Antifouling Made Easy

So the time has come and your pride and joy finally requires a new coat of antifouling paint. As is typical with many facets of ourlives these days you can be overcome by the choice of products available. However once you apply logic the choices can usually be reduced. Getting to that choice however can be stressful and hopefully International make choosing your antifouling far easier. Let’s go through the process of deciding which antifouling you really need and then some hints and tips on how to go about applying it. First we need to decide what type of antifouling you want on your boat.

Type of Antifouling

The types of antifouling available can be split into two types, hard and eroding. You will probably find other descriptions such asablative, polishing or self-polishing. All these descriptions can be put under the umbrella of eroders. The basic and original type of antifouling is the hard antifouling. When immersed and in a wet state this antifouling is hard enough to withstand regular wiping down with a cloth or sponge without removal of substantial quantities of paint. Some local authorities may only allow these types to be used so the decision may have been made for you.

Hard antifouling does not wear away much at all, although abrasive material in the water such as silt and sand may lead to a very minor reduction in film build. Eventually however, you are left after a few seasons with a build up of product that requires removal. The product becomes unsound and does not retain sufficient internal strength to be able to hold together when new product is applied to it. If you have a seriously fast boat or a fast boat that is used very regularly then hard is probably the best way to go. Boats moored in fresh water normally use these types, as the eroding types may not erode very well. Keen racing types sometimes prefer hard products as they can be wet sanded to a smooth finish prior to racing.

Eroding antifoulings, as their name suggests, wear away leaving eventually no antifouling on your hull. In theory, whilst there is antifouling on your hull it will give a degree of protection. With the current generation of paints however this does not happen because as the paint film starts to get thin, the biocides are preferentially washed out leaving paint that is essentially not antifouling paint. This is the time to apply new product.

Hard Choices

If you have decided that a hard type is your best option and you are a keen racer, International VC Offshore might be your choice. VC is specially formulated for racing yachts with its reduced drag qualities brought about by its fluoro microadditive content. The other choice of hard antifouling is International’s Longlife, a high strength copper oxide based product, suitable for all substrates except aluminium, and available in a range of 20 colours. For aluminium substrates International’s Trilux 33 is your best choice.

Eroding Choices

If you have decided you want an eroding antifouling there are several choices for substrates other than aluminium. International Micron 66 is the ultimate in antifouling performance even in the harshest fouling conditions. Micron Extra is an excellent choice for heavily fouled areas and for trailered craft. International Coppercoat is the lower cost option still able to give a very good all round performance.

Surface Preparation and Priming

Having decided what antifouling you are going to apply we need to consider the condition of your hull. Irrespective of which paint is already on your hull, it should be in good condition with little or no damage and be compatible with the antifouling you are going to apply. You will need to give the surface a good wet sand with 80 grit paper. This will remove the top layer of paint that is depleted in biocides, contains salt and calcium deposits and is not in a condition to accept a new coat of paint. Failure to remove this layer will lead to blistering, delamination or even poor antifouling performance as ingredients and biocides in the new paint permeate the old depleted layer.

If the paint is an unknown product, after sanding and washing, allow it to dry thoroughly and apply a sealer/tie coat of International Primocon. This will seal the old antifouling avoiding unwanted interaction between old and new and will create a surface the new antifouling can bond to.Do not be tempted to apply a coat of Primocon over old unsound antifouling in the hope that it will hold it all together as it won’t and the freshly applied antifouling will fall off. If the hull has damaged areas these will require re-priming with International Primocon. This is an easy to use single pack product that is fast drying and uses the same thinners as your antifouling for thinning and cleaning up. The beauty of Primocon when trying to paint damaged areas is that you can simply apply the primer over surrounding clean and dry antifouling areas - try that with a two pack epoxy and you will have major problems. Primocon also has many other uses and any paint left over can always be used as opposed to two pack epoxies that once mixed have to be used. If your hull is new, then choice of priming is one for the individual. You can use single or two pack. The two-pack International Interprotect epoxy primer will give you a harder, tougher finish and, for gelcoat boats, will offer a degree of osmosis resistance. For a more simple priming system however, Primocon is the product of choice. Simply prepare the surface as per the label instructions and apply the required number of coats. Primocon makes future repair work easy as it is re-coated with itself and any antifouling with minimal hard work. Epoxies usually require a fair degree of sanding and for small touch ups mixing small amounts of a two-pack product with special thinners and cleaners can become a major headache.


Before purchasing your antifouling, work out the area of your hull to ensure you purchase sufficient product. Insufficient film build of antifouling is the largest cause of premature failure. Once you have the antifouling apply all of it. Putting some aside for next year is not a good idea as the product may go off in a part can. Part cans may then become a disposal problem. It is better to put the paint on your hull than in a waste disposal area. Ensure that you apply the antifouling evenly, adding only very minor levels of thinners (up to 10%) to help product application. Areas on the hull that you would expect to have greater wear should have at least an extra coat applied, this includes areas that may get direct sunlight, such as the first half metre or so down from the waterline and any leading edges such as keel, rudder & prop wash areas. Grassy growth and slime just love sunlight and are the most difficult species to ward off, so extra paint will help keep these obnoxious species away. Areas under the hull in the dark will generally not attract fouling species so readily and extra coats will not necessarily be required here. Once you have finished painting, protect the antifouling from the sun as some ingredients in antifouling paints can oxidise leading to reduced performance when immersed. If after antifouling, your boat sits on the hard stand for some days in hot weather or direct sunlight, it might be a good idea, prior to launching, to lightly wet sand with 400 grade paper. This will ensure the surface is active. Micron Extra has been formulated with different resins compared to most other antifouling types and will not require such treatment. It is a fact of life that when you launch your boat, the antifouling will not start working straight away. It will take some hours for it to come to equilibrium with its surroundings. Meanwhile, floating around in the water are millions of small fouling species on the lookout for a clean surface to colonise and if you are unlucky enough to place your boat directly in a patch of such activity, the result can be premature fouling. This problem can only be resolved by giving the surface a good scrub or light wet sand depending on the type of antifouling used - scrub hard types and light sand eroding types. Never dry sand antifouling paints of any type. Another important point to remember is that the true colour of the antifouling will develop about 4 weeks after immersion.

Health and Safety

When handling any of the above-mentioned paints please remember to wear the appropriate safety gear. Even when washing down old antifouling care should be taken to avoid splashes in the eye or on the naked skin. And once again, never dry sand antifouling paints of any type.