Check6

My Feedback: (427)

Had to do some glass repair work on my Byron Hellcat. These fuses are polyester resin. Mixed up some resin I had and it doesn't seem to cure. What's the shelf life on resin? Is there anything I can do to kick off the resin? It's at a gummy state and has been on the plane for two days?
Thanks,
Fred

speedracerntrixie

My Feedback: (29)

Fred, you will need to clean it all off with acetone and start over. If I were doing the same thing I would use a good quality epoxy resin system. The epoxy will adhere to the polyester just fine. It's when you try to put poly over epoxy is when you have cure issues. Your problem now is that your MEKP has most likely gone bad. The poly resin usually does not go bad. Clean it up real well, abrade with 320 grit, dry towel to remove dust and apply your fix with epoxy resin within 4 hours of abrading and cure between 70-100 degrees for 12 hours for best bond.

ARUP

Polyester resins like warm temps to kick if spread thin and not enough MEKP added. Try putting some lamps on it for a few hours. Just reposition the lamps every couple of hours. Might takes a couple of days or more. I could be wrong but think UV (sunlight) might help 'kick' the resins, too. If this doesn't work then you can always do as above, right???

Erik Steinbring

Yep, old man winter is upon us, warm things up with a heat lamp and watch things harden up. We deal with this annually with our Epo-Grip epoxy product line when the mercury dips.

GREG DOE

Fred, Ditto on what Speedracerntrixie said. The MEPK can go bad. Get some fresh, and try a "test" batch of resin. Also I fully agree on using epoxy to repair polyester. I do it all the time, including full scale airplane repairs. Just be sure to rough up the surfaces you are repairing. I like West Systems Epoxy, and have been using it for more then 20 years. Unfortunately it ain't cheap. I bought a quart this week, and it was $72.00 with state sales tax. Perfectly good repairs can be made with polyester, so long as it cures. Speaking of MEPK. Some years ago they introduced a "safer" diluted catalyst which had some kind of thinner in it, so once again try a test sample, because it just might be that you need to up the catalyst by 50% or so. Good luck, Greg

Check6

My Feedback: (427)

Hi Guys,
Thanks for all the tips. The polyester resin never fully cured. I had to pull everything off. What a mess. I sanded everything down to bare glass. Cleaned it all with acetone. Then reglassed everything using Enviro-tex Lite. I have been using this epoxy for years to apply glass cloth. It's locked in solid and ready for finishing. Thanks for the tips.
Fred

speedracerntrixie

My Feedback: (29)

Glad it worked out Fred.

T_om

One other thing to keep in mind is that polyester resin will not harden over epoxy.

Tom

sensei

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sensei

What makes you think that properly catalyzed polyester resin won't cure resting on top of properly hardened epoxy, or any other substrate that is a solid, that is like saying it won't cure in the cup. Personally I don't care for polyester resin but that is beside the point.

Bob

T_om

20 years of composite boatbuilding and repair. Polyester won't cure over epoxy unless a tie coat is used.

But no need to take my word for it. A simple Google search will show you all the technical details.

Tom

GREG DOE

Tom, Sorry, I have to disagree too. But I concede you are partly correct. Some epoxies contain WAXES that are not compatible with polyester. I'm not certain if the waxes were just filler, or if they were there to promote a harder surface. 30 years ago it was much more common to have curing issues with polyester over epoxy. Today there are many epoxies that will tolerate polyester over them. I ALWAYS recommend trying a test panel. As I shared in a previous post, I've "slopped" over 50 gallons of polyester, and 30 gallons of epoxy in the last 30 years, so I have had a little experience. When I was really into layups I bought cloth by the bolt; approximately 130 yards at a pop. I'm sure I went through a dozen bolts making mostly small parts. NO full size cars or boats! Unfortunately if you ever have the misfortune of putting polyester over a non-compatible epoxy, it's easier to just never try it again, and warn your friends not to do it either. My guess is that either you, or someone you know had a bad experience, so I understand you don't want anyone to ruin their project. Not everyone has good laminating epoxy in their workshop, but they might have polyester, so my recommendation is to give it a try, but do a test first.

sensei

Tom,

Please note that I stated: What makes you think that properly catalyzed polyester resin won't cure resting on top of properly hardened epoxy, or any other substrate that is a solid, I did not state anything about the adhesion quality between the two technologies, hence a tie coat is needed as a layer that promotes adhesion between those two technologies, a tie coat does not inhibit the curing process of a matrix that possesses a proper mix ratio, proper temperature during cure, properly maintained humidity levels during cure, assurance of non contamination during mix and application, and/or a required dwell time of the cure, and finally fresh resin and catalyst that is not completely out of the manufacturers shelf life. With that said I suggest you get a better grasp on the effects of air inhibition found in polyester gel coat, and an adhesive bond line by means of mechanical abrasion or a chemical "tie" with the use of something like vinylester skin coat that ties the polyester and epoxy together through yet a third technology before you come into a thread like this and make a completely ignorant statement like: One other thing to keep in mind is that polyester resin will not harden over epoxy backed with your 20 years of experience building and repairing boats through the use of Google for your technical details. We see enough BS on line already without more like this. I don't believe in sugar coating the truth so please don't come back with more rebuttals further showing that in your 20 alleged years of experience you have learned just enough to be dangerous on line...

Bob

speedracerntrixie

My Feedback: (29)

Greg, I have not run into any epoxies that contained wax. Not saying they aren't out there. What I have seen is epoxies that have been applied in a relatively thin laminate or coating and cured at below optimum temps. What happens in this scenario is that the epoxy does not crosslink completely and the solvents tend to rise to the surface. This leaves a gummy surface that is a bit like wax. In this situation you are correct that polyester would never properly cure on such an epoxy surface. IMO 90% of epoxy issues are either poor mixing practices, either not correct ratios or simply not mixed well enough. The other is that in most cases epoxies need at least 70 degrees for 12 hours to get to max strength. Even if cured at 70 degrees for 12 hours it will continue to cure for up to a week. For this reason I post cure all my fiberglass fuselages and when I sheet foam wings they are cured at 100 degrees for a minimum of 12 hours. I know this is all asking a bit for the average hobbyist you excluded of course ( your reputation precedes you ) but with a little additional effort those of us doing glass work are able to work faster and make stronger parts with less bulk. Oh and if you do have some epoxy glass work that comes out with a slightly gummy surface, simply wipe with acetone to clean those solvents off and expose to an elevated temp for a few hours ( I sometimes throw things in my car and let them bake in the parking lot at work ). One thing I will agree with is it is my policy to not use polyester over epoxy. Like Bob, I really don't like the stuff to begin with.

MTK

A heads up for those of you that want to use polyester and MEKP catalyst. MEKP, methyl ethyl ketone peroxide, can be dangerous to the eyes. If you spritz the stuff into your eyes get then flushed with water as quickly as possible for at least 15 minutes.

For what it's worth, in addition to MEKP, polyester reactions can initiate and really accelerate from plain old UV light (sun is one excellent, cheap source).

T_om

You have some anger issues. Perhaps your medication or counseling sessions are not working?

Tom

PS: Addressing another post, I have never heard of an epoxy that contains wax. Polyester resin, yes. Epoxy, no. And polyester not curing properly over epoxy is a well documented occurrence.

rgburrill

Please pass the popcorn.

sensei

If I am a blowhard with anger issues because I told it straight then so be it, fact is you don't understand most of what I was stating because you are ignorant on the subject, you know it, and you know I know it, end of story.

Bob

GREG DOE

To everyone who has contributed to this thread, thanks. It's been entertaining to say the least! I have to admit I don't know a lot of the chemistry of polyester, and epoxy, (I do know more then most) but I've got a boat load of experience making garbage. I have consistently seen the same products be incompatible, and other combinations work every time. Don't ask why I would make the same mistake more then once? Many times I have used polyester over epoxy without a "tie coat" and was not able to separate the two after the death of that airplane. I have an oven too. It's a light box that gets to about 130 deg. but in hot weather I mostly throw my project in my car, and it's free. And my reference to there being wax in some epoxies is probably incorrect. However there are "fillers" in some epoxies, and maybe that is what makes the polyester stay gummy? I think there is more going on, then that the epoxy is not properly mixed, or fully cured? Just my observation over a the years.

speedracerntrixie

My Feedback: (29)

Greg, I agree that the fillers in some epoxies could be what is responsible for incompatibility issues. As you have stated before, the best practice is to not mix the two different bases at all or to do test samples. Composites is something that can get complicated in a hurry but for the average R/C guy keeping things simple is best IMO. Most guys aren't laying up their own Fuselages or making hollow wings. Some basic knowledge on mixing, application, cloth matrix/orientation and some simple vacuum bagging will make a good builder into an excellent builder.

sensei

To be honest I have never experienced a polyester layup that did not cure, or have peel quality issues over a fully cured epoxy layup, but now that I think about it I have not even used polyester resin in around 30 years, prior to that I lived with the stuff but in my field of composites since I have had no use for a gel coat surface. Many boat builders today gel coat the molds first for obvious reasons and use epoxy layups because of the structural benefits found with the use of epoxy, this is when the tie layer is needed.

Bob