Originally Posted by sandy daugherty
Assuming there is no non-skid texture on the seats, your best bet is to spray several thin coats of parting compound on the best one, then build the mold
directly over it in glass. It you are going to pull more than a couple seats from this mold
you should consider using a very hard gel coat. Since the design isn't changing much, its likely the new seats will crack too, so make a few spares. The parting compound is water
soluable, so clean up and prep are pretty easy. If the part is small enough, you can bag it in a food
vacuum bagger and get very good control of the resin/glass ratio.
It's a fun way to learn about glass work.
Unfortunately the center of the seats has a non-skid pattern that looks like little pyramids. I've pulled some test molds using POP off of the patterned area and it seems to release fine. I saw an internet
post that suggested covering the male piece with a thin coat of petroleum jelly as a release agent when making the POP female mold. It seemed to work quite well though I'm concened about possible reactions with the gelcoat
when I make my seats. I plan to clean the mold with acetone. I have already purchased some PVA. I haven't built my parts
yet but I've purchased Evercoat Marine
Premium Gel-Kote. Hopefully that will do.
If all goes well I should only be making one of each seat (yea right). Unfortunately the seats are mirror images
so I need two separate molds. I think the old seats cracked because the glass did not wrap around the bottom of the seat. I'm not sure I have explained it clearly. I believe that the molded piece was a hand layup
or maybe even chop. I believe that this was allowed to cure. The plywood
was placed in the molded piece along with some resin, but no glass wrapped the upper surface of the plywood
. The plywood was recessed perhaps an 1/8 inch below the top of the molded piece. A layer of chop was them placed over the plywood up to the top edge of the molded part forming what was basically an unreinforced butt joint. It is this joint that failed. My plan is to allow 4 inches of unresined glass to protrude above the edge of the mold until I have the core
set in place then to wrap that glass over the edge of my core
material. I will then put two layers of biaxial cloth over the entire bottem before applying a layer of gelcoat
. This should result in a 4" lap joint around the entire perimeter instead of a 1/8" butt joint. Hopefully that will distribute the stresses better and prevent the type of cracking I experienced with the current
My planned layup
schedule is as follows.
1 Layer of Gelcoat, 20 mils.
2 Layers 1.5 oz Fiberglass
1 layer 3/8" Divinycell
1 Layer 1.5 Oz mat Note this layer will be put in place and cured before the core is placed in the mold.
1 layer 3/8" Divinycell
Chopped strand resin mixture to fill any gaps in the corners between the layup and the core.
Wrap at least 4" of contigious mat over the edges of the core.
2 Layers Biaxial cloth
Hand applied layer of gel coat.
Sprayed on PVA to cure layer of gelcoat.
I'ld be happy to hear any comments. To make it clear I plan to bond and trim the layers of divinycell before starting the layup. I'll have all the glass precut and plan to do the layup in one continious operation. I'll probably mix a separate batch of resin for the biaxial cloth.
I'd be happy to have any comments on my layup plan.