Hot epoxy


I just finished my first stripper, and I intsalled under deck hatch hold-downs, with bungee cord and padeyes that I made, ala Vaclav at One Ocean Kayaks.  All seemed well until I took the kayak outside for a few pics and some finishing touches. The boat was in the hot sun for about 30 minutes, when the under hatch hooks that I installed by adhering them to the hatch with silica thickened epoxy, popped off.  The sun seems to have warmed the epoxy enough that it essentially melted.  I had installed these hooks and padeyes several days ago, and the epoxy seemed to be rock hard.

How else can I stick padeyes and diy fiberglass hooks to the underside of the hatches, without them popping off?  It doesn't seem to be an issue of adhesion, but rather heat that is warming the epoxy too much.

Thanks for any help,


6 replies:

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RE: Hot epoxy

   Since no one else has answered I'll try.  When I mismatched the curve for a hatch on my kayak I used a heat gun to soften the epoxy between 2 layers of ply and reclamped the hatcn.  That happened a few days after the origional clamping.  

I do not know how long it requires for epoxy to fully set, but my kayak with epoxied on hatch cover hold downs has sat in full sun for a full day in a hot parking lot and the hold downs have never come loose.  there are lots of kayaks out there using glued on hold downs.  

I have also seen a video by Nick showing use of a heat gun to help strip epoxy and glass of a kayak for refinishing.  Presumably many months after the origional. 

So:  my interpretation is that the epoxy is vunerable to heat for several days to a week or 2 until fully cured. Then much less vulnerable but not completely invulnerable.  Perhaps the amount of tension is also relevant.

Suggestion 1) use a bit of fiberglass and some more expoy over the top of the hold down to better secure it. Make sure to really scuff the epoxy  that is in place where you are glueing the hold downs.  2) maybe call a manufacture and ask them about cure times, heat and long term strength in heat.

Good luck, Ed

RE: Hot epoxy

Thank you Ed, I'll try to let it cure longer.  It had cured for about 3 days, and the epoxy seemed to be very hard.  It's not adhesion to the hatch that's the problem, I scratched that up pretty good.  I'm using Raka epoxy, maybe I'll give them a call as well.


RE: Hot epoxy

   Iv'e used Raka with fine results, so I don't think it's a epoxy quality problem. It should have a Tg somewhere up above 150 degrees, which is hotter than a black surface in the sun. Their slow hardener does take a few days to fully cure ("full" cure actually takes weeks, and is the reason most boats have glass weave print through), so it's vaguely possible it wasn't cured enough. I'd expect to see some damage as the joint rips parts from the opposite side. If no damage/splintering occurred, if it tore off cleanly, then maybe there's contamination, maybe a starved joint.

last possibility is differential wood movement overpowering the weak, partial cured bond. When something stiff like a hatch stiffener is glued to something dynamic like a stripper built hatch with no inherent cross-plies like plywood, the hatch tends to want to move more than the stiffener and with fresh glue, hot sun, and your hatch undergoing its biggest environmental shock ever as it goes from shop to sun, well that's a lot to handle. Maybe. 

I'd reglue it, and if it failed I'd switch to a more flexible epoxy like G/Flex. It excels in bonding dissimilar materials.

RE: Hot epoxy

   I'll just add...I don't see that you added any filler, like Cell-O-Fill, to your epoxy. I've had good luck using Cell-O-Fill mixed into MASS resin to attach fittings to my fiberglassed hull. I stirred the epoxy for two minutes, and then add Cell-O-Fill until the epoxy was the consistency of peanut butter. There are several different kinds of filler out there, so there might be something specific for your epoxy. Cell-O-Fill is milky when it's mixed but cures clear as long as it's not underneath the fiberglass. I discovered that if I used it underneath the fiberglass that it stays cloudy. 

RE: Hot epoxy

   I think the Cell-O-Fill creates a matrix of the expoxy aroung the beads and is not a brittle as pure expoxy.

RE: Hot epoxy

   Thanks for the replies.  What I ended up doing was to remove the offending epoxy (which I did thicken with fumed silica), and basically replace it using automotive type vinylester resin with chopped glass.  This stuff sets up very fast, and I've never known it to be affected by the heat.  It's not pretty, but it's out of sight with the hatches closed.  I'll post again if this doesn't work.



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