how to make fake rock
There are several ways to make fake rocks or fake rocks and boulders, all with good results.
The method you select for making faux rock is usually based on what is the cheapest and most readily available fill material you have available on site. Very realistic faux rocks or boulders can be made using any of the following fill materials.
Construction materials and methods
Construction debris such as secondhand bricks or crushed concrete
recycled real rocks
Polystyrene
Alternative methods of making fake rock involve using some way to roughly shape the finished rock prior to mortar application.
Chicken wire bent to shape is widely used for the smaller rocks.
Cardboard boxes of all sizes can be cut to shape.
Rebar and expanded metal
For the repetition of the same design, the use of molds is recommended.
casting a mold
The material and method that you use to make fake rock will be the one that you consider fastest and cheapest to give you the best final result. The time the job takes is based on the amount of detail required. The more definition and finish you give to each rock, the more time it takes.
To make faux rocks of larger proportions, such as garden boulders, a smoother, less detailed finish looks better, while smaller decorative rocks require more work and materials.
A garden landscaping job will often require the use of several of these different finishes to give the required natural look. The more methods you have for making faux rock, the better the final quality of work you will be able to produce.
Solid fill method
While this is possibly the slowest and most expensive method of making fake rock, it is still the most widely used due to the availability of construction material used in most jobs. Not being hollow in construction, it also provides the closest sound and feel to natural rock.
The materials used in this type of construction are:
Construction debris.
It’s usually free or already on the site ready to be disposed of. It is essential to hose it down before use to ensure a proper bond.
Second hand bricks and concrete blocks
Even if you have to buy them, it’s still cheaper than using concrete. Difficult shapes, such as waterfalls, are also easier to build due to the regularity of their shape.
Polystyrene
This is waste material that is used for packing and is easily available for free at your local stores. It can be cut to shape very easily and reduces the weight of the finished faux rock. It maintains the shape of the rock and does not collapse under the weight of the mortar, unlike other fill materials.
Recycled rock and other natural materials
They are usually on the site and are easy to use giving very natural forms. Wash before use.
If the material being used is in small pieces, it can be placed in plastic bags and stacked for easy assembly.
Cut and expose the fill material
Apply two coats of the acrylic polymer stabilizer mix. This must be applied by brush and is designed to guarantee the rigidity of the structure before applying the finishing mortar mix.
Apply two coats of 40 mm mortar mix.
· Finish as with other techniques.
This type of rock is very easy to build. It also uses mass concrete and mortar master mix for final shaping to save even more hassle. First build a small concrete base for the rock, then build the shape out of some of the rubble, then more concrete, then more rubble and so on until you have a rough finished shape.
To make faux rock with this method, it’s a good idea to be making several rocks at the same time. While you are allowing a batch of concrete to set, you may be working on another rock. Once the rough shape is finished and set, the application of the mortar can begin.
Use a throwing action for the mortar as it sticks better than just smoothing it out. Additional coats of mortar also adhere better to the rough texture left behind by the pouring action. Start the finishing coats from the top and work your way down. If you are working on two rock shapes side by side, be careful to emphasize the seam lines between the rocks. Definition is very important with these seams to give the rocks a natural appearance.
Hollow Rock Construction Methods
chicken wire
This method is useful for smaller hollow rocks.
Cut and wrap the chicken wire in the rough shape of the finished rock.
· Bend the sharp ends of the wire inward with a pair of pliers.
Now cover the wire with some newspaper soaked in white wood glue diluted 50/50 and let it dry.
· Cover the wire with several layers of plaster bandage that has been briefly soaked in water and allow to dry.
Decorate with thinned acrylic paint mixed 50/50 with sand to give a rock texture.
Construction of rebar and expanded metal
This is the most widely used method of making fake rock that is hollow. Using this method, rocks can be shaped to cover faucets, pool pumps, and other equipment. Due to its ability to be easily shaped and retain structural integrity, it can be used to make anything from a waterfall to a garden arch.
Once you have set up the shape with the rebar, the expanded metal can be attached. Tie it to the rebar every 100 to 150mm. Make sure it’s not loose. Cover the structure with two 3 to 4 cm layers of mortar mix, leaving a minimum of one hour or overnight between layers, depending on the day’s temperature. Add texture to the project using methods similar to the solid fill method.
Cardboard
Using a mix of large and small cardboard boxes cut to shape, it is possible to build a firm structure very close to the desired rock shape. Used boxes are available free of charge at local stores and provide an easy and inexpensive way to make fake rocks of all shapes and sizes.
Make the structure rigid by stapling, wiring, screwing or gluing the cut box shapes to form the approximate outline of the desired rock shape.
Coat boxes with two coats of acrylic polymer stabilizer mix, using a brush to brush the mix directly onto the cardboard. If too much is applied at one time, there is a danger that the cardboard will become soggy and collapse. Allow the cardboard to dry between coats to give it the necessary strength to withstand the finishing mortar mix coat.
· The cardboard can now be covered with a layer of 80 mm mortar mix applied in two 40 mm coats.
The structure can now be textured, stained, and sealed.
Casting from a mold.
To produce the most accurate reproductions of natural stone, there is nothing better than imitation rock castings from a mold. They are exact duplicates of what you have seen in nature. The same rock can be produced over and over again. Molds can be made with latex or silicone, usually with a plaster backing mold to retain the original shape.
The complete process for making faux rocks with mold casting and decorating will be the subject of a future article along with using texture molds in faux rock making.