Deacon,The biggest benefit to this process, even for one-off pieces is that a perfect mold and a gel coat sprayed into it gives you a near perfect finished product with no bondo and tooling. When the finished product is built over a positive center, the irregularities in the fiber and resin have to be worked out.
Yeah, I agree. I've been reading a bit since I made my one off and I think the next piece I make I'll attempt it this way.
I've learned a hell of a lot about building plugs in my quest to master the craft of fiberglass parts fabrication. It all started with an ill-conceived plan to build a seat pan / rear cowl on the frame with blue masking tape, aluminum tape, spray foam, wax from a commode seal (had one laying around) and bondo - all to form the "plug" for a fiberglass seat. Needless to say, it turned out like shit. It would have worked but I'm too much of a perfectionist. So I moved on to forming a positive mold, core or "plug." Polystyrene foam, like pink foam sheathing, is easy to come by and relatively easy to work with. It has a tendency to "chunk out" when you cut it; I solved that problem by building my own hot wire cutter. (anyone interested in a 30" professional-quality cutter that can be built for around $40, let me know and I'll post a build thread). The biggest problem with polystyrene -- It's non-compatible with polyester resins, which means that a plug constructed of this material cannot be sealed with resin and even bondo reacts with it slightly as it's a polyester-based product. Properly sealing a plug allows you to tool out any imperfections before you create your mold, tooling inside of a mold sucks. Also, I think tooling bondo sucks, so I prefer plugs that require no bondo. Pink foam has it's purposes - sheathing the exterior of your home before your siding goes up and building plugs for projects were an epoxy resin or primer is used. I personally prefer working with polyester resins to epoxy any day of the week. There are two types of high quality and kinda pricey foam that can be purchased from your composite store that are compatible with poly resins -- PolyIso and Polyurethane. The Polyurethane can come in a solid or a mix and pour, the latter is similar to the spray foam lots of guys use. I never cared one bit for the spray foam in a can. It was too light weight, had poor expansion characteristics and rarely cured all the way from surface to center. No one wants to be sanding a project only to pop open a pocket of yellow gooey crap. The mix and pour works well, comes in several weights but must be poured into some sort of cast (which can easily be constructed from plywood, cardboard or whatever you have lying around). The mix and pour will also minimize the likelihood of large air bubbles, is easy to shape and can be sealed with a poly resin. The only real downside to this sort of foam is that it adds yet another curing phase to the project. PolyIso is by far the best product for plug manufacturing but it is also by far the most expensive. I prefer working with solid foams and don't like the price of PolyIso, so I use the super soft light green foam used for artificial plants. This is a polyurethane based foam and is compatible with poly resins. This stuff is easy to shape, almost too easy, you have to be really cautious not to go too deep into your material. I build my plugs with these blocks, shape it out and seal it with 2-3 coats of poly resin. The resin goes on super smooth, almost like glass and is easy to tool to perfection. After graduated sanding up to 400 wet, you now have a mirror surface to wax and pva for your mold. I'm building a custom seat for my buddy and I built the plug tonight in about 2 hours. I have a perfect plug that needs to cure for a full day before I mold over it. Cost of supplies for the plug - $15.
that is one LONG paragraph! but all in all I think I understand what you are saying, and I am definitely going to book mark this and give it a shot when it gets warm enough to work with the garage door open..
I (we) waited at least a few days to pull the mold off the plug. And a few days as well to pull the part from the mold. Please tell me that your not trying to cure fiberglass outside in this weather?
Hey Oldog,I read your post which has inspired me to build my own seat using your directions. I bought most of the stuff which set me back $240 (US dollars). The thing is, I think the guy sold me way too much gel coat and glassing resin. He said I would need at 2 litres of gel coat for the mold and another 2 litres for the seat. Glassing resin needed would be double at 4 litres each.So now I've got 4 litres of Gel Coat and 8 litres of Resin to make one mold and seat. Does this sound about right?Cheers
That sounds like you have way too much. That said, I've only used epoxy, so the process is slightly different.--Chris
That does not sound like "way" to much I don't think. We used resin from a 20 litre pail so can't say exactly how much was used. You have the mold and the final part to make. Be generous with resin on the mold! The gel coat sounds like you have about twice what you will use.BTW...I have decided to sell the mold if any one is interested. It would be a good money maker but I just don't have the time. I'll take $250.00 CAD (plus ship or pick up) for it. It's made 6 seats so far and each part popped out flawless.
Thanks Oldog,I'll see how i go. But for anyone thinking of doing this, it is way cheaper to buy ready made glass seats.