tiles have lifted!

[mikell]

last yeay i laid my bath room floor,but now My bathroom floor tiles have lifted and I thought mabye the plyboards have somehow come loose but upon lifting a few tiles the boards are solid still and my mix remains on the tiles ( a good paste,I cant chip it off!)
I dont understand why they have come off if the paste has been a good mix and the boards have no play in them. The paste is only really adhead to the tiles and not the floor ,im sure I used pva but cant really remember now,could this have been the problem?
I can only guess that the paste I used was not a flexible type ,is that a poss reason? I am dreading ripping them all out and laying new tiles but will do it but cant bear the thought of the new ones comming up again next year as I can see that happening if I lay them the same way!
thanks for any advice gents,appreciated.

 

[gcol]

Oh dear.

If you pva'd the ply then that's probably why the adhesive hasn't got a proper grip on the ply. If you didn't use flexi adhesive, that's another reason they've come loose.

What thickness of ply did you use? You say "plyboards", I'm assuming you meant sheets?
How did you fasten the ply down?

 

[mikell]

Thanks for replying,
I screwed the boards down,large boards about 6ft x 4ft (ish).
and I know I used pva on the walls to stop the moisture being drawn out in to the walls( is that right,its what i can remember anyway!).
boards were not as thick as some posts here have mentioned prob 10mm mabye even less but if they stay solid..... got me thinking now even though solid cos theyre thinner they mabye still have a bit of bounce and over time tiles have come away? it seems all round iv ballsed up !!
pva, boards,and paste( although the paSTE did say it was for use on plyboars amongst other things but did not say it was flexible,so i guess I presummed it was ok).
so to restart do you suggest :
thicker boards, flexi paste, no pva and get a tiler in!!

 

[gcol]

Have a read of the tiling sticky for preparation instructions. Try and go for 12mm ply, staggered joints and screwed down every 200mm over the sheet surface. No pva. Just go on with a powdered flexible adhesive (I only recommend Bal adhesives for tiling on timber) and finish with a flexible grout.

 

[mikell]

thanks for taking the time to help out,much apprieciated.
now to grit my teeth and get on with it!

 

[gcol]

No problem, good luck.