# Aquarium Safe plastic for rock casting?



## GDominy (Jul 30, 2002)

I am building a custom 6 foot "back to nature" style background for my 135 gallon loach tank. I will be casting an entire wall of slate in 2 foot sections (so I can get around the center brace) and "hanging" them from the back wall of glass. Its difficult to explain, but the three pieces will fit together like a puzzle so you cant see the joining line (easy to do with slate).

I already have designed the form for the rock wall pieces and I have the sand and slate required to make the wall I'm going to cast. I've found the casting rubber I'll be using to make the mould for the wall as well as the strengthener to back it up. 

My problem; What am I going to make the wall out of?

Concrete will be too heavy, the local plastics store is telling me that Epoxy is toxic (they were sued because a Koi farmer used it and killed off over 2.5 million dollars worth of Koi. Its safe for humans, but not for fish).

I need to make this casting lightweight, so I was hoping to use some form of plastic resin... Any idea's?


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## m.lemay (Jul 28, 2002)

Polyethylene or polstyrene will work. The biggest problem is that you have to get them hot enough so they'll melt to pour it into your mold. Polyethylene is non toxic as so is polystyrene. Polyethylene is used in milk bottles and has a semi-flexible property to it. Polystyrene is used to make styrofaom which is not toxic, those clear plastic drink cups are generally made from polystyrene also. Poly styrene is much more ridgid than polyethylene and may not be as forgiving when pulling it from the mold. I don't know how well the casting rubber will hold up to hot plastic though. Why not make the whole thing out of the casting rubber?

Marcel


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## GDominy (Jul 30, 2002)

The casting rubber is essentially spongy elastic plastic. Its not rigid at all and is designed to pull freely off the object you are casting.

There is a product I"m curious about that I have seen at the local hobby stores. Its plaster-like, but its 3 times as strong at 1 tenth the weight. I would need to seal it though as it would melt in water :-(


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## m.lemay (Jul 28, 2002)

Heres a page that I found about plastics.http://www.plasticsresource.com/
Would plaster of paris be too heavy?
A lot of people have sculpted styrofoam sheets and glued them to the back of the tank with silicone. 
Epoxy resin shouldn't be toxic to fish once it has fully cured. I would look into it a little further. 
How about making the mold out of plaster of paris and then pouring the hot plastic into the plaster mold?
I'm just throwing ideas out there.

Marcel


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## Work In Progress (Mar 4, 2003)

Hiya
I saw some interesting stuff on the following sites. Maybe you could find something that suits your needs.
Good Luck!

http://www.resinrpd.com/
&
http://www.avesstudio.com/User_Cate...__Special/sculpting___modeling___special.html

Kelly :mrgreen:


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## PDX-PLT (Feb 14, 2007)

People make epoxy-lined plywood tanks all the time. It shouldn't be toxic once fully-cured and thoroughly rinsed.


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## [email protected] (Jul 17, 2008)

Acrylic casting resin should do, - but - research the MSD sheets to verify which ever compound you settle on. The MSD sheets are normally on line. Most manufacturers find it cheaper and less likely to get them sued, if they post them on line. 

I find it difficult to believe that cured epoxy (without inhibitors in it) killed Koi. 

I'd find it really easy to believe someone sprayed boat hull grade epoxy (with inhibitors) to make a pond. Or a gel coat.


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## nillo (Jan 15, 2004)

Use 2 part expandable Polyurethane foam. Basically it is spray foam in a mixable form like epoxy. I would use the 8# (IIRC) foam as it is the most dense. This has been used in aquascapes for a long long time. You can add tint to it and then you can use tinted epoxy over it to make the casting look more realistic and less uniform. I use the stuff all the time for my scapes and have been for years. You can even carve it after the fact. It is completely inert once cured.


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