Question about DIY Background with Quikrete

[Animalnstinct]

I've been gathering everything I need to do a DIY Background and waterfall for the vivarium I'm setting up.

I plan to use foam and then coat it with cement, but when I went to the hardware store the only stuff they had was Quikrete Anchoring Cement and I was wondering if that would still work?

I realize it's going to expand when it cures, which I can live with ( I Think ), but I just want to make sure it's safe to use and if there is anything different I should do when using it?

I also wanted to ask about soaking it? I read that after I coat and paint everything that I should soak it in a bath of vinegar and water for a few weeks. Is this going to be necessary and if so, any tips on how long and how much vinegar to water I should use?

Thanks guys