Final curing of epoxy boats

[Gamma1214]

In response to a conversation started on this thread, I had an interesting conversation with an epoxy manufacturer today. I'll break it out here so as to not derail the original thread and to make it more searchable in the future (probably worth researching IMO):

In the above referenced thread, the question was raised if water temperatures in excess of 120° F would harm an epoxy canoe. I use RAKA epoxy on my stripper builds and they've always been extremely helpful when I've called (one reason why I'll likely never switch) and I was curious what their answer would be so I called today.

I spoke to Kyle who, although he had never heard of washing a canoe for invasive species mitigation, did confirm that their epoxy would soften if it was heated to 140° F (as in extended exposure to get the entire lamination up to temp) and that caution should be used to prevent deformation until the epoxy cooled.

Now, here's where it got interesting...

He went on to say that, after the epoxy was heated to that temperature and had cooled, it would essentially be work-hardened (I forget what term he used) and it would then have to be heated to between 180 & 200° F before it would again become soft.

I then speculated that direct sunlight (especially on a dark-colored hull) could probably exceed 140° F (proven in this study) and asked him if I should intentionally heat an epoxy hull to 140° F in a controlled environment before taking it to the woods. He confirmed that such curing would certainly be beneficial.

Has anyone else heard of heat treating epoxy in this manner? Do any of the commercial manufacturers (assuming they use epoxy) recommend (or condone) such treatments? Do they, perhaps, heat the hulls before shipment?

I'm pretty sure my future builds are going to spend some time in direct sunlight (and get checked with an infrared termometer) or get a nice, hot bath before taking them on their first trip... any thoughts?

 

[Alan Gage]

I don't know about any hull manufacturers but it's common for many epoxy products to be heat cured. They're placed in ovens to cure. I don't know how much of this is for toughness and how much is to extend the layup time as the epoxy won't cure until warmed up.

I don't know if science behind epoxy and setting pitch in wood is the same but part of the process of drying softwood lumber is to run it through a heat cycle up to around 165 degrees for long enough that the entire thickness of the board reaches this temp. This is done after the boards have been dried to the target moisture content. One reason this is done is to kill any bugs in the wood but another reason that's just as important is to set the pitch.

There are a lot of different compounds in wood pitch and they all gas off at a different temperature. So if you heat a pine board to 110 degrees all the compounds that gas off below that temp will gone and the pitch will seem pretty solid until it's heated to above 110 degrees (like when sanding), at which point it will soften again.

Maybe something similar is going on with epoxy.

Good info Gamma. Thanks for sharing.

 

[Ober27]

Thank you Gamma. That's good information.
I need to do some reading on the topic when I get a chance.

 

[MrPoling]

In response to a conversation started on this thread, I had an interesting conversation with an epoxy manufacturer today.

That is an interesting conversation. I've always been paranoid about having my boats out in the hot southern sun.

I'm not savvy about epoxy so I'll limit my comments to mentioning aging and degradation. It matters to the materials thermal characteristics, but predicting how would be tricky. I'd be hesitant to heat an older boat.

I'd also be hesitant to believe the infrared thermometer temps in the sunlight. You can't tell with your eyes, but some surfaces reflect infrared. Maybe there's good testing methodology online. I'd probably just make a shade from a box.

It would also be interesting to see the temperatures inside the hull.

 

[Gamma1214]

I'm not terribly familiar with the properties of sunlight. Would leaning over the hull & taking a reading of the shaded area be sufficient to get an accurate temperature?

Anyone in the South care to do some testing? You should definitely get some hotter surface temps and, honestly, the way it's been raining here lately, it feels like it might be years before we see direct sunlight again.

 

[Boatman53]

I built a cedar strip Adirondack Guideboat using West System epoxy for an older customer and that boat literally sat on saw horses on the shore of the lake in full sun from May to September. Every year I would sand it and give it a fresh coat of varnish. That was its life for twenty years and it looked as good as when I built it twenty years later. I can’t say I saw any issues with a softening of the epoxy. This was on the east end of Long Island and we could get termps in the 90’s for a week or more. I knew epoxy softened with heat and used that to advantage numerous times but I never worried about that boat in the sun.
Jim