Fiberglass Mold Making and Fabrication How To – Project Blog

I begin by applying black tooling gelcoat with a dump gun at about 80 psi. I make sure to keep the gun close to my work because gelcoat makes a huge mess if it gets on something other than your project. I lay down a nice thick layer of gelcoat making sure to get good coverage around the base where the plug meets the board.

Once the plug is covered with gelcoat, I let it cure to a tack. I did this project on a nice hot San Diego day so it cured to a tack in about 45 minutes.

At this step I used a different approach than I am used to. I came into possession of a large roll of veil that I decided to use in the corners and angles of the mold. In the past I have always used a combination of cabosil and resin. I found the veil easy to work with, especially when pushing it into corners with a chip brush. With the veil in place, I proceed to build the mold with three layers of 1 ½ ounce chopped mat.

I begin applying the chopped mat by brushing a nice thick layer of catalyzed resin over the area of the plug that I am working on. Then I place a piece of mat that has been pulled off of my roll and lay it on the plug. I like to keep the pieces fairly small on a project like this, no larger than 6 inches square. Pulling the mat apart will leave many loose fibers that will help the strength of my final product once it has cured. When applying the mat, I like to overlap my pieces by about 20% and build a nice flange around the base of the plug.

Happy Glassing

Steve

www.fiberglassmoldmanual.com

Preparing the plug is the next stage of this build. I begin by mounting the two halves of the plug to a piece of inch thick MDF board. I attach the plugs by using screws from the back side of the MDF. Some people glue or epoxy their plugs to the parting plane. I prefer to use screws because I can remove the plug from the MDF after the mold is finished with out destroying it.

Once I have the plugs securely attached to the parting plane, I need to go around the base of the plugs looking for gaps between the board and the plugs. Any gaps are filled with clay. This is just a matter of forcing the clay into the gaps in order to prevent resin from getting under the plug. When the gaps are filled and all excess clay is removed, I can apply mold release wax to the plugs and the MDF parting plane. I like both McGuire’s and Part-All mold release waxes. It is important to apply at least five coats to the plugs in order to ensure adequate coverage. The plugs should be polished to a shiny smooth finish.

PVA is now sprayed onto the plugs and the parting board. The PVA is an excellent barrier between the mold and the plug. I like to spray a coat, let it dry and then re-apply. Applying two coats of PVA can result in lost detail but that is not a concern for me with this project. An additional coat of PVA will ensure an easy release when I de-mold the plugs.

I apply the PVA with my spray gun at about 60 psi and a distance of 8 to 12 inches. PVA is cheap and valuable at the same time. This set of mirror image plugs is now ready for molding.

For the molding process I need my air compressor and dump gun along with: tooling gelcoat, fiberglass resin and chopped mat, MEKP, rubber gloves, disposable brushes and a respirator or fume mask.

Happy Glassing

Steve

www.fiberglassmoldmanual.com