Stripping Bottom Paint: Boat Makeover Essentials

Removing bottom paint from a boat is a messy, odious and potentially gruesome job, but it is necessary if your boat has gelcoat blistering below the waterline. If left unattended, these blisters can expand and eventually compromise boat speed and hull integrity. There are several ways to remove bottom paint, including soda blasting, chemical stripping, mechanical sanding, and walnut shell blasting. Before starting, it's important to consider personal safety, cost, convenience, and environmental impact.

Soda blasting

The soda-blasting process involves using a diesel-powered air compressor to create high-pressure airflow. The operator of the system sweeps the tip of the compressor hose back and forth over the boat's surface, operating it as if it were a giant eraser. Each sweep causes accumulated bottom paint to fly from the surface, so it is important to wear protective gear and contain the dust and debris.

Before soda blasting, it is important to first remove any large marine build-up and barnacles from the boat's bottom, and then pressure-wash or clean the surface. After soda blasting, some small areas may require sanding to remove any remaining paint.

Chemical stripping

The first step in chemical stripping is to apply the stripper to the bottom of the boat, following the manufacturer's instructions. Some strippers need to be covered with plastic to prevent solvents from gassing out, while others may harden if left on the hull for too long. The stripper is usually applied with a brush or roller, but some can be sprayed on. It is important to apply the stripper thickly, but not so thickly that it starts to drip off the boat.

Once the stripper has been applied, you need to wait for it to take effect. This usually takes a few hours, and it is important not to wait too long or the stripper may harden. After the allotted time has passed, you can start scraping off the softened paint with a putty knife or scraper. It is important to use a scraper with rounded edges to prevent gouging the gelcoat. Place a waste bag under the area you are working on to catch the falling paint and stripper, and move it as you go along to contain the mess.

Depending on the number of paint layers on the hull, you may need to apply the stripper a second time. There may also be some small areas where the stripper doesn't completely remove the paint, and you may need to sand these areas to remove the remaining paint. Finally, give the bottom of the boat a thorough wash to remove any residue.

Mechanical sanding

If you're doing it yourself, you'll need to invest in about $60 worth of 80-grit sanding discs and a six-inch random-orbit sander, which will cost about $100. You can also expect to spend 15 to 20 hours of labour removing the bottom paint from a 30-foot sailboat.

Before you start, it's important to cover up to protect yourself from the toxic sanding dust. This includes a disposable jumpsuit, a head sock, goggles, a tight-fitting dust mask, and heavy-duty gloves.

You'll also need to cover the ground under the boat with a drop cloth to catch the removed paint. If you're using the sanding method, you'll also need to tent" the boat's bottom by hanging plastic sheets from just above the waterline to the ground, reaching all the way around the boat. This will prevent dust from escaping.

When you're ready to begin, use the random-orbit sander with 80-grit sanding discs to sand away most of the old paint. Be careful not to sand too aggressively, as this can damage the boat. It's also important to note that you should never use a belt sander, as it can damage the bottom of your boat.

If you're looking for an easier option, you may want to consider chemical stripping or soda blasting. Chemical stripping is the simplest method, requiring only a paintbrush and a scraper. However, it's important to choose a marine stripper that doesn't contain methylene chloride, as this is considered a carcinogen.

Soda blasting is becoming the removal method of choice, as it doesn't damage the underlying gel-coat surface like sandblasting can. However, it is more expensive, costing between $40 and $65 per foot.

Heat

Step 1: Prepare the Work Area

Ensure you are working in a well-ventilated area to avoid inhaling toxic fumes. Place a drop cloth or disposable tarp under the boat to catch the paint debris and protect the surface underneath. It is also recommended to wear old clothes or a disposable coverall, as the process can be messy.

Step 2: Choose the Right Heat Gun

Select a heat gun suitable for paint removal. Some heat guns have adjustable temperature settings, allowing you to control the heat output. It is important to choose a gun with a temperature range suitable for paint stripping.

Step 3: Start with a Small Test Area

Before beginning the stripping process, test the heat gun on a small, inconspicuous area of the boat. This will help you determine the appropriate temperature and distance to hold the gun from the surface. It will also help you understand how the boat's surface reacts to the heat.

Step 4: Apply Heat to the Painted Surface

Direct the heat gun at the painted surface, maintaining a safe distance as determined in the previous step. Move the heat gun back and forth across the surface, ensuring even heat distribution. You will notice the paint starting to bubble and blister as the heat softens the paint.

Step 5: Scrape the Softened Paint

Using a suitable scraping tool, such as a paint scraper with a sharp blade, begin scraping off the softened paint. Work in small sections, applying heat to an area and then scraping it off. Be careful not to apply too much heat, as it can damage the underlying surface.

Step 6: Dispose of the Removed Paint

As you scrape off the paint, collect it in a suitable container for proper disposal. Bottom paint often contains toxic chemicals, so it is important to follow local regulations for hazardous waste disposal.

Step 7: Repeat as Necessary

Depending on the number of paint layers and the thickness of the paint, you may need to repeat the process multiple times to completely strip the bottom paint. Allow the surface to cool down between each pass.

It is important to note that using heat to strip bottom paint can be a time-consuming and labour-intensive process. Additionally, it requires careful handling to avoid damaging the boat's surface. Always prioritize your safety and follow the instructions provided by the heat gun manufacturer.

Sandblasting

If you do have an aluminium or steel hull, sandblasting is a good option for removing bottom paint. It is a more vigorous approach than other methods, but it will leave the gel coat and barrier coat intact.

Before sandblasting, it is important to create a tent to collect the blasting material and the paint that is removed from the boat. This is done by taping plastic above the waterline and joining it to a plastic floor. This will prevent the dust from escaping and ensure that the marina environment is not affected.

Frequently asked questions