: There are lots of ways to make a mold that works but much of it is using
: professional materials and technique. If you are casting off a surface
: that is pretty much flat with little inclines to worry about then molding
: plaster is pretty simple. This can be bought in different size buckets or
: 50 lb bags. You can wall or dam up around the sides using modeling clay
: and cardboard. More experienced persons can work up a wall but that is all
: timing. If it is a mostly flat area, grease the surface with Crisco or
: something similar and don't leave grease ridges, get the excess off or
: they will show in your cast. Mix the plaster to the consistency of pancake
: batter with no lumps. Then for a good surface lightly brush on a coat of
: plaster. Don't brush too hard or you will brush off the parting. Then
: simply slowly pore on the plaster. You can pat the surface to bounce out
: bubbles and make a better surface. After the plaster sets, wait until the
: heat just goes out of it before removing. It isn’t as strong as it will
: later get but he mold surface next to the seat develops a dampness that
: helps in the removal of the mold. To strengthen the cast just after
: pouring you can pat in rope hemp or some similar material if you have it.
: Actually you could probably just pat in some scrap fiberglass. Just to be
: extra safe you might put a coat of past wax on before the grease.

: John

Just a little more. The plaster mold must then be sealed before you glass your seat from it. I usually use shallac put on several times over an hour untill you have a shiny surface. Then you can prepair the surface with parting as usual for the glass seat.

John