fiberglass molds

i want to build a fiberglass tackle center for my boat. i was thinking of using foam panels as a mold/ form and was wondering if anyone had any suggestions as to weather it would be better to glass over the foam or use the foam form to make a mold to make the glass structure?

 

If you’re only interested in making one and especially if this is a first-time project, I would go for the one-off approach. Building a good mold is more difficult than building a one-off part, especially if you’re not familiar with the materials. A good mold really requires a perfect polished finish, equipment to spray on the gel coat, etc., where as the one-off part just requires work and elbow grease sanding. Building up a mockup with foam preferably with nicely radiused corners, glassing, sanding, fairing with a filler+epoxy, and then adding a topcoat I think would yield a perfectly good result in much less time.

 

I think I'll answer in the forums rather than via email because while I've worked with fiberglass a bit, there are many who have far more experience that might be able to provide more answers:

Are you sure that you want to remove the foam? If you use a high quality foam you might leave it as the core to provide separation between the top and bottom skins and thus give the top stiffness.

I'm not sure what the best way to remove the foam from the part would be. With two hard parts (mold/plug or mold/hull) you would use several coats of wax and PVA (water soluble release agent) to be able to separate, but I’m not sure if a thickly-applied release agent would work with a soft material like foam… I suppose it wouldn’t be a huge problem to chunk it off. I know some builders also dissolve the foam using a solvent. Maybe someone else will jump in with better information. My approach would be to make the foam integral to the one-off part.

Note that Polyester resin will eat the inexpensive foams like Styrofoam, so if you use a cheap foam you’ll either have to coat it well with a paint/barrier to keep the polyester from eating it, or use an epoxy resin.

I personally much prefer to work with epoxy. The only thing is that you have to be much more careful in the mixing and you want to protect it from sunlight. There is a lot of material information at the fiberglass supplier sites that you will want to consider in a context of performance & workability vs. cost. Basically depending on the shape you will use layers of 10oz – 20 oz cloth, or a layer of roving for faster build up, with a lighter cloth near the surface for a finer finish. Then you will take out any imperfections by applying a fairing compound and a lot of sanding. Followed by a build up primer and more sanding, and finally finish it off with a primer & finish coat. Also take a look at some of the project sites to get some ideas: http://boatdesign.net/Directory/Boatbuilders/Boatbuilding_Projects_Sail/ and http://boatdesign.net/Directory/Boatbuilders/Boatbuilding_Projects_Power/ , for example http://www.concentric.net/~Knotreel/

 

Hi Rhett,
I'm not sure of the size of the box you want to build but I would proceed in one of the following 3 ways:
1-Build a plywood box, round over all the outside edges and glass the outside with glass cloth and resin. Use thickened epoxy to fillet all the inside corners and then glass the inside. With a little elbow grease, a bit of filler, and paint you should have a nice looking box.
2-Build a box out of foam and do the same as above. One advantage is that your box will be insulated. You can use epoxy or polyester resins but make sure the foam and resin you choose are compatible with each other.
3-Build a box out of cheap lumber or plywood and cover it with formica or some other brand of laminate. Round over all the edges and coat them with resin and sand smooth. Apply mold release. Then apply a gel coat with a brush or roller (it doesn't have to be sprayed on), followed later by glass and resin. One advantage with this method is that you can use the mold to make more copies of the same box.

I would use epoxy for the 1st method and polyester for the 3rd. If you've never worked with resins ask your supplier to give you some advice, especially with the last method.

 

Plans for Pearson

I just recently got a 1964 24 foot Pearson Yacht(sailboat) that needs to be restored. The previous owner doesn't have the plans, and I would help me greatly in restoring the boat does anyone know of a site where I can get them?
Thanks

 

For a start try the National Pearson Yacht Owners Association at www.pearsoncurrent.com. Perhaps some of the members can help you with specific questions.