How to make a mother mold?
1. Mothermold Part Line
Cut two pieces of thin ply, acrylic or a similar material in the profile of your silicone part line as shown.
These will serve as your mothermold part line.
2. Mothermold
Because the material the mothermold is made of likes to bond to other materials, even silicone, you must cover your mold in a release agent to avoid trapping your part inside the mold.
Begin by applying several (at least 3) liberal coats of release agent to the outside of themold. Wait a few minutes between each coat to ensure proper application.
Place mothermold part lines on the mold and gather mothermold supplies.
Measure parts A:B of Plasti paste in a 1:3 ratio, then combine parts A and B in a new container.
Plasti paste has a relatively short pot life, so work quickly. You will feel it begin to heat up as it cures.
Spread the mixture onto the outside of the mold and sides of the mothermold part lines as evenly as possible.
Think about how your part will be released once the mothermold has cured. Plasti paste will cure to a rigid form so you won't be able to flex it off of your part as you will with silicone. Apply your mothermold with this in mind.
Once side one has been applied, do the same for side two.
Allow both sides to fully cure at least 90 minutes.
After both sides have cured completely, remove the part from the mothermold and silicone.
Clean the mold as best as possible of remnants from the original. Mine had a bit of clay leftover inside.
Close the empty mold and mark bolt placement through the mothermold part line.