Landscaping Secrets: How To Build Artificial Rock

There are many different applications for artificial rock and there are just as many methods for building them. This article will outline the best practices for creating your very own artificial rocks, ponds, and waterfalls. This is specifically an overview to building man made rock made of concrete. Of course there is always the option to buy artificial rock made of plastic or fibreglass, but it can sometimes be difficult to find where to buy artificial rocks. The only way to have a custom made waterfall design with imitation rock that actually feels like the real thing, is to build it from scratch. The following steps are to be used as a guide only. We have been building artificial rock in Sydney for the last 20 years and would suggest that to obtain the best result, you should contact us directly to design and build your pond, swimming pool waterfall, fountain or whatever man made rock designs you may be considering. This will ensure that your rocks/water feature looks amazing and works perfectly. However, if you are feeling brave and creative, here are the basics to building your very own artificial rocks.

STEP 1: EXCAVATION & PREPARATION FOR BUILDING THE POND

When preparing to build a concrete pond with an artificial rock feature, you must first dig a hole that will provide an ample area to catch all waterfalls and the splash that will come from cascading water. As a general rule, for every meter of waterfall height you should allow for 2 metres of pond or catchment area. If you are planning to turn it into a fish pond then there are additional factors to consider. A minimum depth of 30cm is generally required for the health of the fish. Additional pond filters may be required depending on the size and quantity of fish and these can also be purchased as a self contained unit, or created yourself with a bit of extra effort. Most ponds and waterfalls run with a circulating submersible pump. This pump must be placed in a deep section of the pond and considerations must be given to protecting the fish from injury if they get too close to the pump’s impeller. A plastic mesh surrounding the pump works well to protect the fish and also to keep the pump clear of leaves, sticks, and other debris.

Sometimes a rubber liner may be used as the waterproofing membrane for a Koi pond but generally we prefer to rely on concrete ponds to ensure a robust waterproof structure that will not be damaged from UV exposure, sharp sticks, birds, pets or servicing/cleaning. All of these thing can potentially be disastrous to pond liners.

When digging out the pond, the excavation should include an extra 100mm of depth to accommodate for the thickness of the concrete. Make sure to keep the sides of the pond quite steep. The more vertical the walls of the pond, the less surface is exposed to UV rays from the sun and the less algae will be inclined to grow. Predators like birds and cats will also be less able to ambush fish.

All concrete will require a steel framework. The integrity of all concrete structures relies on the steel infrastructure within it and the design and building of this framework will be a key component to a structural and successful pond and artificial rock project. We prefer to use a combination of various types of steel to ensure an extremely high strength for any rock structure that we build. This will ensure a very long life without problems and will allow the concrete rock to be used for structural applications such as retaining walls, rock stairs, and patios.

Before building the steel reinforcement cage that will eventually become the pond, we recommend that you place a layer of plastic into the hole first. This will allow the steel to be protected from dirt and moisture from the ground. It will in fact keep the entire area clean and dry while working and setting up the steel.

The first step in the steel work for the pond is to build a cage using 12mm reinforcing steel. This cage will form a grid and will have the bars spaced no more than 300mm apart. Remember also that steel bars will need to be raised off of the ground and walls. You can purchase concrete “chairs” that are specifically designed for this purpose. Allow some bars to protrude higher than the top of the pond level. These bars will be used as starter bars for the steel design for the artificial rock waterfall after the pond has had its first concrete pour.

Now it’s time to concrete the pond. This stage will not involve any sculpting of artificial rock at all. This pour will only be to ensure that the pond is in place and waterproof and finished. The mix should be 3:1 ratio sand/cement. Use a coarse sand with small aggregate (rocks) in it. Make sure not to use too much water as this can make the concrete slightly porous and weak. Waterproofing additives should be used, a requisite amount of Bondcrete, and plasticisers will also add workability, and extra waterproofing qualities. The pond should be finished smooth with a metal trowel while making sure no holes or cracks are left in the surface. Once troweled the pond should be left to cure slowly for a few days at least to gain strength and allowed to expel moisture. Concrete should be kept moist with wet hessian, canvas, or blankets placed over it to ensure a slow cure.

STEP 2: BUILDING THE ARTIFICIAL ROCK DESIGN

Once the pond is finished, it is time to move on to the design of the artificial rock waterfall structure. Once again you will use steel reinforcing rod to lay out the basic shapes and design. This will require an artistic vision, an idea for spacial design and a keen understanding of the functionality that you will require. The rebar is bent into rock shapes and contours. Fake rock will indeed look artificial if you do not use what we like to describe as “rock sense”. Rock formations in nature will adhere to certain traits and characteristics and if they are not emulated properly, your artificial rock will look entirely man made.

Once the basic shapes and elements have been created from steel bars, the plumbing and any low voltage electrical commissions for lighting the feature must be run behind the steel frame. The plumbing should always be constructed using pvc pressure pipe. (We exclusively use 40mm or 25mm pvc pressure pipe and pressure rated glue)

STEP 3: SCULPTING THE ARTIFICIAL ROCK

There should now be a waterproofed concrete pond in place and the steel framework has been created for the waterfall design. Now comes the tricky part. This is where experience and practice starts to have a very meaningful impact on the final result. You must cover any exposed steel structure with another base coat of concrete. Use all of the relevant additives that were used when doing the pond. Make sure all steel is completely covered and that any plumbing or conduits are in appropriately positioned so they do not interfere with the creating of the cascade. The basic shapes of the imitation rocks are first shaped with a metal trowel. Powder stencil colours are then distributed over the troweled rock shapes. We tend to use 3 or 4 different colours to get a basic colour palette that mimics natural rock. Once these multi purpose surface hardening colours have had time to absorb into the surface, then texture is applied to the rock. This is done using a combination of tools and techniques. Latex moulds taken from natural rocks can be used to get an overall basic texture. Finer details can be added using sea sponges and brushes. Once the concrete has started to harden slightly, you can begin to use carving tools to cut in sedimentary cracks and crevices.

A second layer of concrete is also added to the walls and surrounds of the pond. All concrete is finished using the previously outlined techniques until the artificial rock waterfall and pond begins to look entirely natural.

The water feature must now be allowed to dry completely. All of the fake rock should kept moist for the first few days to ensure proper hardening process. Once cured, the artificial rock needs to be carved and cleaned with a pressure washer. A concrete staining system is now used to spray on additional colourings. Sometimes a diluted exterior acrylic paint can also be used to add subtle nuances and shadings. Make sure that the mixture is sufficiently watered down so that it absorbs into the dry concrete. Once all of the rock has been finished to a beautiful and convincing finish, then a matte sheen acrylic concrete sealed should be sprayed over the entire water feature. This final sealer should be PH neutral for use in ponds that will contain fish.

Now it’s just a matter of connecting up the pump and lighting. Dressing the bottom of the pond with pebbles also makes the fishpond look natural as well as providing a natural environment for fish. Make sure to incorporate plenty of areas around the pond and waterfalls to plant various shrubs, trees, and flowers. These final touches will make all the difference.

Good luck, and we hope you enjoy your new artificial waterfall and pond.

artificial rock
Fake Rock Pond

 

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