Too Many Layers of Bottom Paint?


So, a couple of years back, you acquired a good old boat at a pretty good price-thanks to the market-but now you’re wondering how many coats of bottom paint it has. And what kind? You’ve put on a few coats of ablative antifouling since you’ve owned the boat. It has adhered well and has done its job. But each year, the bottom looks rougher and rougher-with big recesses where paint has flaked off. You sweated out some extra prep-work this season, and thought you had a nice, durable subsurface for painting, but each pass of the roller pulls up more paint. Whats going on here?

More than likely, you probably have too much paint built up on your hull, and this is affecting adhesion. How much is too much? Well, that depends on the type of paint: hard or ablative. With a hard paint, adhesion loss will begin around 20 mils of thickness (approximately 10 coats). Having more layers built up will make the inner layers less flexible and more likely to chip, flake, and lose adhesion. Excessive mil thickness must be removed mechanically with 60-grit sanding or soda blasting. Once a hard-paint coating has used up its antifouling properties, whats left behind is no longer active. It may still look great, but it wont protect against growth. At most, one or two coats of hard paint is recommended. Any more than that, and you are wasting money, locking in antifouling agents that can’t do their work and bringing on the inevitable sanding or blasting job sooner than necessary.

Ablative paints will begin to lose adhesion at around 15 mils of thickness-but since the coating ablates over time, it should not build up like a hard paint. As you use the boat, the paint should wear away, or ablate, and every time the product ablates, it is releasing fresh biocide. Technically, as long as an ablative coating is on the hull, it should continue to combat hard growth. That said, in our tests, we’ve found that this protection, especially against slime, diminishes as time goes on. Regular bottom cleaning can also prolong protection, but it can’t work miracles. Two to three coats of ablative paint are recommended for multi-season use, while a single coat is adequate for single-season use. An initial signal coat of a different color helps you know when it is time to repaint.

If youve been applying two coats of ablative each year for the last three years, thats already six coats of paint for a total of 12 mils, not including the previous applications. If you aren’t using the boat often enough, those layers are building up, and a slow-moving sailboat will not ablate at the same rate as a powerboat.

If you’ve determined that you’re past either of these thresholds, you might want to consider a complete re-finish.

Paint removal options vary, and whats best will depend on how much old paint there is and your personal preference. If there aren’t that many layers of bottom paint, you can sand them off with an 8-inch, dual-action orbital sander and 60-grit sandpaper, but this is hard work and requires careful safety precautions. Overzealous sanding can lead to dings and divots in the gelcoat.

Another option is using a chemical paint stripper like Peel Away or Franmar Soy Strip (PS, October 2011). Chemical paint strippers break down the paints adhesive bond on the hull and make it easier to scrape down to clean substrate that can be repainted. This is messy and noxious work, but its less back-breaking than sanding. We’ve found that the strippers performance varies by boat (and temperature), so review the articles on strippers to see which one best fits your scenario. And if you’re not happy with one product, you might want to try another before giving up.

Both of these methods will be time-consuming on larger boats. Before tackling this project, check out our October 2011 article, A Mathematical Decision Maker, which outlines a formula for determining whether the DIY approach is right for you. On boats in the 40-foot range (or larger), we recommend looking into soda-blasting the hull (PS, October 2011). If you’ve got an old barrier coat that needs renewing, and are still considering a non-blasting regimen, then you’ll first want to read technical editor Ralph Naranjo’s account of his barrier coat removal project.

For owners of older boats with unknown, well-adhered coatings, a tie coat can help make sure successive coatings stick. The major bottom paint manufacturers-Interlux, Pettit, and Sea Hawk-all have priming/tie-coat products. One that we’ve recently used with success is Sea Hawks 1277 Barrier Coat Primer, a chlorinated rubber compound. Pettits version is called Tie Coat Primer 6627. Interlux markets its Primocon for this purpose.

How long you wait to strip down the old paint depends on how bad the adhesion issue is and your tolerance for a rough bottom; work boats go years without stripping. Eventually though, adhesion will suffer. The rough surface will also mean more drag in the water and slower boat speed. If you do start fresh, regular application of an ablative paint-one to two coats for a single season, no more than three for long-term cruising-can prevent paint build up. For help in selecting an ablative bottom paint that is best suited for where you sail, check out our March 2013 report on favorite bottom paints by region.

Darrell Nicholson
Practical Sailor has been independently testing and reporting on sailboats and sailing gear for more than 50 years. Its independent tests are carried out by experienced sailors and marine industry professionals dedicated to providing objective evaluation and reporting about boats, gear, and the skills required to cross oceans. Practical Sailor is edited by Darrell Nicholson, a long-time liveaboard sailor and trans-Pacific cruiser who has been director of Belvoir Media Group's marine division since 2005. He holds a U.S. Coast Guard 100-ton Master license, has logged tens of thousands of miles in three oceans, and has skippered everything from pilot boats to day charter cats. His weekly blog Inside Practical Sailor offers an inside look at current research and gear tests at Practical Sailor, while his award-winning column,"Rhumb Lines," tracks boating trends and reflects upon the sailing life. He sails a Sparkman & Stephens-designed Yankee 30 out of St. Petersburg, Florida. You can reach him at


  1. Sail a lot, sail as fast, use a two-year ablative paint, and stretch it as far as you can with some light scrubbing near the end. Spend a few hours with coarse paper, sanding hard every time you repaint. With a little luck and a bit of work, build-up will be nil. Though a series four of boats I’ve owned for 8-12 years, I’ve never built up enough paint to even consider stripping. With all the scrubbing and sanding, the bottom stays fair. I see this as both efficient, economical, and constructively lazy.

  2. I painted two coats of hard, then 7 coats of ablative hoping to get multi years in south Florida.

    that was Oct 2007. Have not hauled the boat since and it’s still clean.
    Just sailed offshore from Miami to Cape Canaveral 200 miles in a 24 hour run. A beautiful run and bottom was beautiful and clean.

    I don’t understand why everyone else gets only a year or two when I’ve gotten almost 13 year in hot tropical water of Miami. I do use a diver twice a year to check the bottom for blisters and zincs No problems at all. The diver just brushes off a little slime and very few barnacles.

    Maybe it’s because part of my secret is the electronic barnacle buster I installed 10 years ago. It seems to work pretty well even though it was installed after my bottom paint was already three years old.
    42′ Cheoy Lee Clipper Ketch

  3. Where I live (Australia) our EPA does not want you to scrub the boat in the water. How have people dealt with this? You do have to keep the boat sea worthy which could justify some bottom cleaning.

    Keen to hear how others manage this problem?

  4. Sadly, this is a mistake I made. I bought my boat with several layers of CSC Micron, and as a person who was fairly new to sailing, figured that if “a little is good, a bunch must be better”. Every year for 5 years I did a light sanding then slap on several coats of CSC Micron. Two years ago, I started suffering from paint flaking and peeling off while applying the new coats, and had no time to deal with it. Last spring I hired a soda-blasting company who came in and did a great job (considering that I was their first sailboat and had only done a handful of power boats). They saved me from a week (or two?) of respirator-clad misery, holding an orbital sander over my head. I considered it a wonderful investment in my sanity CSC Micron is terrible stuff to sand – you vanish in a choking cloud of red dust.

    I put on four layers of Interlux epoxy base that was nasty stuff to work with – it dissolved almost every paint roller I tried to use, including ones rated for industrial use with glues, but I finally got that miserable job done, and put on three coats of VC17m Extra. The boat came out of Lake Ontario zebra mussel free and looked good. I enjoyed painting with VC17 – it goes on like water, instead of paint, but it evaporates insanely fast – you need a lid on a small paint tray and slap it shut as soon as the roller comes out or you can literally see it evaporating. I’d considered SeaSpeed, but after watching Delos try it and conclude that sailboats don’t sail fast enough to keep the bottom clean, gave it a miss (it’s also extremely expensive).

  5. I try to do the same. Over time I’ve found the areas where the PO had thicker coating mostly where it is harder to sand so he did not remove enough. After a few sessions of selective stripping the hull seems to be in a good state of balance and is faster than it has ever been. I like constructively lazy. When I retire I may have the time in the yard to strip but for now time on the hard is a race against the pocket book.

  6. Here in the SF Bay Area, if you have a good diver, ‘hard’ anti-foul lasts up to 5 years…if you use 2 coats (local boatyards here use Pettit Trinidad). My experience is that only one coat means you will be back for new paint in half the time you would be had you gone with two coats. You don’t buy more paint in the long run going with two coats but you sure as heck spend more on haul-outs and labor costs by pulling the boat twice as often. Not to mention that fresh paint pumps more copper into the Bay than older paint does meaning that the more often you paint, the more pollution you cause. As Monty Python would say: 2 is the optimal number and the optimal number is 2.

  7. Hard bottom paint is best for powerboats or other fast moving boats. It is a longlasting coating that is very hard and has a thick layer of biocide. The biocide layer wears away over time which allows the hull paint to last longer prior replacement. Once the biocide has been depleted, however, the hull must be repainted.

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