West epoxy not hardening?

I have been using West 105 and 206 (slow) for more than a year. It has always worked consistently and fotten rock hard within 24 hours.

But the the batch I used on several parts last night is still gummy/rubbery. It has been more than 18 hours since I mixed and applied it, so it should have firmed up by now. I have put the parts in the oven at 170 degrees to see if helps it along.

Maybe it's just a mixing error, since this was the first time I used an indexed medicine cup to measure the two parts. Usually I use medicinal syringes, which are very precise. This time I filled the cup with hardener to the 2.5 cc mark, then to 15cc with resin, mixed well (2-3 minutes), then applied it with an acid/glue brush.

I am using the same resin and hardener I've had for the last year and a half. I keep it in plastic squeeze bottles in my detached shed, so it has seen temps from about freezing to over 100F. I thought unmixed epoxy was stable, though.

First, what could cause the apparent failure of the epoxy? Should I suspect a problem with the epoxy or hardener, or just the accuracy of the marks on my measuring cups?

Second, if heating the parts doesn't harden the epoxy, is there anything I can do to salvage these parts (metal, blue tube, paper, and plywood).

MountainRocketeer said:

I have been using West 105 and 206 (slow) for more than a year. It has always worked consistently and fotten rock hard within 24 hours.

But the the batch I used on several parts last night is still gummy/rubbery. It has been more than 18 hours since I mixed and applied it, so it should have firmed up by now. I have put the parts in the oven at 170 degrees to see if helps it along.

Maybe it's just a mixing error, since this was the first time I used an indexed medicine cup to measure the two parts. Usually I use medicinal syringes, which are very precise. This time I filled the cup with hardener to the 2.5 cc mark, then to 15cc with resin, mixed well (2-3 minutes), then applied it with an acid/glue brush.

I am using the same resin and hardener I've had for the last year and a half. I keep it in plastic squeeze bottles in my detached shed, so it has seen temps from about freezing to over 100F. I thought unmixed epoxy was stable, though.

First, what could cause the apparent failure of the epoxy? Should I suspect a problem with the epoxy or hardener, or just the accuracy of the marks on my measuring cups?

Second, if heating the parts doesn't harden the epoxy, is there anything I can do to salvage these parts (metal, blue tube, paper, and plywood).

Click to expand...

Not sure why your epoxy didn't cure up initially. You might not have stirred it enough. For large batches, I use mechanical stirring just to make sure it's as well mixed as possible.

For your current attempt at 170F, be aware that the West glass transition temperature is much lower (125F maybe, it's easy to find). At 170F, you will definately succeed in making the epoxy gummy & rubbery. I did this by accident a few weeks back, although I was well short of 170. The epoxy did harden up after it cooled for a while.

Jim

How long has it been sitting? Once it's opened it has a shelf life of about a year, less if it's humid. As for salvage of parts..... Scrape off what you can and the rest scrub with a rag wetted in denatured alcohol. Paper parts are most likely shot but the rest can be saved. May take some time but it will get it. FWIW

stantonjtroy said:

How long has it been sitting? Once it's opened it has a shelf life of about a year, less if it's humid. As for salvage of parts..... Scrape off what you can and the rest scrub with a rag wetted in denatured alcohol. Paper parts are most likely shot but the rest can be saved. May take some time but it will get it. FWIW

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The blue highlighted portion of the above post is FALSE.

Please don't make stuff up. Refer to: https://www.westsystem.com/ss/storage-shelf-life

In closed containers, West Systems epoxy will last a long time. I have never had issues with resin or hardener going bad. I keep a can of 105 resin a can of 206 slow and a can of 205 fast in my shop and depending upon my build rate, I might take 3 or more years to go through an opened can. I measure small amounts by weight on a .1 gram accuracy scale (very precise), and large batches with the West pumps. The slow can take a long time to cure if it is cold, but otherwise, I've never had a problem.

It sounds like the OP is measuring correctly (West is 5:1 for 205 or 206 hardener). Almost certainly, mixing is the issue.

--Lance.

Another issue to investigate is that the measuring by addition is part of the reason. It is more precise to measure each separately and then mix. Am I math addled? No, I'm a chemist and have run into this before. When you mix one part one thing and another part of another you do not necessarily get 2 parts by volume. A gross example is one gallon of sneakers plus a gallon of sand does not equal 2 gallons. It's something much less. Measuring each separately is always the better way to hit a ratio. That's probably the case with your syringes, each volume was determined separately and the ratio was exact.

Another issue is the cups you have might have a mold release on them that may interfere with the chemistry (silicones?) but that shouldn't be if they were from a pharmacy. I had tried to cast some resin with lead shot inside for an odd project and it was flexible, the lead interfered with the cross-linking. It doesn't take much contamination.

Tolppisouth said:

Another issue to investigate is that the measuring by addition is part of the reason. It is more precise to measure each separately and then mix. Am I math addled? No, I'm a chemist and have run into this before. When you mix one part one thing and another part of another you do not necessarily get 2 parts by volume. A gross example is one gallon of sneakers plus a gallon of sand does not equal 2 gallons. It's something much less. Measuring each separately is always the better way to hit a ratio. That's probably the case with your syringes, each volume was determined separately and the ratio was exact.

Another issue is the cups you have might have a mold release on them that may interfere with the chemistry (silicones?) but that shouldn't be if they were from a pharmacy. I had tried to cast some resin with lead shot inside for an odd project and it was flexible, the lead interfered with the cross-linking. It doesn't take much contamination.

Click to expand...

I am pretty sure there is a contaminant on the cups. I found the cup I used to mix the problem batch, and the film left in the cup is not just gummy--it is still runny or syrupy. To me that indicates there is something on/in the cup inhibiting the epoxy. I noticed that the cup/potted epoxy never warmed up while I was using it, but I shrugged it off at the time. In part because I was waiting for it to warm up, I am pretty sure I mixed the bad batch as much or more than than I usually do the dozens or more of good batches I have used. This is the first time I used these cups and the first time I had a problem with this epoxy. Coincidence?

I got these cups from a hobby store, from the glue and solvents section. It is a bag of about 200 cups labeled with cc, ml, oz, dram, and teaspoon markings. I thought the hobby store had just stocked up on medicinal cups, but maybe these are not pharmaceutical grade. Or maybe these were salvaged from pharma and repurposed because they had something on them.

I mixed up a new batch last night, using syringes and a paper cup. It warmed up in the pot and hardened in the paper cup within 6 hours. So, the epoxy is just fine.

Tonight I will use the syringes to measure into the "medicine" cup and see if I still have problems. If I do, I will know it is the cups. If not, I will chalk it up to a problem of measuring resin and hardener in the same cup, or user error in the mixing.

Thanks for all your input.

llickteig1 said:

The blue highlighted portion of the above post is FALSE.

Please don't make stuff up. Refer to: https://www.westsystem.com/ss/storage-shelf-life

.

Click to expand...

Didn't make anything up and don't really care what the URL says. I'm a Composites tech by trade and have used West nearly as long as it's been available. I've learned the Manufacture only posts what the test out and even THAT isn't always accurate. Just because you've seen a certain level of performance dosn't make it so for everyone and in all cases. My info was accurate based on my experience and that of many others.

Just curious, not trying to stir anything up.

Troy how are you storing your resin?


I have been using West for 40 years. [used to build boats]

Keep it in the house at room temp & have had some last 3 years or more.

I did keep some in the garage once and the temp cycling killed it in a year.
Only bad thing is it ages the hardener get thick and dark red, I find I must use a tad less or it fires off quicker.

Semper fly.

Cj

stantonjtroy said:

Didn't make anything up and don't really care what the URL says. I'm a Composites tech by trade and have used West nearly as long as it's been available. I've learned the Manufacture only posts what the test out and even THAT isn't always accurate. Just because you've seen a certain level of performance dosn't make it so for everyone and in all cases. My info was accurate based on my experience and that of many others.

Click to expand...

I'll take the word of the manufacturer, TYVM.

I put a drop of red stamp pad ink in my epoxy as it is being mixed. It makes it really easy to make sure it's mixed thoroughly.

I've used a hot box before to speed up curing, and if I remember correctly, the max temp shouldn't exceed 120 degrees for West Systems.

Always mix by weight to the 1/2 of a gram and you should always be successful. Gram scales are relatively cheap these days, cheaper than a ruined rocket. Volume measurement can be off by 6-8%, especially in smaller amounts. So, +7% resin and -7% catalyst and you have a net 14% deviation from the proper mix.

Pat_B said:

I put a drop of red stamp pad ink in my epoxy as it is being mixed. It makes it really easy to make sure it's mixed thoroughly.

I've used a hot box before to speed up curing, and if I remember correctly, the max temp shouldn't exceed 120 degrees for West Systems.

Click to expand...

The parts were rubbery when they came out of the heat, but they hardened up reasonably firm once they cooled. Interestingly, the excess epoxy I poured out and never heated stayed rubbery, and the film left in the cup is still runny/syrupy.

I guessed that 170 was warmer than optimal, but that was the lowest available setting.

rocketsmith said:

Always mix by weight to the 1/2 of a gram and you should always be successful. Gram scales are relatively cheap these days, cheaper than a ruined rocket. Volume measurement can be off by 6-8%, especially in smaller amounts. So, +7% resin and -7% catalyst and you have a net 14% deviation from the proper mix.

Click to expand...

I think my scale only goes to 1 gram, no decimals. Since I usually mix a tablesppon or two at a time, I do not know that the scale is any more accurate than my 5ml syringes. I have a beam scale I use to measure powder for handloading, but that is not practical for this.

Maybe I will get a digital powder scale like I have been wanting. A tenth of a grain is less than 1/100th of a gram, so that should be accurate enough for mixing epoxy.

I use the pumps - no issues - even after marking off half and quarter strokes

Last night I mixed a batch in a paper cup. Once I had used what I needed on the rocket, I poured the rest into one of the plastic cups and stirred it for a couple of minutes so that any mold release or other contaminants would get mixed in. That batch hardened up just fine on the rocket, in the paper cup, and in the plastic cup. At the same time, I used syringes to measure a 2 + 10 cc batch in a plastic cup. I stirred for about three minutes and overnight it hardened up great, too.

So, I have ruled out a problem with the resin or hardener or a contaminant in the cups. It is possible that it was a mixing error, but I mixed the bad batch as long and thoroughly as I usually do. At this point, I am pretty sure that the problem was trying to used combined volume measurments to meter the epoxy.

As a final experiment, I will use syringes to measure into an indexed cup and see if 2.5cc of hardener + 12.5cc of resin does actually comes to 15cc.

MountainRocketeer said:

Maybe I will get a digital powder scale like I have been wanting. A tenth of a grain is less than 1/100th of a gram, so that should be accurate enough for mixing epoxy.

Click to expand...

There ya go! Very good idea. www.harborfreight.com/1000-gram-digital-scale-97920.html has small digital scales that may intrest you.

JimJarvis50 said:

... For large batches, I use mechanical stirring just to make sure it's as well mixed as possible...

Click to expand...

Jim I am curious as to what mechanical stirring method you use, since it seems that it works well for you. I tried something once and it created a lot of bubbles in the epoxy, which generally speaking isn't good.

Greg

GregGleason said:

Jim I am curious as to what mechanical stirring method you use, since it seems that it works well for you. I tried something once and it created a lot of bubbles in the epoxy, which generally speaking isn't good.

Greg

Click to expand...

I use only the highest-tech methods for my rocket building. No skimping!

My device is pictured below. Popcycle stick on a nail. The drill press is set to a relatively slow speed, and I just pin the mixer at about half the depth of the epoxy for a few minutes. No bubbles get added. When it's done mixing, I lift it up above the liquid and let it spin to remove the excess epoxy.

Jim

A quick tip on the bubbles. If you ---flash --the epoxy with a propane torch the bubbles will rise and disappear. By flash I mean , quickly run a torch over the surface--at a distance--just enough to heat the surface--usually 1 or 2 passes does it. It momentarily thins the epoxy while letting the gas escape. Work easier on long dry time stuff but works on all I've tried. Try it off rocket first--you might like the results.

JimJarvis50 said:

I use only the highest-tech methods for my rocket building. No skimping!

My device is pictured below. Popcycle stick on a nail. The drill press is set to a relatively slow speed, and I just pin the mixer at about half the depth of the epoxy for a few minutes. No bubbles get added. When it's done mixing, I lift it up above the liquid and let it spin to remove the excess epoxy.

Jim

Click to expand...

So a drill press makes a good epoxy mixer?

Who knew?

o1d_dude said:

So a drill press makes a good epoxy mixer?

Who knew?

Click to expand...

Well, it's good for other stuff as well. When I used to mix a full cup of epoxy at a time for rolling tubes, I never felt like I could stir it long enough by hand to get it truly mixed. The drill press does the trick. Now, I put a little double-sided tape on the shelf to hold the cup in place.

Double-sided tape - 1001 uses!

Jim

Heh heh. Maybe a Dremel instead of drill press for tiny batches? :wink:

Or one of those stirrers for mixing drinks and pancake batter, probably best to have a separate one for each.

Robostir?!?

JimJarvis50 said:

I use only the highest-tech methods for my rocket building. No skimping!

My device is pictured below. Popcycle stick on a nail. The drill press is set to a relatively slow speed, and I just pin the mixer at about half the depth of the epoxy for a few minutes. No bubbles get added. When it's done mixing, I lift it up above the liquid and let it spin to remove the excess epoxy.

Jim

Click to expand...

Interesting!

When you say a relatively slow speed, do you have any idea how many rpm's that translates to?

hornet driver said:

A quick tip on the bubbles. If you ---flash --the epoxy with a propane torch the bubbles will rise and disappear. By flash I mean , quickly run a torch over the surface--at a distance--just enough to heat the surface--usually 1 or 2 passes does it. It momentarily thins the epoxy while letting the gas escape. Work easier on long dry time stuff but works on all I've tried. Try it off rocket first--you might like the results.

Click to expand...

Just to clarify, is this epoxy already in the layup? If so, I would assume that the heat pass would be on the vertical surface, to allow upward movement of the bubbles to the surface. I don't have a propane torch, so would a heat gun work, or is the thermal plume too broad?

Greg

GregGleason said:

Interesting!

When you say a relatively slow speed, do you have any idea how many rpm's that translates to?

Greg

Click to expand...

570 rpm.

Jim

JimJarvis50 said:

570 rpm.

Jim

Click to expand...

Great!

Thanks Jim.

Greg

MountainRocketeer said:

I think my scale only goes to 1 gram, no decimals. Since I usually mix a tablesppon or two at a time, I do not know that the scale is any more accurate than my 5ml syringes. I have a beam scale I use to measure powder for handloading, but that is not practical for this.

Maybe I will get a digital powder scale like I have been wanting. A tenth of a grain is less than 1/100th of a gram, so that should be accurate enough for mixing epoxy.

Click to expand...

I use a small digital scale that measure to the 1/100th of an oz or gram. Plenty accurate and never had a problem mixing 5-1 West System or 1-1 Aeropoxy. I also use the clear hard plastic disposable cups from Costco to mix. These cups make it easy to see when the resin and hardener are completely mixed and they are inexpensive. Sounds like you have the perfect excuses now to justify a digital powder scale.