Antifouling Compatibility

Putting a new antifouling over an old one that isn't compatible is the most common reason antifouling flakes, lifts or fails early. Here's how to decide whether you can paint straight over, or need a sealer first.

The basic rules

• Same product over same product is always fine, as long as the old coat is sound and sanded.
• Self-polishing over self-polishing is generally fine when the old coating is sound.
• Hard antifouling is the tricky one. Many self-polishing antifoulings shouldn't go straight over a hard antifouling, and the other way round. Check, or seal.
• Unknown antifouling – you don't know what was used before – should be sealed with a sealer primer such as Seajet 015 Underwater Primer.
• Teflon-based antifoulings need sealing before anything else goes on top.
• Copper over aluminium is never allowed. On an aluminium hull, only use antifoulings approved for aluminium, such as Seajet 038 Taisho or Seajet 034 Emperor, over a suitable primer such as Seajet 117.

When to use a sealer

Use a sealer primer between old and new antifouling when:

• you don't know what the old antifouling is,
• you're changing to a different type of antifouling,
• the old antifouling is Teflon-based,
• the manufacturer's compatibility table says the combination needs one.

Seajet 015 dries quickly and is applied over the sanded old antifouling, then the new antifouling goes on top.

When the old antifouling has to come off

Sealing doesn't fix a bad base. Strip back when:

• the old antifouling is flaking or lifting,
• there are many thick layers built up over the years,
• you're moving to an aluminium-safe system on a hull that had copper antifouling.

Check the manufacturer's table

For exact product-to-product combinations, Seajet publishes a compatibility chart on its website. Other manufacturers publish their own.

Not sure what's on your boat?

Send us the boat's details and any record of the last antifouling, and we'll tell you what can go on top. See antifouling application.