Brown/bluish spots on freshly painted boat

Discussion in 'Wooden Boat Building and Restoration' started by laukejas, Aug 18, 2016.

  1. laukejas
    Joined: Feb 2012
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    laukejas Senior Member

    Hello,

    It seems that troubles with my little home-made boat, Melatelia, are never going to end. I built this stitch and glue dinghy last summer from birch plywood, epoxy and fiberglass on chines. Painted with urethane alkyd enamel on the outside, exterior grade acrylic house paint on the inside. Before painting, all wooden surfaces received 2 sealing coats of epoxy, acting as a primer for paint. Before painting, I washed epoxy with mild soap solution and let it dry to remove amino acids. First season the paint held fine, except for scratches here and there.

    Then, during winter, the boat had to be stored in a very cold and very damp environment. During this storage, the inside of the hull developed some brown/gray spots. I attributed them to mildew. So, this summer, I removed as much of the old paint as I could, re-applied epoxy seal, and painted a new, fresh layer. Inside of the boat was shinning white.

    That was just a little more than 2 weeks ago.

    After letting paint to dry for 3-4 days, I put the boat in the water. I keep it beeched ashore under open sky, and take daily sailing sessions. There's plenty of sun and wind to dry the boat, and the weather is quite dry, though we had quite a lot of rain. The first thing that happened after the first rain was that the cockpit paint became yellow at some places. I attributed it to a bad paint, though I paid a fortune for it.

    But then, over the course of these few weeks, the inside of the hull started developing the same gray/brown/bluish spots all over. Some places are clean, but some are really, really bad. As soon as I spotted them, I tried rubbing them off with a rag, later - with bleach and rubbing alcohol. It helped a little, but not enough to stop these spots from spreading. They have now spread all over the cockpit and decks, and I can't seem to do anything to stop them. They look like mildew, but the boat was painted just 2 weeks ago! With plenty of epoxy sealing. There were quite a lot of rains in these few weeks, sure, but there's also sun, wind, and occasional cleaning to prevent any kind of trapped moisture.

    What the heck is happening? The paint is definitely not a cheap one - I spared no expense this time. It is surely exterior grade.

    I can't tell whenever these spots are on the outside of the hull, because it's deep blue, and they're much more difficult to spot.

    Here are some photos. While viewing them, try to picture that just 2 weeks ago, the boat was shinning white. Now, the paint is yellow almost everywhere, and these spots have overrun everything. Though it appears that the locations where the epoxy is really, really thick (like fillets) are clean of these spots.

    (the pictures are highly zoomable, click on them to view in high resolution)

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    I'd really appreciate any input... Thanks in advance :confused:
     
  2. LP
    Joined: Jul 2005
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    LP Flying Boatman

    I've heard that there may be an incompatibility between alkyds and epoxy. I once did this and it seemed like the paint was never going to dry properly. In the areas where I applied it on top of some varnish, I had no problems. I know this is different than your problem and you don't seem to be having problem on the exterior of your boat, but you may be having an incompatibility issue since you did not use a primer.

    Ive used exterior latex on some homemade kayaks without any problems, but always used a primer.
     
  3. laukejas
    Joined: Feb 2012
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    laukejas Senior Member

    Interesting. The only incompatibility issue I heard about was this thing with amino acids in epoxy - they say you must wash epoxy-saturated surfaces with hot water/soap solution to remove these acids, or else the paint might take forever to dry.

    I red on several sources that epoxy can act as a primer by itself. I saw some "epoxy primers" in my local yacht store (which were outrageusly expensive), but the consultant assured me it is nothing more than thickened epoxy resin. So I just used simple epoxy resin to prime my boat before painting. I confess I know very little about painting, but why would I need another kind of primer on top of epoxy? What does it do?
     
  4. SukiSolo
    Joined: Dec 2012
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    SukiSolo Senior Member

    I take it that the epoxy coat was fully cured and sanded first? I've not had this problem but as epoxy will harden for a couple of weeks or so some leaching of the amines is possible affecting the paint.
     
  5. laukejas
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    laukejas Senior Member

    Yes, of course. I let it cure for a full two days, then washed, sanded and painted on top of it. Anyway, I did the exact same procedure last season when I built this boat, and had no such problems.

    What's puzzling for me here is that these spots don't appear where's a thick epoxy cover, like on fillets and fiberglass. Only where the "bare" plywood is. It seems to be affecting plywood only.
     
  6. Barry
    Joined: Mar 2002
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    Barry Senior Member

    Some random observations

    1) The surface appears to be extremely rough and pitted looking. The dark discolorations appear to lie in the craters of the rough surface. Ie at first glance the
    color looks to be airborne particles that have been captured in the craters. Are there industrial plants with a lot of particulate near your boat? A simple test for this is to paint a section, let it dry then tape over some plastic in the area to keep anything airborne off the area and see how it works out
    You are assuming that the discoloration is coming from inside the paint or a slow leaching of the primer through the surface coat. While the pictures, to me, show an accumulation of dirt in the craters

    2) The pictures do not reveal a gloss finish. Generally with house paints, the duller the sheen, the softer the surface and the more porous the surface is. So you could try a gloss coat on the gunwhale to see how this works out

    3) Your comment re " it does not appear to be a problem where the paint is thicker"
    From the pictures I see one unaffected filet and this filet area seems to be smoother, ie less craters to capture dirt etc.
     
  7. laukejas
    Joined: Feb 2012
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    laukejas Senior Member

    Well, the surface is actually smooth in most of the boat, except for a few spots where I did a poor job of epoxy smoothing and sanding. All open surfaces away from edges are smooth, though. It might be an optical illusion, caused by the multitude of these spots. If it were dust or dirt, it would clean off with a little effort, but it doesn't. There are no industries nearby, I am now located in nature, by the lake. The air is as clean as it gets.

    I do not have my workshop with me here, nor any hardware stores within 50 miles to try another kind of paint, but I'll keep your advice in mind... It's not the first time someone tells me that gloss finish is more resistant than dull one.
     
  8. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    I ran into something like this years ago and it drove me nuts, until I actually saw the damn bug. This little beastie landed, took a poop and flew away. I don't know if it's poop and suspect it actually laying eggs or something. It doesn't wash off very well and can bleed through lacquer, alkyd and acrylic based primers and acrylic and alkyd top coats. My only fix was to wash, which didn't do much except change it's color a little, sand, epoxy primer than top coat again.

    When you do repaint, rig a plastic drop cloth over the work, as close as you can arrange, so bug s land on it and not the wet work.
     
  9. laukejas
    Joined: Feb 2012
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    laukejas Senior Member

    Well, in my case, that would be one big bug, or at least a swarm of them to poop enough to cover my whole boat! I haven't seen any bugs, though. I don't really think that's the case here... But it's something to look out for sure. Thanks for advice.
     

  10. sdowney717
    Joined: Nov 2010
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    sdowney717 Senior Member

    "all wooden surfaces received 2 sealing coats of epoxy, acting as a primer for paint"

    Paint a primer first to go on top of the epoxy.
    I like Zinsser primer, seals well the surface. Perhaps your acrylic paint is reacting with the epoxy, either that of your choice of paint is growing mildew. Some bathroom paints have mildewcides added to the paint and you might be able to find one to add into your paint.

    Mildews actually etch surfaces when they eat the surfaces.
     
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