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Fixing Rubbery Epoxy

08/27/2008 6:08 PM

Hello

I am hoping someone can help me. I am using some Clear Cote brand two part tabletop epoxy resin for a prototype I am building. The stuff normally does a good job in a pinch and it is readily available.

Regrettably this time I must have gotten the (1:1) mixture slightly off because after 36 hours of curing it is still very rubbery. I don't know what way I messed up the mix, too much or too little hardener?? I wouldn't normally care that much but this part was a bear to make and it has some difficult to build parts embedded in it.

Does anyone know a technique for getting it to fully harden? Will it cure to a suitable hardness over time?

Any advice would be greatly appreciated.

Doug

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#1

Re: Fixing Rubbery Epoxy

08/27/2008 9:33 PM

Hello drobertson

Sadly the improperly mixed epoxy cannot "cure over time", because there appears to be a shortage of material to enable full curing.

Either there is a shortage of epoxy, leaving a surplus of hardener.

Or, there is a shortage of hardener, leaving a surplus of epoxy.

In either case, the "part-cured" mixture will remain in the "rubbery" state, because the unused component will always remain intermixed through the fully cured 2-part cured epoxy.

You need to remove the entire partially cured mixture as soon as possible, generally by physical scraping, or spray-on epoxy/paint remover.

The scraped/cleaned surface will remain contaminated by the 'rubbery' mixture, and you need to totally remove that 'rubbery' mixture.

Then sand back as needed, to obtain a proper "key".

Mix up a new "brew", using carefully the correct proportions, and re-coat.

You're not the first to be caught out, during epoxy mixing/application, or to have applied it during temperature/humidity outside the correct range during application/curing time.

Send a photo here, in this Topic Thread, when you have completed your prototype, (If you are able), with so we can admire the completed prototype.

Kind Regards....

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#2
In reply to #1

Re: Fixing Rubbery Epoxy

08/27/2008 9:57 PM

I appreciate the info. I was kinda worried that might be the case.

Usually I am pretty good with this stuff, but in small batches it is easier to have the portions significantly wrong.

I am evaluating what I can do about the problem. The stiffness was mainly to hold a set screw steady and to have something to push against on the back side of a shaft. I may be able to adjust my design and have 4 set screws instead. Note - there is an aluminum box inside the epoxy that the set screws are tapped into.

If you really are interested I would be happy to post some pics of the project and part I am working on.

-Doug

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#3
In reply to #2

Re: Fixing Rubbery Epoxy

08/27/2008 10:39 PM

I am not an expert on epoxies, but I have had a few go rounds with it. Now that it is a mess, what can you do to make it better.

Option 1 Too much hardener, not enough resin. Heating might help this. Do you know the temperature limits of that product?

Option 2 Too little hardener. Is the active ingredient in the hardener MEK? If that is the case you might brush MEK on the outside of the soft project. what harm could it do?

Spark station might have better knowledge on these options> Pictures are always welcome.

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#4
In reply to #3

Re: Fixing Rubbery Epoxy

08/27/2008 10:52 PM

I had considered baking it for a period of time but had to give up that idea since there are 4 NdFeB magnets inside that don't like to get above 200f. I did set it out in the sun for about 7 hours and that didn't help much.

I also tried coating it with a layer of hardener. That didn't seem to do much. I cleaned it then tried with a layer of the resin. That seemed to stiffen up the outside slightly (note - this could be my imagination), but I don't think it did more than add an extremely thin slightly stiff skin to the item. The hardener is the 1:1 mix type, it isn't the small bottle of MEK. I actually have some of that but I am reluctant to just add it to an epoxy that it wasn't meant to be used with.

Right now I added three extra setscrews and I think I have the part working. Time will tell if this solution works.

I will get some pictures up in the next few days. I need some batteries for my camera first.

Thanks for the input.

-Doug

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#6
In reply to #4

Re: Fixing Rubbery Epoxy

08/29/2008 1:33 AM

Even I had similar problems when working with epoxy and polyester resins. Mixing of small quantities by weight is easier than by volume, if possible, to avoid this mess.

When similar problem occurred, to avoid deformation or damage to the item, in some cases I kept the item in an oven at not more than 45-50 C or 125 F for 2-3 hours, switch off the oven and leave it for 8-10 hrs and try again if still wet or sticky. In some cases, I have used hot air blowers, similar to hair dryers to hasten up the drying process. Move the blower uniformly over the object from a safe distance for 5-10 minutes. Try this again after some time, if required.

I hope this will work for you too. Will appreciate your feedback.

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#5

Re: Fixing Rubbery Epoxy

08/28/2008 10:47 PM

Cut it out and redo!

There are no fixes after the product begins to cure.

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#7

Re: Fixing Rubbery Epoxy

08/29/2008 3:27 AM

Possibilities your proportions were wrong. you used components from two different brands - (can be fatal) or you did not mix it thoroughly. Slow setters are best left to stand in mass for a short while after mixing quick setters do noy permit this.

You may have a chance if you use some heat - hair drier, light bulb or similar. Care not to overcook the substrate. If not then it is dig for victory - it will probably stay as it is forever!

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#8

Re: Fixing Rubbery Epoxy

08/29/2008 7:33 AM

Mix a small amout to check hardness, It may be expired! we use lots of epoxies here and many of them when they get old do not cure well.

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#9

Re: Fixing Rubbery Epoxy

08/29/2008 8:32 AM

The advice to start over is the best. You already have the components mixed. The chemical reaction has taken place and "the diie is cast".

MEK (methyl ethyl ketone) is NOT a suitable compound for removing the partially set epoxy. A better solvent is MIBK (methyl isobutyl ketone). This is more agressive against the epoxies than MEK. For instance, if you are required to add an additional coat of epoxy paint to an existing coating, it is recommended that you wipe the surface with MIBK first to make the second coat actually become a part of the first. It pre-conditions the first coat such that the second coat becomes chemically bound to the first.

MEK, sometimes sold under the trade name Xylol, is used for cutting paints and coatings that are, usually, not two part coatings. The MIBK will cut either alkyd cured or amine cured epoxies. Try it and see if it helps you get that epoxy out so you can start again.

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#10
In reply to #9

Re: Fixing Rubbery Epoxy

08/29/2008 9:12 AM

Neither MEK nor MIBK will have any effect upon a cured epoxy Both have a similar solvency but the MIBK will evaporate more slowly. If uncured you might have some softening. Afraid brute force is going to be the answer.

Methyl Ethyl Ketone bears no relationship to Xylene (dimethyl benzene)

What is an alkyd cured epoxy ? - after 50 years in the business it is a new one on me.

This a very dodgy answer.

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#11
In reply to #10

Re: Fixing Rubbery Epoxy

08/29/2008 9:49 AM

The subject of MEK started with me. My question was ''is the active ingredient" in the epoxy hardener that he was using MEK? If it is, and the mix was short hardener, would putting MEK on the outside harden a unhardened mix?

You have referred to it as cured epoxy. In it's current unhardened state, is it still considered cured?

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#15
In reply to #11

Re: Fixing Rubbery Epoxy

08/29/2008 12:01 PM

Perhaps he can read the ingredients or the specifications on the side of the container in which the medium was delivered. Also, it is not uncommon for that information as well as instructions for the proper use and application of this material to be furnished with it.

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#14
In reply to #10

Re: Fixing Rubbery Epoxy

08/29/2008 11:54 AM

"This a very dodgy answer."

Yours or mine? I don't profess to be a chemical expert, but I have used epoxies over the past 35 years or so, and I have used a "solventless" epoxy coating preceded by a "zinc-rich" primer. These coatings were alkyd cured. PPG used to have one that I believe was called EP97 which was a 97% solids epoxy.

As for the relation to Xylene, you miss-read my comment. I stated that MEK is sometimes sold under the name of "Xylol" which has no relation to Xylene. It was simply the trade name of the solvent I used. It came (to me, anyway) in 55 galloon drums. I used it to clean up a mastic coating, a coal tar pitch that I used when epoxy was more than I needed. However, when I needed to clean-up after using epoxies I always used MIBK. You are correct, however, that once the epoxy is set, it is there - period. Especially the "solventless" high solids epoxies I sometimes used. Also, the potlife of those epoxies was about 45 minutes at best. Very difficult to manage.

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#19
In reply to #14

Re: Fixing Rubbery Epoxy

08/30/2008 2:34 AM

Then there is something seriously wrong somewhere.

The only relation ship between this comment and the original is the fact that two part materials can belong to the amine or the polyamide systems. In any case a wrong mixture by proportion or by lack of blending of any two pack preparation will give problems.

The answer to the orginal question remains the same without any "red herrings" Try warming it - you could be lucky - if not remove it and start again and mix properly next time.

I am a professional expert.

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#12

Re: Fixing Rubbery Epoxy

08/29/2008 11:28 AM

Sonmetimes, if you mix small quantities of your components on a plastic surface, polyethylene for instance, some softeners seem to leach out into the mixture which will not set properly. Better do your mixing on a clean metal surface.

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#13

Re: Fixing Rubbery Epoxy

08/29/2008 11:31 AM

Do you have access to an IR or FTIR instrument? Perhaps a local college or university? If you can take a very small amount of the rubbery "cured" epoxy, and determine what the XS is - resin or curative, you may be able to make a dilute solution of the part NOT in XS, and paint the surface with that solution. It may give you a hard surface, and possibly it may penetrate downward to cure up the entire coating. Also, check the expiration date on the component containers. It's possible one or the other component may have weakened, and even if you made a 1 / 1 ratio mix, you still wouldn't have a full cure. If you have any of the components remaining, try a 1.1 / 1 and a 1 / 1.1 mix, and see if either of those cure better.

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#16

Re: Fixing Rubbery Epoxy

08/29/2008 1:06 PM

It seems you need more cure time or higher cure temperature or both. If there is not enough Part-B, then it will result in incomplete cure and lower harness.

So try to heat (slightly) and you should see some improvement.

Also, hardness depends on the amount of rubber content in the mixture.

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#17

Re: Fixing Rubbery Epoxy

08/29/2008 5:13 PM

Here is a general reply to answer some of the questions that came up.

1. This was a batch of Clear Cote brand 2 part Tabletop Epoxy. It has a 1:1 mix ratio of hardener to Epoxy. It does not use MEK as a hardener.

2. The chemicals where fine in it. I had just used the same bottles for a different part the day before and it came out great.

3. After 3-4 days it has hardened slightly more, but it still has the consistency of hard rubber.

4. After immersing it in hardener nothing productive happened. Similar results from immersing it in more Epoxy.

5. I left it out in the 100f sun for 5-6 hours and this did nothing. Note - I can't bake it due to the fact it has NdFeB magnets inside that will demagnetize in any form of high heat.

6. This was setting in a part mold and not a thin application for a boat or table so I couldn't sand it off and do it again. I have used this epoxy for these small parts before with great success, just no luck this time.

The bottom line is that I messed up on the mix and now the part isn't serviceable. It looks like I will be remaking the part over the weekend.

I did make some quick modifications to the original design and hopefully that will help.

I appreciate everyone insights. Too bad there isn't a magic way to make this work, but I guess I wouldn't learn if there was no pain to my screw ups.

-Doug

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#18
In reply to #17

Re: Fixing Rubbery Epoxy

08/30/2008 2:21 AM

Hi drobertson,

I can understand your disappointment. Before you give up, why don't you try my suggestion in # 6. It is simple and you have nothing to lose. You should come to know if it works with in 2/3 hours. Good luck If possible, let me know what you did and what happened.

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#20

Re: Fixing Rubbery Epoxy

08/31/2008 4:36 PM

I have worked with dozens of different epoxies. Most common epoxies have a shelf life of a year or two. I have, in the interests of utilizing old inventory, experimented with older (up to 5 years old) epoxies. Generally, the 1/1 type or the 5/1 type, in both slow set and fast set formulations, do not set up well or get as hard as expected, when over a year old. BUT, I have found that applying heat via a heat lamp (or lamps) eventually produces a cure. It might take a day or more. I always test epoxy older than one year before using it. Generally, if the hardener has changed color (turned from clear to brown), it should be tossed. Most suppliers do not date their epoxies. I write the date of purchase on each container. I try not to deal with companies that do not specialize in epoxies, to avoid getting last year's stock.

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#21

Re: Fixing Rubbery Epoxy

01/29/2009 11:44 AM

If you try some heat (I would but not too much because of the magnets of course, but usually magnets regain their magnetism when cold if I remember correctly!), do please have an extinguisher handy, "just in case!". Many years ago I saw some Epoxy "take off" due to overheating!! Not funny!!!

A CO2 type would be best, cools well and it leaves no mess.....open windows though!!!

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