I've been seeing a lot of examples of concrete mouldings online, and started wondering about making my own flower pots out this material. I've also got an affinity for nature related images and designs, and wanted to find a way to embed branches or leaves in the design.
There weren't many examples of this sort of thing online, but I did find cases where items had been attached to molds with spray adhesive and then removed after the casting was complete. I figured this might work out well with leaves, but was unsure about whether they're come right off after demolding or would fall apart (maybe the cement would "eat" or dissolve the leaves somehow). In the end things worked out well but I did come out with a few "lessons learned":
1. Don't use leaves that have already fallen to the ground, no matter how awesome they look. Leaves that have already turned will fall apart more easily, and their material does stick better to the cement than fresh leaves.
2. When applying the oil to the molds, use just enough to get the surface wet but that's about it. Remove all remaining oil (wipe it with a paper towel for example). Any excess oil will pool at the bottom of the mold and leave impression in the casting.
3. If the outer mold is tall enough, you can drill the skewer holes through it as well, pass the skewers through both the outer and inner molds and avoid having to weigh the inner one down.
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Step 1: Materials and Tools
The overall cost of the project's materials was around $40, but the most expensive items (cement, spray adhesive and sealer) can be reused for additional castings so the cost really does go down if you're making several.
For cement I went for one that had a high resistance to the freeze and thaw cycles since there was a chance the pot might be left outside, and our northern winters aren't too cozy. I did end up screening out all the gravel from the cement, though, so I don't know if that might have removed some of that resistance or not. I used a left over piece of window screening material for this step, and it worked like a charm.
Spray adhesive - this stuff is awesome. Spray the leaves a bit, let them dry for a minute, and stick on to the mold. Couldn't be easier.
Concrete sealer - I bumped into this one quite by accident, but it was perfect. I was looking for a way to seal and protect the concrete (especially the inner sides of the pot and the top of the dish since these would be exposed to water), and was thinking of some sort of varnish. As I looked over the possibilities at the hardware store, I came across this sealer that basically sprays on, smells just like contact cement, and dries into a waterproof and slightly rubbery surface. They recommend 2-3 layers but I think I used about 5, and it looks and feels very waterproof.
Cooking oil - you only need a very small amount of this, and it's basically acting as a release agent. The mold pretty much slides off once it has cured, so this is indispensable.
Molds - the dollar store is your best friend here. For the pot I used a measuring cup and a drinking glass that fit within each other. There was about a 1" gap left between them, which was a perfect thickness for the flower pot. I also got small breakfast bowls that fit within each other to use for the pot's dish. If the bowls are separated slightly from each other it leaves a gap of about 0.5" for the wall and closer to 0.75" for the bottom, and I was comfortable with that.
Wooden skewers - these will come in handy to separate the inner and outer molds and give you the spacing needed between them.
For the tools I used a spatula and bucket to mix the cement, a drill to make the skewer holes in the inner molds as well as the drainage holes in the pot, and a Dremel tool to grind down the saucer's ledges. The Dremel is not a mandatory tool, though, and can be avoided if you find better bowls for the saucer's mold. In my case the gap between the inner and outer molds was too narrow for me to be able to tell how much concrete to pour, so I chose to fill it to the top and then cut/grind down the edges.
Step 2: Preparation of the Leaves and Molds
As mentioned in the intro, one of the lessons I learned was not to use fallen leaves as they tend to disintegrate faster and will be harder to remove from the casting. Pick fresh leaves right off the branches, and go for those that have prominent ridges and veins. Leaf stems can be left on as well, and they look great on the final product.
Once gathered, put them down flat between sheets of newspaper, put a few heavy books on top of them, and leave it overnight. This will straighten and dry them up a bit (in case there was moisture on them), making them easier to apply to the mold.
Once you've picked your molds, hold the inner one inside the outer at the height that will give you a good sized bottom (I kept it the same as the wall thickness) and mark the inner mold at the spot where the outer one reaches it. Drill (or use a puncturing tool if the cup is thin enough) four equidistant holes around the perimeter of the inner mold (at the height of your mark) and insert the skewers. The inner mold will have to be weighted down when the cement is poured, and the skewers will ensure the right thickness is preserved for the bottom.
When the leaves have been straightened out, keep them on the newspaper with the ridges that you want to have embedded in the cement facing down. Spray the other side of the leaves with the adhesive, let them get tacky for a minute or so and apply them to the inside of the outer mold. Letting the leaves overlap a bit and be organized in a random fashion will give the design a more natural and chaotic look, but this is obviously up to you. Ensure the edges of the leaves are pressed into the mold and have not lifted so that cement will not flow behind them and end up burying the leaf in the pot's surface.
Step 3: Preparing the Cement and Pouring
The cement is ready to use out of the bag, but since I had fine details that I wanted to pick up from the leaves I needed to ensure the cement is very fine. It contained a good mix of small gravel, so the whole thing needed to be screened. I took a piece of left over window screening material, positioned it over the bucket, poured a few handfuls of cement at a time and shook it around a bit to separate the gravel; worked like a charm.
Begin adding a little water at a time and continue to mix until you get the viscosity of oatmeal. It shouldn't be runny but shouldn't stay put either. Remember this needs to flow into all the crevices in the leaves, so needs to flow a bit.
Pour the cement into the outer mold, and press the inner one into it until the skewers rest on the outer molds edge and you get the cement to rise along the edges to the height you wanted. Once you've got it, tap the mold a few times to level the top edge, weigh the inner mold down with something heavy and try to forget about the whole thing for two days. I say "try" because I had a very hard time doing it; waiting to demold and see the final product was very hard to do..
Step 4: Demolding, Cleaning and Sealing
Demolding is by far the easiest step in the process. If you've properly covered all surfaced in oil, the mold will literally slide off and leave a very clean surface.
The leaves will also peel off easily, but again - if you've used fallen leaves they might fall apart a bit and you'll have to pick out the pieces. To be be honest, though, picking them out (even the few pieces that separated) was an absolute joke so there's nothing to worry about here.
When everything has been demolded, you can take some sandpaper (I used an 80grit) and a wooden block to sand and level the top edge of the bowl and saucer. In my case I made the saucer way too deep, so had to cut the walls down with a Dremel and a cutting wheel, and then sand that top edge down as well.
It's at this point that you also want to drill a few holes in the bottom of the pot for drainage. Make sure you use a masonry drill bit, and go very slowly. I drilled from the inside of the bowl out, and had a little bit of blow-out at the bottom of the pot, but this is ok since that part will always be sitting on the saucer and therefore be out of sight.
The final step, sealing, is very straight forward. I followed the manufacturer's instructions for this one, and they were to simply spray an even coat from about 30cm away, brush the material to even it out, let it dry for 20-30 mins, and apply another coat. I applied 4-5 coats in total, et voila. All done.
All you need now is some small sized gravel (I didn't use the one from the cement for fear that it might poison the plants somehow), some potting soil, and you're good to go.