New Plywood floor - do I need to glue it to joists?

[gez777]

Hi, I am redoing my upstairs bathroom and would like to use tiles for the floor (total tiling area approx 4 sq Metres). I will be replacing the 18mm plain chipboard!!! the original builder used, with 18mm WBP Ply - suitably sealed and with additional noggins on any unsupported joins. I know 25mm Ply would be the recomendation, but height limitations mean I need to go with 18mm max. I would like to tile over this with 600mmx 400mm porcelain tiles and will be using a flexible adhesive (BAL single part Rapidset Flexible or single part Fastflex, in this case would the Fastflex be the best option?) and wonder if i should glue the sheets of ply flooring to the joists? Is this how it's usually done? I will also be sealing the ply joins with fibreglass tape, is there anything else I need to be aware of? Many thanks for any advice.

 

[Ceramico tiling]

its usually screwed down but glue wont hurt.Pitty about the height issues as I always use ditra on ply.but it will add an extra 4mm or so.Is there no way you can sort out the height limitation?

 

[gez777]

Sorry, i meant would it be a good idea to glue the plywood to the joists in addition to screwing the sheets down (am planning to use 4 x 45mm Turbogolds) and while I am here, what centres would be usual, a screw every 150mm sound about right? I thought about Ditra or Durabase but my problem is that the upstairs hall is carpeted and it looks like I will be lucky to get away with the 18mm ply tiled - let alone adding any more height - as i really don't want any kind of step up into the bathroom :-( Thanks!

 

[Ceramico tiling]

yep 150 sounds fine.I would use lots of noggins, lots of screws and something like kerraquick with the latex additive instead of water.Im not to sure about the tape as I usually leave a small expansion gap between the ply. Why the tape?

 

[gez777]

Thanks, I'll have a look out for the Mapei stuff - I used BAL before as it was easier to source locally.
I saw a post about taping plywood joins to prevent cracking and thought it sounded feasible, though an expansion gap sounds a better option so I'll go with that I think.

 

[judge]

it might be obvious but watch you dont puncture any pipes when screwing ply down

 

[gez777]

Thanks, obvious - but easy to fall foul of! I once had a loose floorboard so i knocked a short nail in to stop it squeeking. That didn't hold it so I pulled up the board to redo all the fixings and found my short nail had just grazed a 15mm copper pipe that some previous genius had ran across the joist just under the floor board! So much for a two inch 'safety zone'