Repairing and painting fibreglass intimidates many boat owners. While the process is involved, if you follow the steps closely you can make good-looking repairs. Just renewing the gelcoat will restore the original shine to your boat and make it look like new. Because fibreglass repair involves hazardous chemicals, you need to use proper safety equipment and work in a well-ventilated indoor area. You'll need shelter for the boat while repairs set and cure, so don't try large-scale repairs outdoors.
- Skill level:
- Moderately Challenging
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Things you need
- Epoxy fibreglass resin
- Fibreglass fabric
- Mesh repair backing
- Sander and sandpaper, 60, 150 grit and 200, 400 wet/dry sandpaper, fine steel wool
- 1-, 2- and 3-inch brushes
- Plastic or metal flat-edged spreading tool
- Latex or rubber gloves and masks
- Disposable mixing bucket
- Stirring stick
- Trim knife
- Duct tape
- Power buffer and pads
- Gelcoat and catalyst
- Gelcoat pigment
- Brushes, bristle and foam
- Soft cloths
- Rubbing compound
- Fibreglass primer
- Two-part epoxy fibreglass paint
- Paint roller
Clean the area around the damaged fibreglass with soap and water and then wipe it down with a rag dampened with acetone. Wear gloves while working with acetone.
Trim the edges of a hole with a knife to make a smooth edge. Glue a piece of mesh and stiff cardboard behind the hole to support the patch. You can scrape off the cardboard afterward. Cut a piece of fibreglass to fit the hole. Make it slightly larger to allow for 1/8 inch or so for shrinkage. If repairing a crack, work resin into the crack at this point, then cover with a layer of fibreglass cloth.
Mix up a small batch of resin and hardener in a small container. Wet the mesh, then lay the fibreglass patch in place. Paint over the fibreglass material with resin until it becomes clear. Overlap the edges with resin. Let the patch set up before applying the next layer.
Mix more resin and hardener, paint over the repaired spot and lay more fibreglass cloth over the top, overlapping onto the surrounding hull three inches on each side. Spread the mixture with the spreader to remove all bubbles, until the cloth turns clear. Feather the resin into the hull around the patch.
Tap the surface of the cured patch with a quarter. Listen for a hollow sound that indicates the fibreglass failed to bond with the hull. Any unbonded section should be removed, sanded and cleaned, and redone.
Sand the patch to remove any rough or sharp edges. Sand the entire hull with fine sandpaper and finish with lightweight steel wool. Allow the fibreglass patch to cure, if possible in the sun. You can finish with a spray on epoxy clearcoat, but you should really redo the gelcoat after a repair.
Clean the hull with soap and water and wipe it down with acetone to remove any wax, grease or oil. Wipe the boat down again with styrene to activate the existing gelcoat and improve the new gelcoat's adherence.
Mix up 4 cups of gelcoat at a time and add the amount of colour pigment recommended by the manufacturer to achieve the colour you want. Your gelcoat and fibreglass supplier will carry pigment that you mix in specified proportions to match colour swatches he can show you in the store. Be sure to mix the same amount of gelcoat and pigment to get a uniform colour. Mix enough gelcoat and catalyst to cover the hull once if you are spraying it on. If brushing on the gelcoat, only make 4 cups at a time so it doesn't set up in the cup before you get it onto the boat.
Thin the gelcoat to the consistency recommended for your sprayer. Use a gelcoat-specific thinner or additive. Use gelcoat full strength if you are brushing it. A thicker application resists brush marks. Thicker gelcoat applications are best.
Cure the first gelcoat for four hours until the surface is tacky to touch. Apply the next coat and wait another four hours. Apply the third and final coat and allow it to cure and set overnight. If spraying, you may want to add another coat or two according to your preference. If you do, don't let the third coat dry hard.
Sand the hull with wet/dry 1000-grit sandpaper to give it a dull lustre. Load a soft cloth with fine rubbing compound and spread it over the surface. Let it set and then buff the hull in wide circular strokes. Start with heavy pressure, then get gradually lighter till the hull shines. Then lay several coats of boat wax over the new gelcoat to protect it from damage and scratching.
Sand off all wax and rough the surface of the gelcoat if you plan to paint the fibreglass instead of restoring the gelcoat. The paint won't adhere to a slick gelcoat. The sanding gives the surface some grab to hold the paint.
Remove all detachable metal and plastic parts. If the paint bridges to a part that can be moved or disturbed, it will create a bridge that can crack and peel the paint. Fill any holes or scratches with epoxy filler.
Apply one thin coat of primer with a paint roller and allow to cure for two hours. Mix 2-part epoxy fibreglass paint and apply with a roller or spray it on with spray paint equipment. Allow to sit till dry to the touch, then apply a second coat with a foam brush or sprayer to prevent set in brush strokes.
Dry and cure the boat for two days before reattaching metal and plastic hardware to the boat.
Clean your painting tools with an epoxy solvent or thinner before the paint has a chance to set.
Tips and warnings
- Apply thick gelcoat layers to give you a deep high gloss.
- Press resin into fibreglass cloth till all the bubbles are gone and the cloth is completely clear. White streaks in resin-covered fibreglass cloth show it still has air bubbles in it.
- Be careful not to use too much hardener or the resin will set too quickly before you can work with it.
- Don't thin the gelcoat with acetone or common paint thinners or it will ruin the finish.
- Be sure to use gloves and eye protection when working with fibreglass chemicals and solvents.
- Clean your brushes with acetone and shake dry before using again.
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