Plywood for tiling on floors? or Tile backer board?

[One Day]

Just imo 6mm ply is useless about as much use as cardboard

On that I agree 100%.

My stance on ply is this: I only have 12 years experience but going back say 6 or 7 years I could get wbp ply and it was great. Adhesive stuck so well it would tear chunks in the ply.
Now though, most ply is coming from dodgy places in the East with dubious certificates to meet environmental restrictions etc etc. In other words; the quality is terrible.
SP101 or FG1 grade ply is the same as I remember being able to buy, but it's now silly money.
Anywhere I can go here in Preston, the ply is the same - paper thin hardwood veneer and nobody will say where it comes from other than "it's far eastern wbp".

I'm probably the single most cynical member of this forum so I know BS5385 has the guidance on tile backer boards - written with help from BAL pushing BAL board. But the fact today is that using ply other than FG1 or SP101 is very very risky.

As tilers with many years of experience, we really need to be careful about the advice we give members of the public or new tilers.

 

[One Day]

Everything I've read on tiling on top of ply says.......seal the underside and edges(not the top)

I agree, but given the rubbish ply now, if I absolutely had to use it I think I would prime the face too!
The thinking was that the hardwood gives a better bond unprimed.

 

[Dan1234]

It doesn't work quite like that. It's still 15mm with a thin layer of 6mm on top doing nothing.

Okay well the 15mm toung and grove ply is staying down as it's structural being timber frame, I don't want to get involved with all of that. I will stick a 12mm ply over the top glued and screwed every 5". SBR the surface and tile onto.

 

[Spare Tool]

Okay I think I have come up with a plan. So the floor at the moment is 15mm structural type toung and grove ply as it's a timber built house. So as the 15mm is too thin I am going to cover with 6mm ply screwed down ever 6" and then fit 6mm multi pro tile backer board over the top glued and screwed. Does this sound okay?

Dan ditch the ply mate, 12mm Hardi or no moreply glued and screwed will stiffen it up a lot and give you a good substrate to tile too..

 

[Spare Tool]

No need to update anything i dont mind which i use but dont tell folk it can not be used maye time to get some knowledge about adhesives

Maybe you should possibly ask yourself why your the ONLY person in the thread advocating the use of ply, it's old hat Brian, qualities not what it used to be and there are a lot better inert moisture resistant cement boards out there now purposely made to avoid Tiling on ply wood..

 

[Dan1234]

Dan ditch the ply mate, 12mm Hardi or no moreply glued and screwed will stiffen it up a lot and give you a good substrate to tile too..

It says the floor has to be 18mm thick min to use hardie over the top on their site. The floor is 15mm, which is why I wanted to put ply over the top to help

 

[Flintstone]

We're going round in circles.

 

[Spare Tool]

It says the floor has to be 18mm thick min to use hardie over the top on their site. The floor is 15mm, which is why I wanted to put ply over the top to help

Why's it only 15mm ply down, who thought that was appropriate for flooring... Personally I'd still go with 12mm hardi or nomoreply, your then 27mm thick, trust me that's going nowhere..

 

[Perry]

This is why I find nowadays it’s difficult to give advice. As someone with less experience comes along and gives poor advise. And because it’s what they already want to do they take it.

 

[acaciaguy]

Is plywood the new pva?

 

[One Day]

You can lead a horse to water....

 

[acaciaguy]

And you can turn them into glue too

 

[822 mp]

1/2” Cement board thinseted-in and nailed with galv roofing nails is the way to go. Be sure to wash the floor good first. While cement board units (cbu) are flexible when stood on edge and shaken, when thinseted-in and nailed flat, it fuses for life to the wood substrate and the resulting lamination thickness of both is exponentially stiffer. Glued and screwed is a waste of time. If your sub floor flexes, and CBU’s are wobbly on edge, glued and screwed just means: now they both flex when stepped on! It results in air pockets and lack of 100% hi bond strength lamination.
That’s why thinseting it in is code. CBU’s will uncouple, top/bottom surfaces, if there is a mass stress event, and not deliver a hi tensile strength fracture to the face of the tile. The C board decomposes in latteral and vertical stress (deflection). The same as old school mortar beds which cracks and compresses or stretches to take-up movement without sending it to the top.
I use nails because, heck, after the acrylic fortified thinset dries, you could literally remove them, as the thinset is doings job for life at about 500 PSI. They just help level -out the board until it dries.

Phil