Tiling on Tongue and Groove

[Softus]

Bal seem to think it's a problem - they recommend sealing the back and edges of ply sheets before tiling.

We seem to have moved away from the point of my question, which wasn't how to make ply resistant, but why you think moisture laden air will reach it.

Obviously by your comments you don't do this.

There was nothing in my previous comments that implies, let alone makes it "obvious", that I do, or don't, do that. FYI, mostly I haven't, but sometimes I have.

Back to the point: is your only reason (apart from cost) for not using WBP plywood the fact that Bal recommend sealing the back and edges?

 

[gcol]

This ranks amonst the most ridiculous posts I've seen from you Softus. But then, I suppose you can't know everything.

I think (on other posts) we've already decided that grout is not impervious to water - so what makes you possibly think that it's impervious to air? Moisture is suspended in air, not just in the bathroom, but in rooms on the other side of bathroom walls. Moisture WILL find its way to ply panels and WILL cause expansion - this is irrefutable. For this reason, I recommended plasterboard which has little or no expansion due to moisture variations, is cheap and is easy to cut and fit.
The very fact that you are asking these questions makes it obvious that you do not seal ply sheets before tiling. To be quite honest Softus, I'd have expected this line of questioning from Joe-90 and not from the likes of yourself.

 

[Softus]

This ranks amonst the most ridiculous posts I've seen from you Softus. But then, I suppose you can't know everything.

I think (on other posts) we've already decided that grout is not impervious to water - so what makes you possibly think that it's impervious to air?

Nowhere in any of that do I see an answer to the simple question I asked several posts ago. And the thing that you say that we've decided - we haven't.

Moisture is suspended in air, not just in the bathroom, but in rooms on the other side of bathroom walls. Moisture WILL find its way to ply panels and WILL cause expansion - this is irrefutable.

As a certainty, I refute it.

For this reason, I recommended plasterboard which under normal circumstances has little or no expansion due to moisture variations, is cheap and is easy to cut and fit.

And I recommend WBP plywood for the reasons I've already given.

The very fact that you are asking these questions makes it obvious that you do not seal ply sheets before tiling.

The fact that I sometimes seal them makes a mockery of your claim of something being obvious. The reason for the question was to find out why you specifically recommended not using plywood. Now it turns out that you don't have a reason, because sealed plywood would be acceptable to the only adhesive manufacturer that you've chosen to quote.

Once again, since you seem to be hard of reading, I don't always seal plywood - I do it when it's necessary.

To be quite honest Softus, I'd have expected this line of questioning from Joe-90 and not from the likes of yourself.

The line of questioning continues, because you, much like joe-90, cannot give a straight answer to a straight question.

Precisely how, pray, does moisture laden air find its way onto so much of a plywood panel that the panel will expand in such a way, and to such an extent, as to cause a problem, and yet not cause a problem to the same amount of plasterboard?

If you think it's through the grout then don't bother replying - you can fool yourself, if you wish, but you can't fool me.

 

[Thermo]

at least he can give a short answer or question!

 

[gcol]

I've answered all your questions clearly Softus. I have also wasted the best part of an hour trying to convince you that plasterboard is more moisture stable than ply and I shall waste no more time doing so.
If anyone else is unsure of anything I have said in this thread please post and I'll try and explain further, but I shall not rise to your inane whitterings any further Softus.

 

[Softus]

at least he can give a short answer or question!

OK then - here's a précis for those who don't like long sentences...

Statement: tile adhesive doesn't adhere as well to ply
Reply: It does if you use the correct adhesive.

Statement: 18mm ply is far more expensive than plasterboard
Reply: Yes it is.

Statement: ...and more subject to failure due to atmospheric conditions.

Q: What do you mean by that?
A: I was refering to changes in moisture

Q: Why not do the same thing as you do for plasterboard?
A: I'm talking about moisture in the air.

Q: How is that air coming into contact with the ply?
A: Bal recommends sealing plywood.

Q: Why do you think moisture laden air will reach the plywood?
A: Moisture WILL find its way to ply panels and WILL cause expansion.

Q: Precisely how does moisture laden air find its way onto so much of a plywood panel?
A:

And here's the absolute classic pair of statements:

I agree plasterboard doesn't like water, but if the tiles and silicone are applied correctly then it's not normally an issue.

I think (on other posts) we've already decided that grout is not impervious to water...

 

[Softus]

I've answered all your questions clearly Softus.

You've answered lots that I haven't asked, but you haven't answered the only one I was interested in. Not even close.

I have also wasted the best part of an hour trying to convince you that plasterboard is more moisture stable than ply and I shall waste no more time doing so.

I'm not interested in which one you think is more stable - that's for the OP to decide. I merely asked you how the moisture reaches the ply and expands it and yet doesn't reach the plasterboard and turn it into mush. And your answer to that is, wait for it:

 

[gcol]

I merely asked you how the moisture reaches the ply and expands it and yet doesn't reach the plasterboard and turn it into mush. And your answer to that is, wait for it:

And if I answer this will you leave it alone? It's getting boring now.

 

[Softus]

And if I answer this will you leave it alone?

Please note that I never said that you shouldn't use plasterboard, I simply wanted to know the source of your prejudice against plywood, which appeared simply to be the cost of it.

You've already failed to answer the question, several times.

Be bored, or don't be bored.
Answer it, or don't answer it.
Believe that air can travel through grout only when plywood is used, or don't believe it.

You've dragged it out for so long that I don't care anymore.

 

[gcol]

Please note that I never said that you shouldn't use plasterboard...

I know this, but you said that ply was a better surface to tile to than Plasterboard (and Aquapanel ). What I've been explaning (for the benefit of people reading this) is that this is not the case.

...I simply wanted to know the source of your prejudice against plywood, which appeared simply to be the cost of it.

I recommended plasterboard which has little or no expansion due to moisture variations, is cheap and is easy to cut and fit.

Once again, since you seem to be hard of reading.

I think the above quotes prove that it is you that is "hard of reading".

Surely you must accept that wood expands with moisture? What you can't seem to grasp is that changes in moisture will affect wood to some degree wherever it is. You don't need "line of sight" for wood to be affected - moisture suspended in air will get everywhere. For this reason and this reason only, manufacturers of tile adhesive recommend sealing the untiled faces of ply to make the ply more stable to moisture variations - this is fact.
The changes in atmospheric moisture necessary to cause expansion and contraction to wood will have no effect on plasterboard, which is why I did and still do recommend it over plywood for use with tiles. Any expansion of substrate could lead to weakening of the adhesion of the tile to the substrate. Don't get me wrong, I'm not saying that your tiles WILL drop off - what I'm saying is that plasterboard is a better surface to tile to than ply..... nothing more, nothing less.