: Hi,
: Yesterday I made a box out of scrap plywood, filled it with cement and sat in
: it, creating a truly custom fit fiberglass seat. I have read other people
: have made seats in a similar fashion, but they make a cement mold, then
: then they use that to make a mold from which the seat is made. Why not
: just skip a step and use the cement mold to make the seat directly?

The reason for the second casting is to get a negative mold, from which the positive cast is made. If you use your impression to make a seat it will be similar, but not exactly like the original. When you use the negative mold then it will be making the face of the seat, and it will be nice and smooth, and exactly like the original. Using your method if you get an epoxy run in the bottom then it will be flattened out.

-Malcolm