Guide to Working with Plastics: A Wealth of Fillers and Paints--Watertight Fiberglass Patches

A gaping hole in a plastic, metal or wood surface that once was smooth and water tight need not spell disaster. Using a variation of the fiberglass-lamination techniques shown, you can apply a strong, watertight patch to any thing from a plastic laundry tub to a fiberglass roof panel. Careful sanding, finishing and tinting can make most such repairs virtually undetectable.

Both the polyester and epoxy resins used in working with fiberglass will also bond well with wood and metal. However, polyester’s relatively short drying time, low cost and easy workability make it preferable to the more expensive epoxy- base resins; the latter adhere more readily but are harder to use because they are so thick. For most household repairs, the best choice is a pre-accelerated, two- component polyester resin with a liquid hardener, available from plastics suppliers and most marine-hardware stores.

Fiberglass repairs are based on the same principles as fiberglass lamination: Overlapping layers of resin-impregnated cloth form a solid surface across the dam aged area. Careful mixing of the resin compound ensures proper bonding be tween the layers of glass and the material being patched. A gel coat applied to the working side of the patch creates a smooth and waterproof surface. (For a discussion of components and mixing techniques.)

Most resins are mixed with 3 per cent hardener by weight. Cool weather slows curing; if necessary, you can increase the proportion of hardener 5 per cent to speed curing, but be aware that excessive hardener can cause brittleness by curing the resin too quickly. In some cases you may be able to speed curing by warming the area of the repair with a heat lamp. If repairs are urgent in temperatures below 540 F., you can use a technique known as cross-hardening, which allows curing down to 32°. Cross-hardening involves first mixing the standard hardener into the resin, then adding a second hardener containing benzoyl peroxide. Ask for specific information on proportions if you purchase materials for cross-hardening.

To get a strong patch, you must pre pare the surrounding surface carefully. Make sure it’s free of loose particles, dirt, paint and grease. If the surface is metal, scrape around the hole with a wire brush until the metal shines, then degrease the metal with soap and water, or with alcohol or vinegar. When the metal is dry, prime it with a thin coat of plastic filling compound.

Since resin-saturated glass fabric is slippery and awkward to handle, it’s convenient to soak the fiberglass in resin, then transfer it to the repair on a sheet of clear plastic household wrap. This keeps the glass fabric from coming apart and minimizes dripping.

Because fiberglass work is messy and stray resin is extremely difficult to re move if given time to cure, use disposable containers and utensils if possible. Otherwise, clean the equipment between steps with acetone or another recommended solvent. Cover the floor and surfaces adjacent to the work area with newspaper to catch drips.

Most of the components used in fiber glass work are irritants. In fact, both the resin and the hardener are caustic, flammable and toxic. Use them only in a well ventilated area, away from any flame, and keep them away from skin and eyes. Al ways wear a respirator and goggles when you cut or sand fiberglass, since fine glass fibers will be released into the air.

A Two-sided Patch for a Plastic Laundry Tub

1. Cutting out the damage. After removing any facing or skirt from the tub, use a saber saw with a metal-cutting blade to remove damaged material. Make the hole a regular shape to simplify patching. Use a sanding block with 80-grit sandpaper to remove loose particles from the edges of the hole.

On the outside surface of the tub, feather a two-inch bevel around the hole (inset), using an electric drill with a sanding disk fitted with 80- grit paper. Cut a piece of cardboard slightly larger than the hole, cover it with plastic wrap, and the tape it to the inside of the tub so that the plastic wrap is facing the hole.

2. Cutting the patches. Cut a piece of fiberglass cloth large enough to cover the hole and the 2-inch feathered area, then cut a piece of fiberglass mat slightly smaller. Continue cutting alternate pieces of cloth and mat, each slightly smaller than the last, until the total thickness of the cut pieces equals the thickness of the tub wall. The final piece should extend about 1 inch beyond the hole on each side. Fray the ends of the glass fibers at the edge of each piece so that they can be pressed flat.

3. Saturating the fiberglass. Lay the largest piece of fiberglass cloth on a sheet of plastic wrap, mix the resin and hardener, and use a soft-bristled brush to saturate the cloth with resin. Work with a dabbing motion to avoid wrinkling the cloth. Center the largest piece of fiberglass mat on the cloth, and dab the mat with resin until it’s saturated. Continue to add alternating layers of glass cloth and mat until you have built up the thickness that you need. Pick up the plastic wrap and transfer the patch to the out side of the hole, centering it over the opening and pressing it gently into place.

111

4. Pushing out air bubbles. With the plastic wrap still in place, use a plastic squeegee to press air bubbles—which appear as white spots— out of the patch, working from the center to the edges. Let the resin cure for several minutes, then carefully peel away the plastic wrap. Allow two to five hours for the patch to cure, then re move the cardboard backing.

Use an electric drill with a sanding disk to make a shallow depression in the patch on the inside surface of the tub, feathering the edge 2 inches beyond the original hole. Cut pieces of glass mat to fill the depression, ranging from the size of the original hole to 1 inch larger on each side. Cut two pieces of glass cloth the size of the feathered area around the hole.

5. Applying the inside patch. After protecting the undamaged surface around the hole with pa per and crepe masking tape, mix a new batch of resin and paint the sanded area with it, then apply the smallest piece of mat. Saturate the mat by dabbing on more resin with a brush. Repeat this process with successive layers of mat, then with the final pieces of cloth, using the brush to force out air bubbles in each layer before applying the next. The final layer should be slightly higher than the original surface of the tub. Lay a piece of plastic wrap over the entire patch, then press out any remaining air bubbles with a squeegee, working from the center outward.

6. Trimming the patch. When the patch has partially hardened, carefully peel away the plastic wrap, then use a utility knife to cut away any loose edges or stray strands. Don’t lift the patch or otherwise di the smoothed area.

112

7. Applying the gel coat. Mix a gel coat and use a soft-bristled brush to apply an even coat over the patch. Cover the gel coat with plastic wrap and use a squeegee to press out air bubbles, smoothing gently from the center to ward the edges. Let the gel coat harden completely, then gently peel away the plastic wrap.

Lightly hand-sand the gel coat, using a fine- grit wet-or-dry paper covered with fiberglass rubbing compound. Brush on a second gel coat in the same manner as the first, allow it to cure, then polish it with a buffing wheel and rubbing com pound (Step 6).

A Supported Patch for a Hard-to-Peach Place

--Attaching backing from the front. To secure a fiberglass patch in a hole accessible from only - one side, you will need to glue a piece of card- - board to the inside surface; First use bastard-cut mill file to chamfer the edges of the hole on both sides, so that the hole is bordered by sharp... edges. Next cut a piece of cardboard to over lap the chamfered area by ½-inch on all sides.- Use cardboard flexible enough to bend through the hole but still retain its shape. Cut a hole through the center of the cardboard and push a thin bolt through, then tie a piece of string to the threads of the bolt. Apply a thin bead of quick-drying contact cement around the edge of the cardboard, on the same side as the string. Bend the cardboard slightly and push it through the hole.

Pull on the string, then use the bolt to center the cardboard behind the hole. Pull the cardboard against the inside surface so that the cement is firmly in contact with that surface (center). Slide a wood slat with a hole in it over the bolt, and tighten a nut on the bolt; these pieces will hold the cardboard in place while the adhesive is drying (bottom).

Remove the nut and the wood slat; push the bolt through the cardboard or cut it off with a bolt cutter. Apply a layer of resin-soaked glass cloth in side the hole, tucking the edges into the space between the cardboard and the chamfered edge of the wall. Allow the resin to cure, then complete the patch as shown in Steps 5-7.