Epoxy Curing Problem

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Jeff in Pembroke

Epoxy Curing Problem

Post by Jeff in Pembroke » Thu May 27, 2004 9:42 pm

I'm starting to sand the inside of the hull. Along the bottom in the middle there is a patch of epoxy that did not fully cure (I did the lay-up last fall). It's about18"X24" in size and involves only the final skim coat of epoxy - the other coats cured fine. The partially cured epoxy is a bit firmer than cured silicon sealant but is still tacky to the touch. I tried sanding the area but the sandpaper clogs almost instantly. It doesn't scrape off very easily either - some of it comes away but the surface still is tacky. I've tried scrubbing with a cloth and laquer thinner and this seems to work but it takes forever to get to the cured epoxy underneath. The uncured layer is very thin but I'm having a tough time getting rid of it. I'm using WEST 105/207.
Any suggestions out there or should I just keep plugging away with lacquer thinner, cloth, and scraper?


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Post by JimND » Thu May 27, 2004 10:19 pm

I have only experienced this once and it wasn't on a boat so others with more experience may have better options. I just poured lacquer thinner on it, then scraped it to work as much loose as possible. Then wipe, wipe, wipe with more lacquer thinner. Not much different than what you are doing. Since the first coats are cured, I don't see many other options. But that is a good thing, considering that if it had been your wetout coat, you would have to remove glass and epoxy.

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Post by Juneaudave » Thu May 27, 2004 11:45 pm

I haven't experienced this, maybe the other builders can give a clue to the solution...here's my thoughts...lacquer thinner acts like a solvent to epoxy, it might work into the glass. Maybe it would be better to "carefully" use a heat gun to soften the goop up and scape away. The problem with a heat gun might be lifting the glass if you are not careful and work it a little at a time till you hit solid epoxy. Good luck, let us know how it goes...Juneaudave

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Dean in Eureka, CA
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Post by Dean in Eureka, CA » Fri May 28, 2004 12:33 am

Hi Jeff,
The book says to scrape as much material that you can with a stiff metal or plastic scraper. Warm the epoxy to lower the viscosity. Clean the residue with lacquer thinner, acetone or alcohol. Allow solvents to dry before recoating. If you are going to be warming the uncured epoxy, be careful because if you get it too hot, you could soften the cured epoxy underneath.
Last edited by Dean in Eureka, CA on Fri May 28, 2004 10:39 am, edited 1 time in total.
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Dean in Eureka, CA

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Post by JimND » Fri May 28, 2004 10:36 am

Lacquer thinner is only a solvent for uncured epoxy, it has no solvent abilities on cured epoxy, so it is safe to use in this circumstance. For the most part, cured epoxy is inert in the presence of most common solvents. Applying heat in this circumstance must be done very carefully since too much heat may delaminate the glass and cured epoxy that you want to keep. The difference between just the right amount of heat and too much is a very thin line. I would never use heat where I am trying to remove just part of the epoxy leaving some of the epoxy and the fiberglass in place, just too risky in my opinion.

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Bryan Hansel
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Post by Bryan Hansel » Fri May 28, 2004 2:50 pm

Why not just take a little bit of hardener and rub it all over the sticky section. If it doesn't solidify the section, then scrap it off after pouring aceton on it.


Jim D

Uncured Epoxy

Post by Jim D » Fri May 28, 2004 4:59 pm

Acetone is the recommended solvent. Wipe with Acetone and scrape, repeat.

Michael Freeman
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Post by Michael Freeman » Sat May 29, 2004 10:17 pm

What Jim D. said. Acetone is a much better solvent for epoxy than laquer thinner. Use it safely though - outdoors, with rubber gloves and safety glasses.

Good luck,


uncured epoxy

Post by Doug » Mon May 31, 2004 3:35 pm

:cry: I had several spots of uncured epoxy under the glass. After a few months, they turned black. I suggest you use due diligence and remove them with heat and a scrapper, followed by laquer thinner or acetone.

BTW. I finally realized the uncured epoxy was the result of not mixing the resin and hardner correctly. I believe I was afraid of mixing in air if I stirred the brew too long, and paid dearly for it. I ended up stripping off the fiberglass and sanding right down to the wood. There are a few tell tale marks left on the canoe from the uncured epoxy.

Jeff in Pembroke

Uncured Epoxy Problem

Post by Jeff in Pembroke » Tue Jun 01, 2004 8:53 am

Thanks for al the advice.
I spent about 5 hours scraping and wiping the area with a cloth containing lacquer thinner (almost like a french polish technique). The occasional pass with the ROS seemed to clump up some of the epoxy and made it easier to scrape.
Anyway, I got it all cleaned up to the hard cured epoxy layer and the problem seems to be solved.
In retrospect, I finished the last of the epoxy work in the late fall and the temperatures were getting about 5 degrees cooler than the lower end of the recommended temperature range for 105/207. That may have been the problem. I was pretty careful about fully mixing the resin and hardener so I don't think that was the cause.
Gunnels going on next!


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