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KBBS Archive 10,000
Plaster & Wax and lessons learned
Posted By: Hank In Response To: Re: Molded seat picture (Shawn Baker)
Date: Tuesday, 28 September 1999, at 9:12 a.m.
> Do you think plaster coated with wax would make a suitable fiberglass mold
> or should it be 'glassed itself first?> Shawn
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.
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.
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
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KBBS Archive 10,000 is maintained by Nick Schade - Guillemot Kayaks with WebBBS 5.12.
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