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Step 7: Mixing the Concrete for the Geometric Planters

When all the parts are prepared, we can now finally start with the main part of this project - pouring the concrete!

For one planter I used d about 200 ml of the dry concrete mix. The volume of your dry concrete mix will shrink once you add water. This seems counter-intuitive at first, but when you add the water to the dry concrete mix, the sand and cement parts will bind more closely, air will get pushed out, and this reduces the volume.

You can use a pre-mixed concrete or mix your own concrete. Just make sure you use a fine concrete with no stones or sand grains bigger than 1-2 mm in the mix if you want a smooth surface. With bigger parts in the mix, the corners might not fill well, and you might get air bubbles. I had an open batch of a self-leveling concrete mix at hand, and so I used that. Also, read and follow the safety instructions of your concrete.

The first step is to add water to the concrete mix. The amount of water you need will depend on the type of concrete you use – check out the descriptions.

Then, use a small putty knife or something similar to mix the concrete thoroughly. I have to confess that did not measure and just added small amounts of water until my concrete mix had a consistency similar to honey. Not using the correct amount of water will reduce the strength of the concrete, but as it is just for the planters and not for a load-bearing element in a building, I can live with that.