Travertine crack accross 4 tiles

[doug boardley]

it sounds to me like the ply has heaved with expansion, due to the sheets being butted tight.

 

[DavieA]

Everyone talks about deflection and no more than 3mm per 400mm but how do you accuratly measure it?

 

[Rich]

No British standard is min of 15mm BWP marine grade ply fixed down at a min of 300mm but 15mm is not so easily available so most use 18mm ply if height is a problem but I like to go as thick as I can. It is still a good idea to seal the underside and edges of the boards, this gives a bit of protection from moisture from underneath. Was that meant to say primer G? That will be fine. When it comes to deflection I have one simple rule "if there is any deflection then you can expect your floor to fail". You are lucky enough to have a say in this before the ply goes down, if the floor needs it, then get the joiner to add some noggins and like I said screw it to death. You want that floor as rock solid as you can get it.

 

[DavieA]

Yeah Primer G, think im loosing the plot!

Ok before i get more info and speak to joiner tomorrow could you help me out?

If floor is deflection free will it make a difference wheither 22mm ply is layed with 2-3mm expansion gap and screw to death up joists or 22mm chipboard layed and screwd to death up the joists?

Are both Ply and Chipboard suitable to have backerboard fixed to using flexible tile adhesive and screw fixing method as per your post?

form experience whats options if deflection exists bering in ming UFH heat transfer?

Thanks again everyone

 

[doug boardley]

chipboard has a tendency to curl up at the joints when only slightly moistened, ply and backer boards all the way for me.

 

[Rich]

As above. If there is bounce in the floor, chipboard or ply, you need more screws and more noggins.

 

[DavieA]

Here's an update on the upcoming floor. Spoken to joiner and he has no way of adding noggins between joists because of the ufh pipework so advised not to use sheets of ply as under every joint must be supported. Which makes sense, so if chipboard is used which is obviously 22mm thick and t&g, screwed to joists can (if the floors solid and bounce free) cement board such as hardi be fixed as per Richs post using a thin bed of addy and screwed at 150mm centers into the chipboard?Thanks all for any input on this.