This will help the concrete fill the edges and should minimize air bubbles. Fill the Outer cylinder with concrete first, smearing concrete around the inside surface as you go along. A mix that's too wet won't be as strong, but for a small project like this it won't make much difference.

The mix in these photos looks a bit too wet. Pro-Formula comes in a range of colors, is easy to use, and gives good results. If you're using CHENG Pro-Formula, follow the directions in this link. If you don't clean the containers out, you'll see it on the surface of the finished concrete for sure.įor tips on mixing concrete, check out the How-To-Mix Concrete Instructable. Clean up the forms, Inside and Out and remove any oils or residue with denatured alcohol. The screws should rest on the lip of the Outer cylinder, helping to keep it lined up during the pour. Screw the (4) 1' screws into the top of the Interior form. After the foam circle is taped to the base, cut a ~2' foam strip to wrap and tape around the bottom edge (to keep that ring from getting trapped). The idea is to tape a circle of foam to the base so when we go to de-mold that metal ring isn't trapped down inside. Starting with the Interior form, trace the diameter on a piece of thin foam padding (this is usually used for packing / shipping). This means the wall thickness is only about 1/2' - do not go any thinner, this is already pushing the limits. The inside tube is about 4' x 7' (shredded potato chip container). In this case it's about 5' diameter and 9' tall (it contained coffee grounds). The largest tube will become the outside form. It might take a few trips to find the right sizes, but keep looking because they're being thrown away all the time. These tubes were found in recycling bins at a nearby apartment complex.

Download cardboard tubes