fixing Tile Backer to brick

[FatFlint]

Morning Everyone..
Tiling bathroom 300 x 500 ceramics , thinking of using backing board prob no more ply , on to brick they recommend fixing with tile adhy dot and dab .
was wondering if anyones used the fixing foam like dow insta stick or pink grip dry fix , i fancy trying it but obviously not if its not up to the job..
and would you go with 6mm or 12mm backer
thanks guys
Flint

[toolbox]

I have used 6mm on brick with dot and dab (although I added mechanical fixings) but it did flex quite a bit the makers did not recommend it but I was stuck for space.
Not tried the foam but, if it is any help when I found it flexing I drilled extra holes in the boards and squirted a splodge of building adhesive through the holes to add stiffness that worked fine.

[FatFlint]

thanks tb which board did you use and would you recomend..

[toolbox]

I used Marmox which has an insulating layer as it was a cold room with two outside walls, but any tile board should do, the Marmox might be overkill in your case.