Tiles coming off ply walls

[djc1960]

Help please...about a week ago, I finished tiling my ensuite and have now noticed that the edges of some are lifting....having prised a couple off it appears that the adhesive just hasn't stuck to the ply at all.
Tiles are 250 by 400 ceramic, walls are 12mm wbp very securely fixed, on studs at 300mm and screwed every 200mm vertically.
Adhesive was Instarmac Ultra Waterproof WR reccomended by my local tile "expert" and used slightly against my better judgement as I was going to use bagged with an additive for wood. Adhesive datasheet does tick all the boxes though but that doen't help me now.
The shower is tanked with Mapeigum up to 3/4 height and the tiles appear to be stuck OK here....one wall is plastered and again tiles appear to be stuck OK.
Any input as to what went wrong, the best way to fix it and what I should use when fixing would be much appreciated.
I've tiled at least half a dozen bathrooms onto ply with no problems before so I don't understand what went wrong this time.
Thanks

 

[Gazzer]

I know it says Timber substrates on the bucket and top of data sheet but then it reads
"SUITABLE SURFACES
Plaster: Tile only onto a finished coat. Leave new plaster for at least 4 weeks in
order that it will be strong enough to support the tiling weight.
Cement/Sand Render: Leave new surfaces to dry out for at least 2 weeks
before tiling.
Brickwork/Concrete: Leave new surfaces to dry out for at least 4 weeks.
Plasterboard/Fibre Reinforced Cement Sheets: Boards should be braced and
screwed horizontally and vertically at 300mm centres.
Domestic Showers: Ensure 100% solid bed coverage is achieved.
Do not leave voids when applying the material as this will trap water and cause
adhesive failure."
No mention of timber....

 

[mikethetile]

:welcome:wrong addy im afraid

 

[hillhead]

Plywood is temperamental at the best of times but no less than a good quality bagged flexi adhesive.

 

[pete f]

yep flexi bagged addy needed and sbr primer djc

 

[DHTiling]

Dispersion adhesive dries by losing it's moisture... PLY is a no no with dispersion IMO..

You should have stuck with your better judgement.

 

[djc1960]

Thanks for the promt replies....pretty much what I expected....any suggestions as to whether the tanked areas will be OK....I'd really rather not take off any more than I have to....the tanked areas seem pretty solid as do the ones on the plastered wall whereas the rest have many with movement at the edges/corners when pressed.

 

[aph257]

large format tiles should not be fixed with tubbed addy. you needed and SPF single part flexible) to do the job.

 

[Scott]

Dispersion adhesive dries by losing it's moisture... PLY is a no no with dispersion IMO..

You should have stuck with your better judgement.

Even worse when its tanked!

 

[Viceroy]

I'm about to tile a 3/4 Plywood Wall ,am I right in thinking that I SBR neat the wood then white slow setting single part flexible addy ?
Never been in this situation in 12 years ! Only sticking 16 x 10 light ceramics on.