Epoxy won't cure. Help!

[kwaltersmi]

I've been applying epoxy paste as a patch/sealer to a few fiberglass areas on my hull and deck. Some of the epoxy paste I applied this weekend won't cure. It remains sticky/tacky. I'm fairly certain I mixed the two parts together sufficiently because most of the areas I applied the paste to during the same application have cured solid. Why won't some of the areas cure? What should I do? Can I apply something that will cause it to cure even after the initial application? Or should I use something (acetone?) to try and remove it and re-apply?

The only explanation I can come up with is that the mineral spirits that were applied to a few of the areas for initial clean-up/surface prep wasn't fully evaporated when I applied the epoxy and is now keeping it from curing.

[sailingdog]

If it hasn't cured, you can generally remove the uncured epoxy using either denatured alcohol or vinegar, depending on what epoxy you used. Then wash the area down with acetone, and re-mix and apply after it is completely dry.

I wouldn't try getting it to cure by applying anything to it, since it will likely cause just the outermost layers to cure, and the interior will still be uncured. That will make the repair worthless in terms of physical strength.

[Gene T]

Agree with Sailingdog. I suspect you didn't get it mixed completely. You might try a heat gun/hair dryer first but don't get it too hot. I would just clean it out and do it over.

[bobmcgov]

West Systems estimates 75% of failures involving its products can be traced to inadequate mixing. The shape and size of the container or stirring stick can make the difference, as can the pattern of motions you use. Blending ingredients is incredibly complex business.

The rule with two-part epoxies is to mix until you are absolutely, positively, 100% certain you have a perfect stir -- then mix another 3 minutes. Scrape the bottom. Scrape the sides. Reverse directions. Pull the bottom up, push the top layer down. Change sticks; stir some more. Don't use your stirring stick to apply.

Yah, your symptoms almost definitely indicate poor mixing. It happens to everyone.

[JohnRPollard]

Thorough mixing is important. But in this case, another likely culprit is hardener-to-resin ratio. Make certain you have your ratios correct. I have heard of instances where the pumps were inadvertantly reversed. Double check those, and triple check the calibration by mixing the two-parts in a graduated container.

But definitely remove the uncured batch and start over as per Sailing Dog et al. Unless by chance you are in a very cold climate?

[Freesail99]

From reading his post, I get the feeling he is referring epoxy putty. The stuff that comes in a tube. That stuff is a different animal.

[sailingdog]

If he's talking about MarineTex or some other two-part putty, then incomplete mixing is still a common problem. With the two-part 1:1 resin/hardener putties that come in tubes, it is pretty hard two screw up the mixing, since the color changes, but contaminating it with mineral spirits or having the wrong ratio of hardener to resin can still cause major problems.

[JohnRPollard]

Ah, I see now. I thought he had mixed up a batch of epoxy and made it into paste by adding micro balloons or colloidal silica powder or some such. Personally, I would not use Marine-Tex or similar for the project he described, but maybe I misunderstood what he's doing.

[PBzeer]

I think of Marine-Tex as nautical Bondo. It's worked well for me in that type of application, particularly where I want a white finish.

Currently at 38 20 10 N 76 27 42 W , Solomons, MD

[Freesail99]

I am just guessing from what I read that he is using epoxy putty. It could well be epoxy mixed into a paste. I have never had epoxy resin fail to cure.