Introduction: Faux Rocks That Look Real
I have been rock climbing and bouldering in the past 20 years and I really like rocks. I already had several small rocks in the back yard and wanted to add some larger ones. Unfortunately, there are no rocks and no boulders in the area where I live.
Real rocks are also expensive and difficult to transport, so I decided I would try to make some rocks out of concrete.
I have seen photos of faux rocks made by other people but they did not look real. My solution to make the concrete look like real rocks, was to build up the surface in multiple layers and to use a coloring powder to get variation in lighter and darker shades. Also I recommend to make more than one faux rock because when there are several faux rocks of different shapes but the same color and structure, they also appear more natural.
- Portland cement
- Black powder to color cement
- Chicken wire
- White paint
All materials that I used were left over from previous projects, so I used what I had. It is possible to use other filler material instead of the styrofoam and it is also possible to use pre-mixed cement instead of the portland cement that I used.
Step 1: Option A: Use Styrofoam and Chicken Wire
I made one really large rock and three medium size rocks. I used the chicken wire only for the largest rock, because I did not have enough chicken wire to wrap all 4 rocks. Both methods worked, but I liked the option with styrofoam better as that gives more strength to the concrete. If you are making faux rocks and never plan to move them, it is easiest to skip the chicken wire.
I used styrofoam to get a rough shape. Styrofoam is light weight, it can withstand moisture and cement sticks well to styrofoam. But you could use for example empty plastic bottles as alternative.
I broke the styrofoam in some large pieces, wrapped a bit of tape around the pieces to keep them stacked together and after that I wrapped the pieces in chicken wire.
Step 2: Option B: Use Styrofoam Without Chicken Wire
Since I ran out of chicken wire, I made the last three rocks by just putting some pieces of styrofoam on top of eachother and then I covered them with cement.
The small rock which is on top of the styrofoam was there just temporarily to prevent that the wind would blow away the styrofoam.
Step 3: Mix the Cement
I mixed the cement in the ratio of 1 part portland cement and 3 parts of sand.
It works best to first put a small layer of water in a bucket and then adding one scoop of portland cement and 3 scoops of sand, then stir the mixture and again add 1 scoop of cement and 3 scoops of sand and stir again. It is real easy to stir the mixture when it is still too wet, so you just keep adding cement and water until you like the consistency. Do not make the mixture too dry as it will not stick very well to the styrofoam when the mixture is too dry.
It is not needed to add the black coloring powder to the mixture at this moment.
I had a second bucket filled with water only, so I had water available to dilute the mixture if that would be needed. Our chicken came to see what was in that bucket.
Step 4: Cement Underneath or Not
I decided to start with a layer of cement under the styrofoam, but that is not necessary. The advantage of starting with a layer of cement is that the cement is all around the styrofoam so the rock can be used in all orientations.
If the rock will be used on it's side, it is best to make the cement at the bottom not flat, so make a dent in the sand before adding the first layer of cement. On the contrary, if you prefer to give the rock a stable bottom to use it upright, it is best to make sure the cement at the bottom is flat.
Step 5: Cover the Styrofoam With the First Layer of Cement
Use gloves to cover the styrofoam with cement. If you make the first layer too thick, it will fall off by it's own weight. So just add a layer of about 2 cm (3/4") thick. The surface of the cement may be quite rough, as a second layer will be added soon.
Step 6: Same As Step 5 But Now on the Other 3 Rocks
I repeated the process of step 5 on the 3 rocks where I did not use the chicken wire. The method is basically the same only here I needed to start covering the styrofoam from the top so the weight of the cement would keep the pile of styrofoam in place.
Step 7: Take a Break
Wait for 30-60 minutes before adding a second layer of cement. In that time the first layer has started to set so the second layer can be added without the cement falling off due to the weight.
The time that I mention is based on me using portland cement. If you use a quick cement mixture, the time might be different.
Step 8: Second Layer
Add a second layer of cement over the first layer. It is a bit like a gentle massage. In principle you want this layer to have a really smooth surface, but you can make some small sharp ridges just like real rocks have.
The second layer is also the moment to add the black powder to get different shades of gray. The variation in color is very important to get the rock to look real. I used a spoon to drop a little bit of powder on the wet second layer of cement and used my hand to rub the powder into the cement. I made sure that I varied where I added the color so that some parts are dark and others are light.
Step 9: Add Small White Details
After the cement had cured for some days, I added a bit of white paint to add some details. I added some white dots and also some lines. It works best to highlight the areas where there are some edges and ridges.
Step 10: Quality Inspection
Our chicken checked the result and I think it was approved.
Step 11: Enjoy
I placed some of the small rocks around my new faux rocks and I like the result.
On these photos you can also see the metal sphere that I made one year ago. I also made an Instructable about that, so check out my previous Instructables if you want to know how I made that sphere.
Second Prize in the
Stone Concrete Cement Contest