: 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?

This may sound stupid, but how about Simplicity?
When you make the single mold, as you and others have done, you now have a concrete block or box of sand and plaster to lug around or find storage for until it's next use. For most folks, the chances of making a second, third or more is fairly inevitable. So, get that block out again.... and/or, don't break that sand and plaster mold... and so on.

By making a glass mold, you have a lightweight piece that can be moved quite easily and stored off the floor on a shelf, grabbed at a moments notice and you're good to go. And.. if you have to make two seats, or four, in different sizes you will end up building a concrete wall of seat forms to keep them all.

I have several friends and my kids and grandchildren that are wanting boats, so the glass mold idea works VERY well for me. My yard and garage are way too full to build a wall of concrete blocks.

If you are just building one boat, or a fleet... for yourself, the block idea is O.K. provided you have a spot set aside to shove that cement block.

I think that I would use the sand and plaster method and when you have a nice mold for one, break up the layer of plaster and the box and sand are ready for another seat.

Either way works, just depends on the room for storage and how many tushies you are having to work on...Uh.. with..

Rehd