Grab Adhesive on plaster? [b]Urgent[/b] please help.

[r896neo]

I have just removed tiles from a large splashback area and am replacing them with formica faced plywood sheets. I will be securing these with Hi grab adhesive but when the tiles came off they took large areas of the skim with them leave just scratch coat in places. I dont need the walls dead level but will but filling these areas rougly with bonding. It will only be 5mm depth at maximum so how long should i leave it before applying the adhesive and should i seal it with anything prior to using the evo-bond adhesive on it.

Cheers

 

[big-all]

i wouldnt worry to much 1"balls of grab every 6 to 8" in a grid patern and push untill level

just make shure both surfaces are completely clean of dust or loose particles then you only need worry about what you can see