How to Make Fake Rocks with Concrete

Steps

1. Building a form - You will need to use a form to build your artificial rock since concrete is very heavy. Make the bulk of the size of your rock from foam and cover with concrete at a thickness of 2-3”. This will make an artificial rock that feels and looks very real while being much lighter than real stone. You will need to wrap the form in chicken wire and steel reinforcement mesh so the wet concrete will have something to cling to on vertical surfaces and to provide overall cohesive strength to the concrete.
   • Mixing concrete - This is done in a bucket by hand or with a point trowel, or in a wheel barrow with a pointed shovel, OR on a piece of plywood with a square head shovel OR in a cement mixer. These options are listed in order of smallest to largest batches of concrete needed. Mix 3 parts fine grade clean, washed sand with 1 part type 1 (also known as type 10) portland cement. For additional strength you can add glass fibers to your mix in small quantities. Wood glue, fly ash and silica fume are also used for professional level rock sculpting. Add water to a thick paste and mix a very, very long time before using. If your muscles are not burning you have not mixed it enough
2. Sculpting the concrete - Use a point trowel to sculpt the concrete after applying to the form. Become familiar with how rock formations look and plan to be patient. Sculpting rock is a very marketable skill and takes practice to achieve consistent results.
3. Texturing the concrete - Use a sea sponge to create a pock marked, weathered effect. Texture mat imprints from real stones will drastically increase the cosmetic value of your rock. Nothing looks more like real stone than an imprint made directly from a real stone. Texture mats will also help to provide inspiration for the sculpting process as you can continue the veins by hand past the edge of your texture mat impression.
4. Curing the concrete - Concrete takes a full month to cure and is about 75% cured after the first week. If the rock is left to sit in direct sunlight during curing stage hairline cracking will be excessive. Soak with water often to minimize hairline cracking and proper curing.
5. Scraping the concrete - Wait a minimum of 3 full days of curing before commencing this stage. More if you are not in a hurry. Using a fine grit scraping stone grind the entirety of your artificial rock to remove rough edge that concrete has to the touch. When finished your rock with be smooth just like real stone.
6. Washing the concrete - Wash the rock thoroughly before proceeding to add color. Use a stiff (but not wire) brush to clean concrete dust out of all the nooks and crannies as this will look unsatisfactory later. Dry completely before coloring.
7. Painting the concrete - Using spray bottles and water based paints you will mist multiple layers of complimentary colors over and over again to create a deep and realistic rock color. Inspect real stone closely to learn what colors produce which effect. Common upon close inspection of real rock are blue, green, red, orange, yellow, brown, etc. The higher quality your spray bottle system, the better your finished results. Ideally you should be able to gently mist each application of color without any blotching.
8. Sealing the concrete - Use water based concrete sealant and apply 3 layers allowing time to dry completely between. Reapply once yearly via spray bottle to retain color.

Warnings

• Lots of warnings. Beware of power tools, concrete mixers and heavy construction. Proper safety attire and work habits are required. Safety glasses, protective gloves, cartridge ventilators are an absolute must. Concrete contains Quick Lime, a strong alkaline substance that can cause chemical burns on exposed skin…imagine what it can do to your lungs or eyes.
• Do not attempt to build anything bigger than what your skill level allows. Features like ponds / swimming pools or rock-climbing walls can be extremely dangerous and you should not attempt to build items like these unless you are sure that you have all the required experience to do so.