Allow the Concrete to further Harden and Strengthen
Wait 2 Days – allow the concrete to sit undisturbed in a warm environment for at least 2 days. Ideal temperatures are 60-80 degrees F. Cooler temperatures will require waiting longer before unmolding. Warmer temperatures may make the concrete dry too quickly. A chemical reaction is taking place in the concrete called hydration. Bonds are being formed giving the concrete its strength and hardness. This happens faster in warm environments than in cool ones.
Flip Mold Over – with two hands grab each end of the mold around the ends where the pipes were removed.
While maintaining a sturdy stance, slide it toward you and lift it slightly off the work table.
When clear of the edge of the table, slowly rotate the mold and lower it pushing the top of the mold against the edge of the table while you rotate it over the rest of the way so it is sitting on the table face down.
This is to prevent standing the loaded mold on the edge or flange of the plastic cavity. The flange of the form is not designed to support the weight of a loaded form and may cause cracks in the plastic.
Unmolding – work the concrete casting free by gently flexing the plastic on each end alternatively.
When pulling up on an end apply a little pressure to the bottom of the mold with your other hand.
The concrete should come free of the mold with minimal effort. It may take a few gentle flexes of the plastic on each end to free the casting. The draft angle of the form was designed to the minimum so the walls would be as close to 90 degrees as possible. So, the casting is a snug fit inside the mold.
Clean Mold – with a clean dry cloth wipe the inside of the mold to remove any leftover excess oil or dried concrete pieces. A good pour with adequate time inside the mold will leave very little behind that needs cleaning.
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Smooth Edges – with a rubbing tool or brick, gently sand down any sharp edges left over from the casting process.
The concrete will be relatively soft at this point so be gentle. This can also be done later when the concrete has cured longer. I like to wait a few days before “dressing” each panel. I will ensure there’s no edges formed in the area around the hole where the panels mate together.
Wrap Panel in Plastic – keep the concrete panel wrapped in plastic to slow the drying process. You can also spray water on the concrete daily to aid in curing to full strength that usually can take 3 weeks. Keeping the panels wet will slow the natural drying process allowing the hydration reaction to continue. Most concrete will reach full strength in 3 weeks of curing.