Non-blistering water absorption

Discussion in 'Materials' started by Jamie Kennedy, Jul 27, 2015.

  1. Jamie Kennedy
    Joined: Jun 2015
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    Jamie Kennedy Senior Member

    Non-blistering water absorption in polyester-glass composites.


    I have 27 year old laser sailboat that has absorbed a lot of weight. The original 130 pound hull now weighs about about 150 pounds. I suspect also of that is water in the airex foam core of the deck and cockpit sole, and in the hull stiffeners which run lengthwise. When I dry it out it might get down to 140 pounds but it very quickly will reabsorb back to 150 pounds. I used to race competitively but now race more recreationally and rather than replacing the boat I don't mind doing a little research and experimenting to see if I can learn something and have some fun.

    Questions and ideas:
    1. POROSITY: I suspect the gelcoat on the exterior and the non-gelcoat interior cured polyester-glass has become more porous over the years through the action of wetsanding, cleaning with acetone, UV rays, and perhaps acids from pine needles and stuff sitting on and inside the boat over the years. I also understand lower layers of gelcoat are more porous than the original surface layer. There is also some spider cracking here and there, so mechanical flexing and crack propagation will also increase porosity.
    2. DIFFUSION: In addition to pores in the polyester through which water can be absorbed more easily, water molecule can also diffuse into the gelcoat ad polyester, although much more slowly.
    3. WICKING: Once in contact with the glass fibres, through cracks, pores, or diffusion, I suspect the water might be able to wick along the glass fibres, particularly where the bond between the polyester and glass fibres have weakened over the years. In addition to being a means through which the water can migrate and weight can increase, this makes the hull considerably less stiff in places.
    4. WEIGHT INCREASE: Other than the foam core, how much water might be absorbed in polyester-glass construction. There is no blistering. Could it be as much as 10 pounds in a 130 pound hull? Of this weight increase, is it a molecular absorption, where the polyester chains have broken down and some hydrogen and oxygen has been molecularly combined with the polyester causing the polyester to expand in volume while also weakening due to broken bonds?

    REMEDIAL ACTION: Here is where I want to go crazy. My goal is try to get the boat back down to a competitive weight.
    1. Repair the deck and cockpit where the airex core has failed.
    2. Wash the interior of the hull with acetone, by dumping in a quart and tumbling the boat around with a guy on each end of the boat, in order to mix with whatever moisture is in the fibreglass, displace some of that moisture with acetone, and then drain the acetone-moisture mixture out and let evaporate the rest of the acetone out using a shop vac on blower. I will not use a hair dryer inside the hull until most of the acetone is out as I think it could actually explode.
    3. Next do the same with 99% isopropyl alcohol, to try and get more of the acetone out so that it won't continue to eat away at the polyester-glass increasing its porosity.
    4. Finally, try to seal off the cracks and porosity by poring in some very thin urethane, and tumbling it around as before, draining excess out the hull plus, and then putting it on its deck to let any remaining excess spread as evenly as possible, and because I am most keen on sealing off the airex core deck. Possibly two coats?
    5. Weigh the boat before and after each stage and document everything.
    6. Give the hull itself a good cleaning with acetone, and good wetsanding, and even grind down the gunnels 1/4". Seal the gunnel hull deck joint with gelcoat or thickened epoxy. Repair any serious chips or cracks in the gelcoat.
    7. Seal the bottom with wax to try and make it less porous.

    Comments?
    I don't think I can get it back down to 130, but I am hoping I might get it down to a stable 140, meaning if I get water in the boat and drain it out it will weigh 140.
    Which of the above steps are either really bad ideas and why?
    Which of the above steps are just a waste of time and can be skipped?
    Any alternative ideas or experiments you think I might try?

    p.s. Of the 200,000 lasers produced over the past 45 years, how many do you think have made it to a land fill, and when should this one join them?
     
  2. Jamie Kennedy
    Joined: Jun 2015
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    Jamie Kennedy Senior Member

  3. ondarvr
    Joined: Dec 2005
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    ondarvr Senior Member

    First, don't over think it, everything absorbs water and is affected by it.

    Several things can determine how long it takes to gain weight, and it won't gain much weight at all unless it been kept in the water for long periods of time, you aren't going to gain weight through absorbtion in the laminate by the end of the day. The foam would be a more likely candidate for rapid weight gain.

    The exact resin, catalyst, catalyst %, how well it was mixed, ambient temp, exotherm temp, method of lamination, type of glass, glass to resin ratio, gel coat type, gel coat thickness (and other variables just like in the resin), Humidity, experience level of the workers, age of the laminate, plus other things will determine how well it holds up to water permiation and the speed at which it takes place.

    Typical lab testing takes place with one general purpose resin in a controlled environment that doesn't come close to real the world production conditions, and real world production can produce parts that can be far better, or far worse than those done in the lab for testing.

    Rinsing with acetone and alcohol isn't going to do much, warm circulating air will be far more effective in removing the small amount of moisture in the laminate.

    How long has it sat in the water over the last few years, does it sit in the water for days on end now, or will it in the future? You estimate you've absorbed about 3 gallons of water, that's a significant amount.

    Coating with anything will add weight, and if you coat it with something, epoxy would be about your best bet. Figure out your sq ft and you can do the math as to the amount. You need about 10 mils of epoxy to seal the surface well, less for shorter immersion periods.

    There can be far more to discuss on this subject, but I need to go right now.
     
  4. Jamie Kennedy
    Joined: Jun 2015
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    Jamie Kennedy Senior Member

    Thanks for the comments. It's a 14 foot dinghy that is dry sailed, but they do tend to get water in the hull. Freeze thaw cycles during winter storage also causes a lot of micro-damage. Just picked up an old boat today, 1982, for $560. Just the hull and 3 old spars but I needed some spare spars and I now have one hull to sail while I work on the other. I agree most of the water is probable in the core material. I will weigh the boats and dry them out as much as I can with a hair dryer and weigh them again and not do anything to drastic. I have some old fiberglass kayak skins I can do some tests on though. Cheers.
     
  5. CloudDiver
    Joined: Jun 2014
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    CloudDiver Senior Member

    Not sure if this helps, but I just did a blister repair on the bottom of my Catalina 22. All the solvents you mentioned are probably a waste of time/effort. I took my boat out the water in September, it was on the trailer until November, then it went indoors on stands through December. All this was drying time. I took the keel off and inverted the hull, sanded off the old bottom paint and ground off the gelcoat below the boot stripe. ground out the blister pockets, there were over 200 but very shallow and the size of a dime or less.
    I let it dry out for another 8 weeks in-doors. It got epoxy filler in all the pockets then a coat of epoxy resin, faired, then a new single layer of 8.9 oz glass, epoxy bottom primer and then new bottom paint.

    Anyway... on a Laser that is lighter/easier to invert... I'd take off all the old gelcoat and let it dry out for 2 months. Take advantage of the summer warmth. If you do it in a garage use a de-humidifier to speed the process. If you have it outside don't worry about it being rained on, spraying the bare glass down with water helps speed the drying process like they do with concrete slabs.
     
  6. Jamie Kennedy
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    Jamie Kennedy Senior Member

    I agree the acetone will very probably do more damage than good. I got the idea from a chemistry prof that uses acetone to speed up a process of drying a filter during a test for sulfur content in fuels. The trouble is any acetone left behind will further weaken the polyester further where it is already weakened and permeable with micro-cracks and fissure. My hope is that I can follow that up with urethane, but only if the urethane can get into those same cracks and fissure. I don't expect the urethane to strength those cracks and fissures just to seal them. I am wondering now if a better approach might be a one step process where I thin the urethane with something, perhaps acetone perhaps not. Heat up the hull as much as possible, within reason, and then throw in the thinned urethane and swish and tumble. As the hot hull cools the action of condensing water vapor may help suck in some of the thinned urethane. The urethane itself cures by combining with some of the moisture does it not? What is the best thinner for urethane? I think I asked that before and I think the answer was whatever the manufacturer recommends on the can. I may do some test with strips of the old kayak parts. I suspect I will add as much weight as I remove, but I am hoping I will end up with a hull that might at least now absorb as much water going into the future.
     
  7. ondarvr
    Joined: Dec 2005
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    ondarvr Senior Member

    What type of urethane are you planning to use? People typically use epoxy to seal water out because not only does it do a very good job at that, but it is also quite strong.

    Acetone isn't going to damage the laminate in a short term exposure like this, it just won't really help in drying it out.

    You are stressing over things that mean little to the performance of the boat. If the boat was stored out of the water, and not under a tree with a plugged drain in the bilge, the laminate shouldn't be saturated with water. The foam could easily be though.
     
  8. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    How about a different approach. How much do you weigh and can you afford to shed 20 pounds?
     
  9. waikikin
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    waikikin Senior Member

    Or if he cant shed the weight..... move on to a Finn...........
     
  10. Jamie Kennedy
    Joined: Jun 2015
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    Jamie Kennedy Senior Member

    touché :)


    [​IMG][​IMG]
     

  11. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    I fixed your "IMG" post . . .
    [​IMG]
    What you're describing is why so many are for sale cheap. They just wear out, usually from hard racing and/or well fed skippers.

    In reality, fixing an old gal isn't usually worth the bother, but you pretty much know what has to be done. She needs to dry out. Once dry, there's a few different treatments you can apply.
     
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