Applying A New Gelcoat: Revitalizing Your Boat's Exterior

Applying a new gelcoat to a boat is a common maintenance task for boat owners. Gelcoat is a resin used to protect the underlying fibreglass of a boat from water intrusion and UV damage. It is the outermost layer of a fibreglass hull and gives the boat its colour and shine. Over time, the gelcoat can become dull and chalky, so it is important to know how to restore it. This involves cleaning the surface, preparing the damaged area, mixing and applying the gelcoat, and finishing the repair. The process requires patience, attention to detail, and a methodical approach.

Prepare the damaged area

Before applying gelcoat, it is important to prepare the damaged area properly. This includes cleaning the surface and removing any loose or damaged material. Identify each crack, chip, scratch, damaged or worn-out surface, and mark them using masking tape or painter's tape. Cover and protect parts of the boat that will not be worked on.

If the damage is deep, it may be necessary to apply a fiberglass patch before applying the gelcoat. Remove rails, cleats, louvers, snaps, striping tape, etc. Duct tape off adjacent gunwale moulding and deck fittings that cannot be removed. Remove seals from the edges of parts or fittings when doing a repair around that part or fitting. Take steps to cover and protect the rest of the boat before starting. When working on the deck or cabin, tarp off the adjacent areas.

The next step is to sand the damaged area. Sand the surface to create a mechanical bond with the gel coat. Start by sanding the surface with 150-grit sandpaper. Heavier fast-cut grits (40/80/100) are used to feather sand and ground out a routed area before filling. They are also used for the first sanding of gouges, dock dings, scratches, and blisters. When sanding areas that have been filled with putty, use 40 or 80-grit sandpaper, depending on the size of the repair. Once the fill area is level or contoured to the desired shape, sand with 100-grit paper to remove the coarse scratches from the previous sanding. Also, feather the surrounding area of the gel coat repair with 220/330-grit sandpaper. At this point, the repair is ready to be prepped and sprayed/brushed with gelcoat.

It is important to feather the edges of the damaged area into the surrounding surface to ensure a smooth and seamless repair. The area should be sanded to create a rough surface for the gelcoat to adhere to. After sanding, clean the surface with acetone, as it does not leave residue and evaporates easily. Dust and dirt particles are your enemy here, so make sure you clean the surface thoroughly.

Mix and apply the gelcoat

Gelcoat comes in two forms: brushable and sprayable. The choice between the two depends on the size and nature of the repair. For smaller repairs, brushable gelcoat is often sufficient and easier to manage.

Mixing Gelcoat

Gelcoat needs to be mixed with a catalyst (usually MEKP) to initiate the hardening process. The ratio is critical and should be followed according to the manufacturer’s instructions. Typically, it’s around 1–2% of the catalyst by volume. The amount of catalyst added will also determine how long the gelcoat will take to harden, so be sure to mix only slightly more than you need.

Applying Gelcoat

Before applying the gelcoat, ensure the repair area and all tools are clean. Use acetone for this, and be sure to clean the surface again if it has been sitting for some time. Dust and dirt particles are your enemy here, so make sure you clean the surface thoroughly.

Apply the gelcoat in thin, even layers. Start with a thin coat to cover the repair area and allow it to cure slightly before adding subsequent layers. It’s important to apply gelcoat in different directions with each layer to avoid creating air pockets and to ensure a uniform thickness.

If you are using a brush, choose a good pure (natural) resin-resistant brush with tapered ends. Avoid brushes that are either too stiff or too soft. For most work, a 3″ or 4″ wide brush will suffice. If there is a trim colour, you should have a narrow trim brush on hand. If you are using a roller, be sure to use a 1⁄4" solvent-resistant nap. Do not use a foam roller as these tend to leave bubbles.

If you are using a spray gun, it is recommended to use one designed specifically for applying gelcoat and resins, such as the professional-grade spray guns offered by FGCI and ES Manufacturing. You will also need to thin the gelcoat so that it can run through the spray gun. There are two thinners recommended by manufacturers for this: Patch Booster and Duratec.

Curing Gelcoat

Gelcoat requires a certain temperature to cure properly, usually above 60°F. The curing process can be accelerated with mild heat, but it’s important not to overheat the area as it can cause the gelcoat to crack or discolour. Once the gelcoat has cured, the repair area will likely need to be sanded to achieve a smooth, flush finish with the surrounding surface.

Cure the gelcoat

Curing the gelcoat is a crucial step in the process of applying a new gelcoat to a boat. Here are some detailed instructions to guide you through the curing process:

Firstly, it is important to understand that gelcoat requires a specific temperature range to cure properly. Ideally, the curing process should be carried out at temperatures above 60°F. Working in a well-ventilated area or choosing an overcast day is recommended, as direct sunlight can affect the curing process. Mild heat can be applied to accelerate curing, but be cautious not to overheat the area, as this can cause the gelcoat to crack or discolour.

The curing process itself involves allowing the gelcoat to harden. After applying the gelcoat in thin, even layers, let each layer cure slightly before adding the next. The number of layers required depends on the product you are using. Typically, 4-5 layers are applied, with a total thickness of 20-25 mils. A gelcoat thickness gauge can help ensure the proper thickness is achieved.

It is important to follow the manufacturer's instructions for curing times. Once the final layer has been applied, you will need to wait about 20 minutes for the gelcoat to "tack up" before proceeding with the next steps. The total curing time will depend on various factors, including the amount of catalyst used, room temperature, humidity, and air movement. Refer to the catalyst chart provided by the manufacturer for specific curing times.

During the curing process, it is essential to protect the gelcoat from dust and dirt particles, as these can affect the final finish. Additionally, ensure that you are wearing protective gear, including gloves and a mask, throughout the curing process.

Once the gelcoat has fully cured, you can proceed with the finishing steps, such as sanding, polishing, and waxing, to achieve a smooth, glossy finish that blends seamlessly with the rest of the boat's surface.

Finish the repair

Once the gel coat has been applied, the repair process is not yet complete. There are several additional steps to finishing the repair and ensuring a smooth, glossy, and durable surface.

Firstly, it is important to allow the gel coat to cure completely. The curing process requires a certain temperature, usually above 60°F, and can be accelerated with mild heat. However, it is crucial not to overheat the area, as this can cause the gel coat to crack or discolour.

Once the gel coat has fully cured, the repair area will likely need to be sanded to achieve a smooth, flush finish with the surrounding surface. Start with coarse-grit sandpaper and gradually move to finer grits. This process will help to remove any imperfections and create a uniform surface.

After sanding, it is important to polish the repair area to restore its shine and blend it with the rest of the boat's surface. Polishing will also help to remove any fine scratches or swirls that may have been created during the sanding process.

Finally, waxing is essential to protect the gel coat and enhance its finish. Waxing provides a protective layer that shields the gel coat from UV rays, water impurities, and minerals, which can cause damage over time. It also adds depth, shine, and luster to the surface.

By following these finishing steps, you can ensure that your gel coat repair is long-lasting and aesthetically pleasing, contributing to the overall longevity and beauty of your boat.

Clean the boat before applying gelcoat

Before applying a new gelcoat to your boat, it is important to clean the surface thoroughly. Here is a step-by-step guide to ensure a proper cleaning process:

Step 1: Wash the Boat

Start by mixing a solution of mild detergent and warm water. Use a sponge to wash the entire surface of the boat with this solution. This will help remove any dirt, grime, or water-soluble stains. Be sure to wear rubber gloves to protect your hands.

Step 2: Remove Stains

If there are any stubborn stains, such as mildew, bird droppings, or waterline scum, you can add a cup of household bleach to your cleaning solution. For more difficult stains, you may need to use a concentrated cleaner specifically formulated for fiberglass. Apply these products directly to the stains and then rinse thoroughly.

Step 3: Degrease the Gelcoat

To ensure that your new gelcoat adheres properly, it is crucial to remove any oil or grease from the surface. Wipe down the entire surface with a rag soaked in methyl ethyl ketone (MEK) or acetone. These solvents will effectively remove any oily contaminants. Be sure to wear thick rubber gloves and work in a well-ventilated area to protect yourself from the noxious fumes.

Step 4: Rinse and Dry

Once you have completed the cleaning and degreasing process, thoroughly rinse the boat with clean water. Then, allow the surface to dry completely before proceeding to the next step.

Step 5: Inspect and Repair

Before applying the new gelcoat, take the time to inspect the surface for any scratches, dings, or cracks. It is important to repair any damage to ensure a smooth and even finish. You can use a gelcoat repair kit or seek professional assistance for more extensive damage.

Remember, a proper cleaning process is essential to ensure the new gelcoat adheres correctly and provides a long-lasting finish. Take your time and follow these steps to achieve the best results.

Frequently asked questions