Epoxy Problem

Discussion in 'Boatbuilding' started by Ike, Sep 16, 2015.

  1. Ike
    Joined: Apr 2006
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    Ike Senior Member

    About two months ago i was refinishing a wood dinghy I built about 7 years ago. I used 4 oz glass cloth and epoxy resin. The only thing I did different was I used a different brand of resin. I have always used system three. But my usual source wasn't available so I bought resin from a different company. It's Pro Glas. It is a lot less viscous than System 3. Anyway I followed the instructions (it's 2 to 1) mixed it for two minutes with an electric drill. Most of it set up fine but in spots it did not gel at all. These brown spots were tacky for a long time (I'm talking days) Now they are kind of plastic and can be scraped off with a knife. They gum up sand paper bad! (ignore the pine needles. It's been sitting outside for two months.)

    In addition it ran like crazy so I am having to do this all over again anyway.

    Any ideas?

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  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    I'm not sure Peter, but I do notice a lot of fabric weave visible in those spots. Has it been 7 years already, since you built that puppy? It's difficult to tell what it is. What plywood is it over? Some types of pine and fir can develop a mold like substance on the surface, which initially isn't visible, but with the presence of moisture can show up as dark spots. Are the spots depressions too?
     
  3. SukiSolo
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    SukiSolo Senior Member

    Could be PAR, I don't like Doug Fir Sapwood very much for this very reason. Heartwood is excellent, and suspect some other species are very similar. Could also be some 'oils' in the ply leaching through pinholes in the old epoxy/fabric and causing a reaction with the new stuff.

    I've assumed the surface was solvent cleaned and sanded prior to application. Petrol and cellulose thinners will mostly remove any nasty oily scum from the surface prior to sanding. Even fresh water lakes seem to generate enough algal growth and 'scum' to require thorough removal. Best done prior to sanding so the paper does not mix the contaminate onto the 'fresh' surface....;)

    Hopefully a bit of wire brushing the sand paper will get the plastic lumps out.
     
  4. Ike
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    Ike Senior Member

    Here's a link to the building of this dinghy http://newboatbuilders.com/pages/Dinghy.html

    The wood is 6mm Okoume BS1088 marine plywood. The bottom had not been glassed at all. I had taped the seams with glass cloth tape during the build but had not glassed the whole boat. However, the bottom was getting dinged up a lot so I thought I would glass it for more protection.

    There were at least 4 applications of Sys 3 epoxy to the bottom (maybe 5). I lightly sanded it with 120 grit, wiped it with acetone. This was all done in a tent (of sorts) so the crap that falls from the trees here wouldn't get on it. But I wonder about the continual rain of sap from the Douglas Firs here. Every day the windshield on my car has tiny spots of sap on it. Anyway, I cleaned it, wiped it down, actually several times.

    The spots are depressions. It is as if there was something there that caused the resin to sort of shrink away from what ever was there. I have to assume it was some sort of contamination.

    I had done the same thing (glassed the bottom) on a 12 foot rowboat, with no issues. So I didn't foresee any this time. As I said the only thing different is the resin.
     
  5. Ike
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    Ike Senior Member

    After reading Suki's comments about freshwater lakes, I got to thinking about that. The only place I use this boat is American Lake, near Lakewood Wa. It is notoriously contaminated with fertilizers from the lawns and gardens of the mini mansions that surround the north half of the Lake. The Southern half is in Fort Lewis, but water doesn't recongnize boundaries. The I/O on my Sea Ray is constantly covered with white powdery crap from the lake. At first I thought it was some sort of galvanic corrosion but the local Mercury dealer informs me it is the crap in the lake and is very common and essentially harmless to my I/O and plastic boat, but what about wood?
     
  6. SukiSolo
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    SukiSolo Senior Member

    Thanks for the extra information Ike. One other thing comes to mind, was it dry enough to epoxy? Might sound odd, but I once had a dinghy shell stored 'dry' (unfinished), for a couple of years and even after leaving for a few weeks in a bone dry workshop in summer the applied epoxy sheathing started to show signs of not saturating the ply, and lifting. I had to strip it off and allow it to dry longer, and redo the job. Just shows how water vapour can remain in the top ply veneer quite a long time, even when it seems dry enough!. Second attempt worked fine and still solid 12 years on.
     
  7. gthemans
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    gthemans New Member

    I had a problem similar to this once, the epoxy hadn't hardened properly because it had been left to set overnight in the cold.
    Instead of starting again, try adding a layer of hardener or resin with a ratio of say 1:5 (epoxy to hardener)
     
  8. JR-Shine
    Joined: May 2004
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    JR-Shine SHINE

    my first inclination when seeing the pictures was a contaminate in the glass, but after reading the epoxy never cured that probably rules that out (not 100% ruled out though :))

    If its a thick epoxy, it may not have mixed all the way. I would not use a drill to mix, its hard to scrape the sides of the mixing cup adequately. Check your mixing pot, if there are tacky places inside the cup then you have your answer.

    Its very odd
     
  9. Ike
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    Ike Senior Member

    Unfortunately I tossed the mixing cup a long time ago. But you may be right about uneven mixing. With a much thicker resin my mixing method probably works fine but with this thin epoxy maybe not so well.

    Interesting comment about the wood being dry. The boat sits outside all the time. We have had the hottest, driest summer on record. Rather remarkable for the Pacific Northwest. More like eastern Washington than western Washington. But still, it has also been more humid than usual.

    Let me clarify. The epoxy did not cure in those brown areas. Everywhere else on the boat it cured just fine. It also did this more on the left side than the right. But then the left side was the second cup of resin, which lends support to the mixing idea. Maybe the first cup was more mixed than the second.

    I use the drill with a large allen wrench chucked in as a mixing paddle. I found along time ago that this eliminates air mixing into the resin and and helps eliminate bubbles. But you have to make sure you stir it for long enough to get a good mix and get around the sides and the bottom. Using a wood stirrer by hand never worked well for me and got too much air into the resin. Also keeping the boat in the shade out of direct sunlight prevents bubbles.

    I'm beginning to think there was some contamination in or on the wood that I couldn't see, and the sanding and acetone didn't remove, and my mixing wasn't good enough.

    Well, I have to do it all over again anyway. But it's a good exercise to try and figure out where it went wrong.

    Thanks to everyone for their thoughts.
     
  10. PAR
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    PAR Yacht Designer/Builder

    If it was a bad mix, then the spots are the accumulation of dirt in the goo, possibly some beasties finding it's enrichened state tasty too.

    I do machine mix, but only big patches. It's too hard to get the mixer in all the corners of the mixing tub and scraping the sides is sketchy too. To keep bubbles down, I use a wholly different technique, I call the slow roll. I pour the resin/hardener combo onto a shallow pan (tupperware) and let it pool along one edge. Using a plastic applicator, I slowly drag the epoxy up the bottom, after inclining it several degrees. Gravity tends to cause the goo to run back down to the corner, I started pulling the goo up from, so with rhythmic strokes, I can time them to scrape a fresh batch on each stroke, with the rest is running back towards the pooling goo. The motion is deliberately slow and you're rolling the goo over on itself, as you move the plastic applicator. 2 minutes of this and you're ready to pour it on the work or add some fillers. I use large, shallow "cake carriers" which I've found at the local discount department store. the smallest is about 12x18" and just 3" deep, so the epoxy can run out and pool in a shallow film, as I take to the work or add fillers, keeping it cool.
     
  11. LP
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    LP Flying Boatman

    I once had a problem with some epoxy where the resin had crystallized and I put the jug in hot water to decrystallize it. I thought that I had fully done so. Also of note was that the resin was about two years old. When it cured, it had a waxy looking coating that I thought to be blush, but no amount of water or acetone seemed to touch it. I gave it a thorough sanding and went on with the next coat. The next coat had all kinds of pin hole locations where it looked like the second coat was trying to draw awayfrom the underlying. Not your scenario, but if you had some crystallized resin in your mix, it would not have mixed with the hardener and been semi-encapsulated by the portion that did mix. A hot day in the summer sun could then decrystallize that portion of the resin and turn it liquid again creating your soft spots. But, to absolve myself of any responsibility of the last statements, I must say that while I may sound like I know what I'm talking about, it sheer conjecture on my part. :eek:

    The moral of my story though is to always make sure there are no crystals in me resin (microwave it till it's watery if there is a doubt) and if I screw the ratios in any direction I go on the resin rich side every so very, very slightly. If I had crystallization of the resin, my mix could have been going rich on the hardener side causing my so called blush, though the it wasn't behaving like blush. :confused:
     

  12. SukiSolo
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    SukiSolo Senior Member

    Good point LP, you may have nailed it. I've always been fastidious especially when clear coating with epoxy to warm up the base resin 'til glass clear. I tend to use an oil filled radiator to do this, but occassionally the top of the woodburner....;)

    Naturally it must be cooled again to get 'normal' setting times but it does stop a certain cloudiness/milkyness that can occur when the resin has been stored a while. If your going to varnish over the top, it is essential to do the heat/cool cycle as a wise precaution.
     
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