# Making Artificial Rock Backgrounds, Techniques and Suppliers



## acromyrmexbob (Oct 3, 2010)

I have been meaning to detail the technique and mix for making the fake rock I have been showing here for a while.

Technique 1: Hollow Rocks

Hollow rocks are basically a lighter way to create the same look as solid rocks. This is a useful technique where they are being built in a tank that is smaller or not structurally capable of holding enormous weight.


1. Create anchor points on tank background. I normally use glass because I've got loads of it. Another technique is blocks of wood. On a glass vivarium you can silicone this on all over the back. In a wooden vivarium you can screw or glue them on. A brick or stone back will be best glued or rawplugged and screwed. Make the lengths coming out from the wall vary to provide shape and interest for the final piece. Where you want ledges this can be a shelf of wood or glass.


2. Now hook a sheet of landscape weed barrier or muslin or netting, any material really, over the frame and attach this to the anchor points. Again if these are glass use glue, if wood use tacks. You should try to get the material quite tight between anchor points since you want this to be in close proximity to the wire mesh that goes on next.

3. Attch a large sheet of cheap chicken wire, 10 or 12mm is best, to the top anchor points. Working downwards, bend the wire into interesting shapes and try to create ledges and depressions. Work to the rough shape of the anchor points and mould the wire to press against the material where possible. This step should be done roughly, don't spend too much time trying to get perfect shapes and features. If you plan to grow plants on the rock face cut slits now and push pots in. I normally use cups with no holes in the bottom and I fit a short length of tubing into the bottom and back out through the mesh so the water does not drain down behind the rock when the project is finished. Once you have reached the bottom of the rock face use strips of wire and patches to fill in any missed sections at the edge or in areas where there are larger projections. Remember that the wire needs a material behind it to allow the cement to stay put.

4. Mix a wet cement mix, exactly the consistency of brick mortar. I normally use one part cement, 3 parts sand and some plasticiser (squirt of washing up liquid). Mix this lot together and add water until it is the consistency of porridge. If the material layer is in close proximity to the wire and if it is very tight then you can throw the cement mix onto the wire and the material will stop it. If not then smear handfuls of it on. Normally we smear it. All you are doing at this stage is filling the wire holes. Don't do any sculpting just now. Once the wire is covered with a thin layer of cement then take some small dowels of wood or some screws / nails and place them into the cement where there will be overhangs. This is to give the final coat something to adhere to. Now leave the background until it becomes stiff and score it all over with a trowel to again provide some adhesion points for the final coat.

5. Now mix the final coat. This is one part cement, one part coarse (sharp) sand, three parts fine, silver sand (play sand?) and a squirt of washing up liquid. Mix this thoroughly and then split the mix into two halfs. Add water to the first until it is the same consistancy as the undercoat cement you put on previously. Add small amount of water to the second mix but keep it quite dry. It should not settle when dumped on the floor, should not be sloppy, should form a ball in your hand when shaped, so quite dry. If you think it is too dry to use you are probably about right. Take the dry mix and use this to create rough shelves where you have planned for them to be. These will be the ledges. One flat hand presses vertically and the other down from the top to create the ledge. Because of the pegs sticking out and the roughened surface as well as the very stiff mix, you should find the cement pretty much stays where you put it. Repeat this until all of the shapes you wish to create have been done. Again, do not spend too much time on this stage. Stick the cement roughly where you want it and move on. Don't smooth it out or hand sculpt it, this makes the next stage much more difficult. Now take the wet mix and very forcibly throw it onto the sheer vertical surfaces. Also use this technique to apply mix to the underside of overhangs. If you try to add this by hand it will always fall off. If you throw it and it does not stick you are either not throwing it hard enough or your mix is too dry.
In this way cover all of your rock face.

6. Now wait for an hour or so until the cement starts to firm up. Spray the surface of the rock face lightly to make it easier to work. Start to smooth the ledges of the rock with two small brick layers trowels. If you are wishing a highly sculptued finish then spend time on the features and try to get as many sharp edges to your rock as possible. This is best acheived by using the two trowels together, one on the vertical face and the other on the top face. If you are looking for a natural rocky cave then skip this step altogether. The more you work it at this stage the more refined a finish you will get. Also the more work you do the closer examination your work will bear.

7. Now decide on what combination of colour you wish to acheive. You will need to preorder your colour / hardner. I get mine from Pattern Imprinted Concrete Colour Samples - Elite Crete UK. They are very good. Check out the colours they sell. They are also very cheap but unfortunately they come in 25kg bags. Use the main colour and completely cover the surface by throwing the powder at the rock. Any that falls down can be rethrown. If the powder does not stick to the cement then lightly respray the surface with some water. Now add some other colours to provide tome. A darker colour applied in small dusting quantities will look great. Build up the colours until you are happy. Now take an old paint brush and dip it in water. Start to stab the powder and work your way around the project, redipping your brush. If you find that the powder is falling off with some of the cement when you do this then the brush may be too dry or you are not stabbing hard enough. Only thing is make sure you do not start to move the cement with your jabs of the brush. And be careful to preserve the sharp edges of your ledges and features. It is easy during this process to turn sharp edges into curves which just looks rubbish. This will enhance your rock in the final scene. Work over all the rock. Using a brush adds natural texture to the work also. You can also use wire wool, a dish washing sponge or a paint pad. Experiment with what works best.

8. Buy a strong Satin varnish and apply two coats when the colour is dry. You will be amazed at the finish. The hardner makes the finished concrete 2.5 times harder than untreated cement!

Technique 2: Solid Rocks. 

This technique is used outside for waterfalls and features, and inside when there is a structural capability to take much more weight in your enclosure. Simply put you pile up rubble, rocks, soil, anything to hand and form the shape of your project with this. Next cover with wire and proceed exactly as above.

If you have any questions about this technique, post a reply and I will do my best to answer.


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## cold blooded beast (Mar 17, 2011)

Andrew. . .worth your weight in gold:notworthy:. . .a true gent. . .and thanks for the offer in pm. . .
Marcus


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