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Tools & Supplies: Glue and Adhesives
Talk about sticky stuff.
Hosted by Matt Leese
Two Part Epoxy Will Not Cure - Way To Fix?
Damraska
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California, United States
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Posted: Wednesday, August 12, 2009 - 04:29 AM UTC
I have a weird one: about three weeks ago I mixed up a small batch of clear, two part epoxy to simulate a small pool of water on a figure base. Everything seemed to go fine and I applied the epoxy a drop at a time until satisfied with the look. I expected the epoxy to set up rock solid within an hour. After about 8 hours I touched the "water" surface and it was hard but still tacky, leaving a fingerprint. Okay, I can fix that. A day later...still tacky. A week later...still tacky. Three weeks later..._still_ tacky.

I have used various two part epoxies in the past and never experienced this result. The product label reads "2 Ton Clear Weld Epoxy" but I tossed the rest of the packaging. I bought it at ACE Hardware or Walmart and know nothing else about it. The epoxy was applied to a base sculpted from Milliput, painted with Model Master enamel paints, and sealed with Model Master gloss clear acrylic. Everything was nice and dry before I applied the epoxy.

Does anyone know a way to force the epoxy to finish curing? Did I accidentally use the wrong product? I really do not want to remove the stuff because it will take most of the ground work I sculpted with it. Could I lay some Micro Crystal Clear or Gloss Clear Acrylic over the stuff?

I like a good mystery, just not on my carefully sculpted and painted ground work!

-Doug
DaveCox
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England - South East, United Kingdom
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Posted: Wednesday, August 12, 2009 - 09:16 AM UTC
I have found this before, when the top layer stays 'tacky' to the touch. What temperature is the room that it's in? A warmer room for a few days may help.
jabo6
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Posted: Wednesday, August 12, 2009 - 10:45 AM UTC
either the epoxy was not mixed well enough or it was past its best used by date, most epoxys have a shelf life unopened of about a year, once they are opened to the air they go down pretty fast unless you keep it in a fridge.[the swabo will realy like that] . the two part epoxys that come from the hardware store and sutch are inexpensive so if your not sure how old it is then toss it and buy new. as for you puddle not drying it probably never will, you will have to dig it out and start again. you also might try passing a hair dryer over it sometimes a little heat will set it off but be warned too much heat will kill it. hope this helps
CMOT
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ARMORAMA
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Posted: Wednesday, August 12, 2009 - 10:56 AM UTC
If resin is exposed to cold temperature or moisture it will also sometimes act like this.
Damraska
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Posted: Wednesday, August 12, 2009 - 01:11 PM UTC
Thank you for your help, gentleman.

The epoxy was stored in a fairly cool room for 6 months or more before initial use. During the winter, it may very well have been exposed to temperatures approaching freezing. It was probably from ACE and probably old stock when purchased. I took care to mix the epoxy well, but there may have been more of one component than the other because the plunger mechanism initially stuck. It appears I screwed up three different ways on this one. The remaining epoxy was consigned to the circular file.

I tried the hair dryer on high for 15 minutes, which heated up the base considerably. This made the epoxy gooey, though a toothpick could only make small dents in the surface when applied with some force. I will place the base in the garage for a few days and see what happens. Perhaps the heat out there will cure it, but it appears I have some digging to do. At least I can save the figure.

-Doug
mvfrog
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Posted: Wednesday, August 12, 2009 - 04:04 PM UTC
A thought: get a new tube of very hot epoxy-5 min. kind of stuff; mix it up, and brush on a ver thin coat over what you already have down on your diorama. Or: some surfacing resin. Mix it up. and brush it on; it seals off the air in order to cure and will be hard to the finish. You can thin it if you want with acetone. Try it on something other than your diorama first. I think either of those would work. I would rate the epoxy 1, and then the resin #2.

Matt

The garage will intorduce the element of humidity into the equation. You don't need that.
CMOT
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ARMORAMA
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Posted: Wednesday, August 12, 2009 - 10:27 PM UTC
Resin that has been exposed to freezing temperatures will never cure completely. I made that mistake when I glassed a roof, I had to free birds off of it almost daily for 6 months and now 6 years later it is still a little sticky.
mvfrog
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Posted: Thursday, August 13, 2009 - 04:44 AM UTC
Resin will not cure if it is exposed to air. I learned that when I used the wrong resin in Grad School on a project. I bought and used Bonding Resin because it was cheaper. It didn't cure and remained 'tacky' for longer than it should have. My advisor took a look and told me it was the bonding resin issue. We got some Surfacing Resin and put it over the top, and ALL of it hardened up and I could sand and polish it with no trouble. Surfacing Resin has a micro fine ingredient (carnauba) that reacts to the heat given off by the chemical reaction that takes place between the resin and the catalyst...it rises to the surface, and seals off the surface from the air, and the surface will dry hard, as it should. Also, layers beneath it (bonding layers, fiberglass, etc), will also harden up, and everyone is happy. A little thinned surfacing resin could help the problem of the epoxy, because it would seal the sticky surface and put a hard topping on it. Bonding resin seemed like such a good deal at them time because I could buy a lot more because of the difference in cost. The result was that I then had two types of resin, instead of the one that I needed.

Matt

AJLaFleche
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Posted: Thursday, August 13, 2009 - 04:59 AM UTC
Great timing on your question, I've been having the same problem with some Envirotex epoxy "water". At the club meeting last night, it was suggested to look for clear hardener to replace the one I have. I sort of circumvented the issue with a thin coat of Woodland Scenics Water Effects smoothed mostly out. For my purposes, the slight waviness is good.
Damraska
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Posted: Thursday, August 13, 2009 - 11:52 AM UTC

Quoted Text

Resin will not cure if it is exposed to air.



Thank you for that, Matt.

I pulled the base out of the garage after a few hours--still tacky. Using a cotton swab I used some acetone to try and remove the tacky film--no success. I pulled the resin out of the trash, mixed up a new batch, and found it dried hard and much less tacky. I mixed a second batch and applied a thin coat over the top of the old one--it dried hard and less tacky than the first coat. At this point I was out of space to add more layers without overflowing the pool. Then I read Matt's post about exposure to air. I painted a thick coat of Model Master Clear Gloss Acrylic over the resin in the hope it would form a chemical barrier against air. Now it is rock solid--no give and no tackiness.

In hindsight, I think Matt's original suggestion of laying a thin coat of 5 minute surfacing resin over the top of the tacky resin would have worked best, given that the original surface was tacky and pocked with fingerprints and toothpick dents.

Thank you again to everyone who pitched in on my little experiment!

-Doug
mvfrog
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Posted: Friday, August 14, 2009 - 04:37 AM UTC
Glad to have been of help. This is fun!!!

Matt
CMOT
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ARMORAMA
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Posted: Friday, August 14, 2009 - 03:55 PM UTC

Quoted Text

Resin will not cure if it is exposed to air.
Matt




Matt I am sure that depends on the type of resin being used.
mvfrog
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Posted: Friday, August 14, 2009 - 07:42 PM UTC
No (mostly), that is why the surfacing resin has the added ingredient in it to 'seal the surface;, allowing it to cure hard and dry ( not 'sticky'). There may be some new polymer that I am not aware of, but I am speaking af the type of resin that is used with fiberglass..not the resin that you all work with in casting small precision parts for models. I might be wrong in the name, but I believe it is called polyester resin. It is used for laminating layers, bonding, finishing, and casting. You can also cast finae art sculpture with it. This is also the type of resin that is also used in 'layups' for large molded objects (gel coats) with fiberglass cloth. You are correct, I think, when it comes to the molding resin for the parts that people make for models, or for resin models (kits) themselves.I have no experience with that type of resin. I wasn't thinking of that when I wrote my post. I was thinking and talking about the type of resin and catalyst used with fiberglass...surfacing and bonding resins. That's all that I have worked with...not the wonderful resins that folks use today to make amazing things. I think we're both right on this one.

Mastt