How to Make a Fiberglass Hardtop

by Contributor

This article will show you in depth how to make a custom fiberglass hardtop.

Step 1

Determine the measurements for your hardtop. Measure across the body, front to back, top to bottom, even diagonally, to ensure a straight and true top.

Step 2

With the measurements made, build a frame out of lumber. The frame can be built one of two ways. The first way is to build a frame that will sit up side down on the ground, a negative, and fiberglass will be layered inside. When finished, the frame will be on what is the outside of the hardtop. The second way to build a frame is to build it so that the fiberglass is layered around the outside of the frame, a positive. When finished, the frame will be on the inside of the hardtop.

Step 3

When you have decided what type of frame to build, it's time to start building. Using your measurements, make a frame skeleton. Use plywood to make ribs that conform to the contours you would like, and use 2"x3" boards to act as a spine between ribs. Then, cover the skeleton with thin sheet aluminum sturdy enough to support the fiberglass without sagging. Staple the aluminum sheeting to the skeleton.

Step 4

Cover the aluminum with mold release agent, sold at most auto body supply shops. Do not use petroleum based oil or grease as it will react with the resin and inhibit adhesion of later layers.

Step 5

Cover the frame with a large sheet of fiberglass roving(looks like woven fabric). If you can't get a sheet large enough to cover the entire frame, use a couple sheets overlapped by about 3-4 inches. Mix the fiberglass resin according to the directions on the package. Wear nitrile gloves and safety glasses and work in a well ventilated area. Pour the resin on the fiberglass roving and spread with a paint brush.

Step 6

When the first layer is fully coated in resin, apply a second fiberglass layer, this time using fiberglass matting(looks like shredded fibers). Pour more resin over this second layer. Repeat until the layers add up to about 1/4" to 1/2" thick. The final layer should be fiberglass roving, to ass surface strength.

Step 7

An optional method to add strength to the hardtop is to add aluminum mesh in the middle of the layers. Lay it on as you did with the fiberglass and pour and spread resin, then add another layer of fiberglass and resin and repeat until you reach the desired thickness.

If at any time the resin fully dries in between coats, the surface must be sanded with 80 grit sand paper or an angle grinder before applying another coat. When the hardtop is completed, allow to dry according to the directions on the resin package. When it has fully cured, remove from the mold. Sand the hardtop to the finish you want, it may require body filler to fill in low spots and imperfections. Once the body work is complete, prime and paint as you like.


  • You can use fiberglass roving for the entire hardtop, it may offer a stronger final product, though it usually costs more than matting.
  • Plan ahead and work quickly, you don't want to have to grind a layer before you can go on because it dried.
  • Mix the resin as directed, too much hardener will make it dry a lot faster.
  • Hot and humid days make the resin dry faster.


  • Use all safety equipment when working with chemicals.

Items you will need

  • Lumber for a mold frame
  • Fiberglass matting and roving
  • Fiberglass resin
  • Paint brushes
  • Sand paper
  • Primer/Paint

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