Filling the Mold
Place your funnel into the hole and start filling the mold with the wet concrete. I use a length of fencing wire to help the mix down the funnel if it gets blocked. The handle of a long wooden spoon or a length of wood dowel would also work.
Give the mold a slight shake from time to time to settle the mix. Check to see your progress. You may need to lift the funnel when the mold is almost full to allow the concrete to slide out. You can find large, sturdy funnels like this at most winemaking supply stores.
I shortened the stem of my funnel using a hacksaw as it was longer than I needed plus, it also tapered to a small diameter at the end that restricted the flow.
Use a small trowel or the edge of the shovel to smooth the top.
For concrete to properly harden it needs to be left undisturbed in a warm environment. 70 degrees F is ideal.
Unmolding and Curing the Geo-Sphere
After three days you are ready to unmold the geo-sphere. At this stage you will need a hair dryer or heat gun, some plastic sheet or thick garbage bag and a paint scraper. Start by removing all the fasteners. Then gently apply some heat to the lower mold cavity keeping the heat gun or hair dryer moving around the mold so the heat is even.
This should take about a minute and the plastic should not be so hot that you cannot touch it. We are looking to just slightly expand the plastic mold to free it from the concrete.
Now the bottom half of the mold should come free. You may need to gently pry it with a paint scraper.
Now pick up the casting and flip it over so you can heat the top half of the mold. Again, keep the heat gun moving all around the form for even, gentle heat. You may hear a click when the plastic becomes free of the casting.
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If you do have some bug holes caused by bubbles stuck to the upper walls of the mold, you can fill them with a cement paste. Add a little water to some portland cement to make a slurry. Work this mixture into the holes and smooth with a paint scraper. This will be polished smooth later so don’t try to be too fussy here. Later I’ll show you how to almost eliminate these.
Wrap the casting in plastic and leave to cure and strengthen for a few weeks. For the best results, keep the casting wet.
Use the paint scraper to remove the latex caulking. It should scrape off easily at this point. Any residue concrete stuck to the plastic can be removed by a light scrubbing with a soft brush or rag.
