Corner structure advice

lorax84

You can also build in tank decor out of Styrofoam and seal it with drylock. Drylock is a masonry sealer used for sealing basements, once dry it is 100% aquarium safe. Cement will take a very long time and cure as bear said. I have never used Drylock but someone on another forum used it for angel fish and turtles. Here is a thread about it.

3D Background with Drylok - Turtle Forum

There is a lot of info on 3d tank backgrounds that I am not even going to try to reiterate.