Be careful, you have to do this step outside or in a room very well ventilated and do not breath vapors because polyurethane foam as long as it is not completely dry, emanate dangerous and flammable substances! Use the "dry brush" technique: take a dry brush, take a few white paint and strum long time on something clean for leaving just a little bit quantity of paint. google_ad_height = 15; Step 3: Build the Background. Welcome to Part 2A of the 10 gallon aquarium to vivarium miniseries. The Rock Terrarium Background from Exo Terra is an easy to cut background that has an incredible natural look. However, three-dimensional backgrounds – such as faux rock walls or cliffs – can take your vivarium to another level. This how-to guide will walk you through the steps of making an easy to construct, durable, light weight, and convincing fake rock background for your terrarium or vivarium. But it's up to you to decide according to what you wish. These are used to spread silicone on the glass background of a terrarium as the 1'st step towards building a custom vivarium background. Second method for making fake stone for terrarium, aquarium or paludarium: Tape off areas that you don't want spray painted.5. DYNWAVE Single-Sided Adhesive Aquarium Background Backdrop Fish Tank Reptile Terrarium Vivarium Wallpaper Decor - Undersea World - L 2.9 out of 5 stars 3 $13.98 $ 13 . //-->. People often use extruded polystyrene (green, blue, ...) but I think this one is harder to work with. Our first method for making fake rocks in now achieved. But in this case I use five colors: black, grey, white, brown, yellow and a little bit green.