Painting Mold Surface with Thickened, Pigmented Epoxy.
With the female mold waxed and polished, the first step in making the part is to coat the mold surface with thickened and pigmented epoxy. To do this, I thicken the catalysed epoxy with West #404 and add a small amount of micro spheres to make it resist sagging. This is allowed to gel before painting into the mold with a disposable brush. With a little practice, one can put on a thick coat that covers the mold surface and does not run. The technical term for this propensity not to run is thixotrophy, meaning liquid when stirred or shaken, but semi-solid when allowed to rest. The addition of a small amount of micro spheres makes the resin thixotrophic.
Lay Up Glass Materials
While the coated mold is allowed to partially cure, glass materials are cut and prepared. Fine weave materials are layered in first and increasing in fabric density. In order to make all parts the same, a lay up schedule of glass fibre material is necessary. For such a small part, all the fibreglass is cut and stacked for all six parts being made. This next picture shows the various materials used to make the part. The heavy fabric will not conform well to the tight corners, so must be cut with some precision and carefully placed into the mold in such a way as to allow the fabric to cling to the mold surfaces.
When the lay up is complete and the materials saturated with epoxy, it is set aside to cure, a process that may take two days to become hard enough to remove from the mold without damaging the part during removal. The last 3 pictures show a completed part as pulled from mold being trimmed with Dremel tool and sanded a little bigger than finished size and ready to be installed on deck in its proper place. It will be set aside waiting until all parts are complete.
Part is removed from mold and being rough cut with Dremel tool.
Finished part trimmed to size by sanding
Finished Part w Metal Trim
Cam: The finished part looks great. When you install the part onto the chain plate are you going to add some type of sealant? This idea of yours should certainly help to keep out the moisture.
Usually a polyurethane type sealant is used, often Sikaflex or 3M 5200 or 3M 4000, the latter staying more pliable. All of these seal the through deck hole against water penetration but also starve oxygen to the surface of the steel. Areas that are oxygen starved begin to rust and form pits, eventually leading to a crack or fracture. Stainless steel needs oxygen to form the thin protective oxide layer on the surface that prevents rust. Without available oxygen the protective oxide skin cannot form to protect the metal. Most damage to chain plates occurs exactly where the sealant coats the metal. So there is the rub. How do you prevent water penetration yet not oxygen starve the part? The raised pads help prevent water penetration when the sealant becomes worn, but does little to protect the metal. Water, especially salt water penetration damages the interior of the boat, like cabinets, bulkheads and chain plate “knees” and causes mold and mildew behind cabinets and liners which are areas usually inaccessible to clean. Keeping water out is a good idea.
Fellow sailor, Tim and I discussed this at length and collectively came up with the idea of using a rubber “O” ring to seal the chain plates. I could envision a molded pad with a recess to accommodate a heavy “O” ring where the metal cover when tightened squeezes the “O” ring and completes the seal. Only the small area where “O” ring meets metal will be oxygen starved. Not a cure, but better than what is currently available. Sometimes chain plates are bolted directly to the outside of the hull and leaving them exposed and visible. They rust where the surface meets the surface of the hull, but can easily be inspected for cracks or signs of pending failure. But many sailor prefer their shrouds to be closer to the mast so as not to interrupt a large jib sail. It is all a big compromise. Even composite chain plates have a flaw… the metal bearing for the load transfer via pin to the rigging. Often a piece of stainless steel pipe is bonded into a uni-carbon wrapped chain plate to receive the rigging pin. You can guess where that fails.