Epoxy Working Temperatures

Discussion in 'Materials' started by mariobrothers88, Dec 12, 2020.

  1. mariobrothers88
    Joined: Sep 2020
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    Location: San Diego, CA

    mariobrothers88 Senior Member

    Hi guys, I purchased the Raka UV Epoxy system with Slow UV inhibited Part B. This is what the website says about it:

    "The slow hardener is very slow (pot life of a 3 oz. mass at 77 F is more than 25 minutes). Working cure strength, using slow hardener, will take about 24 to 48 hours at approx. 77 F. 606 hardener should be used in temperatures above 60 F. "

    I glued the timbers to my bulkheads last night when temperature was in the 50s throughout the night. Today, the temperature should be from 60-63 for about 8 hours then dropping to the 50s overnight. Tomorrow should be a bit warmer during the day, probably upper 60s for about 8 hours.

    Should I just leave it clamped for 6 days or longer in order for the epoxy to fully cure? Will I have any issues with using the slow hardener with these temperatures as long as I give the epoxy enough time to fully cure?
     
  2. mariobrothers88
    Joined: Sep 2020
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    Location: San Diego, CA

    mariobrothers88 Senior Member

    This is what Raka saysa bout the UV inhibited system:

    "We feel this hardener is second to none in its ability to resist blushing, UV breakdown, color change, white clouding and water spotting.

    We tried many UV inhibited type epoxy systems before we settled on the best formulation. With several UV Inhibitors this formulation has excellent UV resistance. This formulation also has the best resistance to cratering and trapped air bubbles in the cured epoxy coating.

    Raka UV Inhibited System
    like our other hardeners has good strength properties, excellent water resistance and the best general chemical resistance of our hardeners. The cured epoxy system gives great stiffness and was designed to work well for surfboards and other clear coating applications. The UV Inhibited Hardener
    is mixed by volume one part hardener to two parts of our UV Inhibited Resin. This system has a good pot life approximately thirty minutes at room temperature yet is relatively quick curing compared to other hardeners and can be used in temperatures down to 60 F . The wide temperature use ability of this system will simplify the needs of many customers who do not want to have to carry a combination of fast and slow hardeners. The UV Inhibited Epoxy System reaches a tack free stage quickly and can be sanded in less than twelve hours at room temperature. "

    It says this system can be used in temperatures down to 60F, but are they referring to daytime temperatures or nighttime temperatures as well. Would it be ok if daytime temperatures are above 60F but night time temperatures are below 60F?

    Thanks everyone!!!
     
  3. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    They mean keep it at 60 or above for it to cure in the time-line they describe.

    Chemical reactions tend to become slower as the temperature drops.

    They list 60F because they need to put some number down on paper, and 60 is used by many manufacturers for different resin types. They could use 59F just as easily.

    Going to lower temps will slow the curing process, as you go colder the process will eventually come to a stop.

    The slowing and eventual stopping of the curing process will be different for every resin.

    So, let it sit as long as possible if you have an environment that will stay below 60 for any length of time.

    And remember that the epoxy within the joint will warm and cool at a different rate than the surrounding air. Just bringing the temperature up from 50 to 70 doesn't mean the epoxy is experiencing that temperature increase. It will need to be exposed to those higher temperatures for an extended period of time.

    A thick fillet will cure quicker than a thin glue joint that has been clamped. So don't assume that because the leftover mass of epoxy left in the container is an indication of how cured the epoxy in the joint is.
     
  4. mariobrothers88
    Joined: Sep 2020
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    Location: San Diego, CA

    mariobrothers88 Senior Member

    Thanks for the reply ondarvr!

    For the bulkhead timbers, when can I remove the clamps (to use for other things) given the current temperatures? I feel like the epoxy is hard enough after 24 hours where I can remove the clamps and allow it to sit and finish curing without clamps, is that correct? I would like to use the clamps to work on some other things. Or should I leave the clamps in place for longer?
     
  5. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    I do not like temperatures under 60F for epoxy curing and have found it to be problematic.

    Oftentimes, those temperatures will result in amine blush. Or, those temperatures will not result in full cures.

    The greatest problem is you will be concerned about whether your mixes were good enough. If you mixed something and it is close to the ground and the ground temperatures are low and air movements little; you will get slower cures and the next day, you will find yourself wondering if things were okay.

    I realize it is winter, but you will need to make sure the epoxy is hard enough to not show fingernail marks.

    Most of the times; you will be fine.

    Open cures of sheathing are especially prone to the blush issue.

    You can remove clamps if the epoxy is not gummy.

    Also, for the sake of boatdesign.net, I think you need to parse your questions into a build thread versus asking questions each step of the way in a new thread, but that is just my opinion.
     
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  6. hoytedow
    Joined: Sep 2009
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    hoytedow I'm not a cat.

    Once you start a build thread you may be able to persuade the moderator to consolidate the smaller question thread contents into it if you ask him nicely.
     
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  7. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    I thought I might add... pieces glued to the boat as cleats and not fully cured will or can result in fooling you.

    I glued horizontal cleats to the sides of the bench seats a couple weeks ago and heated the building to say 60F, but the wall was probably closer to 45F. I sat on the bench supports and they slowly sagged a half inch. But I did not notice until it had happened. The epoxy was very close, but not cured.
     
  8. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    When can you remove the clamps.

    When the epoxy is hard enough to resist any tension created by clamping them together.

    If the two timbers are fit together and little to no pressure is needed to hold the joint in place, then the epoxy won't need to cure as long. Assuming you aren't going to be moving them around.

    If you needed to force them into a particular shape, then much longer.

    And size matters, the bigger the timbers, the longer you'll need to wait.
     
  9. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Ondarvr brings a good point. For the curved beams in my boat; I left them in the jig from Friday until Monday.

    Also, epoxy tends to shrink when cured. If you find your clamps are loose; it is a good indication of some curing.
     

  10. missinginaction
    Joined: Aug 2007
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    Location: New York

    missinginaction Senior Member

    Mario, again I have no issues with the advice already offered. You can also, depending on the size of the parts you are gluing up, put one, two of even more heat lamps on the assembly. just make sure that you know what you are doing and don't put the lamps too close to the surface. I most often use System Three Resins. Their instructions say that their "fast" hardener can be used down to 35 degrees fahrenheit. Of course without some help the cure time is going to be pretty long.

    You wouldn't want to do waterproofing coats of a surface at that low a temperature. The resin would be too thick. I have used it to glue parts together though right down into the 40 degree area with no issues.

    Another way to speed up the process is by pre-reacting the epoxy. This takes a little practice so I'd suggest trying it on some scrap first. Mix enough resin for the job and let it sit in the pot for a bit. As you know, epoxy cures with by an exothermic process, it generates heat. You can give the resin a little "head start" by letting it sit a bit. After you've practiced this technique a few times, you'll start to get the idea. Don't do it when it's warm in the shop or boat

    If you feel the pot heating up, it's time to get to work. As you spread the resin out, it will cool down and the curing reaction will slow, giving you more time to work. Even though the resin will cool down once it's out of the pot it will have already reacted to a greater or lesser extent. This will help your cure go a bit faster at low temperatures.

    Regards,

    MIA
     
    bajansailor likes this.
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