Removing Antifouling

You may be one of the lucky ones, and not need to remove your antifouling paint this winter - just jet wash the crud away and apply a fresh coat of paint before relaunch. But if the paint is starting to crumble, or if you have built up too many layers, or worse still you have found some blisters under the paint, you will unfortunately need to take it all off to investigate.

Antifouling paint falls roughly into two basic types - hard and soft. The hard paints are designed for fast motorboats and racing yachts where they will be hammered at high speed for many hours on end. The softer antifoulings are for slower boats, and are designed to gently erode during the season. Either way, both types are designed to stick to the hull, and care has to be taken not to cause any damage in prising them off.

Luckily you have plenty of weapons available: you can engage the enemy with cold steel or chemical weapons, or simply blast them out with volcanic sand or exploding pellets of ice.

Before Starting

By its very nature antifouling is poisonous stuff, so care has to be taken with its removal, especially in environmentally sensitive areas.

Some boatyards will have a 'dirty' area, where the boat will be exiled for blasting or jet washing, with facilities for catching as much debris as possible. Before working on your antifouling, ask your boatyard what provisions they have, and what they will allow.

As for personal safety, much of that is common sense. Goggles and face mask are essential, and always wear gloves. Clothes that cover your arms and legs are also a good idea. Wash any paint flakes off your skin at the first opportunity, and take special care with paint strippers.


Manual scraping

Perversely, the more layers of antifouling on a hull the easier it is to scrape them off with a sharpened steel scraper. Some people even find this labor-intensive method therapeutic.

I have used an old wood working chisel on my hull of my GRP hull. I find that grinding the leading edge down to 70 degrees means that this flat sharpened edge can't dig into the gel coat but shatters the brittle antifouling coat which comes away with ease.

Use an angle grinder to hone up the blade every 10 minutes or so. Assuming you are right handed it is best to work from right to left and to position a bucket under the area of work to catch the flakes of discarded paint for safe disposal. Goggles are especially important, as shards of paint literally fly off as the edge takes them out.

The modified chisel will get nearly all of the paint off (you may have to go over it all a second time to catch the stubborn bits) and if used carefully should leave the hull unscathed.

After scraping, run an electric palm sander with a medium grit over the underwater hull, as this takes the last flecks of paint. It also gives a good 'key' for an epoxy treatment or for the new antifouling.

File scraper

A custom-made scraper I can recommend is using an old file, the sort found in old boot sales. Get the biggest flat file you can find, and use a pedestal grinder to take the serration off on both sides to about 5cm (2 inches) back from the end. Then grind a slight radius on the end at 90 degrees to the flats and importantly, take the sharp edges off. This will prevent your gel coat getting gouged. You can now use this 'chisel' with both hands to rip the antifoul off in no time. You have two edges which are easy to sharpen, and being heavier and longer than a chisel you can put your wight behind it.

More Scrapers

Adding to the array of weapons are triangular scrapers, and long handled scrapers with detachable blades, as sold in most DIY superstores. The blades themselves are tungsten steel, and retain a sharp edge for a long while.

For best results keep the blade as sharp as possible.


Gelplane International has developed a metal scraper with a hollow plastic body that is designed to connect to a vacuum cleaner. This allows all the dust and paint flecks to be sucked away as you work. The scraper comes with a blister pack of spare tungsten-carbide blades, and is equally effective on other marine paints and varnishes.


If mechanical assistance appeals, then you could attach a P*erago to your power drill. They come in several types and the manufacturers claim that the wooden substrates version will remove antifoul from both wood and GRP hulls without damage provided care is used.

Another version for those with steel hulls uses hard metal studs to strike the surface with similar results to a grit blaster. It uses and interaction between the metal studs and the oscillation of the rubber backing pad to remove even sticky materials such as bitumen without clogging. It can be used to remove the gel coat entirely.


Chemical stripping

Tough on paint but easy on the environment, chemical strippers have come a long way. There are several chemical preparations available, which are usually in the form of a paste (rather like wallpaper paste) that can be sprayed onto the hull. Make sure you use a stripper designed for antifouling removal, as some of the high-street brands can also soften up your gel coat!

Strippers are messy but often very effective. The least labour intensive method of application is to use an airless spray gun, and once the paint has softened up, blast it away with a household jet washer. If the paint is too thick, you may have to resort to several applications of stripper, and some scraping, which will take more time and effort.

Tip: Cover the ground under the boat with a garden fleece, of the type to protect young plants from frost. As you pressure wash the softened paint, it will allow the water to escape, but catch the waste.

Home Made Stripper

A bit of searching and reading around you can find recipes for home-made stripper. One that I found while looking is a stripper made from caustic soda crystals dissolved in water, and not the other way round. Stir it, then add some wallpaper paste so it sticks to the hull. Leave it to burn into the paint, and then scrape it off. You can make a whole bucketful for about a fiver.

Sea-Jet 361

Similar in appearance to Nitromors and easy to brush on, although it needs vigorous stirring. Spraying using an airless spray is recommended for large areas. The stripper is water-based and non-toxic, with virtually no odour. The gel coat is unaffected by the stripper, which is easy to wash off and is biodegradable.

International Coatings

International has recently reformulated their range of gel type strippers to be gentler to the user. This new stripper works as effectively as the Dilunette, without the aggression to the skin. It also has little odour and the consistency of custard, which makes it easy to apply

Removeall 610

One of the active ingredients is ethyl alcohol, and the process involves two applications - the first is sprayed on and left for a few hours, and the second coat follows this. These two combined coats work overnight, and then the paint can be removed with a jet wash the following day. The stripper is water-based, and non toxic, with little odour. The suppliers advise the stripper to be sprayed on and sell the airless sprayer for about £50.


Slurry Blasting

Most boat owners are familiar with shot blasting. Basically anything from steel balls to ground garnet can be fired under pressure to remove layers of paint or rust from a substrate. Sand blasting has been around for many years (look at what it has done to the Sphinx in Egypt!!) and works well on metal, but is too harsh on GRP. However, slurry blasting mixes water into the equation for a less aggressive mix, and this is perfect for taking off anti fouling without causing damage to the hull.

A mineral such as Olivine is mixed with the water and shot out of a nozzle at between 7-12 bar of pressure to create an abrasive jet. Not only does this blasting remove all the paint from the hull, it also gives the GRP a slight key for a good paint adhesion.

Slurry blasting is not yet a DIY option. However, the blasting units are highly mobile, so a competent operator at your boatyard can do the whole job. It is quick, often taking less than a day for smaller boats, so is ideal if time ashore is limited.

The water used in slurry blasting traps the paint and drops it to the ground mixed with the spent grit. This is easy to shovel up and dispose of in an environmentally friendly way.

Grit Blasting can take rust off steel, paint off wood, or oxidisation off brass. Blasting can also be used to remove solid materials like gel coat. It all hinges on the skill of the man with the nozzle.

Dry-ice Blasting

Exploding pellets of frozen carbon dioxide will remove paint, and pop your blisters.

Dry ice is the term given to frozen carbon dioxide, which has the ability to go from a solid to a gas without passing through a liquid state first. This process is called sublimation, and is key to blasting off your anti fouling. However, dry ice treatment has another side effect. It will freeze the water in the osmotic blisters on a GRP hull and blow them wide open, without the slightest scratch to the rest of your hull.

Dry ice arrives as frozen strands stored in an insulated box at -78 degrees Celsius. It is then poured into a machine, which breaks the strands into pellets. The operator decides how big the pellets should be depending on the job: the smallest are 1.2mm, for fine restoration work, and the most powerful are 3mm, which can be used on anti fouling. In a similar way to grit blasting the pellets are often fed under pressure into a hose and directed against the hull.

As the pellets strike the anti fouling, they suck out the heat and use the energy to sublimate into gas. The volume of gas produced is 800 times greater than the volume of the pellet so several things happen at once.


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