Instructables
Picture of DIY CONCRETE:: Cylinders from Cardboard Tubes
This Instructable will explain how to make concrete cylinders using discarded cardboard packaging tubes (potato chips, ground coffee, mixed nuts, baby formula, etc.)

Materials:
(2) Cardboard Tubes (best with foil or plastic linings for water resistance)
(4) 1" Screws
Clear Packing Tape
Thin Foam Wrap (a packing / shipping material)
Sacked Concrete / Rapid Set (if you're in a hurry, although it tends to wash out colors)
CHENG Pro-Formula Mix

Tools:
Permanent Marker
Tin Snips / Wire cutters
Long Needle Nose Pliers
Phillips Screw Driver ( + )
Scissors
Weights / Rocks / Sand
Diamond Sanding Pad / Sandpaper

Safety:
Particle Mask
Rubber Gloves
 
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Step 1: Prepare Tubes

Picture of Prepare Tubes
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These tubes were found in recycling bins at a nearby apartment complex. It might take a few trips to find the right sizes, but keep looking because they're being thrown away all the time.

The largest tube will become the outside form. In this case it's about 5" diameter and 9" tall (it contained coffee grounds). The inside tube is about 4" x 7" (shredded potato chip container). This means the wall thickness is only about 1/2" - do not go any thinner, this is already pushing the limits.

1. Starting with the Interior form, trace the diameter on a piece of thin foam padding (this is usually used for packing / shipping). 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.

2. 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).

3. Screw the (4) 1" screws into the top of the Interior form. The screws should rest on the lip of the Outer cylinder, helping to keep it lined up during the pour.

4. Clean up the forms, Inside and Out and remove any oils or residue with denatured alcohol. If you don't clean the containers out, you'll see it on the surface of the finished concrete for sure.
dana-dxb1 year ago
so lovely
godzy2 years ago
Good work!
How did you get no bubbles? The surface is very smooth!
Maybe it's all about vibrating?
CHENG Concrete (author)  godzy2 years ago
Hey godzy,
It's all about vibrating! Concrete will always have some air bubbles but they can be minimized by vibrating (and not using a mix that's too dry). In the shop we have a small table vibrator (Vibco PJT-100) that works well for tabletop projects like this. For something larger, like a concrete countertop, we'll use a few table mounted vibrators (Vibco US450T) hooked up to a variable speed controller.

When you're filling the form it also helps to smear concrete on the inside of the form walls and brush over any air bubbles that might be clinging to that surface.

If you don't have a table vibrator, you can still get pretty good results using drop compaction (picking up one end of the form and dropping it over and over), and there's a technique called rodding (basically pushing a broom handle up and down in the concrete). You can also take a reciprocating saw, remove the blade, and tap-tap-tap on the form walls, though I'd avoid that if your form is just a cardboard tube like the one in this instructable.

bob6572 years ago
I tried doing this using PVC instead. I assumed that if I greased the PVC I would be able to just slide the concrete out. Boy was I wrong I finally got the tube out of the mold after spending 2 hours wrecking it with a bandsaw and chisel but it looks horrible from the accidental damage incurred by removing it.
CHENG Concrete (author)  bob6572 years ago
I'm sorry to hear it didn't work out! PVC is a little bit too thick and too rigid to be used for the exterior form. And if you used it as the knockout for the inside you might never get it out!

PVC works best when you don't plan to remove it, or if you score it very deeply beforehand so you can easily break it apart later.

You could make an umbrella stand with a bucket and a length of PVC pipe. Just pour concrete in a bucket, cap the PVC pipe on one end, push that end down into the wet concrete and hold it in place with some kind of frame (or duct tape!). If the bucket is tapered the concrete will drop out and you can cut down the PVC pipe to be flush with the top surface.

You might also use PVC tubing for a concrete lamp, or something that you'll be installing wires inside. The tubing stays in place and makes a tunnel for the wiring, and you can use fittings to make bends, etc.

Smooth-on makes a good mould release that we use in the shop. Cooking spray can work in a pinch, but something very oily might have an effect on the appearance of finished piece.
CrLz2 years ago
Solid!
CHENG Concrete (author)  CrLz2 years ago
definitely solid!

Just added is a step showing how to use a wine cork to make a drain hole in the bottom of the planter.

thanks for the comments
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sms0172 years ago
Sweet!
breumer2 years ago
Awesome!
Very cool and looks easy :)
Awesome! These are so pretty.
foobear2 years ago
gorgeous