Fiberglass Mold Making Kit - Standard, Tooling Gelcoat + Gallon Isophthalic Resin

The middle rung, and the one most first moulds actually need. A quart of tooling gelcoat covers far more face than a quart of resin can back up, so this kit pairs it with a full gallon of isophthalic tooling resin and enough glass to laminate about five square feet to a working thickness.

What is in the kit

• 1 quart tooling gelcoat with hardener, no wax, black or orange
• 1 gallon isophthalic polyester tooling resin with 4 oz MEKP
• Partall #2 paste wax 12 oz and Partall #10 PVA 32 oz
• 1 yd 0.75 oz veil mat and 3 yd 1.5 oz chopped strand mat, 50" wide (50 sq ft of glass)
• 8 oz fumed silica and 1 lb of 1/4" chopped strand for filleting corners
• Wet/dry sandpaper prep pack for finishing the plug
• 3/8" x 4" fiberglass roller and a 1/4" corner roller
• Five 2" chip brushes, 6 graduated cups, stir sticks, gloves
• 2 oz surfacing wax, two 4" flexible and two 6" rigid release wedges, instruction card

Why two rollers: a flat roller cannot reach into a corner, and a corner is exactly where a hand layup traps air. Air under the veil mat prints straight through to the mold face and every part you pull afterwards carries it.

The three waxes, because everyone mixes them up

• Partall #2 paste wax is the release barrier. It goes on the plug, 3 to 5 coats, buffed between each.
• Partall #10 PVA is not a wax. It is a water-soluble green film brushed or sprayed over the wax as insurance on new plugs and first pulls. It washes off with warm water.
• Surfacing wax is an additive you stir into the last layer of resin only. Polyester cures tack-free only when air is sealed off it, and that is what the wax floating to the surface does. Put it in an intermediate layer and the next layer will not bond.

Why the gelcoat says No Wax: a mold face gets laminated over. Wax at that interface is exactly what you do not want. That is the difference between tooling gelcoat and the waxed gelcoat you would use as a finish coat.

Flanges: build your flange into the plug before you start. Adding one to a cured mold is far more work than laying it in on day one, and it is what lets you clamp a two-part mold in register.

Why chopped strand mat and not 1708

This is the most common question in mold building and the answer is not the one people expect.

• Chopped strand mat is random-oriented, so it has no grain and prints no pattern through to the mold face. A tool copies itself into every part you ever pull off it, so fibre read on a mold is permanent in a way it never is on a part.
• Mat conforms. It goes into compound curves and tight radii without bridging. 1708 is a stitched structural biaxial: stiff, prone to bridging in a corner, and its stitch bundles telegraph as the laminate shrinks.
• 1708 is a structural fabric, built for directional strength in a part. A mold does not want directional stiffness, it wants dimensional stability and thickness. 1708 also costs nearly twice as much per yard for a job mat does better.

Use 1708 to repair a transom or lay up a hull. Use mat to build the tool that makes them.

Fillet your internal corners before you laminate. A sharp inside corner is exactly where glass bridges and traps air, and a void behind the gelcoat becomes a chip on the first pull. Thicken a little resin with the fumed silica into a peanut-butter putty, run a radius into every internal corner, and let the glass follow a curve instead of a crease.