Epoxy Problem

Discussion in 'Boat Yard Basics' started by Frank_Sebastian, Feb 19, 2011.

  1. Frank_Sebastian

    Frank_Sebastian Well-Known Member

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    Hi Everyone,

    I have worked with epoxy for many years. I have had my share of problems in the past, but the last 15 years I thought I had it figured out. Yesterday proved that I do not.

    I have been working on my sons aluminum boat for a week now. I prepped the boat with 80 grit 3M sanding supplies and then coated it with the high strength Raka HP 900 and 631 hardener. No problem and a near perfect job with a few runs to sand out. After 10 hours I started applying the same mixture of 5 oz resin to 1 oz hardener into which 2 tablespoons of powdered graphite was added. I was heating the 6 oz mixture for 15 seconds in the microwave to make it flow out well and rolling it on with a 6" adhesive roller. When getting nearly complete I figured a double batch would finish the job and could be poured out on the broad area near the stern so it wouldn't kick off too quick. I heated the 12 oz mix for 30 seconds and poured it on the hull near the transom. I started rolling it out and it worked perfectly at first, then the roller started to smoke and what hadn't been spread was boiling on the hull. It affected an area about 3 ft long and one foot wide or 3 square feet total. I removed the worst of it with a scraper while it was soft (and hot). This morning I started to sand with the 80 and got nowhere. I switched to a 3 M stripping tool. (they look like a sponge grinding wheel) I have most of the worst ground off including the base. I will re-sand prime with pure epoxy and then re-coat with epoxy graphite. I figure the mess up cost me 10 hours labor and loss of the satisfaction of a near perfect job.

    The moral of this story is if your system is working fine, don't get lazy and try to save a little time. Also microwaves may not heat on a uniform linear scale.

    Best regards,
    Frank_S
     
  2. Brett

    Brett > PRO STAFF <

    That's a new one for me...thanks Frank.
    Another technique to research, pre-heating epoxy in a microwave.
    I would never have thought of that one.
    Although I'd recommend not using the one in the kitchen.
    The little lady might get a mite irritated...

                                [smiley=microwave.gif]
     

  3. Frank_Sebastian

    Frank_Sebastian Well-Known Member

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    I have an old microwave in my shop. Other than heat things with it I occasionally toss in a bag of popcorn. Probably not a good idea.

    Frank
     
  4. DuckNut

    DuckNut Brandon, FL

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    And I thought that I was the only one who melt trash cans.

    I found that the foam rollers are really good at soaking up a lot of resin and then not relesaing it. Then all of that epoxy in the roller starts to heat up.

    Luckily I have never had a fire.

    Fun sanding graphite, eh?
     
  5. jasonrl23

    jasonrl23 Plays with Glass...

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    An aluminum/foam box with a 120W lightbulb will heat resin up really well. Super cheap too.
     
  6. Brett

    Brett > PRO STAFF <

    Another good one, a big boy's Easy Bake Oven... ;D

    I've used heat lamps to speed curing on patches.
    Warm water in a tub to raise the temperature of quart containers of FLAG epoxy before mixing.
    And an oil-filled radiator style heater under an inverted hull so that the epoxy would cure on the warmed hull.
    But I still prefer to keep the epoxy containers in a warm room the night before using.
    Less chance of mistakes in the shop that way...
     
  7. jasonrl23

    jasonrl23 Plays with Glass...

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    I used that method a few years back for heating resin prior to infusing. Needed to get resin through up to 1/2" worth of 9oz E-glass. Works really well for reducing the resins viscosity .
     
  8. firecat1981

    firecat1981 BBA Counselor

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    Are you guys using standard resin? I've been using laminating resin but never had to heat it up, and wouldn't that speed gel time?
     
  9. jasonrl23

    jasonrl23 Plays with Glass...

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    I believe the rule of thumb is every 10 degrees above 77 halfs the gel time. Works backwards also.

    When I used heated resin, the full part was infused in less then 2 minutes. Gel time didnt matter much. Was also a closed mold. Was also mil spec resin. The same can be done with your standard EPON epoxy that almost everyone carrys.

    Just to be clear I mean pre-heating the resin, not the hardner. And not to where it burns your skin or anything. Luke warm or maybe a little hotter.


    Hand layup or vac bagging I try to avoid any kind of heat unless it can be applied uniformly. Thats just me.
     
  10. Frank_Sebastian

    Frank_Sebastian Well-Known Member

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    I wasn't using a standard resin. It is a high strength resin and hardener that is mostly used for boat bottoms. The heating is needed to get the mixture thin enough to apply. Once it kicks it gets hot. To avoid overheating it must be poured on and spread very quickly with adhesive rollers. (not foam). I have used this same product many times without problems. Ordinarily I would mix and apply it in my air conditioned shop. Since it was a cool day I did it outside. The sun likely warmed the aluminum somewhat and made the problem worse. Next time I will be a little more careful.

    Best regards,
    Frank_S
     
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