Short answer
Old antifouling often contains copper, zinc or TBT. Remove it with a scraper or a sander connected to a vacuum, or with paint stripper gel and a scraper. Cover the ground with heavy-duty plastic, screen off the wind and dispose of all waste as hazardous waste. If you are just painting over it, wet sand. Which paints you are allowed to use is covered in rules for antifouling.
Methods
| Method | Good to know |
|---|---|
| Dry scraping with a scraper connected to a vacuum | Recommended by the Swedish Transport Agency. Little dust. |
| Machine sanding connected to a vacuum | Recommended by the Swedish Transport Agency. Requires a vacuum rated for hazardous dust. |
| Paint stripper gel and scraper | Recommended by the Swedish Transport Agency. Test on a small area first. |
| Blasting with sand or dry ice | Should be done by a professional. Spreads the most dust. |
| Pressure washing | Only removes loose paint and fouling. The water becomes contaminated. |
Protect the ground and yourself
- Lay heavy-duty plastic under the whole boat.
- Tape plastic around the hull so nothing blows or runs away. Do not work when it is windy or raining.
- Wear a respirator, eye protection, gloves and dust-tight clothing. The Swedish Chemicals Agency recommends the same protection.
- Collect paint flakes, dust, the plastic, vacuum bags and rags as hazardous waste and take them to the recycling station.
Ask your boat club or marina before you start. Many have their own rules on where and how you may scrape.
Sanding before repainting
Hempel states that old antifouling should always be wet sanded so you do not breathe in toxic dust. Only dry sand with a machine connected to a vacuum. Choose the paper to suit the surface:
| Surface | Dry paper | Wet paper |
|---|---|---|
| Gelcoat before primer and antifouling | 150 | 180 |
| Old, worn gelcoat | 80–120 | 120 |
| Epoxy filler | 60–100 | – |
| Painted surface | 150–180 | 180–240 |
| Hard antifouling for a smooth finish | – | 400–1200 |
Hard antifouling leaves a leached layer at the end of the season. Hempel recommends wet sanding it before new paint. If you change paint type, check the manufacturer's instructions for what can be painted over what.
Weather when painting
According to Hempel, humidity should not exceed 65 %. Drying time roughly doubles for every 10 °C drop in temperature. A simple test: wet the surface. If it dries in 10–15 minutes, it's fine to paint. Avoid early mornings and late evenings when condensation can form.
Found gelcoat damage?
Once the paint is off, the damage becomes visible. Repair small damage following repairing gelcoat, and holes following repairing holes in a GRP boat. Blisters in the gelcoat may be osmosis. A bare, dry bottom is also the right time to apply epoxy primer.
Frequently asked questions
Am I allowed to sand antifouling at my berth?
It depends on the marina and the municipality. Many boat clubs require collection or have designated areas. Ask before you start.
How do I know if the paint contains TBT?
You can't see it. Older boats may have TBT in the lowest layers. Ask your boat club about testing, and read the section on old paint layers in the antifouling rules.
What sandpaper should I use for the antifouling?
Wet-sand with 180 before new antifouling on gelcoat. For a smooth racing finish on hard antifouling: 400 to 1200, wet.
Sources
- Sanering av båtbotten, Transportstyrelsen transportstyrelsen.se
- Båtbottenfärger – om du måste måla, Kemikalieinspektionen kemi.se
- Hempel Yacht – How to paint your boat (slippapper, temperatur, osmos) media1.svb-marine.es