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Thinned out Epoxy question

Old 12-13-2015, 05:04 AM
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Trax540
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Default Thinned out Epoxy question

Perhaps someone can help with this issue.
I used some 30 Minute epoxy thinned with 95% denatured alcohol to fuel proof a firewall. I thinned it 50% and brushed it on and I let it dry overnight. Roughly 8 hours later I notice that its not 100% dry. Although it isn't gooey its still slightly "Tacky" to the touch. So i checked the little bit of remnants left in the cup, and its the same result.
I know i used equal parts of hardener and resin. Is there anything i can do to cure it? or is it common for it to take this long to set up once you thin with alcohol?
Old 12-13-2015, 05:13 AM
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Rodney
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While some get by with using thinners, I recommend that thinners not be used. At the very least, it results in a weaker bond. Using alcohol will result in some water content being retained as it cures leaving a less than desirable finish. Much easier to just spread a thin coat and then use your hot air gun to warm the area. You will see the epoxy suddenly weep into the wood and smooth out any excess. It also speeds up the cure time. do not get it to hot, just warm enough to suddenly weep into wood and smooth out.
Old 12-13-2015, 05:38 AM
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Trax540
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Hmmm, Well is there anything i can do to help it cure now that it already has been applied. Or is this never going to harden up? I don't know how i would strip it off even if i wanted to. Sanding it is only an option for exposed area. I wouldn't be able to sand out the tank area.
If it will eventually cure I'm alright with it, my concern at the moment is that it will never harden up.
Old 12-13-2015, 06:03 AM
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ByLoudDesign
 
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The other 5% is water!!! Might put a heat lamp on it, and try and drive it out!
Old 12-13-2015, 07:19 AM
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Water is bad news as far as epoxy is concerned. Better to use acetone or pure methelayted spiirits.

As far as fixing what you have I would leave it for a day or two and see if the cure improves. Bit I think it will stay chewy and tacky.

As others say warming it is the best way to improve flow.
Old 12-13-2015, 08:14 AM
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I rarely have needed to use it for epoxy glue. I use the hobbypoxy type thinners for the paints, and they work ok for the glue. You want the thinner to evaporate before the glue sets IMHO. We have a brand name of Klenks epoxy thinner that is used for bathtub type epoxies. It mentions acetone and toluene as the main ingredients for medical emergencies. It seems to thin out anything that I have tried it with, and smells like the old Hobbypoxy and K&B paint thinners that are not available any more. As for fixing what you have? If it is soft all the way through, maybe removing it and starting over, or use a thinner to wipe it away, which is also removing the top surface of it. At least to see if it is soft all the way through. Then something can be put on top like maybe some other type of epoxy and thinner or even an epoxy type paint with maybe a bit more hardener to try to cure the stuff underneath. It would depend on a lot of variables. I think a heat gun is best for fuelproofing firewalls, so maybe a heat gun may help to speed up the cure too. Likely the easiest way to evaporate the water out, at least to try as has been mentioned numerous times.

Last edited by aspeed; 12-13-2015 at 08:26 AM.
Old 12-13-2015, 09:30 AM
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speedracerntrixie
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You have what is called Amine Blush. This is when all the solvents in the epoxy do not flash off completly. Thinning the epoxy can cause this as well as trying to cure at too low a temp. Either way it's not a huge issue, expose to some heat greater then 80 degrees for a day or two. I used to think that thinning epoxy would create a weaker bond as well until I got some training on the matter. It's fine to thin as long as you cure at the correct temp, the alcohol will slow the flash and cross link. Additional heat is required to keep the molecules moving to promote a full cross link. I now thin laminating epoxy resin when I lay up fuselages and then post cure them by carrying them around in the car for a couple sunny days.
Old 12-13-2015, 10:15 AM
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Like to suggest you use Sig Clear buterate dope
It dries supper fast , is fuel proof and is lighter than epoxy
Dry in one hour or less
I use it over any seams i may have in my ultracoat ,gets invisable and seals
Building since the mid 50's
Old 12-13-2015, 10:25 AM
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Like to suggest you use Sig Clear buterate dope
It dries supper fast , is fuel proof and is lighter than epoxy
Dry in one hour or less
I use it over any seams i may have in my ultracoat ,gets invisable and seals
Building since the mid 50's
Old 12-13-2015, 01:45 PM
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tailskid
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Do what I do....put the plane in a car, roll up the windows and let the sun "bake" it for you.....being that you used alcohol you did not hurt your fuel proofing intentions!!!

Of course I live in the Valley of the Sun and do this often LOL
Old 12-13-2015, 02:15 PM
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DGrant
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Climate plays a big part in epoxy curing. The colder the climate, the longer it will take... and in some very cold climates it might take days or more. I'd say just be patient, let it sit in a warm house for a week... the warmest spot in the house... In my experience it does take more time when the epoxy is thinned.... so yeah... wait it out a few days with the project in a warm environment and I think it will set eventually.
Old 12-13-2015, 02:37 PM
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THERCAV8R
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Just warm up the area with a heat gun. Make sure it is really warm through out the structure. Then leave it in a window in direct sun lite it will cure. also wipe off the surface with alcohol and let it dry before you heat it up. Heat will also speed up the curing time of epoxy and cold will slow it down.
Old 12-13-2015, 03:02 PM
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jester_s1
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If you have a heat gun, heat up the epoxy for a few minutes. It may take a few times doing it, but the heat should help it finish curing. It's really ok though. Soft epoxy will keep fuel from seeping into your firewall just fine.

For future use, your epoxy will be a lot more reliable if you mix it then let it sit for about 10% of the working time. So if it's 30 minute epoxy, let it sit for 3 minutes. Then mix it again. Mixing should be for at least a minute each time.That allows the chemical reaction to get started that makes the epoxy harden and then spreads those reacting chemicals around again to the tiny spots that didn't get mixed right in the first place. If you're going to thin it, put the thinner in during the second mixing.
Old 12-13-2015, 06:25 PM
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tailskid
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I know how to make 30 minute epoxy cure in 10-15 minutes! All you have to do is add some Micro balloons and try to glue two very large wing halves together in a small room! <g>
Old 12-13-2015, 07:01 PM
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Originally Posted by Trax540
Perhaps someone can help with this issue.
I used some 30 Minute epoxy thinned with 95% denatured alcohol to fuel proof a firewall. I thinned it 50% and brushed it on and I let it dry overnight. Roughly 8 hours later I notice that its not 100% dry. Although it isn't gooey its still slightly "Tacky" to the touch. So i checked the little bit of remnants left in the cup, and its the same result.
I know i used equal parts of hardener and resin. Is there anything i can do to cure it? or is it common for it to take this long to set up once you thin with alcohol?
I thin epoxy with denatured alcohol anytime I cover with fiberglass or want to fuel proof an area and never had a problem. If you use to much hardener however it will take longer to set up. Can't answer why but it just will. I tend to error on the short side of hardener and seems to work for me. A heat gun or time will help in your situation. As a side note; most of the strength of fiber glassing come from the fiber glass material itself.

K. O.

Last edited by K.O.; 12-13-2015 at 07:06 PM.
Old 12-14-2015, 01:28 AM
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drac1
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I use Isopropanol - Isopropyl Alcohol for thinning epoxy. It always fully cures without the need to heat.[h=1][/h]
Old 12-14-2015, 02:55 AM
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Trax540
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Thanks for all the help. I was about to start trying to strip it! I heated it with the heat gun for about 10 minutes. Then got very bored of standing there lol. I set the light near the top and now its started to really cure.
That was the first time I tried the thinning method so i was nervous when it went longer that 8 hrs to harden.
Old 12-14-2015, 03:19 AM
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One thing you need to be aware of is not all epoxies take being thinned with solvents well. If you use West Systems, like I do, it says right on the manufacturer's website NOT TO THIN WITH SOLVENTS. The manufacturer specifically calls out heating the materials and epoxy if getting it to flow is needed
Old 12-14-2015, 03:59 AM
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hawkerone
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I frequently thin epoxy to seal firewalls with Isopropyl Alcohol, but just a few drops . Drying time does take noticeably longer and I've had it tacky for a couple of days when I've overdone it but never had it completely fail to eventually harden. Heat will speed up the process and make it flow even better. I suggest you not thin if patience is an issue (as it frequently is with me).
Old 12-14-2015, 06:10 AM
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Hey, did you get the answer you were looking for? If not try this for fun http://www.westsystem.com/ss/thinnin...-system-epoxy/
Old 12-14-2015, 07:01 AM
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Out of a dozen planes I never had a problem with thinning epoxy with alcohol. And never did anything special. The only time I had a problem with 30 minute epoxy not curing was due to mixing it incorrectly. Some 30 minute brands seem to be overly sensitve to exact proporations. My solution was to stop using those brands. Unfortunately I don't remember what they were and I don't use 30 minute anymore.
Old 12-14-2015, 07:09 AM
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RCVFR
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Originally Posted by hawkerone
I frequently thin epoxy to seal firewalls with Isopropyl Alcohol, but just a few drops . Drying time does take noticeably longer and I've had it tacky for a couple of days when I've overdone it but never had it completely fail to eventually harden. Heat will speed up the process and make it flow even better. I suggest you not thin if patience is an issue (as it frequently is with me).
I agree with the "few drops" of isopropyl, it has worked for me. "Few drops" means just enough to get the epoxy to brushing consistency. I don't know where the 50/50 dilution idea comes from, but that is plainly too much alcohol. I learned that lesson the first time.
Old 12-16-2015, 01:13 PM
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I have thinned epoxy with 91% isopropyl alcohol and it stayed tacky awhile but eventually hardened OK. I think it's OK for fuel proofing.

But later I tried the heat gun with no thinning like Rodney suggested and I thought it was great. You could blow it across the surface wherever you want and watch it soak in. Next day it was hard.

Next material for me will be System 3 paint with cross linker. No chemical hazards.

Jim
Old 12-19-2015, 05:34 PM
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I've never used isopropyl alcohol to thin epoxy. Always used denatured alcohol. Isopropyl has water mixed in and water is the enemy of epoxy before it's set. Denatured has no or very minimal water. Never had a cure take longer than normal time with the denatured.

Ken
Old 12-19-2015, 05:51 PM
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drac1
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I've used both Methylated Spirits and Isopropyl for thinning and never had a cure take longer than normal with either.

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