Epoxy. Fish safe epoxy. In this situation - a hard-working situation - for coloring use no paint
, just use dry pigments like for concrete. Don't bother mixing in a bunch while mixing up the epoxy, you can just dust some on after you're done fabricating but the epoxy hasn't cured - while it's still very sticky.
Aside - I believe Mod Podge is similar chemically to PVA acrylic fortifiers for concrete, and PVA acrylic glues lie Elmer's. It is
, therefore useful in dryland "habitat builds" like fake rock for leopard geckos and bearded dragons. It is NOT
, therefore it's NO DAMN GOOD for high-humidity situations let alone immersion in standing water, and JUST FORGET IT for flowing water.
Are we clear? Ha ha. Seriously though, you asked, so please listen.
OK, so back to epoxy. I've personally used these two for immersed & high-humidity viv/palu builds:
1) Polygem's zoopoxy (https://www.polygem.com/products/zoopoxy
) - specifically their 307 lite, and:
2) Smooth On's cast & coat (https://www.smooth-on.com/products/habitat-cast-coat/
- 307 lite is a putty, kind of like super-duper sticky peanut butter.
- Cast & coat is a liquid, kind of like a super-sticky honey.
- Each has a learning curve.
- Both kick ass. Bomber-strong, totally waterproof, absolutely animal safe.
- For your situation - you already have your foam carved up - I'd probably recommend the liquid. Note that Polygem has liquids too (see this page https://www.polygem.com/products/zoo...alers-coatings)
(If you didn't have your waterfall carved up already I might recommend getting some of the thickening agent too (see polygem site), and using the 307 putty, to free-throw your sculpture.)
I got through the learning curve on my own, but no lie, it was kind of a bitch. That was quite a long time ago. Maybe nowadays there's some YouTubes or something. Anyway, now that I've found epoxy I don't really like to use much else for covering foam backgrounds. (No shade on the other guy, but personally I think silicone is best used where it can't be seen - and in a flowing-water feature, it's gonna be seen
before very long.)
If you wind up going the epoxy route, do some testing first on scrap, and for God's sake buy a box of disposable gloves and wear beater clothes. Remember that water is your friend, water is what keeps the epoxy from sticking to your gloves and tools. So keep a disposable "cup" (e.g., an old butter or sour cream tub) of water on hand at all times to dip into. But if you get in a bind, feel free to PM me for advice. Or just post here and maybe I'll find you again. Happy to help.