[Katieam]

if i use the polystirene (spelling?) to make the structure of my rocks, can i just cover it with cement? i would sand it smooth and paint it to make it safe. I guess im asking if i have to use tile grout since i already have cement lying around.

thanks

[Dave1992]

id suggest using something to fully waterproof the polystyrene (ive probably spelt it wrong aswell :P) to make sure nothing starts to get mould, and i found that it gives a very natural feel afterwards and then the cement makes it look like the real deal with a bit of acryilic paint mixed in

[Katieam]

ok cool. i was planning to even cover over the cement for extra water-proofing.

[Dave1992]

yeah that would be just as good lol good luck

[Tdizzle10]

dont bother doing all the extra stuff, get that polystyrene or even use spray foam for the back round and apply silicon behind it so it doesnt peel off the glass, then buy that habbacrete stuff from www.herpinvert,com the stuff is cement but its waterproof and its ph neutral as well so it doesnt make the water in you tank acidic, once all the foam or polystyrene is cover with that stuff you wont need to waterproof any further and you will be able to colour it how ever you want with non-toxic air brush paints or you can just leave it up to u