Fake rock wall question?

[Dutchy88]

Jst a quick question to those of you that have built them before. When you glue your foam onto the backing board do you leave say a 5 or 10mm gap to allow for grout and paint build up it would seem to me if you filled the foam out to the edges once all the grout and everything went on it wouldn't fit without allowing for build up is this correct??

 

[Mitch_89]

i would say yes leave a rather small gap butbi dont use this method i use a pond sealer membrain paint paint it while it js in the tank

 

[ssnakeboyy]

I didn't have a gap and I did three layers of grout and the build up is barely visible if your not looking for it.