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Fiberglass Still tacky

P

PilotjohnS

Well Known Member
So i been using the Aeropoxy fiberglass resin system for most of the build and it has worked great... until now.

A few months ago, when it was really cold, I decided to coat the inside of the cowling with Aeropoxy. It was about 40F for a few days. Even after the outside warned up, after a month was still tacky.

So i overcoated the original epoxy with some fresh stuff from Aircraft Spruce. While it was curing, the outside air temperature was a more reasonable 60F.
It has been two weeks and it is still tacky. So even the new batch, put over the old batch, is still tacky.

What do I do to get this to cure?
Or do i just put down the heat insulation material and move on?
 
If you’re only putting on a thin coat of resin , I find it requires more catalyst. If installing multiple layers, then he build up creates heat and cures. Thin coats don’t do this. You could try a heat lamp on your part to see if that helps finish off the cure.
 
Try a few minutes with a Harbor freight heat gun.. do a couple of cycles and see it it hardens up
 
If it won't cure then I would clean it off and start again. Messy job, but then it's done right.

As others have said, it may still kick off with application of heat, or it may remain tacky.
 
I recently had a similar experience with West Systems. I had no luck with a heat gun. It is impossible to have a consistent and prolonged heat cycle that is needed to cure.
I recommend a heat lamp or a 100W drop light under the cowl with several insulating blankets over the outside. Get it up to 100-120 for 12-24 hrs. I bet it cures right up. In my case it was a small part that I could get into the oven in the kitchen. It only took 4 hrs to harden right up after having been soft after 48 hrs.
Good Luck!!
 
andoman said:
I recently had a similar experience with West Systems. I had no luck with a heat gun. It is impossible to have a consistent and prolonged heat cycle that is needed to cure.
I recommend a heat lamp or a 100W drop light under the cowl with several insulating blankets over the outside. Get it up to 100-120 for 12-24 hrs. I bet it cures right up. In my case it was a small part that I could get into the oven in the kitchen. It only took 4 hrs to harden right up after having been soft after 48 hrs.
Good Luck!!
Click to expand...

Another option is solar heating. Put it in the sun, maybe on your driveway, under a dark tarp. The Canard guys used to post cure parts this way.
 
A couple saw horses with a tarp over them and a temperature controlled box heater creates a nice and simple post cure oven for your cowling. If you have an old fashioned electric blanket, that would work also.
 
I suspect your epoxy has cold-inhibited and will never cure. I have had this happen a few times with West.

I found that I could put a part that had cold-inhibited in the oven at 175F for several hours and it wasn't tacky anymore, but it was rubbery. It never got hard. I scrapped the part.

In your case, I suggest removal. warm it with a hair drier a small area at a time and scrape it all off.


Folks - the hardener systems used with epoxy are not a "catalyst". It is not a matter of enough heat for enough time for a catalyst to bring about a chemical reaction to harden the resin, such as happens with polyester and vinyl ester resins. The hardener system in epoxy becomes an integral part of the final chemical compound. But whether or not that compound properly cross-links into the intended structure depends on the temperature at the time when the basic compound is formed.

If it hasn't cross-linked, it is not going to. Ever.
 
scsmith said:
I

suspect your epoxy has cold-inhibited and will never cure.

Epoxy becomes an integral part of the final chemical compound. But whether or not that compound properly cross-links into the intended structure depends on the temperature at the time when the basic compound is formed.

If it hasn't cross-linked, it is not going to. Ever.
Click to expand...

My understanding and experience with Expoy is exactly the same.
 
What Steve said.

As a big 'ole general rule, temperature condition the shop and materials to 72~75 F in advance of a work session, and hold that temperature for 24 hours after a layup.
 
Darn

scsmith said:
I suspect your epoxy has cold-inhibited and will never cure. I have had this happen a few times with West.

I found that I could put a part that had cold-inhibited in the oven at 175F for several hours and it wasn't tacky anymore, but it was rubbery. It never got hard. I scrapped the part.

In your case, I suggest removal. warm it with a hair drier a small area at a time and scrape it all off.


Folks - the hardener systems used with epoxy are not a "catalyst". It is not a matter of enough heat for enough time for a catalyst to bring about a chemical reaction to harden the resin, such as happens with polyester and vinyl ester resins. The hardener system in epoxy becomes an integral part of the final chemical compound. But whether or not that compound properly cross-links into the intended structure depends on the temperature at the time when the basic compound is formed.

If it hasn't cross-linked, it is not going to. Ever.
Click to expand...

Darn.

Double Darn.

lesson Learned: trying to save a minute may cost you a month.....
Thanks for the feedback
 
Last edited:
I must have gotten lucky.. I used Jeffco epoxy, I mixed up some micro that wouldn't harden for over a week. I knew it was throughly mixed, but cold. I gave it a couple of heat cycles with a heat gun, and it did harden up.
 
Epoxy

Just curious and not trying to hijack but interested.
Those who have had issues with epoxy not curing, was it mixed with a scale by weight?
 
Yes

wirejock said:
Just curious and not trying to hijack but interested.
Those who have had issues with epoxy not curing, was it mixed with a scale by weight?
Click to expand...

In my case, yes, always.
I am going to try and put a blanket over it with a temperature controlled heater.
 
Had this happen with the "skim coat" I tried on my canopy skirt. Never cured, just stayed gummy. Had to sand it all off.

One more of many, many reasons I hate this [expletive deleted] fiberglass.
 
rmartingt said:
Had this happen with the "skim coat" I tried on my canopy skirt. Never cured, just stayed gummy. Had to sand it all off.
.
Click to expand...

Same here. Tried the skim coat recommendation for pin hole covering. Total disaster, as it wouldn't harden. Even left it in the sun for several hours and no joy. I mostly use the West or Total Boat (west copy) with the slow activator and have otherwise never had something not cure, even in temps below 60. I do know that they have a recommendation not to use the Fast when temps will not stay above 60 or something like that. They say slow is good down to something like 45.
 
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Skim Coat

Seems others have a similar problem with a skim coat. Maybe the skim coats need a higher temperature cure?

I have got my cowl under a heat source about 90F. Lets see if there is a change after 24 hours. Otherwise peel it off, and redo, but let it set up under a heat source. Seems like in thin layers, the epoxy performs differently then in a glass epoxy matrix.
 
Well, I am not familiar with the epoxy system that JohnS used. I only use MGS for fiberglass lay-ups and West for any fill that will require sanding. Early in the Cozy MKIV build, I was very interested in the prepeg fiberglass available. As an experiment, I was laying up fiberglass taping with the MGS. After it was wet out, I immediately placed it on a frozen plate right out of the freezer and put it in the freezer for a couple days. After removal and thawing, the wet out tape was slightly pliable with a touch of tackiness. The next day, that tape was fully cured. I did that experiment in hopes that I could save some time making the taping in advance. MGS does benefit from a post cure per manufactures specifications, It may or may not work with JohnS epoxy but it is certainly worth a try.
scsmith said:
I suspect your epoxy has cold-inhibited and will never cure. I have had this happen a few times with West.

I found that I could put a part that had cold-inhibited in the oven at 175F for several hours and it wasn't tacky anymore, but it was rubbery. It never got hard. I scrapped the part.

In your case, I suggest removal. warm it with a hair drier a small area at a time and scrape it all off.


Folks - the hardener systems used with epoxy are not a "catalyst". It is not a matter of enough heat for enough time for a catalyst to bring about a chemical reaction to harden the resin, such as happens with polyester and vinyl ester resins. The hardener system in epoxy becomes an integral part of the final chemical compound. But whether or not that compound properly cross-links into the intended structure depends on the temperature at the time when the basic compound is formed.

If it hasn't cross-linked, it is not going to. Ever.
Click to expand...
 
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