Fiberglass Repair Kits: What Is in One and Which Damage It Covers

Boat Suppliers

22 September 2026

A fiberglass repair kit is worth buying when the damage needs laminate put back, not paint put over it: a crack you can flex, a hole through the skin, a soft spot in a floor, a split seam on a composite hull. The test of a real kit is the contents list: laminating resin in a can, not a tube; catalyst or hardener measured for that can; cloth or 1708 for strength and mat for buildup; fumed silica for fairing putty; and the sandpaper, cups, brushes and spreader. Here is what is in each of ours, which damage each one covers, and where a kit stops and a full materials order starts.

What is in a fiberglass repair kit, kit by kit

Kit	Resin	Catalyst or hardener	Reinforcement	Finish	Covers
Fiberglass Repair Kit (DIY)	1 qt Silmar 249 polyester laminating resin	2 oz MEKP	1 yd 6 oz cloth, 1 yd 1.5 oz mat, 38 in	Fumed silica putty, sand to 2000 grit	Cracks and holes to about a hand's width
Boat Fiberglass Repair Kit	1 gal Silmar 249	MEKP for the gallon	3 yd 1708 biaxial 50 in, 3 yd 1.5 oz mat 38 in, laminating roller	Fumed silica putty	Hull holes, soft decks, stringer tabs, transom skins
Bathtub and Shower Kit	1 pt Silmar 249	2 oz MEKP	1 yd 1.5 oz mat	1 pt white gelcoat with wax	Cracked or flexing tubs, shower pans, surrounds
RV and Camper Kit	1 qt Silmar 249	2 oz MEKP	1 yd 6 oz cloth, 1 yd 1.5 oz mat	1 pt white gelcoat with wax	End caps, sidewalls, Filon delamination, wet baths
Kayak and Canoe Kit	12 oz epoxy, 2:1 by volume	4 oz hardener included	1 yd 6 oz cloth, 2 yd 6 in 1708 tape	Fumed silica putty	Composite hull cracks, punctures, seams, stems
Surfboard Ding Kit	1 pt Silmar 249A water clear	MEKP	1 yd 4 oz E-glass, 30 in	Sand and gloss coat	Dings and cracks on polyester (PU) boards

Every polyester kit runs on the same catalyst math: 1.5 percent MEKP at 65 to 85°F (18 to 29°C), which is 1.8 mL (about 1/3 tsp) for a 4 oz mix and 14 mL (about 3 tsp) for a full quart, with 15 to 20 minutes of working time. Above 85°F drop to 1 percent; at 60 to 65°F go to 2 percent; below 60°F wait for a warmer day. The MEKP catalyst calculator does the arithmetic for odd batch sizes. Nitrile gloves, eye protection and a fitted P100 respirator with organic vapor cartridges cover the styrene and the grinding dust.

Cracks and gouges that do not go through

A stress crack you can open with a thumbnail, a gouge from a trailer bunk, a chipped corner: grind the damage to a shallow dish with 80 grit, well past the ends of the crack, then lay a piece of 1.5 oz mat into wet resin followed by a cap of 6 oz cloth, fill proud with fumed silica putty, and sand fair from 120 through the grits. That is the Fiberglass Repair Kit - Complete DIY Kit with Resin, Cloth & Mat, and a quart of resin covers several of these. The 21 sheets of wet-dry paper from 120 to 2000 grit let you polish the patch back instead of leaving a scar. It does not include gelcoat; if the surface is a white finish you want to hide, use the RV kit or the tub kit, which do.

A hole through the hull or deck

A through-hole is a structural repair: 12:1 bevel around the hole, a backing plate from the far side, then plies of glass stepped into the dish until you match the original thickness. Up to about a hand's width on a small boat, the quart DIY kit handles it with mat first and cloth to cap. Bigger than that, or anywhere the hull carries load, the Boat Fiberglass Repair Kit - Professional Grade with Gallon Resin & Roller is the one: a gallon of Silmar 249, 3 yd of 1708 biaxial at 50 in, 3 yd of 1.5 oz mat, and a serrated laminating roller, which is the tool that separates a solid laminate from one full of air. Mix no more than you can roll out in 15 minutes; a gallon catalyzed at once boils in the bucket. It covers holes, soft decks, cracked stringer tabs and transom skins above or below the waterline. What it does not cover is a rotten transom core, which is a rebuild with plywood or composite core and epoxy, not a patch.

A soft or cracked floor in a tub, shower or wet bath

Tub floors crack because they flex, and a tube of filler cracks again in a month because the flexing was never fixed. The Bathtub & Shower Fiberglass Repair Kit with White Gelcoat puts a ply of 1.5 oz mat and a pint of Silmar 249 under the crack to stiffen it, fumed silica putty to fair it, and a pint of white gelcoat with wax on top so the last coat cures tack-free and wet-sands to gloss. Two coats of gelcoat about a business card thick, 30 to 45 minutes apart; the gelcoat calculator sizes the batch. It works on fiberglass and gelcoat tubs, shower pans and surrounds, and on acrylic-over-fiberglass after a hidden-spot test. It does not bond to cast iron, porcelain-over-steel, one-piece ABS or PVC liners, or polyethylene. A bathroom is a small closed room, so ventilate hard and use sealed splash goggles around MEKP.

RV and camper skins, end caps and Filon

Fiberglass RV bodies fail at the corners: cracked end caps, a holed sidewall, Filon panel delaminating from the substrate, wheel well trim torn by a blowout. The RV & Camper Fiberglass Repair Kit with White Gelcoat is the DIY kit plus a pint of white gelcoat: a quart of Silmar 249, 2 oz MEKP, a yard each of 6 oz cloth and 1.5 oz mat, fumed silica, and the full grit run. Grind, mat, cloth, fair, two coats of gelcoat, wet-sand from 320. It is for fiberglass and Filon skins and interior wet-bath glass. It is not for aluminum-skinned campers, EPDM or TPO rubber roofs, or polyethylene tanks; polyester resin does not bond to any of them.

Composite kayak and canoe hulls

A hull repair on a cured composite is a secondary bond, and epoxy grips cured laminate far better than polyester does, which is why the Kayak & Canoe Repair Kit - Epoxy & Fiberglass for Composite Hulls is epoxy: 8 oz resin plus 4 oz hardener at 2:1 by volume, a yard of 6 oz cloth for patches, 2 yd of 6 in 1708 tape for seams, stems and long cracks, and fumed silica for the edges. Measure the 2:1 in the graduated cups; off-ratio epoxy never fully cures. It covers fiberglass, Kevlar and carbon hulls: cracks, punctures, split seams and worn stems. It does not cover rotomolded polyethylene, which is most sit-on-tops; nothing bonds reliably to polyethylene and the kit will peel off it.

Surfboard dings

The Surfboard Ding Repair Kit - Silmar 249 Pint with MEKP + 4oz Cloth is glass-shop resin: a pint of Silmar 249A, the UV-stabilized water-clear polyester surfboard laminating resin, MEKP, a yard of 4 oz E-glass at 30 in, and cups and sticks. Catalyze at about 1 percent at 77°F (25°C), 10 cc per quart, for an 11 to 19 minute gel; it cures nearly water clear over foam and glass. A pint is a season of dings. Silmar 249A is unwaxed laminating resin, so the sanding coat needs surfacing wax added to cure tack-free. It is for polyester boards over polyurethane foam only; polyester resin dissolves EPS foam, so an epoxy board gets epoxy.

Which kit for which damage

Crack, chip or small hole on a boat, tank, fender or mold: the quart DIY kit. Anything structural on a boat bigger than a hand, or more than one repair: the gallon boat kit with 1708. Tub or shower pan: the bathtub kit. RV body: the RV kit. Composite paddle craft: the epoxy kayak kit. Polyester surfboard: the Silmar 249A ding kit. Nothing in a kit fixes polyethylene, aluminum, or a rotten transom core, and no kit replaces the grinder, the acetone, and the respirator you supply.

Frequently asked questions

How big a hole can a fiberglass repair kit fix?

The quart DIY kit, with 1 yd of 6 oz cloth and 1 yd of 1.5 oz mat, handles a hole up to about a hand's width once you bevel it 12:1 and back it. Past that, or anywhere the hull carries load, use the gallon boat kit with 3 yd of 1708 biaxial and the roller, and match the original skin thickness at about 0.044 in per ply of 1708.

Will a fiberglass repair kit work on a plastic kayak?

No. Rotomolded polyethylene, which is most sit-on-top kayaks and many canoes, does not bond to polyester or epoxy; the patch peels off in a season. The kayak and canoe kit is for composite hulls only: fiberglass, Kevlar and carbon. For polyethylene, the repair is plastic welding with matching polyethylene rod, not a fiberglass patch.

How much MEKP do I add to the resin in the kit?

1.5 percent at 65 to 85°F: 1.8 mL for a 4 oz mix, 3.6 mL for 8 oz, 14 mL for a full quart, about 10 drops per ounce as a field rule. Above 85°F drop to 1 percent, at 60 to 65°F use 2 percent, and below 60°F wait. Mix only what you can lay up in 15 minutes. The surfboard kit's Silmar 249A runs about 1 percent at 77°F.

Can I use a fiberglass repair kit on a bathtub?

Yes, on a fiberglass or gelcoat tub, shower pan or surround, and on acrylic-over-fiberglass after a hidden-spot test. The bathtub kit adds a pint of white gelcoat with wax so the repair finishes gloss white and sands from 320 to 2000 grit. It will not bond to cast iron, porcelain-over-steel, ABS or PVC liners. Fix the flexing floor with mat first or the crack comes back.

Does the surfboard ding kit work on an epoxy or EPS board?

No. The kit is Silmar 249A polyester, which dissolves EPS foam on contact. It is for polyester boards over polyurethane foam, which is most traditional shortboards and longboards. An EPS or epoxy board needs an epoxy ding repair. If you are not sure what the board is, a drop of acetone on the foam in the ding will melt EPS and leave PU alone.