tiggerracing

For some reason my 30min Z-Poxy will not set. Im using it on my parkzone F4U which is made of Z foam. I reglued my landing gear a week ago (yup definitly more than 30 minutes) and after i took it up the other day i realized the LG were loose again. When i felt it, the epoxy was slimy and tacky. What im i doing wrong?
Thanks for any help.
max

lejongleur

My Feedback: (10)

I suspect you didn't mix it up enough. Is that possible?

TedMo

Kind of strange that you didn't determine that shortly after having used it??? Are you sure you added the hardener? Mix up a small batch just to check it.

Props4ever

It sure sounds like not mixing it properly according to directed mixing ratios of resin and hardener!.

This is typical with epoxy resins, if they are not mixed according to directions with ratios of both bottles, they will never cure!. It wouldn't matter how long you try to dry it, it simply will not!!.
I learned this the hard way and almost had one of the outer wing panels completely ruined, but i had managed to save it by peeling off the half wet fiberglass skin of the foam core panel.....

mboland

Z-Poxy and some others eventually "go off"

If you have used them over time, check where you used it and you will find that each use is a bit more rubbery than the one before it.

I also had this happen, unfortunately it was a friends plane I was repairing.
He brought it back a couple of days later and the epoxy was still as runny as when it was mixed, and yes, it was mixed and mixed well.
Had to use alcohol to clean it all off and buy some fresh epoxy.

I now always keep them in the fridge, along with all the other goos and glues.

So don't be too quick to blame someone for making a mistake, the answer is not always the obvious one to you.

tiggerracing

Thanks for the info everyone. I know i had eqaul ratios though. I probably didnt mix it very well. Im used to the spray on stuff. I'll go re glue.

Bob93447

What is the lowest temperature which will allow Z-Poxy to cure?

Tom Nied

From the product sheet. http://supergluemsds.com/Docs/PT39%20%20-%20Z-poxy%2030%20Min%20System%20-%20PSS%20-%20Rev%202%20-%202013.pdf

30 minutes at room temperature (77F or 25C) with full cure in 24 hours. Note – For cooler
temperatures, setting time may be longer. Product can also be heat cured at 200F for 35-
45 minutes for full cure properties.

Cooler temperatures will slow the curing process.

Bob93447

Thank you. My garage is a bit cooler than recommended so I will need to wait a few months for things to warm up. I did get a small sample to cure using a heat gun but I don't want to risk messing up a full model.

extra300crazy

Bob,
Last year I built a H-9 p-40 and reenforced the cowl with fiberglass cloth and epoxy. I had used some Hobby Poxy 45 min. epoxy ( remember that brand?) and it remained rather soft the next day to my surprise. Thinking I would have to redo it, I let it set in my Michigan basement workshop while I continued construction on the rest of the plane. Lo and behold after almost a month it was cured correctly. I discarded the rest and bought new epoxy. By the way, if epoxy begins to crystalize in the bottle, I find that a few seconds in the microwave clears it up.
Hope this helps.
Karl

jester_s1

I had some Z poxy finishing resin not cure last year. Heat got it to work though. I then changed my mixing procedure for finishing resin. I mix it for 1 minute, then let it sit for 2 minutes in the container. Then I mix for 30 more seconds and apply. I read somewhere that being in the container lets the polymer chains start forming, then remixing gives those chains new molecules to start bonding to. If you spread it thin immediately after mixing though, the chains can have trouble forming as thoroughly as they should to get a full cure. That procedure does cut into your working time as it accelerates the curing time, but I've never needed more than 10 minutes to spread a batch of resin on glass anyway.

extra300crazy

Jester,
That's a great tip, I'll try that in the future. Years ago using Hobby Poxy paint the instuctions stated to let the paint sit once mixed for 30 min. before spraying. It worked great. I sure miss Hobby Poxy products.
Karl

raptureboy

There's no advantage to storing epoxy in the fridge. It can get old though and will take longer to cure, so heat from a blow dryer on low will help and won't damage the foam. I once got distracted and mixed equal quan of resin and resin then looking at my bottles I noticed the issue. don't let epoxy sit too long in a small container or it will generate heat and shorten the working time.

extra300crazy

Yes, I've mixed up some epoxy for wing spars in a typical medicine cup and had it get so hot I could hardly hold it!
Karl

Pylonracr

What you experienced is exothermic runaway. It can be a problem any time you mix a fairly large batch of resin. There are a couple ways to combat it. You can mix the resin and pour it into something flat like a pie plate. The extra surface area will let the heat rise away from the resin a little better. I mix in red SOLO cups, so if it is hot in my garage I put the cup into a bowl of ice to keep the resin temp down.

Jester, your new method of mixing is correct. Several resin manufacturers recommend just that. Measure accurately, mix well, let rest for a minute, mix well again. With any laminating resin, accuracy in measuring resin and hardener is very important.

Scott