Expanding Foam and Background Questions

[Rio_]

Hi all,

I want to make some fake rocks to stick to the back of my Bioactive tanks. As all the rest of the décor is already in, rather than emptying it all out and doing a background the traditional way, I'd like to create the individual rocks and stick them to the back at my own leisure.

So, the questions I have are:

1.- Are there any brands you recommend for expanding foam? I've never bought it before and I'm not sure where to start. Obviously I need something none-toxic.

2.- After shaping I intend to paint them with acrylic paint- do I need to seal this in some way, and what would I need to use that is safe?

3.- Attaching them to the wall- I read some people use hot glue but I'm concerned that they wont stay up, it's a jungle setup and as such I spray my tank a few times a day and it's very humid. What can I use to ensure it doesn't get washed away?

Thanks in advance for any help!

 

[Entomologist210]

For my vivariums I use "Great Stuff" foam sealant for the backgrounds. I will clean up the glass and apply a thin layer of silicone so it has something firmer to hold onto (wait for it to dry before applying the foam), and then foam it up the way I want. I haven't used any acrylic paints, but maybe Krylon? (I think I've heard of people using it in aquariums) You can also push real rocks and wood pieces into the soft foam at this point.
The foam will hold them up when it cures. After the foam cures, you will need to carve it up the way that looks best to you, making sure to cut all the smooth parts so you're left with a rough texture. Then apply silicone to the foam (LOTS), making sure to get it in all the nooks and crannies. While it's still wet you should apply your dry background material so it will adhere when the silicone is dried. This also waterproofs the background. Just make sure to wait for everything to set and cure in between the applications of foam and silicone. Here's a pic of my dart frog viv that I've had running for a few years at very high humidity. No issues and everything is still tightly stuck in place.