It’s been too long since my last post on this subject. I have 3 or 4 lined up but have not had the time to dig into them. I thought I would get back into it with a post on how to make concrete planters.
Quite a few friends and readers have e-mailed me and asked for more information on how I made the pot shown at the end of the second article in this series, A Thinner Mix. I have made a lot of progress since then. Here is an example of some new planters/pots I have made.
Making The Molds
To make the molds, I used a variety of containers, and drilled a hole in the center of them.
TIP: Be as accurate as possible finding center as this will ensure that the concrete planters have an even wall thickness.
This first one, my medium-sized mold, uses a Paderno melamine mixing bowl for the outside, and an old plastic light dome for the inside. The dome gives a beautiful rounded interior to the finished product (see images at the end of this post). I found it in a second-hand store. I have been looking for more in different sizes but they are really hard to find and new ones are REALLY expensive!
This smaller concrete pot mold is made from 2 Paderno mixing bowls.
Note the bottom of the smaller red one, above. The bottoms of these bowls have a ridge as you can see in the blue one below. These ridges leave an unfinished look to the inside of the bowl. I used an orbital sander with 60 grit to remove the ridge from the red one. Then I worked up to a 220 grit to get it nice and smooth. I then gave it 3 coats of carnauba wax.
Another way to do this is with Bondo automotive body filler. This next image shows a plastic pot which is perfect for the inside half of my extra large mold. I used Bondo on it, then sanded with 220 to get it super smooth. Then I gave it 3 coats of carnauba wax.
TIP: Note that I am using melamine and plastic pots for the molds. Stainless steel also works – BUT these molds do not release nearly as well and will dent easily.
The spacer is a very important part of your mold. It will form the drainage hole for the concrete planter and also hold the 2 halves of the mold together, like this.
The parts below are a 5/16 bolt, 2 washers, a copper plumbing fitting (3/4″ OD) and 2 smaller pieces of plastic tubing cut to the same height as the copper fitting. In the second picture, you can see that the tubing has been placed inside the copper fitting. This gives me a nice snug fit for the bolt and also, when it is tightened up, the plastic tubing helps make a seal that the concrete can not leak through. I use a copper fitting only because it makes for a nice detail in the concrete planter as you will see in the images at the end of this post.
Here is the outside part of the mold with the bolt through it and the spacer in place.
TIP: If you do not want the copper detail, you can make a simpler spacer out of a rubber stopper which you can easily find at brew-it-yourself wine/beer supply shops or at any place that sells stoppers for test tubes.
Here is the assembled unit. Note the nice symmetry – even spacing between the mold halves.
The steps on how to make a concrete planter mold
Once you have all of your parts made, all you need to do is:
- Wax the outside of the inside part of the mold.
- Wax the inside of the outside part of the mold.
- Spray some release agent on the outside of the inside part of the mold.
- Spray some release agent on the inside of the outside part of the mold.
- Assemble the mold as shown above. Take your time here, being sure to get as even a spacing as possible between the 2 mold halves.
- Pour your concrete as shown in the graphic above. You will need a thin mix for this!
- Allow to set for up to 24 hours (unless you are using the Kast Krete mix I discussed in A Thinner Mix.)
- Unbolt the mold.
- Gently pry on the inside part of the mold. It should slide out pretty easily.
- Now flip the outside half of the mold upside down and lay it flat on a towel, or a piece of Styrofoam. Using a rubber hammer, gently tap on the top and sides until the concrete planter releases and drops out. If it is not coming out, turn it over and gently apply outward pressure on the side of the mold. Work your way around the mold. You will see a very small gap start to develop between the mold and the concrete. Now turn it upside down and again tap on the top and sides. Just be patient. It will pop out – unless you forgot your release agent!
- Optional: I always sand the top edge of the planters. Some folks like to leave them rough. Experiment and see what works best for you. I talk a bit about sanding in this post.
For steps 1 and 2, I use a spray-on car wax. It just makes the mold more slippery and easier to release the concrete (especially if you forgot to apply the release agent, which I have done several times … DOH!). Every 4 or 5 times I use the molds, I give them a coat of carnauba wax to seal them up and cover over tiny scratches that come from cleaning them after each use. I use Trewax clear paste wax for this.
For steps 3 and 4, I use Smooth-ON Universal Mold Release. It’s a great product and easy to use. I have also used mineral oil which works very well. Pam also works but I find it leaves a food odor on the finished product. It does wear off over time though.
For step 6, I typically use Starpatch Concrete Products Kast Krete because it can be mixed to a pancake batter-like consistency. Very easy to pour. But I have also used Starpatch’s Countertop Mix and Quikrete’s Countertop Mix. Both are harder to pour in that small space. BUT – Starpatch sells something called a flow kit. When I add this to their Countertop mix, the mix becomes MUCH more fluid and easy to pour. ALSO – there is a new product out there called ShapeCrete. It’s available in the USA from Home Depot but not here in Canada yet. Looks great! Do a YouTube search for shapecrete and you will find many cool videos. I am really looking forward to trying it when it becomes available up here.
TIP: A great thing about these molds is how flexible they are. If you want lower sides (a shallower concrete container) pour in less concrete. If you want higher sides, pour in more. Have fun experimenting.
Here is a concrete planter made with Kast Krete. You can see the copper detail in the drain hole.
Here are 6 more images for you to look at of concrete planters and bowls using the molds described in this post. The rougher ones were made with Countertop mix. Click any image to see the large version.
I hope that you have found this information of use and that it will be helpful to you making your own concrete creations. If you have ideas you would like to share, please leave a comment. I’d love to hear about what you are doing with concrete!
Read more in this series:
Part 9 – Concrete Creations: Rubber Molds! – coming soon!
All photos by Gil Namur – All Rights Reserved