Concrete Jack-o-Lantern Planter

I have always toyed with doing some concrete casting, but I always put it off. Now, I finally went for it and jumped in. I was surprised how relatively easy it was and the results were outstanding.

The method I used is called Slush Casting because the mold is not fill completely with concrete. Instead a sufficient amount of concrete (a thinner slush) is poured into the mold and rolled around until all the internal surfaces of the mold are coated. When the concrete sets you have a thin wall of concrete coating your mold. I did 3 layers (applications) of concrete and the finished product ended up with a wall about half an inch thick.

The real trick to this process is the Rapid Set brand Cement All product that is a cement and sand mix that sets in about 15 minutes. The fast set time makes slush casting possible.

My family didn't want me to paint the finished planter so I have included an AI generated image showing what the painted planter might look like if you wanted to paint it.

It is interesting that black cats seem to be instinctively drawn to jack-o-lanterns. Not really, but I think our cat would get inside it if he could fit.

The mold was as simple as using a plastic Halloween Trick-or-Treat candy bucket. You may have to look around to find one with a pleasing expression. One year all they had was goofy looking ones. This one came from Walmart. I also tried making some skulls using a Dollar Store hollow plastic skull as a test before I went for the jack-o-lantern. Both turned out great.

These blow-molded plastic items make excellent molds. The molds are called 'sacrificial molds' because they are intended to be used once and are destroyed during the de-molding process (removing the cast concrete). But at less than $2 each, I certainly can't complain. In fact both came out in a condition that would probably let me reuse them if I wanted.

MAIN SUPPLIES:

1. Plastic Halloween Trick-or-Treat Candy Bucket
2. Hollow Plastic Skull (optional)
3. Non-stick Cooking Spray
4. Rapid Set brand "Cement All" multi-purpose repair material
5. Duct Tape
6. Tube/Rod (For a drain hole mold - I used a mini hot glue stick)
7. Mixing Containers (Large yogurt or cottage cheese containers work)
8. Stir Stick (I used a cut up yard stick)
9. Nitrile/Latex Gloves
10. Dust Mask
11. Measuring Cups
12. Rinse Water Bucket
13. Drop Cloth
14. Razor Knife
15. Drill & Bit

OPTIONAL:

1. Timer
2. Cement Board Fiberglass Mesh Tape - Alkali-Resistant
3. Epoxy Resin (For internal coating)
4. Masonry Sealer (Internal / External use)
5. Masonry Primer
6. Spray or other Paint

Some modifications have to be made to the plastic jack-o-lantern candy bucket before it can be used as a mold in order to make it easier to remove the finished concrete. If you don't do this you may end up with a concrete lined trick-or-treat bucket. Which if you want your kids to pick up less candy, this might be an option to tire them out by lugging the super heavy bucket around with them.

The bucket is slit all the way down the back and across the bottom out to the front surface. This makes it easier to peel the plastic off of the concrete after it's set. Think of peeling an orange from a slit cut in the rind.

I left two gaps in the cut, one at the top rim and one at the transition from the back to the bottom surface in order increase the strength of the slit bucket. These gaps of intact plastic will be cut through after the concrete has set. They were just a bit of an 'insurance policy' to keep the bucket together as I'm rolling concrete around inside it.

Any good plant custodian knows that you need to have a drain hole in your pot. (Well, you can put a drainage container / gravel in the bottom of the pot, but we won't go there.). It is much easier to mold in a drain hole than to try to drill a hole in the finished concrete pot and possibly brake your jack-o-lantern.

Anything that displaces concrete leaves a void after the concrete has hardened and the 'displacer' is removed. To make the drain hole you just need something to take up space where you want the drain hole to be located. I used a mini glue stick I had on hand. I drilled a hole in the candy bucket where I wanted the drain hole to be and pushed the mini glue stick up into it. A dowel, or even a piece of vinyl tubing can be used to create the path of the drain hole. If you use tubing make sure you close off the tube so it won't fill with concrete during the casting process.

I slit the pumpkin, but now it has to be held back together to allow the concrete to be rolled around inside it. I chose to tape the slits together with duct tape. I tapped the entire length of the slit. I also tapped over the holes that were in the top of the bucket for the handle (the bail, which was removed).

To make the mold (candy bucket) easier to remove from the hard-set concrete some type of mold release needs to be used. Otherwise it may be really difficult to get the plastic and concrete to part ways... The have become best buddies.

You can use a commercial mold release spray, but why use that when cooking spray seems to work just fine. You can follow your own preferences for the spray, whether it's Canola, Olive, Butter Flavor or a name brand such as "Pam" -- It makes no difference! Exercise your agency and you choose!

You need to keep some things in mind when you are working with concrete. Like a good Boy Scout, you need to Be Prepared.

The dust from the mix can be very annoying and it can be hazardous to your health if you inhale it. You should wear a dust mask. A good one, not just one of those flimsy white ribbed ones. I couldn't find my regular mask, but I did find an N95 mask used for Covid, and those do a great job filtering small particles out of the air.

Don't forget to wear gloves as the concrete can irritate you skin.

Concrete makes a mess so it's good idea to put down a drop cloth. I also made sure my measuring and mixing items were all cheap and/or disposable. You don't want to ruin a good quality kitchen measuring cup set.

It is important to be able to clean up after and between pours. I read it was a good idea to have a bucket of water near by in order to rinse off the stir stick and mixing tubs. This came in really handy as I could rinse the mixing containers and swirl the stir stick in the water and use my gloved hands to break loose the concrete residue stuck on everything.

The Cement All mixes in a 4 to 1 ratio by volume. 4 units of dry concrete mix to 1 unit of water. This makes it easy to mix a one cup scoop of Cement All with 1/4 cup water using household measuring cups. You always want to add the water to your mixing container before the powder. This reduces the likelihood of clumping, or creating nodules of undissolved powder and generally makes it easier to mix together.

I did a small test run on the small plastic skull with a single cup of Cement All with 1/4 cup water. This was a good test run as it gave me experience mixing as well as pouring and getting used to how fast the mix sets up. I had read that some people used a little bit more water and I did that with my first test. I'm glad it was a test since the consistency seemed a bit too runny. The consistency you want is like a thick pancake batter. Using the recommended 4:1 ratio provided a good consistency. Not too thin and not too thick.

I noted some inconsistency of thickness between batches and I think this might be attributed to how tightly the powder is packed in the measuring cup. I think in the future I may use weight instead of volume to measure out the ingredients. The Cement All manufacturer states that the maximum amount of water should not exceed 5 quarts (4.7 L) of water per 55‑lb (25‑kg) bag. That works out to a ration of ~0.19 water to cement. I have not tried mixing by weight yet so I can't give any guidance on how it works.

The most Cement All I mixed at one time was 3 cups. I should have done 4 or 5 for the jack-o-lantern as I didn't have enough material to coat the entire inside surface of the candy bucket at one shot. I had to mix up a second batch to finish coating the interior and there is a visible difference in color between the first and second pours.

I also found it useful to use a timer that I started when I combined the Cement All powder and the water. You have a couple of minutes you can mix and then you'll want to pour it into the mold (candy bucket) and start having it flow around covering the surfaces.

If you want to have the concrete stay liquid a little bit longer you can use cold water as it slows the reaction.

Pour the concrete into the candy bucket and start rotating it to spread the concreate around over all the surfaces. I ended up just holding the mold in my hand, mostly horizontal, and turned it every which way to coat the inside.

It is important to rotate the mold in all directions so that all the inside surfaces are coated. As I mentioned earlier, I did not mix up a large enough batch of concrete to coat the entire inside surface in one go. So make a larger batch - you might have extra but you can just pour it out (maybe into a skull;-) if you have extra.

You keep rotating the mold (candy bucket) as long as the concrete is liquid enough to keep coating the surfaces. As the concrete gets thicker you can use your gloved hand to pull it up to the rim in order to build up the thickness at the opening. I also used my fingers to scrape up cement left in the mixing container and added it around the rim where it was thinner.

Adding reinforcement is optional but it is supposed to increase the strength of the finished planter and prevent cracking. Before I even started mixing the concrete I cut lots of strips of the fiberglass mesh to be used for reinforcement. The mesh is alkali-resistant Cement Board Fiberglass Mesh Tape. There is a link in the material list.

After the first layer has started to set up and is no longer flowing you take the strips of fiberglass mesh and gently push them into the concrete layer to slightly embed them into the concrete. A subsequent pour will trap the mesh inside the concrete.

After the concrete has hardened to the point it will not flow it is getting close to the time you can pour another layer. I would wait at least the full 15 minutes from when the batch mixing started and then pour another layer. If you pour too soon the layer below is not sturdy enough to support the weight of the added layer.

I poured 3 layers, but I guess you could do as many as you wanted if you wanted a really thick wall. Three layers gave me about a half an inch wall thickness.

The concrete sets in about 15 minutes. Another layer of concrete could be added at this time. As mentioned, I did three layers but it probably would have been sufficient to have done two.

The poured concrete stopped flowing at around 10 minutes after mixing the Cement All with water. The concrete gives off heat as it cures. After an hour the concrete has reached a partial cure and it was not giving off much heat anymore. I let it sit another hour before removing the mold.

Now it is the moment of truth! Remove the duct tape. Cut the plastic tabs that were left to increase strength in the bucket and start removing the mold by lifting an edge at the back slit. I started pulling the mold toward the front while spreading the halves. It came off without too much struggle.

Welcome your new concrete Jack-o-Lantern into the world. Congratulations on being a new parent!

At this point you can wiggle the mini glue stick or whatever you used for the drain hole and pull it out of the concrete. You now have a drain hole.

If you are going to use the jack-o-lantern as a planter it is recommended that you seal the inside surface to protect the concrete from having water seep into it. I am not sure if I will use a commercial concrete sealer or use a 2-part epoxy resin.

I did not finish the exterior of my concrete Jack-o-Lantern. However, if you choose to do so you need to do a few things to get a great outdoor finish.

First, wait - Now I know we are all impatient, but you really need to wait. The concrete has water in the mix that needs to fully react with the cement and any excess evaporate. You need to wait at least 3 days but keep in mind that the concrete is not fully set until after 28 days. The longer you wait the better. So get ready to exercise those patience muscles.

Here is a summary of the steps needed to get great finishing results:

1. Clean off the mold release. Use common dish soap to thoroughly wash the exterior of the concrete.
2. Neutralize. Concrete is extremely alkaline. The alkalinity will cause paint and other coating to react and flake or bubble. After the concrete is fully set you can neutralize that alkalinity by mixing water and common vinegar in a 1:1 ration and wipe or lightly scrub the surface with the mixture, then rinse with water and dry.
3. Roughen. The surface of the concrete takes on the smoothness of the mold. Use 220 - 330 grit sandpaper to lightly sand the surface and give a good texture for paint/sealers to adhere to.
4. Seal. Use a concrete sealer. This was listed as optional in some instructions I read.
5. Prime. Use a masonry primer.
6. Paint. Use an outdoor acrylic or spray paint.
7. Top Coat. Use an outdoor rated, non-yellowing clear coat.

There you have it. Enjoy your fabulous concrete jack-o-lantern planter!

As mentioned earlier, I used a plastic skull as a test mold to get a feel for the process while not worrying about ruining my Jack-o-Lantern candy bucket. The steps are the same for the skull as the jack-o-lantern. I should note that I was not trying to make a planter out of the skull, just cast a concrete skull; so my openings for adding concrete were not on the top but on the bottom.

1. Cut the mold in half. I followed the parting lines (the joins in the mold used to blow mold it.) that were visible on the outside of the skull. Don't forget to cut an opening in the skull to pour the concrete into. (I also tried drilling a large hole in a second skull with a hole saw. The thought was that I would not have to tape the halves together and that I would just tear or cut this mold apart when the time came to de-mold.)
2. Tape the halves together.
3. Coat inside with cooking spray.
4. Mix Cement All and pour in the mold.
5. Rotate the mold to coat all inside surfaces.
6. Add fiberglass mesh, if desired. (I didn't on the skull)
7. After 15+ minutes you can pour a second layer
8. Let the concrete set an hour or two. Longer is better.
9. Remove tape and peel mold off. (The skull that was not cut, but had the hole drilled in it was very hard to de-mold. I had to cut and tear the plastic to get the concrete out. I would highly recommend using the slit-and-tape-the-mold method.)

Enjoy your concrete skull!