plywood on bathroom floor

[jtomo]

My bathroom floor has been previously tiled straight onto the chipboard and now i'm replacing cos tiles all coming loose.

Anyway all the tiles have been removed but the adhesive is stuck to the chipboard, also small layers of chipboard have come away. The biggest uneven ridge is max of 2mm depth. Will putting down 6mm WBP plywood deal with these gaps and provide level surface for either vinly or tiling?

Also was told by guy in B & Q that plywood should be coated with 1 part PVA glue and 3 parts water to provide waterproofing, is this correct?

Bit confused and fairly new to the whole DIY thing, any advice plz?

 

[Symptoms]

jt - forget the B&Q PVA advice. Scrape all the lumps off the old floor, fix the ply with glue & screws to the chipboard, then lay vinyl. Forget ceramic tiles on your sort of floor as there's likely to be movement and so the tiles will loosen (which has happened before).

The glue to use is polyurethane wood adhesive (get the cartridge type that goes in a skeleton gun), lay zig-zag worms of this on the ply and press down onto the CLEAN and DUST FREE chip/b. Insert the screws to hold the ply in position and flat (don't use over-long screws in case these penetrate the back of the chip/b and puncture pipes/cables. Remember it the glue holding the ply down, the screws are acting like clamps till the glue dries.

 

[Richard C]

If your going to tile, a 6mm ply overboard is not thick enough, it should be 12mm minimum if you want your tiled floor to last; that's assuming the existing floor is in good condition & it sounds like yours isn't. Forget the chipboard, it’s next to useless when new but if it’s stuffed don’t overboard it, rip the lot up & replace with 18mm (minimum) WBP ply screwed ever 200mm. Support any joins along the centre of a joist, fit noggins across the joists if necessary & tile directly onto that using a trade powder, flexible adhesive & grout. Do not use PVA or any other sealer unless recommended by the tile adhesive manufacturer; as for the B&Q advice, PVA is not water proof it’s actually water soluble!

Read the tiling forum sticky & search the archive for loads of info.