How to make fake rocks

Fake rock for terrarium with polystyrene First method to make fake rocks background for reptiles:
If you wonder how to build fake rocky wall (faux rock) background for your terrarium, vivarium, paludarium or aquarium, I will explain two methods. This is a simple way to do and not very expansive. We need just a cutter with very new blade, gloves for avoiding cutting , a brush, a sponge, acrylic paint (for the first method i used grey, black and white color), Styrofoam sheet (I used a sheet with following dimensions: 120x60x5cm), tile grout and something for cleaning paintbrush and water.

The very first step consists to choose your material, in my case I chose expanded polystyrene (the white or black one, which flake off). People often use extruded polystyrene (green, blue, ...) but I think this one is harder to work with.



First, take a look at the video i made which shows my complete fake rock background with waterfall in Exo Terra tank:

Expanded polystyrene to carve for making terrarium fake rock Before all, don't forget to measure your polystyrene sheets as precise as you can, it could be logic but when you have finish, if your creation is to wide or to high for entering in the terrarium or aquarium tank, it's too late.
We start by drawing quickly the shape we want. Then we can carve our rocks, for this simple example, I decided to make the whole thing in just one part. It is possible to make different rocks separately and past them on a polsytyrene sheet with aquarium sealant. Carve that until you get the shape you like.

Tiling sealant to make fake rock for terrarium When you have finish the shape carving of your terrarium fake rocks, you have to apply something which will give the hardness to the whole thing and give the rocky appearance. For doing this, there are many solutions, you can use SikaTop 121® of the Sika brand which is usually used for exterior water tank for example. This product avoid use of varnish or resin even in aquarium. But this material is used by professionals so it's quite difficult to find in a small quantity and for a price a bit high in relation to the chosen solution. Some people use cement too but I find it to heavy. I choose tiling sealant which is often used for making faux rocks. Take it only in powder, by the way you can do the mixing as you want (maybe more liquid, maybe less). Blend it with water with enough quantity for applying with a paintbrush. But avoid splatter. Then apply with a brush all over the surface included the back. For mine I applied three layers. Wait that a layer is dry before applying the next. It is good to know that some people blend the last layer with sand for having a grainier surface, I tested it but I didn't like the result (to grainy and to fragile). Keep in mind that you mustn't put the background under sun or warmness because sealant will crack!

Dimensions of differents parts of terrarium When the three layers are dry I obtain this:

How to make fake rock with tiling sealant When all layers are fully dry, we can start the most artistic part. Take acrylic paint, brush, sponge and some bowls for blending and cleaning. I just take cut water bottles

Fake rock painting First prepare a very dark layer but not pure black because it could decrease the realism. Blend black color with 50% of grey, but it's up to you making your own blend the way you like. This first layer will permit to bring out hollows. Then use a brush to paint all the rocks with obtained blend color. For me, two layers was necessary for covering all the surface. At this step the result looks like the photo on the right.

How to paint fake rock - black color When those two layers are dry, cut a piece of sponge (the same we use for dish-washing) and I make a blend with black and gray but with less grey for getting a lighter color than the previous step. Then I strum many times on an empty piece of polystyrene (or something else clean) for removing surplus. It must stay on sponge just a bit paint. And I strum (without pushing to strong) on the rocks but not in the hollow (it's important).

How to paint fake rock - gray color For the next step, we must accentuate the rocky surface with a very little bit of pure white. 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. Give very slight blows of brush only on highest reliefs without pushing too much. The final result of this first method looks like the photo. Our first method for making fake rocks in now achieved. Take a look at the photo on the right.

How to paint terrarium fake rock - third color white Before looking at the next method, you can see a close-up photo of the fake stone background we did.

According to what you want and where you plan to place your faux rock background, you might have to protect it. If you create fake rock for aquariums you will need to cover it with epoxy resin. Apply 4 or 5 layers and when all is dry, wash it a lot. after at least 1 month, you can place it in the tank and gluing with aquarium silicon. Try to avoid as much as possible space between glass and background. In my case this terrarium background was for a rhacodactylus ciliatus (now correlophus ciliatus) so I chose a product which is used to blend with cement for making pond or drinking water tank( SikaLatek of Sika brand).

Faux rock with polyurethane foam Second method for making fake stone for terrarium, aquarium or paludarium:
For the second method, the way to do is almost the same but the base is different. Rather than carving a thick piece of polystyrene, we use polyurethane foam (great stuff) usually used for filling holes and insulating in building. In this case I apply it on a thin sheet of polystyrene and I let the foam dry during four hours (according to what is wrote on the back of the product).Don't forget to use with gloves because it stains on clothes and skin.
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! For more it can cause skin irritations.

PU foam carving Next we carve polyurethane foam giving desired rocky aspect of the stone. Expansion of foam give random shapes, so it's easier to imitate uneven reliefs of stone than with polystyrene sheets where final render depends essentially of your sculptor skills.

Tiling sealant for terrarium cliff Next step is the same but required more layers or tiling sealant. In fact, In some countries, laws have changed and polyurethane foam are now less dangerous but is less hard when dry. So apply at least 5 or 6 layers for being sure that the whole faux rock is hard enough for what you plan to do with.

Rock cliff in terrarium tutorial When 6 layers are applied and are dry I obtain what you can see on the photo.

How to paint fake stone Following steps are the same as in the first method . But in this case I use five colors: black, grey, white, brown, yellow and a little bit green

Paludarium fake stone You can see the final result. I used the same method, dark color for deep hollows and more you come to the surface more you use light color and dry brush for bringing out reliefs. But in this case, it is not pure white but blend of white, a little bit grey and a very little bit yellow. But it's up to you to decide according to what you wish. I think that polyurethane foam is better because it permits to get more realistic fake rock stone background for our tanks.

Fake rock close-up On right and below you can see others photos of the final result. Foam fake stone final result