Hi,
I'm planning on building a 3D rock background out of polystyrene to place inside my aquarium.  The plan is to sculpt and shape the polystyrene 'rocks', stick them individually onto a thin flat polystyrene backing sheet and then brush it with several epoxy resin coats (with suitable dyes if needed) to achieve the right colours and a bit of strength (the polystyrene itself is inert and does not need to be sealed off completely from the aquarium water).  I'm hoping to achieve a matt dark grey slate colour (or ideally shades thereof).

The polystyrene is then glued to the inside of the tank with silicone aquarium sealant.  The size of the 'wall of rocks' will be 7ft x 2 ft with depths of up 3 inches.

Researching on the web shows others have done this but I'm a novice in terms of resins and am not sure of the products available and sutable for this.  Looking at your products, I'm guessing if anything is suitable in terms of my planned process, it'll be the Epoxy Coating Resin?

Are any of your epoxies and dyes aquarium-safe (usually anything ok with potable water is fine)?

I'm hoping you can recommend resins, dyes and approx. amounts (I appreciate the latter will be a guesstimate! to the nearest pack size will do). Also I get the feeling the resin dries to a gloss finish - any techniques to reduce the gloss effect also appreciated.

Thanks in advance
 
Hiren.

When fully cured Epoxies like EC coating epoxy should be safe for use in an aquarium.

I have done "fake rocks" for model railways and plastic model "dioramas" using several materials as base, and using a mixture of Marine Epoxy (West Systems) and oven dried  "washed" sand as a filler. I have used mixed colouring additives to get a good colour.

The very fine sand mixed into the coating Epoxy makes the surface look a lot less glossy, and you can sprinkle the sand onto the surface when wet, to make it even more matte, this affects the colour though.

most of my "rocks" were painted afterwards with matte paint, to get them to look even more "real" .. You can probably do the same by mixing different shades of Epoxy resin and simply painting it on ... any shiny spots can be matted using steel wool ..

Good Luck!  

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