What sub base for tiles

[Craigo007]

Hi. I'm after some advise. I am shortly going to be ripping out water damaged patchy chipboard flooring in our utility room. We have purchased the floor tiles ready for this. Can I use 25mm WBP ply fixed to the joists with noggins on the ends and tile straight to this or is this wrong. Any advise much appreciated.

 

[Ajax123]

Use 18mm ply but then overboard using 6mm cement based backer boards.

 

[Andy Allen]

Are you sure it's on joist and not a floating floor..?

 

[Ajax123]

Good point Andy...

 

[Waluigi]

Nah, he has joists

 

[Waluigi]

Quite unusual on a downstairs having chipboard with joists. Actually good point and worth checking

 

[Craigo007]

Hi, thanks for your replies. It is a ground floor extension that was done by previous owner. It has 6x2 joists with a 12" space to the ground with supports spaced out. Sorry I'm not sure is this classed as floating. The room is only 2.1 x 2.8.

 

[Ajax123]

lots of floating floors are placed on battens which to a novice could be mistaken for joists.

 

[Ajax123]

Not a floating floor then.

 

[Craigo007]

Thanks. I've just read something about sealing the underside of the ply. What's the reason for this and does the ply need priming for adhesive to bond to.

 

[WetSaw]

Thanks. I've just read something about sealing the underside of the ply. What's the reason for this and does the ply need priming for adhesive to bond to.

Ply needs overboarding for adhesive to bond to. Don't stick tiles straight on to ply, not unless you want to be doing it again very soon!

 

[Waluigi]

Just had a lengthy and detailed reply typed out. Decided to delete it. Sad state of affairs. My apologies to Craigo. I hope you find the information you’re looking for. Over and out.

 

[Craigo007]

Thanks for all your replies. Just been and got 18mm ply and going to overboard with backer board. Thanks again.

 

[Bond]

Aye it’s a good idea to seal the underside of the ply as sub floor areas can have a high relative humidity, and by sealing with SBR or similar it will help prevent the ply from absorbing moisture etc.

 

[J Sid]

British Standard states
6.3.4.2 New timber bases New timber bases should be constructed with noggings between the joists. Water and boil proof (WBP) exterior grade plywood of 15 mm minimum thickness should be screwed to both joists and noggings at 300 mm maximum intervals. The lower face and edges of plywood should be sealed against the ingress of moisture using preferably non-aqueous sealers, e.g. polyurethane varnish, or styrene butadiene rubber, to prevent distortion by changes in atmospheric humidity before being screwed down. All junctions between boards should be supported by noggings or joists.