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How do you handle epoxy that will not cure


Noklin

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I have seen post from several other people that indicated they have run into the same problem because of incorrect ratio or poor mixing, but I am not sure how they corrected the problem.

The up side is that this happened on a honey-do-job and not on the CS20. I figured this group would be the best place to find out what I needed to do.

I have a small area of glassed material that is dry to the touch but every time I attempt to sand it clogs the sandpaper in large lumps. The area around it is fully cured. The coating below the glass was fine. I have scrapped the fill coats off down to the glass, but am not sure how to proceed. It has been a month now with temperatures in the 80s so I believe that if it was going to cure it would have by now.

Do I need to scrap the area down to bare wood and totally redo it?

Since the coating below the glass was cured, do I only need to remove the glass and rework it from there or would the bad coat have damaged the cured coat?

Can I cover this area with a proper mixture and expect it to cure properly? I believe that the wet out coat was the problem and that the other two fill coats were correct, but did not cure properly because of the fill coat. So I do not think this is a real option.

Can I ignore the problem and paint over it or will the uncured epoxy cause problems with the paint.

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All I can tell you is what I've experienced.  I applied epoxy at the wrong ratio when glassing the hull of my first boat.  I thought it had cured, even though I realized I had mixed wrong.  I put a second coat over it.  Then, when popping some small air bubbles later, the glass started coming up in big strips - almost no adhesion to the wood.  So I pulled all the glass up.  I tried to sand the bad goo off, but all it seemed to do was move it around.  I thought I had removed it all and so re glassed and filled.  A week later, when I was about to prime, I found a large air bubble and when I tried to cut it out, the glass came up in strips again.  I had not gotten all the bad stuff off.  I called the tech people as MAS - which was the stuff I was using - and they told me 1. I could use lacquer thinner to remove it.  I tried that but it wasn't doing much.  Finally, I found the solution - 7 in 36 grit grinding disc on sander/polisher - this was the only thing I found that worked to completely remove the goo back to the bare wood.  The goo clogged the 7 in discs like the finer ones I had tried before, but not nearly so easily.  I did grind too far into the wood in some spots, but I was painting over it anyway and so did not care.  Uncured epoxy is a real nightmare.

I have since learned to use the same grinder and 36 grit disc to cut my scarf joints.  Very efficient here too.

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A coat of uncured epoxy simply has to be removed however you do it.  One best way (if you don't mind chemicals) is with paint remover which, in the strong ones, is methlene chloride.  I use Stripeeze.  Brush on a heavy coat of the thick variety and cover the area with a sheet of plastic to keep the air out and let it work longer.  Let sit for a couple hours or more.  After getting all that will come off by scraping, treat it like any other paint removal job.

At some time all of us have to learn how to do this.

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Yeah I tried the vinegar without any luck.  I had a fairly large area so I scrapped as much goo off as possible with a paint scrapper.  It was impossible for me to get it all up.  So then went back with another coat of epoxy with a little extra part B in it since I figured that was what was short on the gooey batch. Hard as a rock now.

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Since it sounds like I will have to rework the bad area anyway, I think I will try some experiments.

I plan on trying a light coat of Part B over part of the bad area. Another part of the bad area will have a good batch of epoxy applied to see if it will cure properly. The bad area appears hard and dry, it only showed up when I tried to sand it down.

Might as well learn as much as possible from the problem in addition to what I have to do to fix it.

I had let my 12 year old grandson mix the epoxy that had been applied. He had helped me when we glassed the CS20. We are not sure what went wrong with this batch.

Thanks for all of the suggestions.

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  I'm working from my years-old memory of the West System website so I may have things wrong, but:  If you mix the epoxy with too much hardener (part B) the epoxy wil not cure.  Too much hardener prevents the molecules of resin from linking or something like that.  If you mix too much of the resin (part A) you will get brittle epoxy (I don't remember why).  The proper cure of epoxy is very dependant on the ratio of hardener to resin and the skim coat of hardener will make that ratio almost impossible to achieve - It'll be a crap-shoot.

  My guess (not from my memory of West Systems website) is that if you start with epoxy that didn't cure properly and try to fix it you aren't going to do anything but end up with what you've already got plus a coat of uncured hardener.

  If you're dead set on doing the experiment of applying the light coat of hardener I hope I'm proven wrong.  Keep us posted - I'm always happy to hear a new way to fix my (numerous) mistakes.  Otherwise, try to get all of the bad stuff cleared off your boat before proceeding.  I know it's a pain, but I think the experiment may well make things worse.  At least take a look at the West Systems (or raka or whoever) faq on curing problems before you proceed.

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Even if you succeed in making the surface seem hard and cured will you know what you have underneath? Will your experiment be properly bonded to the wood?  I have a funny feeling you will discover the answers to these questions months later while sailing, or upon returning from sailing.  I suggest you bite the bullet and do what ever it takes to remove the mess now.  Save your experiments for scraps of wood.

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As I indicated in my original post, the only good thing about this situation is that the problem in not on the CS20, but a conversion unit to make my boat trailer into a utility trailer.

I am using Fir ply and covering it with glass to prevent checking and to improve its resistance to stone chips and other road damage. Not sure that it is worth the trouble, but having the material laying around, I find the bare plan tends to take on a life of its own.

So if it causes trouble later down the road it will still be no big deal.

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