Glassed tube still tacky after 1 week

I Have finally managed to glass the main airframe, and the payload tube of an EZI-65 . I used 1 layer of 6 oz, and AeroPoxy.

A week later The epoxy has cured, but, it is still a little tacky. The excess epoxy all cured hard, so I am pretty sure I mixed it properly. I know that a large emount of epoxy will cure faster, and a thin layer will cure more slowly.

So should I continue to wait and see wait happens? it has been pretty humid in my area since I glassed the tube.

I would still be suspicious of the mixing ratio, though I have not worked with Aeropoxy yet. You could try heating with, say, a blow dryer, or maybe start with a light sanding and see what happens.

Hmmmm ...

What was the PR and PH numbers of the Aeropoxy product?

The 1-hour hardener requires no heat cure (well, 90 F is recommended), but the 2-hour hardener does and may remain tacky until it sets. From the PTM&W In dustries, Inc website:

PH3665 hardener should be given a cure of 12 to 14 hours at 120oF to 130oF to in sure a hard gel sufficient for demolding and sandability.

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For laminating (for fiberglass or carbon fiber layups) I use Aeropoxy PR2032/PH3660 (1- hour pot life) or PR2032/PH3665 (2- hour pot life). If you have used the 2-hour hardener, put it in your attic (if it's warm up there) for a day.

Below is my primer on how to use epoxy systems successfully (I have been using Aeropoxy for FG for several years):

Greg

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1. Use nitrile gloves, not latex. Constant skin exposure to epoxy can lead to sensitization (body reacts badly). It does happen to people.

2. Get a digital scale that can weigh to the nearest gram and has a tare feature. Weighing the portions to get them to manufacturing specifications is important.

3. Mix thoroughly (and for 5 minute epoxy, quickly!). I am almost certain that I have had bad epoxy sessions because I didn't thoroughly mix the resin and hardener. I use a craft stick chucked in my drill press and let it do the job for me. An electric drill can do the same thing.

4. Epoxy gains additional strength by adding amendments. These can be milled fiber, fumed silica, chopped carbon, etc. It can be made lighter and more easily sanded by adding microballoons.

5. Use a quality epoxy (like Aeropoxy, WEST System). Use Loctite/Henkel 5 Minute is fine to use for quick bonds.

6. Use the right epoxy for the right job, typically either for adhesion (tends toward high viscosity) or laminating (tends toward low viscosity).

7. Use per the directions (when I had a question about the directions, I contacted the manufacturer for clarification).

8. Epoxy is a thermosetting compound, typically the more heat that is applied the faster it will cure, but to a point. Typically you don’t want the initial cure to be higher than 140 F. Some epoxies benefit from a post-cure thermal cycle. Look for vendor data for specifics, and again, follow the directions.

9. Epoxy has a thermal limit called the glass transition stage, or “Tg” for short. At this temperature, the epoxy significantly weakens and bonding degrades and the condition is often permanent. Use high temp epoxies (like JB Weld, or Cotronics) for applications where bonds are exposed to a significant thermal soak.

watermelonman said:

I would still be suspicious of the mixing ratio, though I have not worked with Aeropoxy yet. You could try heating with, say, a blow dryer, or maybe start with a light sanding and see what happens.

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I agree with watermelonman, although I am not sure heating will resolve the issue.

I am assuming you used the laminating resin PR2032 and one of the hardeners and not the ES6209. Regardless of what you used if the epoxy is still tacky at this stage then you very likely got the ratio wrong. I did this on a small CF layup for an internal structure and the sticky eventually diminished but never fully went away, and this literally took months.

It is not hard to do especially if you're mixing up a small batch, this is why I purchased a scale that is sensitive to 1/100th of a gram, just for mixing up small batches.

Good luck.

I had the same issue recently and decided in the end that it was a humidity problem. I was curing in my garage since it's warmer in there and ended up bringing it back into the cooler (but air-conditioned and therefore less humid) house after a couple of days. 24 hours later most of the tackiness was gone and the rest was able to be sanded out. This was with PR2032 and 3660 hardener.

Is it tacky (soft) or just sticky? If the later it could just be "blushing" that sometimes occurs with lamination. For blushing, just take some solvent (I tend to use either denatured alcohol or xylene) on a white cloth and rub the piece down applying a bit of pressure. Repeat if necessary until you remove the sticky film layer.

I lean toward the mix raito being off. The excess epoxy may have cooked off and cured because of the heat generated during the cure, while your layup, being thin and without the thermal mass that is in the cup, didn't cure.

It is PR2032/3665. it has a slightly tacky feeling, kind of like dried spilled soda.

I set the tubes out in the sun. hopefully it is just environmental.

My:2:
I have had the pleasure of doing field repairs on kevlar and fiberglass in less than ideal conditions. In these circumstances, your good 'ol calibrated Mk1 eyeball is often your best choice when it comes to measuring your mix, so some cure faster than others. In my experience, regardless of environmental conditions, if it hasn't fully cured in a week it will likely not cure out. Heat may finally finish it off but keep it low (I would recommend less than 200 degrees) to avoid breaking down the resin.

I am not a structures guy by trade but I did stay in a Holiday Inn Express the other night, so take this for what it's worth.

I use the 3660 1 hr cure and it has a mix ratio of 100: 27 by weight.


JD

I recently switched from West to Aeropoxy and noticed that even though my laminations were hard after 8 hours, they were a bit tacky even after a couple days. Using 3660, I measure by digital scale to the gram (100/27). My shop runs around 68 degrees. By running the space heater to up the shop temp to 80 degrees or dropping the item in the heat box for 8 hours or so, made the difference - the tackiness was gone. Seems Aeropoxy is a bit more temp sensitive...

Wipe it down with solvent. If it's still tacky, mix another batch of epoxy with the correct ratio and apply a coat over the whole thing. This will help the first batch to cure.

It's carbamate, mate, just like Han Solo Try baking it on your dashboard for several hours in the sun. I've done this over multiple days and had success cooking away Aeropoxy tackiness before.

From the Aeropoxy website FAQ:
Why is the Back of the Laminate Tacky the Next Day?
There are several reasons why this can occur. First, the mix ratio could be off. Under or over catalyzed epoxy resins can have the same net effect – rubbery and/or tacky laminate. Second, if the temperature is below 65°F, chances are the laminate has not fully cured, leaving a tacky finish. Third, in extremely humid conditions, moisture can react with the uncured surface forming a tacky compound, called carbamate. This carbamate will not affect the cured properties of the laminate, but will affect adhesion of subsequent layers of epoxy if not removed prior to laminating. The easiest way to prevent this potential problem is to peel ply the final layer of your laminate, protecting the epoxy from the moisture.

It should be noted; laminating in high humidity conditions will not affect the cured properties of the laminate. The tacky condition described above will only occur while the laminate is gelling or curing.

Insufficient mixing is another way to get the mixture ratio off, even with accurate weighing. At a minimum, mix twice as long as it takes for the appearance to go clear. Ditto not getting it scraped down so that an excess of one or the other is left on the mixing cup or on the mixing stick.

I'd like to propose a simple test of the laminate on the tube. Take a straight pin and put the point against the outside of the tube. Apply steady pressure but not extreme pressure. If the point slowly penetrates the epoxy, then throw it away as a bad job and start again. If it does not penetrate with moderate pressure then the tackiness is likely surface only and may be due to humidity. Heat it up for a post cure for some hours - inside a car will do it in the sun. Then clean off with solvents to remove any remaining tackiness. Just don't use a solvent which attacks cured epoxy, or the glue in the laminations of the tube you glassed.

Another quick and dirty test is to squeeze the tube some so it ovalizes some, and hold it there for several seconds. Then let go. If the tube immediately springs back to round it is probably fine. If it doesn't come all the way back, or comes back slowly, it is not fine.

Gerald

mpitfield said:

I agree with watermelonman, although I am not sure heating will resolve the issue.

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Hah, neither am I! Low on other ideas for this case, though.

Ok, thanks for the suggestions, I think I may be ok.

I was barely able to push a pin in to the tube

The tube was hard to squeeze, but at the end it was easier to squeeze, and it popped right back.

I poured some denatured alcohol on a rag and wiped down an area on the tube, and it did not feel tacky afterwards.

So, the next step, once I get the tackiness gone, is to use a high fill primer, sand and repeat?

That is what I would do. If you were concerned you could do another layer but it also greatly depends on how hard you plan on hitting this piece.