Bottom Stripping Basics

Perfect bottom paint! But then you have to put it in the water, and the evil forces get down to business.

Perfect bottom paint! But then you have to put it in the water, and the evil forces get down to business.

Scene 1: A kitchen, springtime. A couple sits drinking coffee.

Man (looking miserable): “I can’t hold out any longer. It’s been years.”
Woman: “What has, dear?”
Man: “There’s no way I can keep covering it up. It’s embarrassing as hell.”
Woman (alarmed): “What? What’s going on?”
Man: “No hiding it now. It’s gone too far.”
Woman: (steeling herself) “Tell me. Just tell me.”
Man: “I’m going after her bottom. Today. I’m going to strip it bare.”
Woman: (gapes, speechless)

Scene 2: The morgue…

Boat language spawns all sorts of goofy humor. But when it comes to removing antifouling paint, that’s pretty much where the fun stops. That guy in the kitchen above represents all of us. We hold out as long as we can, and then we march to meet our fate.

That’s why, if you’re considering a used boat to buy, you need to pay close attention to the condition of its bottom paint. The state of that paint, especially if it’s very good or very bad, is playing a role in the seller’s mind when it comes to the asking price for the boat. It should play a role in your mind too, because someday, maybe this year, maybe five years from now, that paint is going to have to come all the way off.

Long overdue for a change, some of this paint will come off easily, and more will resist. A scraper, especially one with sharp blade corners like this, is the wrong tool for the job. Tape off the paint and blast it, or let a biodegradable chemical stripper do most of the work.

Long overdue for a change, some of this paint will come off easily, but more will resist. A scraper, especially one with sharp blade corners like this, is the wrong tool for the job. Tape off the paint and blast it, or let a biodegradable chemical stripper do most of the work.

If you’re lucky, the boat has been dry-launched for its whole life and the bottom is paintless and perfect. Otherwise you’re like the rest of us, always somewhere between a new, smooth coat of paint and the misery of a strip-job.

Given that removing antifouling paint is going to be unfun no matter what, your choice involves weighing cost against effort. If you pay someone else to do it, it’s expensive. If you do it yourself, it’s hard on your muscles, joints, patience, and nerves. But it’s inevitable, whether a paint is hard or ablative. Sooner or later it’s going to lose its antifouling properties and start separating from the substrate, maybe in small flakes, maybe in sheets. Or maybe it will just get unacceptably patchy and ugly.

At first glance, bottom stripping looks easy when the paint is so loose that a putty knife can just push it off. And certainly the more paint that can be pushed or scraped off easily, the better. But here’s what will happen: You’ll get rid of 20 percent of the paint very easily, and another 20 percent with increasing effort and time, and your first gelcoat gouges, and a growing suspicion that this won’t be a day at the beach after all. Then you’ll be left with 60 percent that’s not going to budge.

If you’re looking at, say, an 18-foot runabout with flaky bottom paint, your best bet is probably to arm yourself with a Tyvek suit, goggles, gloves, putty knife, cheap brushes, and quite a bit of paint stripper.

But let’s cover the options first.

Professional Blasting: Fastest, Cleanest, Most Expensive

Soda-blasting and shell-blasting (usually with ground-up walnut shells) are established, reliable processes for bottom-stripping, available in many boatyards on an in-house or a contract basis. In this process the bottom is taped off and the underbody of the boat “skirted” with plastic sheeting to contain the paint flakes and dust. The paint is blasted off right down to the boat’s gelcoat. It’s very important that the person doing the blasting has a good eye and a sure hand, or the gelcoat can be damaged. (There’s a similar, new blasting process called Dustless Blasting that uses water and ground recycled glass. See the YouTube video below.)

If you have room in your garage or shop you can buy your own soda-blasting gear, but you’ll also need a sizable air compressor to go with it. The more paint — antifouling or otherwise — that you contemplate stripping, the more justified a purchase like that becomes.

In many cases, especially with old boats,  the next step should be the application of an epoxy barrier coat, which will prevent water intrusion and seal off any surface abrasion of the gelcoat. More about that below.

Do-It-Yourself by Sander:  A Horrible Option

It can be done, and is still done, but it’s brutal work, terrible for the environment and the neighbors, and often damaging to the boat. Most boatyards won’t let you do it, and for good reason. Even with a good collection system, copper- and pigment-laden dust goes everywhere. Boat owners around you, especially downwind, will have a fit. And you’re likely to damage the gelcoat anyway. Anyone who has spent much time on his back under a boat holding a heavy sander over his head, sanding pounds of copper-laden paint onto his face, will assure you that there are much better options.

Do-It-Yourself by Scraper and Putty Knife: An Even More Horrible Option

If you have even the slightest sensitivity to fingernails on a blackboard, this will put you over the edge within 30 seconds. Tools you will need:

  • A very sharp two-handed scraper with the corners of the blade ground off to help prevent gouging the gelcoat.
  • A file to sharpen the blade every few minutes.
  • A putty knife, also sharp, because pushing sometimes works when pulling doesn’t.
  • Goggles, work gloves, a paper mask, and ear protection.
  • Fillers and gelcoat repair materials, because you will damage the gelcoat.
  • A psychiatrist.
Biodegradable strippers like Aqua-Strip do a good job of penetrating and loosening antifouling paint. Patience is key.

Biodegradable strippers like Aqua-Strip do a good job of penetrating and loosening antifouling paint. Patience is key.

Do-It-Yourself by Chemical Stripper and Putty Knife: A Pretty Good Option

OK, now that you’ve been talked out of the horrible options, let’s focus on a positive one. Paint-stripping chemicals work, given time and patience, and the good news is that the best ones for stripping antifouling paint are non-toxic or reduced-toxicity, and biodegradable. That’s right – the most effective are also the safest, both for the environment and for you, the applicator.  Here are a few good ones recommended by the testers at Practical Sailor:

All of these strippers are applied a bit differently. Franmar Soy Strip, for example works best if you brush-daub or spray it on in a thick coat, then cover it with an occlusive film plastic, like Cling-Wrap, to keep it moist. Pettit BioBlast calls for application with a coarse-bristle brush.  So read the literature and follow the instructions. (Seriously. Read the manual.)

Here’s Franmar Soy-Strip at work:

Further Realities

In all cases, paint strippers reward those who are patient. They need to be applied thickly and left alone for the right amount of time to penetrate and soften the layers of paint. Brush it on, cover it with plastic if it’s called for, and walk away long enough to let the breaker-downers do their job.

For multiple layers of paint, the stripper will probably need to be applied at least twice,  sometimes several times, especially if you’re working in cool weather. It’s worth putting on more stripper and letting it do the heavy lifting as opposed to getting impatient and starting your attack with blades, even if it costs you another gallon of the stuff.  You’ll still need a putty knife to remove the softened paint, but the less you have to bear down with tools, the better. If you use enough stripper and wait for the right amount of time, you should be able to push the paint off easily.

You will make a big mess, so plan ahead. Cover the ground under the boat with plastic or a disposable tarp, weighted to stay put. Tape off your topsides carefully. Wear a Tyvek suit or clothes you don’t want any more. Get yourself a supply of rubber gloves. Use a trash can or bucket lined with a contractor-weight bag that you can drag along with you as you scrape and peel. Drop the wet, heavy flaps and curls of paint right into the bag.

In many cases, you’ll have to lie under the boat to get part or most of this job done, and you won’t be much better off than the miserable sander mentioned above. In fact you’ll probably look even worse. But it’ll be over quicker.

Repair any dings and gouges in the gelcoat, clean everything with hand-sanding and a wash, then finish with a wipedown using acetone or fiberglass dewaxing solvent.

Contact your town recycling center, your boatyard manager, or your local haz-mat people about what to do with the trash bag of old paint. Unlike the stripper used to remove it, copper bottom paint is definitely not biodegradable.

While the bottom is clean and before you do anything else to it, consider the benefits of adding an epoxy barrier coat like Interprotect, Pettit-Protect, or Water Gard. A barrier coat protects against water intrusion and the formation of blisters in the gelcoat, especially on older boats and those built with polyester resin instead of vinylester.

A boat bottom encased in Coppercoat instead of bottom paint, after a post-season  pressure-wash.

A boat bottom encased in Coppercoat instead of bottom paint, after a post-season pressure-wash.

Unless you’re planning on racing the boat and believe that a hard antifouling paint will grant you that extra fraction of a knot to vanquish the competition, go with an ablative (sloughing) paint. It will wear better and slough away more evenly over the long haul. Put on three coats. Make the bottom coat one color and the top two coats another color. That way you’ll know when the paint is wearing thin.

If the boat in question is over 25 feet or so, also consider Coppercoat as an alternative to antifouling paint. It’s expensive at the front end, but can last 10 seasons or more, solves the epoxy problem, is easy to maintain, and is environmentally superior to copper-based antifouling paints. The more bottoms you strip, and the more you paint, the better solutions like this look.

Good luck, strippers, and let us know how you do.

Comments

  1. Peter says:

    Hi
    ,
    After I scrape the old bottom paint off of my boat, where do I dispose of the paint chips?

    Thanks.

    • Doug Logan says:

      Hi Peter –

      Collect the paint on a tarp as you scrape it. Empty it from the tarp into a closeable container. Then check with your town hall or local waste-management people. Most counties or big towns have haz-mat facilities, or “haz-mat days” at the town dump, and will take the old paint off your hands.

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