Which is best plywood to tile on ?

[Pobinr]

Hi
I'm getting a bathroom floor tiled. I've taken up the chipboard as I understand that's not a good surface for tiling.
I need to know which 18mm plywood I need ?
Is it softwood, hardwood or external ply I should use ?
Thanks

[Aztectiler]

Firstly make sure that hte floor is solid and deflection free.

An external WPB ply is the only ply to use.

Prime the ply on the underside and sides with an sbr primer prior to fitting and fix at no less than 200mm centers

Tile with a flexible adhesive and grout with a flexible grout as this will compensate for slight movement.

[Pobinr]

Thank azrec
Not come across sbr primer before.
Would a 2 water to 1 PVA solution be OK for priming ?

[Aztectiler]

Never use PVA as a primer

If you use the search facility at the top of the page you will find a massive amount of info on not using PVA as a primer

Really PVA is a wood glue and not a primer. I recommend an sbr primer for the underside pf ply.

[gonk31]

should he not overlay existing chipboard with ext ply as opposed to replaceing it. ie if he has put ply down now, then he should still put an 18mm ply overlay on top of the `subfloor`

[Pobinr]

That would take the level too high with respect to other floor at threshold.

[John the tile]

just to confirm you only primer the UNDERside of the external plywood. what about the top side, i.e what the adhesive wil be sticking to/??

ta

[Pobinr]

You clearly don't need to prime the face that is facing downwards do you.
I don't understand why PVA would be no good to prime the top face

[david campbell]

some cement based adhesives tell you to use a suitable primer on the tiling face of the bag(read instruction per make you are using)
p.v is however no use as you will be tiling onto p.v.a and not the ply
http://www.tilersforums.co.uk/tile-a...ght=primer+pva
please read above and this will let you understand!

[John the tile]

thats clearly why i asked.

[Pobinr]

Thansk David
I'll ensure I use primer recomended by adhesive manufacturer