Sealant For Fake Rocks

[noop]

hi

i'm about to make a fake rock background for my new tank. i'll be making it from polystyrene (styrofoam), with layers of cement on top. i'd rather not go to the hassle of curing the cement so it's safe for the tank, and was wondering whether i should seal the rocks with pond sealant (clear, and safe for fish ponds) or epoxy resin (which i've used once a long time ago to fix a surfboard)

i'd be grateful for any suggestions as to the pros and cons of these two methods

cheers
noop

 

[Lateral Line]

If the cement is encased in a water/air proof barrier, will it ever cure or will it simply not set and slump?

 

[noop]

If the cement is encased in a water/air proof barrier, will it ever cure or will it simply not set and slump?

i was planning on letting it set before sealing it

but having just read up a bit about curing, maybe i should go to the trouble after all. i will still want to seal it afterwards though, as my fish wouldn't like any increase in pH that might still result from cured cement