Finishing and Polishing
After the geo-sphere has cured it’s time to finish it. I set the casting on a towel draped over a small pail to hold it steady. There will be a small ridge where the two halves of the molds met. Here’s the simple hand tools we will use to smooth down this ridge and polish any portland patch we applied to the bug holes.
I have a set of diamond hand polishing pads that go from 60 to 1000 grit. I also have a coarse concrete rub brick and a wire brush. The wire brush is used to clean the rub brick and polishing pads if they get caked with concrete.
I’ll start with the edge of the rub brick to remove that ridge. I don’t want to just round it over but to keep it sharp so it matches the other edges formed by the mold.
I rotate the casting as I work my way around the parting line. Then switch to the 60 grit polishing pad. Then to the 240 grit to get this smoother.
I’m working outside and only making a bit of dust but, you can go dust free (and get better results) by wetting down the concrete. I’ll use the polishing pads to smooth and flatten the cement patched faces. And here’s the final result.
For the next geo-sphere I’ll do some polishing with round diamond pads on a drill. This set of pads comes with a drill adapter. You need to keep wetting the concrete and work your way through the various grits. I started with a 50 grit then switched to a 400 here. The pads are hook and loop like velcro.
I decided to polish the faces of the entire casting here to bring out more of the aggregate in the concrete. And I think it turned out really well. And you can see the comparison of the two.
Finally, once the concrete on these castings fully dried I applied a few coats of a concrete sealer. This is totally optional.
