I've been researching what the best resins to use on home made Polystyrene backgrounds. I've called a few manufacturers and had communication with the Chemist from Norski. A rather helpful bunch of people actually, and they seemed quite interested in my project.

Their response: Although we can't guarantee this, it would work fine in a cold water environment. The potential hazard is when heat is applied. 26-27C will overtime cause the poly to release a styrene gas which is toxic and will continue to expand the foam. This gas WILL find a week point and escape. We do not advise any type of resin being used on Polystyrene as in time, it will kill your fish.

That was from the chemist who creates their resin products. I couldn't get anything out of Epiglass.

So, just thought I'd post this for anyone's interest if they've looking at this type of project. Many people on here have used resins and had no problems what so ever. Just thought the side of the manufacturer would be an interesting read.

Interesting thanks.. wouldn't want to slowly kill our fish..

...26-27C will overtime cause the poly to release a styrene...

So it is the polystyrene that is the problem on tropical tanks?

From what he said, it's a combination of the poly and the heat. Says the same reaction is unlikely to happen in cold water. He suggested finding another substrate, but could not comment on other reactions unless they knew the product forming the structure.

The part that I found interesting is that it's apparently a slow reaction. Anyone had any long term luck with poly and resin?

yes 3 to 4 yrs no probs

What did you use can I ask? I find this all rather interesting.

i think the amount of gas produced would be so small that it wouldnt be a problem espcially if you use poly with bigger beads as these have been heated more and the gas that forms inside the bead to expand it will mostly be exhausted. any gas released would likely be dissapated very quickly with sufficent water movement

I started the project and opted out in the end. Pic below of starting point. I used 80mm poly with a head gun (mild) and noted it caused a significant honey combing effect. The large beads created this. Looked great, but created a nightmare from a sealant point of view.

Perhaps a finer poly, not so trigger happy on the heat gun, and I would have had better luck. I think the advise from the Chemist would be valid from my projects perspective as I'd carved it to fail. I'll give it a go again one day. Have settled for rock with black gravel and shist this time round.

rocks by danaj2009, on Flickr