Step 4: Grind, Polish, Seal

14. Take a diamond hand pad or sandpaper and clean up any sharp edges.

15. The top surface will be a bit rough, and if you don't have a 5" orbital polisher, you might try sanding it with 60 grit sandpaper on a rubber pad or fixed to a block of wood. It will take forever but you can get it looking decent if you're patient. You can also grind and polish concrete using the same equipment you would use to grind and polish glass. At this step you'll get the best results if you have the right tool for the job (5" orbital polisher with pads for concrete).

16. (Optional) Seal the concrete with something like the CHENG Acrylic Sealer. Sealing concrete is a whole other thing, but there's some step by step information at that link. Sealing isn't necessary but it will protect the concrete and keep it looking good over the long term.

17. (Optional) If the cylinder is going to be a planter, drill a 1/2" hole in the bottom with a masonry bit.
so lovely
Good work! <br>How did you get no bubbles? The surface is very smooth! <br>Maybe it's all about vibrating?
Hey godzy, <br>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. <br> <br>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. <br> <br>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. <br> <br>
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.
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! <br> <br>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. <br> <br>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. <br> <br>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. <br> <br>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.
definitely solid!<br><br>Just added is a step showing how to use a wine cork to make a drain hole in the bottom of the planter.<br><br>thanks for the comments
Very cool and looks easy :)
Awesome! These are so pretty.

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