The Complete Guide to Bottom Painting Your Boat

You can enjoy your boat for many more years with a proper maintenance and care plan. We’ll talk about one of the most important aspects of boat maintenance: bottom painting.

Bottom painting is an important preventive maintenance procedure that will help keep marine growth off the boat’s hull. Bottom paint is not usually included in the manufacture of most boats, so you will want to include this on your list of boat maintenance. You should apply a few coats to your bottom paint if you keep your boat in the water or use it regularly.

A protected, clean hull will offer speed, safety, and efficiency. However, a dirty bottom can cause you to slow down, make it difficult to maneuver, and cost you more money at the pump. Our complete guide will teach you how to paint the bottom of a boat.

Conditions for Bottom Paint

You should bottom paint your boat every year or whenever necessary, particularly if it is used frequently or stored in water. If you don’t use your boat as often or if it is stored on land, you may be able skip a few years. Each year, check the bottom of the hull to see if it requires a fresh coat.

Consider the weather conditions and the specific instructions for applying the paint when planning to bottom-paint your boat. Bottom painting can take up to a week, depending on the size of your boat, the paint type you choose and the conditions you paint it in.

Weather

You will get the best results if you paint your bottom on a sunny day. Three important factors are temperature, relative humidity and dew point.

Check the manufacturer’s specs before painting your bottom. To ensure a smooth paint application and a faster drying time, choose a day that is warm, dry and without excessive humidity.

Avoid painting when the relative humidity or dew point is high. Dew point is the measure of how much water vapor is in the air. Relative humidty is the difference between the amount of water vapour in the air and the maximum that the air can contain at a certain temperature. Dew points drop when relative humidity decreases, and vice-versa. Wait until all the dew has evaporated before you bottom paint.

We recommend that you start painting the next morning, after the dew-formation window has closed. Paint should not be painted in direct sunlight as it can dry the paint too fast.

Paint-Specific Applications Windows

Your choice of antifouling can also influence the timing of your project. According to the manufacturer’s specification, the boat must be put into the water after the painting process to activate its antifouling qualities.

Water-activated paints can have a generous timeframe for launching, whereas others need to be launched relatively quickly. Consult your paint manufacturer to find out the exact launch time.

Choose a bottom paint

Biocide is used in antifouling paints to stop marine life from sticking to your boat’s bottom. This includes mussels, barnacles and algae. Antifoul paint comes in two types: soft antifoul, and hard antifoul. Each paint releases biocide in a different way. The speed of your boat will determine which paint you should use.

Consider how you plan to use your boat, and what type of paint has been applied previously to the bottom. This will help to eliminate compatibility issues. You can apply softer paints over harder paints but not the other way around. Vinyl paints should only be applied over vinyl paints, with some exceptions.

Refer to a compatibility table or consult a paint expert to make sure you are using the correct products for your surface.

Soft Antifouling Coating

Self-eroding or self-polishing antifoul is another name for soft antifouling. It works by slowly wearing away as the boat moves in water, so that a new layer of biocide will always be present on the bottom.

Soft antifoul works best on boats that do not reach high speeds. High speeds can cause the antifoul to erode faster. Consult the paint manufacturer to find out what speed limits apply. Regularly operate boats painted with antifouling soft paint to maintain the biocide.

Hard Antifouling Coating

The hard antifouling, also called scrubbable, burnishable, or antifouling, paint works by releasing biocides continuously. It doesn’t wear away like soft antifoul.

Hard antifoul works well for boats with high speeds and moorings which dry out. It is ideal for racing boats, as you can burnish or scrub it to create a smooth and low-drag surface.

Gathering Supplies

It is a large project that involves several steps. Refer to the instructions of the paint manufacturer to find out how many square feet a single paint coat will cover. This way, you can know exactly how much paint to purchase. Prices for bottom paint vary depending on your location and availability. Bottom paint is regulated differently in different states, and this can affect the paints available to you.

As you paint, you’ll need these additional supplies:

• Paint thinners and solvents
• Paint tray and Liner
• Roller and frame with a solvent-resistant roller
• Painter’s Tape
• Chip paint brushes in 2 and 4 inch sizes for cut-in
• Drop cloths for mess
• Rags and tackcloths
• Paint buckets with stirring sticks
• Paint mixing tool
• Electric or air-driven orbital or disk sander
• 80-grit sanding discs
• Fairing compound
• Plastic Spreader
• Plastic fairing batten
• Painter’s suit and hood
• Foot Covers
• Gloves
• Eye Protection
• A vapor-dust mask and/or respirator for paints based on solvents

You should match your paint accessories to the antifouling you are applying. Rollers with solvent-resistant, short-nap roller covers are required. Use only roller covers, brushes and tray liners that are designed for household use. The solvents in bottom-coat paints will dissolve them.

Preparing the boat for paint

Preparation is key to achieving the best possible results. Before applying bottom paint, you should thoroughly clean, dry and prime the boat. It may also be necessary to remove old bottom paint.

When you are ready to paint your boat, consider the material:

• Bare Fiberglass: If you do not remove the mold release wax, it will interfere with adhesion of paint. Wipe down the hull using a dewaxing solution, and change rags frequently. Sand the boat using a sandless prime or 80-grit paper. Wash the sanding residue with clean water.
• Bare wood: Use seam compound on bare wood, working with a clean, dry surface. Fill and smooth any seams. Sand the bottom of the boat with 80-grit paper, then wipe it with water and a lint free rag.
• Aluminum: Remove all rust and debris. Sandblast until the surface is shiny, bare and low-profile. Vacuum any sandblasting debris. Prime the surface with a protective layer, and then use a de-waxer to remove any residue.

Removing Old Paint

You’ll have to prepare the existing paint to accept new paint if you want to apply antifouling.

First, clean the hull. Power washing works well to remove dirt, grease, paint and loose particles. Wear eye protection, gloves and a respirator when using a powerful acid-based bottom cleanser to remove marine growth.

These scenarios will help you prepare your boat based on the current condition of its paint. Sanding is mentioned here, but will be covered in more detail in a future section.

• If you know the type of existing paint and it’s in decent shape:  If you are able to identify the paint type and the condition of the existing paint, you can sand the hull using 80-grit paper after cleaning it. Once again, clean the surface using solvent. Then use a paint thinner recommended by the manufacturer. If you don’t want fiberglass to blister, apply a protective gel coating.
• If you don’t know the type of existing paint, but it’s in decent shape:  If you do not know what type of paint is on the boat, but the condition is good, clean the boat thoroughly to remove any dirt, grime, and paint flake flakes. Sand the hull using 80-grit paper and then rinse it with fresh water. Follow the instructions on the coat-tying prime to ensure that the new paint adheres.
• If you don’t know the type of existing paint and it’s in poor shape:  If you do not know what type of paint is on the boat and the paint is in bad condition, use a paint-removing product compatible with the hull. You may need to use several layers of paint remover in order to get through all the layers. After you have removed all the paint from the boat, inspect the blister protection coating for any damage. Fill in any damaged areas. Now is the perfect time to install a protective barrier coating on your boat.

Sanding and Fairing Hull

Sand your boat after it has been cleaned and dried. Sanding the hull is done to make it rougher so the paint can adhere. Paint will not adhere to a smooth surface and will eventually wear off.

To protect yourself, you should wear eye and respiratory protection and cover your skin when sanding the old bottom paint.

Cover your work area first with a dropcloth. Sand the hull with 80-grit paper using a dual action, dustless sander. Pay special attention to any unevenness or high spots. You want to achieve the smoothest bottom possible.

After sanding the hull you can proceed to level it. The bottom of a boat can be “faired” by removing high and low spots to create a smooth surface. Filling holes, reshaping gaps or grinding bumps can be part of the process.

Use a fairing compound (or fairing putty) to shape and fill the boat. Fairing compounds are typically made of epoxy resins and low density fillers. Here are the steps to epoxying your boat’s hull:

1. Apply the fairing compound with a plastic spreading tool to the bottom of the boat. Overfill the low areas a little to make it easier to sand down later. Use a notch spreader if your hull has a lot of unevenness.
2. Use the fairing material to achieve your desired shape. You can avoid having to sand the compound after it has cured.
3. Blend it in and blend it out.
4. To level the fairing, adjust the plastic batten to fit the contour of the boat and drag it slowly across the filled area.
5. Before sanding, let the fairing compound dry according to the instructions of the manufacturer.
6. It may be necessary to sand and fill the low areas several times before they are leveled.

Taping off the Borders

Apply the long-mask mask tape to the bootstripe, as close as possible, and create a smooth, even border. Tape off metal elements such as transducers, marine struts and through-hulls. Copper in the bottom paint or on metal will cause corrosion.

How to Paint a Hull for a Boat

After you have taped the border, it is time to paint. Just before you apply the paint, shake and stir it thoroughly.

Pour the paint in the basin of the paint tray. The excess paint can be poured on the slope of the tray. Roll the paint up and down the hull from the waterline towards the keel. Bottom paints dry very quickly. Before you refill the tray, stir the paint in the container.

After you have painted the hull completely, it may be ready to receive a second coating. You can check the manufacturer’s instructions to find out how many coats you should apply. Also, make sure to note that drying times may vary between ten minutes and a dozen hours.

Multi-coatings can extend the life expectancy of bottom paints. Apply one or two additional coats to bare hulls. Also, apply them around the waterline and in other areas where there is a lot wear, like leading edges of keels and rudders.

Let the paint dry and cure
Refer to the instructions on your bottom paint to find out how long you should let it dry before moving your boat.

Some antifoulings paints also have activation windows. This means that you need to put your boat into the water in a specific time frame to activate the antifouling agent in the paint.

Bottom paint your boat with All Marine Services Products

All Marine services Supplies offers everything you need to complete a successful project. We have a large inventory of high-quality boat maintenance products. Our knowledgeable staff will help you to make the most out of your shopping experience.

We want to keep you on the water whether you are a new boater or an experienced one. All Marine Supplies can help you with all your boating requirements. Contact us today!