> Hi Shawn,

> If you were going to make one seat you could work directly from a plaster
> pattern coated with mold release. I guess that a couple of coats of melted
> wax brushed on to a dry, pre-warmed plaster pattern would work OK. I like
> that hard-soap based release that I have been using. I posted the recipe
> on this BBS a while ago.

That's what I was thinking of doing; then I'd make a really smooth negative mold from that and go into "production" and make 4 or 5 seats in that mold.

> Plaster will give a beautiful smooth surface to the mold. I used mortar
> mix because it is very inexpensive, it is more durable and I was going to
> coat the surface with fiberglass anyway. That and the mold used about 40
> pounds of mortar! The mortar is not as dusty to work with as plaster. You
> have to make sure that you clean up the mold and make adjustments to the
> contours while the mortar is still "green" and can be shaped
> with a stiff brush or you will be in for a hell of a job.

For my "day job", I'm an estimator for a precast concrete manufacturer--I know how much of a pain Portland-cement based mortars and concretes are to grind! That's why I'm thinking the plaster route.

I'm seriously considering one of Mike's suggestions from last night. I have a fairly decent carved minicell seat in my boat now. I'd probably put a 1/2" or 1" piece of open cell foam over that and then do the plastic/plaster'n'cloth/ plastic layup to make a form. Then, I'd strip out the plaster/cloth and smooth the backside to make my form.

Hmm...it's all coming together in my mind!

> BTW, when you say "plaster" I am assuming that you mean
> "Plaster of Paris" or the equivalent and not the plaster (also
> known as "mud") that is used to finish gyproc walls. That
> quantity of "mud" would take eons to dry and it would shrink and
> crack.

> Lessons learned...

> - When making a seat. Put a one layer of glass on the mold, let it cure
> and then remove it from the mold. Replace the seat on to the mold and
> build up and reinforce as required. It is easier to remove one flexible
> layer.

> I am currently working on a second seat which I have made much heavier
> because it needs to be self supporting. To stiffen up the seat I added
> pieces of luan to the four sides during the initial glassing. The wood
> made it much more difficult to remove the seat from the mold - it was hard
> to break the seal. Next time I will add the wood at the second stage.

> - The sides on my mold are quite vertical and square. I did that so the
> weight would be transmitted straight down, the next time I will taper the
> sides a bit more.

> - The seat is a bit difficult to get a hold of to pull it off the mold so
> I use a plastic ruler to help push it off. Next time I think I will add a
> couple of fiberglass tabs in the seat area to pull on. They can be cut off
> later and glassed over later anyway.

> Enough rambling, got to get to work. I hope this helps.

> Hank