why prime the back of the ply and not the front?

[Chris1397]

Hey folks, ive just laid 12mm Marine ply on my bathroom floor in preparation for tilling, its screwed down on 200mm grid formation then i primed the ply with SBR bond as i have done in the past. Today i mixed up sovereign tile adhesive and glanced at the instructions which stated i was to prime the back of the ply and not the front????? why.... this goes against everything i have learnt about tilling, slowing the suction rate etc and why on earth would you ever need to prime the back. Can anyone explain?
Thanks

 

[Qwerty]

The back of the ply is primed to protect it from any vapour/ moisture underneath. You still prime the face of the ply before applying decoupling membrane or tile backer boards prior to tiling.

 

[Chris1397]

Thanks Plan Tec, phew well there will be no vapour as its on a first floor, but the instructions clearly stated qoute "do not" prime the front of the ply. Its a bit late now anyway as i went ahead and laid the tiles today regardless.

 

[J Sid]

I don't know of any adhesive company that says prime top surface of ply before tiling, only backs and edges.
not saying there isn't any that recommend priming the front, just not any I've used.

 

[Dumbo]

After having a discussion on priming on this site I was told by some members bal said not prime ply if using rapid flex . They were correct that is what it said on spec sheet . I then rang bal the next day and asked why not and they then said it would be OK to do so . So where I'm getting to is this I always prime everything and if someone on here wants to give a reason not to I will then take it up with the relevant technical company .

 

[jobdone]

I always prime all sides. The face always ends up a bit dusty.

 

[J Sid]

have just checked , weber say no, Ardex say yes, all say prime backs and sides. But I'd put money on most don't have the backs and sides done unless the boards are fitted by the tiler

 

[Chris1397]

Ok thanks Julian, i thought it was standard practice. If the suction rate is not controlled with cement render and plaster than you end up with a crumbly mess. I thought a longer cure gave a greater bond and strength, you know yourself if you get adhesive on your jumper it dries and crumbles away! Do you think it will matter that i primed the ply when i shouldnt have? ooops

 

[Chris1397]

my boards were covered in plasterboard dust so i thought it would be a good idea.

 

[J Sid]

personally I never tile direct to ply, either ditra, hardie type backer board or insulation board.
can't see it can do much harm to prime face but really need to follow manufactures' instructions. If dusty a damp sponge wipe may be enough.

 

[Dumbo]

Ok thanks Julian, i thought it was standard practice. If the suction rate is not controlled with cement render and plaster than you end up with a crumbly mess. I thought a longer cure gave a greater bond and strength, you know yourself if you get adhesive on your jumper it dries and crumbles away! Do you think it will matter that i primed the ply when i shouldnt have? ooops

Absolutely no problem as far as I'm concerned always prime . But as above never Tile directly to ply as I have seen many failures over the years and lots of brown grout .

 

[Flintstone]

I always prime the face of ply If I am going to tile on it, which I would prefer not to but some people I do jobs for just repeatedly use it

 

[Chris1397]

thank you all for your input.

 

[Dave]

I stopped using ply years ago .. its outdated imho..

 

[Dumbo]

I still use ply for over boarding I much prefer to other options as I think it is stronger . But I always use ditra on top .

 

[demi34]

Bal fastflex rubber adhesive no problem with plywood

 

[Dumbo]

My opinion if you have to use s2 type adhesive your background prep isn't good enough .