Expanding Foam Background, Sealing It?

[atticus22]

Hi guys, my first post on here, been browsing for a while

I'm just wondering if anyone can help me, I have just made a fake rock background to go into a tropical tank, using expandable foam. I am a bit apprehensive about any toxins being released/fish eating parts of the foam (especially where the solid top layer has been broken when I have been shaping it) etc, and so am just wondering what would be best to seal it all with, whilst still keeping the 'rock look' that the foam produced.

I have seen people use grout, concrete mix and all sorts of things, but then have seen others say they are each a bad idea for some reason or other, which would be the best method of sealing to use?

Thanks very much

Chris

 

[saltynay]

Pond sealant or latex paint have no side effects.