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Interlux Antifouling Outdrives, Underwater Metals and Keels


  • Good preparation and priming is essential to ensure that the antifouling adheres to the surface for the duration of the product life.

  • Make sure you stir the paint thoroughly before application and again during application as it contains very heavy compounds that can settle to the bottom of the can.

  • Antifouling paint should not be applied over a topside finish.

  • Propellers, outboards and outdrives are either constructed of aluminum, stainless steel or bronze. There are no reaction problems in using paints containing cuprous oxide on stainless steel or bronze.

  • Care should taken not to paint zinc anodes, which are often located next to the prop shafts, as this will seriously reduce their effectiveness.

  • When painting your outdrives, underwater metals and keels, the longevity of any antifouling is difficult to predict, as the coating adhesion is an issue, particularly on propellers, due to the harsh treatment these areas receive.

  • Common application methods include brush roller or spray. Spray application may require specialized equipment and spraying of antifouling paints is not permitted in Canada.

  • Never add anything to antifouling paints other than small amounts of the recommended thinners. The addition of oil, varnish, other paints, powders and foreign compounds can upset the critical binder balance and impair the release of biocide.

  • For brush application, it is advisable to use a large width brush. The finish achieved is unlikely to be as good as a topside paint; therefore, the type of brush used is not critical.

  • It is very important to apply the correct thickness of antifouling paint even if it means putting on an extra coat. Different people apply products at different thicknesses, so take care to apply all of the paint calculated using the chart at the back of this manual. The recommended thickness is normally achieved by the application of two coats.

  • When using copolymer and ablative type antifoulings it is advisable to apply an extra coat of antifouling to the leading and trailing edges, waterline, keel and rudder. These are all areas of high turbulence where the antifouling lends to wear faster.

  • The overcoating and times to launch should be followed very carefully, as this is the biggest cause of anti-fouling detachment. Water is a very aggressive environment for paint and it is very important that the paint is allowed to dry thoroughly between coats and prior to launch.

  • Colors of the same type of antifouling paints can be mixed but do not mix paints of different types. For example, Fiberglass Bottomkote® Blue may be mixed with Fiberglass Bottomkote® Black, but not with Ultra-Kote®.

  • Antifouling paints are to be applied as they are received in the can so the addition of thinners is not usually recommended; because of the cost of antifouling paints there has a tendency to stretch the paint to achieve more coverage. This procedure is a false economy and will usually result in premature failure due to inadequate film thickness. Small amounts of thinners may be required under difficult application conditions due to extra cold or hot weather, but amounts should be kept to a minimum.

  • For roller application use, a 5/16th inch or 3/8th inch nap, solvent resistant roller.


Antifouling paints are not meant to be cosmetic or decorative coatings and while every effort is made to make them as aesthetically pleasing as possible. The copper compound within the antifouling is difficult to mask with color pigments.

All antifouling paints change when they are immersed. So don’t be surprised when you have finished and the color is not what you had hoped from the color chart, the true color will establish itself after the boat has been launched. Copolymer and ablative type coatings tend to fade more than hard antifouling paints.

Along the waterline the antifouling will often look dirty or faded, and can even turn green. This is due to the reaction of the paint with oxygen forming green copper oxide. For these reasons you should try keep the paint as close to the true waterline as possible. Fading is more noticeable in copolymer or ablative coatings than in hard coatings.

Information provided by Original article from Interlux (printable)

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Interlux Antifouling Basics
How Antifouling Paint Works
Interlux Antifoulant Selection Guide
Painting Bare Fiberglass Bottoms
Antifouling Paint Systems for Various Substrates
Handy Specifications
How To Paint Previously Painted Bottoms
Interlux Applying Antifouling Advice
Antifouling Paint Calculator
Antifoulant on Aluminum Hulls
Interlux Antifoulant on Metal Outdrives, Keels and Centerboards
Hints for the Perfect Bottom Finish
Interlux Antifoulant FAQ
What is Osmosis Gelcoat Blistering
How to Recognize and Treat Osmosis Gelcoat Blisters
Protect Against Gelcoat Blisters with Interlux Interprotect
Interlux Gelcoat Blister Repair FAQ

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