(another) Plywood thickness question!

[MrZ]

Hello

Hi
I'm tiling a bathroom floor and have laid 9mm plywood (screwed down) over the floor boards.

Like an idiot i didnt research this and have since read that thicker plywood is advisable.

I have some more 9mm plywood leftover that i had earmarked for other uses.

If i screw this on top of the plywood i have already laid, will it have the same effect as if i had laid one sheet of 18mm thickness in the first place?

Is 9mm definately going to be too thin, ideally i dont want to increase the height any further due to aesthetics?

cheers

 

[Softus]

It all depends on the rigidity of the flooring underneath.

9mm could be perfectly fine if you ensured that all loose boards were screwed down first. The advantage of 18mm is that you can screw through into the joists and it will pull down any loose boards underneath, whereas 9mm is too flimsy for that.

 

[MrZ]

thanks. Think it needs a thicker level of plywood.

Will screwing another layer of 9mm have the same effect as one 18mm layer?

 

[Softus]

Will screwing another layer of 9mm have the same effect as one 18mm layer?

I can confidently say that it won't, because there'll be a layer of glue missing.

However, whether it being less rigid (in theory) is significant in your application is too hard to say.