The Ultimate Guide To Refreshing Your Boat's Bottom Paint

Replacing the bottom paint on a boat is a messy and tedious job, but it is necessary to keep the hull free of marine growth and maintain the boat's performance and efficiency. Bottom paint, or antifouling paint, helps prevent the build-up of barnacles, zebra mussels, weeds, and slime on the hull, which can increase fuel costs and reduce the boat's speed and manoeuvrability. This article will provide a step-by-step guide on how to replace bottom paint on a boat, covering topics such as choosing the right paint, preparing the surface, and applying the new paint.

Choosing the right bottom paint

Type of Bottom Paint

The two main types of bottom paint are hard bottom paint and ablative bottom paint. Hard bottom paint is a durable, modified epoxy paint with a higher ratio of pesticides, typically copper. It is suitable for boats that remain stationary or have minimal movement in the water. Ablative bottom paint, also known as self-polishing bottom paint, is softer and allows the coating to wear off at a controlled rate as the boat moves in the water, exposing a fresh layer of paint with active protection. Ablative paint is ideal for boats that are frequently trailered or taken in and out of the water.

Boat Usage and Storage

Consider how you use your boat and where it is stored. If your boat remains in the water year-round, a hard, high-copper-content modified epoxy paint may be the best option to prevent growth. If your boat is frequently used and stored in varying conditions, a copolymer ablative paint might be a better choice as it can be applied in the fall and launched in the spring.

Compatibility with Existing Paint

If you are repainting your boat, it is crucial to ensure that the new paint is compatible with the existing paint. Refer to compatibility charts provided by manufacturers to determine which paints can be applied over others. In general, softer paints can be applied over harder paints, but not vice versa. Vinyl paints, for example, can only be applied over existing vinyl paint.

Boat Material

The type of bottom paint you choose should also depend on the material of your boat's hull. For aluminum hulls or outdrives, select a paint that does not contain cuprous oxide to avoid galvanic corrosion. Instead, opt for paints that contain zinc, cuprous thiocyanate, or a non-metallic agent like ECONEA.

Environmental Regulations

Be mindful of environmental regulations and choose paints that comply with the guidelines in your area. For example, restrictions on copper-based paints have led to the development of pharmaceutical alternatives, such as ECONEA, a metal-free antifouling agent.

Aesthetics

While the primary purpose of bottom paint is protection, you can also consider the colour options available. Bright colours can be achieved with paints containing white copper (cuprous thiocyanate), zinc, or ECONEA. White copper produces the brightest colours and whitest whites.

Preparing the boat's surface

Assess the Condition of the Boat's Surface:

Start by evaluating the type and amount of surface preparation needed. If the previous bottom paint is in good condition and not too thick, you may not need to strip or sand it down completely. However, if the old paint is unknown or in poor shape, you will need to remove it using a suitable method like soda blasting, chemical stripping, or mechanical sanding. Consider factors such as the number of layers, compatibility with new paint, and the presence of any damage to the hull or barrier coat.

Choose a Suitable Removal Method:

Select an appropriate removal method based on the boat's surface material and the condition of the old paint. For fiberglass boats, soda blasting is recommended over sandblasting as it doesn't pit the underlying gelcoat surface. Chemical stripping offers better control over environmental hazards and is relatively simple, but ensure you use a marine stripper without methylene chloride and follow the manufacturer's instructions. Mechanical sanding is the least expensive option but is messy and labour-intensive.

Prepare the Work Area:

Before starting the removal process, cover the ground under the boat with a disposable tarp or plastic drop cloth to catch the falling paint and stripper. Tent" the boat's bottom by hanging plastic sheets from just above the waterline to contain the dust and prevent it from escaping. Ensure you have the necessary safety gear, including gloves, safety glasses, a disposable jumpsuit, and a high-quality dust mask or respirator.

Remove Old Paint:

Apply the chosen stripper according to the manufacturer's instructions. Cover it with a plastic barrier if needed. Wait for the recommended amount of time, then use a putty knife or scraper to begin scraping off the softened paint. Be cautious not to gouge the gelcoat. Place a waste bag directly under the work area to catch the falling paint and stripper, replacing the bag as it fills up. You may need to repeat the process for a thorough removal, especially if there are multiple layers of paint.

Sand the Surface:

After removing the old paint, use 80-grit sandpaper or a disc/orbital sander to sand the entire bottom surface. This step helps create a smooth surface and remove any remaining high or uneven spots. Work carefully to avoid sanding through a protective barrier coat or damaging the gelcoat. Spend extra time on areas that need more attention. Remember to cover your exposed skin, shield your eyes, and wear a respirator to protect yourself from toxic dust and fumes.

Clean and Prepare for Painting:

Once sanding is complete, wipe down the surface with a solvent recommended by the bottom paint manufacturer to remove any residual dust, grease, or dirt. If necessary, apply a tie coat primer to ensure optimum paint adhesion. Mask around transducers, prop shaft struts, through-hulls, and any other metal parts to prevent galvanic corrosion. Choose a solvent-resistant masking tape designed for lengthy bottom painting jobs, such as 3M's 2090 Scotch Blue Painter's Tape.

Applying the paint

Before you start, pay attention to the dry time between coats and the recommended number of coats, as indicated by the manufacturer. Also, be sure to check if there are any maximum limits on the amount of time the boat can remain out of the water after bottom painting and prior to launch. For example, copolymer ablative paints dry faster, which means their overcoating times are shorter. They also have longer or unlimited launch windows.

Once you know the characteristics of your coating, and you're ready to paint, here are some tips to expedite the process.

To make it easier to get as much copper off the bottom of the can and into the paint, take it to a paint shop and have it shaken first. This will make it easier for you to stir the paint thoroughly.

Do not thin bottom paint or it will lose its antifouling effectiveness.

Use a solvent-resistant brush or 3/8" nap roller to apply paint thickly, without drips, onto the hull. Keep the thickness even, and paint from one end of the boat to the other.

Because ablative paints wear away faster in areas of greatest turbulence, apply extra coats to these places such as the leading edge of the keel and the bow.

Remember to paint underwater metals such as transducers with a copper-free antifouling paint that will not cause galvanic corrosion.

Recoat based on the manufacturer's directions for overcoat times. Ensure that the weather conditions are optimal for recoating.

As you choose your paint and schedule your haulout, consider how much drying time you should allow between coats and how long the new paint can be left out of the water. Drying time between coats can vary from ten minutes for Teflon-based VC-17m to a 16-hour (or overnight) minimum for Trilux 33. For proper planning, it is important to check the manufacturer's recommendation in advance, both for the drying time and for the recommended number of coats. For example, West Marine's most popular modified epoxy paint, BottomShield, has a drying time of four to six hours, and a maximum of 60 days before relaunch. Copolymer ablative paints have minimum overcoating times, and no maximum out-of-water time. Copolymers are a good choice for trailerable boats that need antifouling protection while in the water, but also spend time on the hard. Recoat following manufacturer recommendations regarding overcoating times, which can vary based on temperature.

Once the paint is dry, remove all masking tape and clean up the area. Be sure to properly dispose of the old paint and any solvents used for clean up. If your boat is on jack stands or a cradle, painting under pads can be tricky. Depending on the drying time for the paint, you may be able to paint under the pads or bunks when the boat is on the Travel-lift for launch. Check with your yard. Some paints will dry adequately in the short time it's "in the air".

Drying and recoating

Before you begin the drying process, it is important to choose the right type of antifouling paint for your boat. There are two main types of antifouling bottom paint: hard and ablative. Hard bottom paint dries hard and stays that way, but it needs to be removed and reapplied seasonally. Ablative paint, on the other hand, wears away gradually as the boat moves through the water, exposing fresh layers of biocide. This type of paint can be single or multi-seasonal.

When it comes to drying, the timing and environmental conditions play a crucial role. Manufacturers recommend applying boat paint when temperatures are between 50°F and 85°F, and the humidity is below 65%. If you are using a copolymer ablative paint, which dries faster, you will have a shorter window for drying and recoating. In contrast, hard bottom paints have a longer drying time, usually around four to six hours, and can remain out of the water for up to 60 days before relaunch.

After applying the paint, allow it to dry according to the manufacturer's instructions. This can vary from as little as ten minutes for Teflon-based paints to 16 hours or overnight for other types. Always refer to the specific guidelines for your chosen paint. During this time, it is important to ensure that the area remains well-ventilated and free from any debris that may stick to the wet paint.

Once the paint has dried, it is now time for recoating. Start by inspecting the surface to ensure that it is smooth and free from any debris or imperfections. If necessary, lightly sand any uneven areas with fine-grit sandpaper. Next, refer to the manufacturer's instructions for the recommended number of coats and the time required between coats. This can vary depending on the type of paint and the protection you need. For ablative paints, apply extra coats in areas of high turbulence, such as the bow and the leading edge of the keel.

When recoating, use a solvent-resistant brush or a 3/8" nap roller to apply the paint evenly and thickly onto the hull. Ensure that you follow the manufacturer's guidelines for the recommended thickness and number of coats. Allow each coat to dry completely before applying the next one. Finally, remember to paint all underwater metals with a copper-free antifouling paint to prevent galvanic corrosion.

Cleanup and disposal

• Contain the Work Area: Before starting the paint removal process, make sure to contain the work area to prevent the spread of toxic dust and chemicals. Use a disposable tarp or plastic drop cloth to cover the ground under the boat. For soda blasting or sanding, hang plastic sheets from just above the waterline to the ground, ensuring they reach all the way around the boat. This will help capture the dust and debris generated during the removal process.
• Personal Protective Equipment: It is crucial to wear appropriate personal protective equipment (PPE) during the cleanup and disposal process. This includes items such as gloves, safety glasses, a disposable jumpsuit, and a high-quality dust mask or respirator. When working with chemicals or heat guns, upgrade to an organic vapour respirator for added protection.
• Collect and Contain Debris: As you scrape or sand off the old paint, use a waste bag or container to collect the falling paint chips and debris. Move and replace the bag as it fills up to minimise the mess and facilitate easy disposal.
• Separate Hazardous Materials: Depending on local regulations, you may need to separate the removed paint from the removal medium (e.g., baking soda or chemical stripper). This process typically requires specialised equipment from a company that specialises in hazardous waste disposal. Fees for hazardous waste disposal can vary, so be sure to contact your local waste management company for specific instructions and pricing.
• Wash the Hull: After removing the old paint, thoroughly wash the hull to remove any remaining residue. Be cautious when washing, as the runoff may contain toxic chemicals. Use a felt-like carpet or an absorbent material to capture the runoff and prevent environmental contamination.
• Dispose of Solvents and Paints: Properly dispose of any used solvents, paint cans, and other hazardous materials according to local regulations. Do not pour them down the drain or into natural water bodies. Contact your local waste management company or recycling centre for guidance on how to safely dispose of these materials.
• Clean Tools and Equipment: Clean all tools and equipment used during the paint removal process. This includes brushes, rollers, scrapers, and sanding discs. Dispose of or recycle any single-use items, such as disposable jumpsuits, gloves, and masks, in accordance with local regulations.
• Ventilate the Work Area: Ensure proper ventilation in the work area, especially if you have used chemical strippers or other toxic chemicals. Open doors and windows, and use fans to circulate fresh air and remove any lingering fumes or odours.
• Follow Local Regulations: Stay informed about local laws and regulations regarding the disposal of hazardous waste and toxic chemicals. Adhere to any specific guidelines or requirements for the disposal of paint chips, solvents, and other materials used in the bottom paint removal process.
• Seek Professional Help: If you are unsure about the proper disposal methods or feel overwhelmed by the cleanup process, consider hiring a professional boat maintenance company or environmental cleanup service. They will have the expertise and equipment to handle the disposal of hazardous materials safely and in compliance with local regulations.

Remember, the key priorities during cleanup and disposal are safety, environmental protection, and compliance with local regulations. Take the necessary time and precautions to ensure a thorough and responsible job.

Frequently asked questions