sub floor... T&G chip or ply?

[cheekymonkey101]

Hi guys,

laying some thin slate flags in kitchen & bathroom (10-12mm)

ripping up old ropey floorboards & looking to lay new subfloor... question is...

tounge & groove P5 chipboard (water resistant ) i.e.
http://www.wickes.co.uk/Sheet-Chipboard-Flooring/Tongued-and-Grooved-Chipboard-Flooring/invt/164516

or

18mm ply (WBP) i.e.
http://www.wickes.co.uk/Sheet-Exterior-Plywood/Exterior-WBP-Plywood/invt/110037


thoughts?

Or could i even get away with 12mm????

 

[Richard C]

Absolutely no contest WBP ply; 18mm is the minimum & you may need to up that with heavy tiles & depending on how rigid the floor is. Use only high quality trade flexible adhesive & grout.

 

[cheekymonkey101]

ok thanks for your thoughts richard.

i've chosen the thinnest flag i can get to keep weight down

using a Keraquick adhesive - recommended to me

 

[gcol]

Absolutely no contest WBP ply; 18mm is the minimum & you may need to up that with heavy tiles & depending on how rigid the floor is. Use only high quality trade flexible adhesive & grout.

On the contrary Richard, the thicker the tiles, the less trouble you have with the substrate. If the OP is using thin tiles, they want to be going for 25mm WBP ply. Whenever replacing boards, I always recommend 25mm WBP ply anyway. No problems with that.

 

[cheekymonkey101]

Absolutely no contest WBP ply; 18mm is the minimum & you may need to up that with heavy tiles & depending on how rigid the floor is. Use only high quality trade flexible adhesive & grout.

On the contrary Richard, the thicker the tiles, the less trouble you have with the substrate. If the OP is using thin tiles, they want to be going for 25mm WBP ply. Whenever replacing boards, I always recommend 25mm WBP ply anyway. No problems with that.

25mm !!!! that sounds crazy, you'd need to build stairs to get into the room by the time yo've added tile & adhesive height to that!

 

[Richard C]

On the contrary Richard, the thicker the tiles, the less trouble you have with the substrate. If the OP is using thin tiles, they want to be going for 25mm WBP ply. Whenever replacing boards, I always recommend 25mm WBP ply anyway. No problems with that.

I don’t have your level of practical experience but I can’t follow that. From an engineering viewpoint, heavier tiles increase the distributed load, the greater load will increase the bending moment on the joists in the centre of the span; thicker, well fixed plywood will increase the “I” value, reduce the bending moment & therefore the amount of flex.