Introduction: Make Concrete Rocks for Rock Walls, Fire Pits, Walk Ways, Water Fountains and More!

Learn how to create your own concrete rocks for building rock walls, fire pits, decorative piece and more!

Step 1: Mold Preparation

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The mold box was built by using plywood plastic and cardboard. The rocks are laid out so that their height are as even as possible. It is a good idea to spray or brush mold release onto the rocks. I have not come across a mold release that won’t work with ComposiMold just don’t over do it. Using too much mold release will cause undesirable lines and marks in the mold. Some examples of mold release that can be used are vegetable oil, WD40, Vaseline, and silicone mold release.

Once the mold release has been applied it is recommended but not required for a medium coat of bubble buster to be sprayed. Bubble buster is an easy method to reduce bubbles. It works by breaking the surface tension and allowing bubbles to rise rather than sticking to objects.

Step 2: Creating the Mold

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Once the rocks are wet with bubble buster it is a good time to pour the ComposiMold.

To melt the ComposiMold use a double boiler, microwave or any controlled heat source that will not expose the ComposiMold to temperatures above 200F.

Pour in increments if there isn't enough ComposiMold to cover the rocks in one pour. When pouring in layers the melted composimold will melt and fuse into the layer that has already been poured.

Be carful when handling ComposiMold because it will be hot, gloves should be worn.

Once all the ComposiMold has been poured it is time to wait for it to solidify. For this mold I waited overnight before removing the rocks from the mold. ComposiMolds cure time will vary depending on the mold size and room temperature. This mold was 75lbs of ComposiMold and the room temperature was 50-60 degrees overnight.

Step 3: Removing the Rocks

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If the mold box is designed well and sprayed with mold release it should be easy to remove. Just make sure not to use a mold box that can’t be taken apart.

The nice thing about composimold is that it is flexible enough to remove objects without too much struggle but still strong enough to create concrete rocks.

While removing these rocks I did a lot of trimming to reduce the undercuts, ComposiMold can be easily trimmed with a knife or scissors. Because ComposiMold is re-usable the pieces that were cut off should be saved and re- used when needed.

Step 4: Prepping and Pouring the Concrete

Picture of Prepping and Pouring the Concrete

Now that the rocks are removed the mold can be prepared for the concrete.

Vegetable oil mold release works great with cement. Apply a very thin and even layer. Other mold releases that work well with cement include WD40 silicone mold release and others.

Place rebar or a metal mesh in the mold. When molding large parts like this one it is a good idea to use Rebar or a metal mesh to increase the strength of the piece.

The concrete I used was ProFinish 5000 by quickrete because it works great with ComposiMold and cures fast. Other concrete and cement mixes will work as well. Ideally you want a concrete mix that needs very little water and has a fast cure time. just make sure it doesn’t create too much heat. If your cement mix creates a lot of heat keep your mold cold!

mix ¾ gallons of water with 80lbs of cement. The mixture will seem very thick but that is normal, just make sure your drill can handle mixing it. Also It is a lot easier to have help, if possible have one person mixing wile the other is pouring the concrete, but it is possible to do it alone if no one is available.

Now smooth out the concrete. The easiest way to even out the concrete to remove voids and air pockets is to pat the concrete with your hands, kick The mold and shake the mold. For even better results set the mold on a vibrating table for a few minutes.

The next step after the concrete has been poured and smoothed out is to wait. This piece was removed after 8hours and looks great! For a smoother texture use a concrete mix with less rocks. Or you can add sand to a cement mix. A cement mix that works well with ComposiMold is Quikrete Masonry Cement Type N.

Step 5: Thank You!

Picture of Thank You!

Thank you for watching I hope you enjoyed the video! If you have any questions please leave a comment or email us at


SamL56 (author)2016-01-28

Could you make bigger ones than this for a long rock wall? I don't want to wait a long time to cast these multiple times. The wall is about 35 feet long.

ComposiMold (author)SamL562016-01-29

Thank you for the question!

Yes, you can make a bigger mold to create a long rock wall. To make a large rock wall you will need either a thicker mold or something to help the mold keep its shape such as a wooden box. If you are new to mold making I would recommend starting small.

zzth1 (author)2015-12-16

I really like this idea to make concrete rocks. I wouldn't have thought to use these. Then at least when making a rock wall you have rock that is shaped how you would want it shaped. Thinking about this is making me want to try and get concreter to come and do this to my home.

ComposiMold (author)zzth12015-12-16

Thank you so much for your comment! Very nice website, It looks like you could definitely put ComposiMold into great use. I hope we inspired you to get even more creative with your concrete projects. You could also use ComposiMold to create concrete stamps. Let us know how your project goes if you do decide to give it a shot.

MegL1 (author)2015-07-13

I think making your own rocks out of concrete is such a good idea! It's easy too-- all you have to do is create a mold, and you are able to use that to make your own rocks. I think that this is something that you can use for so many different things to help enhance the aesthetics of your home. Thanks for sharing!

demon6666 (author)2015-03-10

With Composimold coming in at $37 for 40 oz that would make this mold $1,110 to buy just to make concrete rocks! You could buy 1020 overlapping rocks at home depot for the same price. Also the $1,110 does not include the concrete.

Neat concept, not cost effective at all.

ComposiMold (author)demon66662015-03-10

Thank you for the Comment!

I love the re-usability of ComposiMold!

What type of project are you working on?

Kafukai (author)2015-02-08

This is nice! I can't buy this product or something similar in my country(Israel) and shipping is too expensive due the weight.

Anyway, another great tip is using a cement color powder, it can make the final product much more alive and realistic. And for the finish to apply some concrete sealer to make it waterproof and UV proof to stand for some years.

ComposiMold (author)Kafukai2015-02-09

Thank you for the comment and tip! Adding color powder, sealer and UV protectant to cement is a great idea!

Out of curiosity do you have any concrete/ rock projects you are currently working on?

Kafukai (author)ComposiMold2015-02-09

Every summer I'm making at least 10 gardening projects out of concrete - walk paths, stone walls, rockeries etc.

But this trick I've learnt when my uncle and I covered my wooden grandma's house with stone veneers and we did this process:

1) We covered the house walls with rubber rolls to seal the wood, we attached the sheets with nails using a nail gun.

2) After that we've installed a metal mesh over the rubber sheets, that when we apply the stone veneer it will be attached and won't fall.

3) We bought stone veneer molds - it's cost lot of money relatively for what your product can do. And we've started making the stone veneers - we bought few shades of color powder and we mixed the color powder into the cement.

4) After we let it dry, we'v attached the stone veneers with cement to the metal mesh.

5) After we was letting it dry, we have sprayed cement sealer to make an extra sealing, we;ve sprayed 2 layers . The sealer was also an UV proof.

This house is still looks like a stone house and nothing happend for the color - I think anyone can do that, and with your product people can save a lot of money on the molds and also if you are creative you can do design molds.

* Sorry for my English :-)

ComposiMold (author)Kafukai2015-02-09

Thank you for the reply, very cool project! It sounds like the house will last forever, you guys did a really good job. do you have any photos? I would love to see it.

Kafukai (author)ComposiMold2015-02-09

Don't let the color full you it's a colored white cement and it looks real veneer stones.

ComposiMold (author)Kafukai2015-02-09

Wow! That looks great, it looks like real brick!

Thanks for sharing the photos.

Kafukai (author)ComposiMold2015-02-09

Don't thank me, I was back then only the assistant, my uncle not only a great civil engineer he is also a great construction worker. He was plan, design and made the entire house from wood, drywalls and cement boards. We the grandchildren were helping only with lifting the heavy things, sanding and mixing all day cement or glue. And while the working(it took 8 months to built it from zero) I've learnt a few things - I also study engineering but industrial field.

I hope this summer I will have a few more projects, one of them I'll try to upload to the site with pictures and videos :-)

mccoolll (author)Kafukai2015-02-09

Really great job!!!

Kafukai (author)Kafukai2015-02-09


SextonS (author)2015-02-09

You could buy a truckload of rocks for the price of that much composimold!

ComposiMold (author)SextonS2015-02-09

Thank you for your comment!

Its great! I have used the same ComposiMold for so many other projects.

Do you have a rock/ garden project that you are working on?

bricky62 (author)2015-02-07

type n cement is mortar. not nearly the same strength as Portland cement. this seems like a lot of work for such a bumpy surface to walk on. I would use a group of slightly flatter stones. 42 years a cement finisher and mason

ComposiMold (author)bricky622015-02-07

That is a lot of experience with 42 years as a cement finisher and mason. Thanks for the tip! Using flat rocks would work great to create a concrete walkway. Thanks!

Out of curiosity, do you have a project that you are working on?

bricky62 (author)ComposiMold2015-02-08

dead of winter here , no masonry projects...have a woodshop that occupies my time when laid off...looking for retirement

ComposiMold (author)bricky622015-02-09

Let me know if you do any cool projects, I would love to hear about them!

technosasquatch (author)2015-02-02

I didn't know concrete was fire safe.

Mefoo (author)technosasquatch2015-02-04

For high temp direct flame with concrete use refractory cement and lava rock and black sand (crushed lava rock). Must cure with no heat for minimum of thirty days for moisture release. Then the first few fires must be small and short for final curing. I worked for a cement firelog and refractory firewall manufacturing company.

ComposiMold (author)Mefoo2015-02-06

That sounds like a cool job, thanks for the info on high temp/direct flame concrete! Out of curiosity do you have any rock projects you are working on?

eggert (author)technosasquatch2015-02-02

It depends on the fire and on the concrete. If you build something what gets really hot, a furnace for forging or melting metal for example and your build should withstand the heat (no one time use furnace) you need special cement and bricks. If you just want to surround a fire pit normal concrete should do the job fine.

fzumrk (author)eggert2015-02-03

I would probably avoid using concrete where it is going to be in direct contact with even a campfire or cooking fire. I have seen chunks explode out of a concrete slab when someone (not me, honest!) built a small campfire on top of it. A google search reveals this is a common occurrence. I am not sure if it is due to moisture getting trapped in the voids of the concrete, or possibly moisture trapped in the aggregate that causes the explosion. In any case, it is probably best to always line the fire box with fire brick.

danzo321 (author)fzumrk2015-02-05

Portland cement has H2O as a real part of its molecule. High heat breaks down the molecule and frees the water. No way around it.

ComposiMold (author)danzo3212015-02-06

Thank you for explanation!

Do you work with cement often? What type of projects have you done?

ComposiMold (author)eggert2015-02-03

Thank you for explaining this, great explanation! Out of curiosity have you done any cool mold making or concrete projects? I would love to hear about them!

Thank you for reading our post! Yes Concrete has excellent fire resistance. Do you plan on creating a fire pit? Or do you have another project in mind? We would love to hear about your projects and ideas!

cool project, having cast concrete small scale in plastic molds, I can imagine that the flexible material would make it easier. also, the rocks look great-a neat, cheap concept for landscaping. I would be wary of promoting concrete around fire, however, as I've seen concrete slabs crack when used under a even a small wood fire. this is because water bubbles trapped in the concrete heat up and pop the concrete around it. larger scale, you risk burning hot rocks being ejected with some force. as an outer decorative touch well away from direct heat, they should be fine, though.

Thank you for the compliment, and for your insight! Out of curiosity what type of concrete objects did you cast using plastic molds? Did you make or purchase the plastic molds?

eatteyah (author)2015-02-06

Very Good Job and Easy .. But Can you explain more what ComposiMold conssist of and how to select the material and mix ..?

ComposiMold (author)eatteyah2015-02-06

Thank you for the compliment and question!

ComposiMold is a bio-based chemical free thermoplastic rubber.

Here is a brief explanation of how to select the proper material for your project - ComposiMold-LT is preferred unless you are pushing a material in the mold such as clay then you may want to select PowerMold because it has a higher stiffness/ shore hardness. And select ComposiMold-FC if you are making food such as chocolates.

Out of curiosity do you have a project in mind?

danzo321 (author)2015-02-06
There's an essay someplace online

jsadler1 (author)2015-02-05

I wonder if the money involved would not be low enough to justify the method. I would think that simply getting rocks and preparing the soil in advance making sure the rocks had an orderly height and then simply pouring cement or concrete directly into the voids would not be easier and less expensive. Using the method shown how much does a square yard cost and how thick is the slab ?

ComposiMold (author)jsadler12015-02-06

Thank you for your comment!

The dimensions of the rock formation used in this project was about 16"X16"X5" this took most of an $8 bag of concrete (80lbs). Do you have experience building rock walls? I would love to hear about your rock projects!

gaiatechnician (author)2015-02-05

My video about using an sds hammer drill as a concrete vibration tool is at I think it could be perfect for vibrating molds. Brian

Hi Brian,

Thank you for the comment and the great tip! That sounds like a very easy method for smoothing out the concrete. I will have to check out your video!

PZ456 (author)2015-02-05

Can you use ComposiMold with Hypertufa/papercrete? It's a mixture of paper slurry with concrete to make lighter weight objects.

ComposiMold (author)PZ4562015-02-05

Thank you for your question!

I have not used Hypertufa with ComposiMold. But it looks like it should work the same as the cement used in this instructable. If you try it I would suggest you use as little water as possible in the mixture for best result.

Yardster (author)2015-02-05

I could see using this in an application where you'd want to tint the rocks individually or overall. Would you suggest using a thinner layer of tinted concrete which might also take greater detail, then backfilling with the tough stuff? Also, would a stain work after unmolding?

ComposiMold (author)Yardster2015-02-05

Thank you for your comment and questions!

Pouring a thin layer of a tinted fine grain cement/concrete is a great idea! Just be carful when pouring the tough stuff. If you are too aggressive the thin layer could crack in some areas which will leave lines in the finished piece.

A Concrete stain will work great after unmolding.

Out of curiosity, do you have a project in mind?

Yardster (author)ComposiMold2015-02-05

Not immediately (it's cold here now in WI). Possibly some application in making Japanese lanterns for outside. I've used hypertufa in the past using cobbled together molds. I'm toying with the idea of making garden lanterns that are more natural looking than most I've seen.
I have an acquaintence who is casting and staining his concrete house, possibly a surface skim coat. He's a stone mason by trade.

ComposiMold (author)Yardster2015-02-05

I just imaged searched: cement Japanese lanterns and there are a lot of cool designs, Awesome project idea! We would love to see how it turns out if you get a chance to make it. What did you make with the hypertufa?

danzo321 (author)2015-02-05

This is a vinyl rubber, was not aware it was available as ComposiMold. What country are you in?

ComposiMold (author)danzo3212015-02-05

Hi danzo,

ComposiMold is worldwide and manufactured in the USA. ComposiMold is not a Vinyl rubber, ComposiMold can be described as a bio-based chemical free thermoplastic rubber.

HollyHarken (author)2015-02-05

What a great instructable! I'm thinking that it would be nice to make the mold so that you can make interlocking pieces like patio pavers.

ComposiMold (author)HollyHarken2015-02-05

Thank you for the compliment, I am glad you liked it!

Also great idea, that would give the rocks a nice flow.

About This Instructable




Bio: Make your flexible rubber molds with ComposiMold. Make more unique molds with 1 pound of ComposiMold than with 20 pounds of other mold making materials ... More »
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