new build). The problem is the chipboard has a grey waterproof coating and I have been told that this will prevent the adhesive (I would normally use Ultra Proflex SP EX) from curing properly, so I should cover the floor with 4mm ply screwed at 6 inch centres.Has anyone had experience of this? Can I tile direct to the chipboard? Thanks.

[Rad2474]

You should have used at least 12mm ply preferably 18mm 4mm is to thin screwed down every 250mm centres.

[biker mike]

Thanks Rad 2474, are you saying that I should not tile directly onto the chipboard?

[grumpygrouter]

It is best not to tile directly to chipboard if it can be avoided and a lot depends on the size and condition of the floor. As a particle board, it is possible that the board can deteriorate with the fibres breaking loose, and of course if it gets wet for any period of time it will "blow".

I have tiled directly to chipboard but only on small floors and only with adhesive that is up to the job. 4mm ply is, in my opinion, worse than tiling straight onto the chipboard as it is too thin and there is a stong possibility of having voids between it and the chipboard. It is imperative that the floor is solid and with no bounce.

if you need/have to tile directly to it look at the likes of Ardexflex 7001, BAL Fastflex of Granfix Ultimateflex adhesives.

As an extra precaution, you may want to try a decoupling membrane such as Schluter Ditra this will provide some isolation against lateral movement and also give some waterproofing protection.

[pjc]

dont tile directly on to it over ply 12mm at least it screw the chipboard to the joists then the ply to the chipboard i think the best way is to stick 10 mm PCI Pecidur® to the chipboard with 2 part then tile it :Pete

[doug boardley]

and don't forget to prime underside and edges of your ply overlay with an acrylic primer, NOT PVA!!!