It’s Painting Time Again

It's hard work keeping a boat looking good

As the old saying goes, you pay for your pleasures, and that’s certainly true when it comes round to the annual re-fit. The many little jobs that were just too awkward afloat, added to the big ones like antifouling, can all back up and lead to a formidable worklist. And to top it all, there’s the curse of aluminium boats – the paintwork.

There seem to be two schools of thought with aluminium boats and paintwork. The first is to touch up as you go along, then sand and paint on an annual basis when time and conditions allow. The second is to pretty much leave it alone and then blitz the job every five years or so. We tend to the former, as we think that there’s less chance of corrosion getting a hold under blistering paint, and in any case, some of the ‘let it go’ boats we’ve seen looked pretty terrible to us.

Tackling The Problem

We’ve been meaning to get to grips with the one area that is badly affected on Pèlerin, our OVNI 435 – the topsides around the rubbing strake. We had a welded strake fitted from new, and have suffered considerable amounts of blistering along the line between the unpainted strake and the topsides. As we’re out in the yard at the moment and have staging alongside to get at this area comfortably, we’ve tackled this head on, and have got the affected paint off to the point where we can start to prepare the surface for painting.

But what a job it has been. It’s now obvious that moisture was able to get under the paint along the unpainted edge, and also under a fillet of polyester filler that was used to fair up the weld before painting. All of the areas of damaged filler have had to be removed, and we now face the choice of how to best make the paint surface look good, preferably without recourse to filler. Our plan so far is to fair it up by hand, then get a couple of coats of epoxy primer on and see how it looks. Minimal amounts of filler could then be used (if necessary) to achieve a good cosmetic appearance, before two further coats of epoxy primer, then undercoat and topcoat. We also plan to paint the strake, so that there will be no ‘edge’ for moisture to creep under in the future. Whatever route we choose, it’s going to be a lot of work.

The good news is that there is no corrosion, but that’s about it! It has been a long and painful business, largely due to a bad cosmetic decision in the first place. And it’s a pity, because this is about the only area on the whole boat that has been affected. Areas of high wear and tear, and where paint has been chipped, have of course suffered, but on the whole it’s more than manageable.

A Changed System

We’ve always used an International Paints system, and had always used their Etch Primer as a base coat, as all of the factsheets insisted that this was vital to achieve an effective tie with the epoxy primer. Now it seems that Etch Primer has been withdrawn from the market, it’s now straight on with the epoxy primer, so we’re hoping that this will work OK. I’m always a little suspicious when things that were once so essential before are no longer necessary today. No doubt there are good reasons why Etch Primer is no longer available, but it would be good to know just what those are, and gain some reassurance that the new system will work just as effectively in the future.

Because I know one thing – we don’t want to be doing this job again next year!

{ 23 comments… add one }

  • Chris May 1, 2011, 12:08 pm

    Colin, as to etching primer, it may be that International has dropped it because they couldn’t compete on price. It is still actively used in the automotive and aircraft painting businesses where people still swear by it. (Some at it as well I’m sure.)

    It’s available for ~$100 a gallon +/-. Is it possible you are in a location that prohibits it? Here is a supplier (page updated within last month)


    • Colin Speedie May 2, 2011, 1:50 pm

      Hi Chris

      I’ve no idea, but I’ve tried on two occasions here in Portugal, and the yard just can’t get it.

      Etch Primer also seems to have been taken off International’s website, and I did try one or two of the bigger chandlers.

      Thanks for the link, though, and if I find out any more, I’ll post the details.

      • John May 2, 2011, 3:59 pm

        Hi Colin,

        OK, now I’m really confused. I think Interlux and International Paint are the same company. But now I find that Interlux is part of AkzoNobel which also owns Awlgrip, which I thought was US Paint.

        Anyway, no matter. The etch primer that I used with such success in the engine room of MC (see comment below) seems to be still available, or at least listed, here.

        • Colin Speedie May 3, 2011, 8:49 am

          Hi John

          Interlux and International are indeed the same company, part of the Akzo Nobel Group.

          The primer in your link is very different from the one that we have used in the past, and is well worth looking at for us in the future, although it doesn’t appear in the International listing in the UK. The Etch Primer we have traditionally used we called the yellow peril, and seems to have been removed from sale – a pity.

          Best wishes


  • John May 1, 2011, 12:08 pm

    I’m very disappointed to hear about the discontinuation of the acid etch primer. Like you, we have used that International Paint product with great success in the past and are great believers in acid etching generally.

    When we painted our old aluminum mast some years ago we were told that we could just use the gray standard primer. The paint failed in two years.

    When we did the boom some years later, we insisted on etching with a two part acid system from WEST, followed by acid etch primer from Awlgrip and then epoxy primer. The paint is still sticking to that boom 15 years later.

    This is now our standard system for all paint repairs on MC, and when done this way we pretty much never have an adhesion failure.

  • RDE May 1, 2011, 12:50 pm

    About 15 years ago I hired on as PM with a company that had two aluminum megayachts under construction. A week later a million dollar paint/fairing failure emerged on one of them. So I’ve had an intensive education in some of the things that can go wrong with painted aluminum boats.

    As you are aware, the transition edge between paint and bare aluminum is always problematic. Your choice to paint the rub rail is the best option– just sand and temp patch areas that become damaged on its face.

    Polyester fillers have no place on aluminum and should be ground off to bare aluminum and replaced with more moisture resistant epoxy.

    International Paint always recommended their 545 primer as the first coat on bare aluminum, a practice I don’t favor. The adhesion of the first coating to the bare metal is the most critical operation in the painting process. There are two procedures that I have found to work.
    1- Create a rough profile to promote mechanical adhesion, a 36 grit grinder works best.
    2- Thoroughly clean any grinding residue.
    3- Within a few hours, before any oxidation can take place, coat with an unfilled epoxy like WEST or MAS. If it is a high load area like a winch base, don’t hesitate to wet sand the raw epoxy into the aluminum surface. Let it cure to a green cure state and apply filler, or lightly sand being careful to not break through to the raw aluminum.
    4- If fairing is necessary, use raw epoxy filled with microballoons or one of the commercial pre-mixed epoxy fillers. If you have any Sterling fairing compound throw it in the garbage can.
    5- Lightly scuff sand before applying primers.
    6- If you fall through into bare metal the bare spot must be treated exactly as if starting from scratch.

    1- grind as above.
    2- Acid wash and alodine as per aircraft practice. Prepared surface is now protected and doesn’t require immediate attention.
    3- Pre-coat with epoxy.
    4- fair and prime as per above.

    Whenever anything is bolted to aluminum, whether aluminum, wood, or stainless, it should have a 4-6mil layer of plastic or mylar tape under it as an isolation barrier. All threaded bolts and screws need teflon anti-sieze compound or something similar.

    Fair winds

    • John May 1, 2011, 3:41 pm

      Hi RDE,

      I would certainly agree with everything you say above. We often use West System resin as the bonding coat on the aluminum and sand it in with wet or dry 80 grit paper.

      The only difference is that we have got even better results by using the West two part acid treatment first. This has worked much better for us than alodine.

      Having said that, some years ago when I painted the engine room on our boat, I scuffed things up and cleaned them as well as I could, but you know engine rooms–lots of nooks and frames that are hard to get to. So I used the Interlux acid primer and had great results even though I did not acid wash first. The great thing with the Interlux product was that you could paint it on with a brush, whereas the Awlgrip product must be sprayed.

      • Colin Speedie May 2, 2011, 1:59 pm

        Hi John and RDE

        Thanks for the useful comments, which we’ll certainly bear in mind for next time – we’ve gone ahead and painted over the rubbing strake, and we should be back in the water in a couple of days.

        We’ll see how the paint stands up to the next year, and if it works, great, and if not, we’ll look at alternative suppliers, and do a really thorough job. The simple fact is that we currently haven’t the time to start again, as we badly want to get back on the water!

        All our fittings are isolated as you suggest RDE, and I wish I’d bought shares in Tefgel, at the rate we use it. Alloy machine screws are used wherever possible for smaller fittings and below the waterline (such as the plates that cover our rudder hydraulics).

        But, like John, I liked the versatility of the International system, especially for touching up.

        Best wishes


  • Martin May 6, 2011, 10:00 pm

    “We often use West System resin as the bonding coat on the aluminum and sand it in with wet or dry 80 grit paper. ”

    Just requesting a clarification – it seems you’re not talking two-pack epoxy primer, but a thin layer of “normal” epoxy resin?
    And do you brush on a very thin (?) layer of this epoxy resin, and then sand through this painted layer, leaving the sanding grit to harden in this layer?
    I’ve been sanding the substrate, then I wipe off the sanding grit, and then quickly, within one or two minutes, get the paint down, hoping the aluminum does not oxidize in that one or two minutes. Sounds like I should change my method.

    • John May 8, 2011, 9:35 am

      Hi Martin,

      Yes, I’m talking about using standard WEST system two part epoxy resin with no filler as the first coat when we are going to use a filler to fair things out. When I say “sand in” I mean that you can get an even better bond by using a piece of 80 grade sand paper to key the wet resin into the aluminum, not sand said resin after it is dry. Once the resin goes tacky, but before it dries completely, we then put on a layer of filler made from WEST resin and their 410 sanding filler. When that is dry, we sand for the first time being very careful not to go through to the bare metal.

  • Gianca May 7, 2011, 7:44 am

    My choice is for no paint at all above the water line, but I remember Mr Garcia, owner of the French yard, suggesting to use a tape to cover the junction paint-bare aluminium.

  • Phillip Carr January 23, 2012, 9:29 am

    My boat is 13m aluminium, twinscrew motor boat built as a one off to Lloyds Class in Southampton UK in 1973. In 2009 the ultrasonics revealed hull thicknesses as new. I re-painted with International Interlux in dark blue. Adhesion is good but paint has dulled and appears to be still soft. I suspect low temp and high humidity during application. Anyway time to repaint and thinking of Awlgrip in white. Do I go back to bare aluminium and begin again or prime over the International and then apply Awlgrip? Would welcome comments.

    • John January 23, 2012, 6:33 pm

      Hi Phillip,

      If the adhesion is good, I can see no good reason to strip the paint back to bare Aluminum. We painted over dark blue Awlgrip with white, without any problems. Check with the Awlgrip rep though.

  • Richard William Lord September 28, 2013, 9:45 am

    My little aluminum boat and I are close to the bottom of the food chain compared to you ocean going heavy weights.. But for what it’s worth, when I “decommisioned” my 14′ 1980 MirroCraft last fall, I sanded her down to bare metal.. Then used a “poor man’s acid etch”—-vinegar and water.. Rinsed well, dried and hit her with 3 spray can coats (light, wet sanding between) of Rust-Oleum’s “Self Etching Primer”.. I finished up with 3 coats of Behr’s oil based semi-gloss paint, rolled out with a Harbor Freight foam roller..

    Almost a year later now and no blistering, peeling, chipping or cracking.. Granted, my “semi-gloss is now kinda-gloss” but, the main thing is— the paint’s still stuck..!!

  • Todd Huss January 19, 2014, 4:52 pm

    Colin, I’m curious to hear how the paint job has held up?

    • Colin Speedie January 23, 2014, 3:48 pm

      Hi Todd

      Like the curates egg – good in parts!

      Three years on, and most of the patches we repaired are OK, but some have done badly, mostly where they’re in areas that get abrasion or chipping. And then there are a whole new crop of blisters. At the moment I’m sanding and just leaving those areas until we’re at rest and able to finish them properly and start the painting process in perfect weather in one go.

      Best wishes


      • Todd Huss January 23, 2014, 5:42 pm

        Hi Colin,

        Will you continue to go straight on with epoxy primer or will you try and find etch primer next time? Just curious about your opinion on the necessity or lack thereof of an etch primer.


        • Colin Speedie January 23, 2014, 7:08 pm

          Hi Todd

          It depends on where we are, I think. If we’re in a yard where there’s a lot of painting being done then I think it will be available. Where we were last year at Peake’s in Trinidad I reckon they would have some, for example.

          However, I’d have to say that I haven’t noticed much difference in the long term condition of the touched up areas where we used the etch primer compared with those where we went straight on with epoxy. Preparation seems to be the key, as others have mentioned in the above comments.

          What we have to do is get the last bits of polyester filler off, and get right back to the bare metal – what a pain!

          Once we know what we’re doing, and get going on it I’ll post again. And next time we’ll do some trial areas, to see what works best.

          Kind regards


  • Norm May 19, 2014, 3:33 am

    Dumb question……how do you securely store partial cans of paint on a cruising boat? We have paint that we’d like to carry for touch ups, but I’d hate to the mess it could make of the interior if it got loose in a real storm….

    • John May 19, 2014, 12:00 pm

      Hi Norm,

      Not a dumb question at all, in fact a very sensible one.

      What we have done on Morgan’s Cloud is to fit an old plastic kitchen garbage can into a deep locker to hold paint cans. We cut it down so that it only just fits and the locker lid, which has securing barrel bolts, fits snugly down onto the top of the garbage can. The result is that any paint that leaks will be confined to the garbage can and can be easily cleaned out by removing the whole works from the locker and dealing with it on deck, or better still, on someone else’s deck! :-)

      We have had at least two cans leak over the years and were very glad of this set up on both occasions.

  • David October 6, 2014, 11:23 pm

    Hi Colin, can only commiserate at the fun of painting aluminium. We bought an Ovni 435 last year and are currently fixing up similar blistering problems. We’ve been using a Gerni high pressure washer with a simple sand blasting attachment that sucks garnet from a bucket, and produces a really nice profile. A wash and a meths rinse to dry the area, and hopefully the Interprotect primer will be long lasting. One challenge is the built in water tanks, which are impractical to sand blast, and suffer from a pox of white alu oxide spots and pitting. Have you had similar issues, and any suggestions as to how to treat? Cheers David ‘Mirabooka’ (ex Calypso Music’)

    • Colin Speedie October 7, 2014, 8:39 pm

      Hi David

      Interesting way to deal with the paint stripping issue – presumably you run the device at fairly low pressure? One thing I’d look at is the use of meths as a degreaser, as it’s not the best in my experience – I use acetone liberally on a cloth, until the cloth comes up clean, and got good results.

      The unpainted tanks are indeed an issue, probably to do with the water quality/acidity wherever you are. I always favoured epoxy painted tanks, but after talking to a number of people who have had problems with that system I’m no longer so sure. Monitor them is all that I do, and so far nothing major to report..

      On thing that we do is clean the tanks twice a year, with a product called ‘Hydroconazole’ which a water purifying compound that is suitable for use with aluminium. This seems to work well, although it’s hard to come by outside France.

      Kind regards


  • David October 13, 2014, 6:46 am

    Hi Colin, thanks for the tips, the sandblasting is done with the normal water pressure from the Gerni, ie about 2000 psi, and is pretty effective, but we find it quicker to sand first. We are using a water based 2 pot epoxy paint in the water tanks, so will see how it goes…let you know in a few years! Interesting that it sounds like yours are bare metal, as ours were painted by alubat. We have taken to using a filter to get rid of the chlorine when we fill them, as I suspect you are right about the problems being caused by the water quality. Cheers David


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