Paint Blisters

Discussion in 'Wood and Canvas' started by Greenlander, May 25, 2011.

  1. Greenlander

    Greenlander New Member

    Hi There,

    I just took my recently restored 16-foot wood-canvas canoe on its first trip. We had a lot of rain and a lot of in and out of the canoe on creeks and at portages. On the fourth day I noticed the beginnings of a few paint blisters on the hull. Each day more blisters were observed, and on the drive home (in a huge rain storm) more blemishes appeared yet again. The canoe is now drying and recuperating in my basement (boathouse).

    Some details:

    I used Northwoods Canoe Co. filler and let it cure for 10 weeks at 60 degrees F.

    I used Rustoleum topside marine enamel for three base coats of paint and finished with two coats of Epiphanes topside enamel. Painting began in February and took me about a month to complete, so the finish has had a bit of time to season.

    Based on my research on this site and others I imagine the problem was caused by:

    (a) improperly cured filler (seems hard to believe with 2++ months of drying time)
    (b) incompatibility of the Rustoleum and Epiphanes finishes
    (c) excessive water inside the canoe causing the finish to pucker

    In any case, I'm pretty bummed out after working so hard to achieve a decent finish. Any tips on what I should do next? Wait and see if the blisters disappear? Strip and repaint?

    Thanks in advance.
  2. Andy Hutyera

    Andy Hutyera The Red Canoe Guy

    Many of us have had the same experience. If you do a search you will likely find some older posts on the blister issue. I would suggest you just wait awhile and see what happens. I had a siimilar problem with one of my canoes. Eventually they just went away. Sometimes the problem reoccured, but each time it was less severe.
    Give the canoe a chance to dry out and see what happens. Doing nothing can't hurt and time just might get rid of the problem.
  3. Todd Bradshaw

    Todd Bradshaw Sailmaker

    It would be interesting to know what, if anything, is inside the blisters?
  4. goldencub

    goldencub Carpenter

    I don't think this sounds good at all. When the paint blisters, it loses all adhesion to whatever is below it - wood or primer or whatever. I think this adhesion is gone forever, even if after drying out, or over time, the blister might disappear, but it doesn't magically adhere itself to the substrate. The next small scrape on the suspect area will remove the entire old blister, won't it?? It would make me nervous, I think. Al D
  5. Todd Bradshaw

    Todd Bradshaw Sailmaker

    Yup. Though it may take months for paint to reach a final cure state, the chances that dried paint is going to magically re-bond in areas where it has delaminated are not at all good. Those spots are now being held in place by little more than the tensile strength of the paint film itself.

    There are a number of issues which could be at play here. The blisters may go down, but they really aren't going away. To start with, it's probably worth cutting one open to see what delaminated from what? The Filler from the canvas? (probably the least likely) The Rustoleum enamel from the filler? The Epiphanes from the Rustoleum? Something between the multiple layers of the same enamel?

    Other issues:

    Most enamels are labeled "not for continual immersion" for a reason. They'll survive a day or two of paddling, but if they get wet and stay that way, they can blister and peel, so that's one possible cause.

    Mixing brands of modern enamels could also cause some problems. Some contain ingredients to help maintain gloss, help it smooth out better or last longer that may inhibit the bond of other brands. Interlux Brightside literature, for example, says "With Fluro Microadditive for easy cleaning, resistance to staining and added abrasion resistance". In a nutshell, this means it has a form of Teflon in it and we all know how hard it would be to try to paint the inside of a Teflon frying pan. Other brands may well have similar substances in them which don't get along well. Different brands also use different solvent mixes and that might create compatability problems. I'm sure that if you asked the Epiphanes folks what makes a great base for their enamel, three recent coats of some other brand of paint wouldn't be their answer.

    Film thickness - When I hear of someone putting five coats of enamel on something, the first question that comes to mind is why? This is followed by "What was wrong with the first two or three coats?" and "What did you expect to achieve with all that paint buildup?" Maybe even "What did the directions call for?" When it's a mixture of layers of two different brands of enamel, it becomes even more curious.

    We all know that many coats of varnish can provide a deep-looking, glossy finish that is hard to achieve any other way. However, assuming that your surface is sanded smooth, paint is a different story. You're not looking through paint and seeing depth, you're looking at the surface of the last coat. If you can achieve a uniform color, a smooth surface and good gloss with a couple of coats (which is usually quite possible) putting more on top isn't going to gain you anything - and it may cost you some durability. Many modern paints have a target film thickness that has been proven to give the best results and life span. Additional thickness just makes it brittle and less durable, as it does with just about any unsupported film, including stuff like epoxy resin. You don't gain any more UV life as it is blocked by the pigment at the surface, you don't gain any more gloss if your original surface was fair, you don't gain (and may even lose) abrasion resistance and you may also be losing the paint's ability to flex a little bit. On a wood/canvas canoe, which isn't entirely dimensionally stable, that could be important.

    By all means, paint, scuff-sand and paint again until you have a good looking paint job, but you are deluding yourself if you think piling up many coats of modern enamels is going to give you a better, longer-lasting paint job. It very well may be doing just the opposite. And be very careful about mixing brands. With manufacturers scrambling to meet strict VOC requirements these days, they aren't all made from the same old stuff.
  6. OP

    Greenlander New Member

    Thanks for the comments so far.

    I've searched through the old discussions on this topic--there's lots of theorizing on why this is a terrible predicament (and how not to encounter it again) but my big question is, if waiting doesn't work to remove the bubbles, what should I do?

    Todd--thanks for your detailed response. I appreciate it. I did apply five coats of enamel however each received moderate to heavy sanding in between. I roughly followed Pam Wedd's painting procedure, as outlined in the Journal: Each coat of enamel was used to fill the tiny irregularities in the filled canvas and I sanded thoroughly in between coats with #180-#220 on a random orbit sander hooked up to a Shop-Vac to take down the high points.

    I opened up one of the blisters and it was dry and right down to the filler, I believe.

    If alkyd enamels aren't meant for multiple days of being wet, then shouldn't we be painting with something else? What did the old-timer guides use for canoe paint back when wood-canvas canoes were used day in and day out?

    For now I'll wait and see but I am very tempted to go at it with the orbital sander and take the finish back down to the base coats/filler and go back through the painting procedure. I guess a compromise would be to sand/refinish the blistered areas.

    Thanks again.
  7. goldencub

    goldencub Carpenter

    I don't think I'd spend time sanding and refinishing just the blistered areas. All that effort and next month a new set of blisters might appear?? I'd bite the bullet and take all the paint off and start all over again. And good luck whatever you decide to do! Al
  8. MGC

    MGC Paddlephile

    If you went through the old postings you may have read about my report of the same issue, blistering.
    In my case I did not paint as many coats, and I only used one type of paint, Pettit.
    I may not have waited long enough after painting before I took the canoe on a four day paddle.
    The filler had dried for several months before I painted.
    I am quite convince that my problem was due to finish of the filler.
    I think that I sanded the filler almost to a glassy surface in some areas of the canoe and that the paint did not grip properly.
    I re-sanded and painted the canoe again, this time with Epiphanes paint. So far so good.

    If you shellack the bottom instead of painting it, you'll never worry about blisters again.
  9. Todd Bradshaw

    Todd Bradshaw Sailmaker

    I mentioned in a previous thread that wood/canvas canoes are kind of a painter's nightmare in concept. I think this has always been true and most likely always will be. It's a combination of a number of different materials (wood with grain running various directions, canvas, which can shrink or swell, filler, which has enough "stuff" in it to be rather brittle and primer and paint. All of these elements can have different rates of expansion and contraction with weather changes, as well as different amounts of tolerance for these changes. If your 17' canoe gets hot or humid and the wood expands just 1/2 of one percent, that could mean a length change of over an inch! Some coatings may tolerate and recover from this, others won't, and the thicker and more filled with pigment and/or other hard mineral stuff they are, the less they may tolerate. If they can't tolerate it and return to "normal", then something is probably going to crack, peel, blister, etc. and it makes a pretty good case for getting enough paint on, but not over-painting and making your paint film even more brittle. When you toss in the fact that there are very few coatings that are actually waterproof (epoxy resin and tar being among the best, but still not perfect) we introduce another potentially destructive element into the mix (and actually INTO the layers of coating)....moisture.

    Sanding: Paint is not a particularly good defect-filler. That's what primer is for. It contains ingredients to help fill tiny voids and sand down smoothly. Everybody has their own methods, but personally, I put paint on for color and gloss only - and I don't start painting until the surface defects have been filled as needed and sanded smooth. Paint will get a light scuff-sanding between coats for better adhesion of the next layer and on some items, I may sand and polish the final coat for a smoother, more shiny finish, but I don't use multiple layers of paint as a fairing compound or defect filler. Other folks have their own methods, but I think there are better products for the job.

    MGC's point about sanding to the proper grit is also very valid and not to be ingored. You can peel just about any coating from just about any other coating if the first one was sanded too smooth. Fight the tendency that we all have to over-polish underlayers in an effort to achieve the perfect finish and follow the directions on the can. If it says sand to 100 grit, do so - not 220, 320 etc. as you are often just asking for trouble in doing that. The paint maker usually wants you to have the best-looking, toughest finish possible, so that you'll come back and buy more paint from them, as will your friends. They will nearly always give you the best directions they can for achieving that finish without problems, including what grit to sand to. Going off on your own and thinking you know better can be a serious mistake.

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