Best way to check if Poly Resin is still good

Daniel1947

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Best way to check if Poly Resin is still good.

Seems there is some different opinions on Poly Resin in regards to shelf life, temperature extremes, etc. I still have 5 gallons of unopened general purpose laminating poly resin. I have keep it stored in the utility room adjoining the garage with the electric water heater. I am relatively positive it has not been over 90 degrees or under 35 degrees in that utility room. The container shows a date of 05/14, so all indications are that it was packaged in May of 2014. Every week or two, I have shook the pail, rolled it around, etc. to keep it mixed. I turn it over and let it sit till the next time I shake it etc.

My questions are: What is the best way to know if it is still a viable product to be used on the boat? If I mix a quart at 1.5% to 2.0% MEKP, apply it to a scrap piece of plywood, give it time to saturate and then lay down a piece of 1708 or CSM saturated with the resin, what should I look for to verify it is giving a good bond etc. Losing the 5 gallons isn't acceptable, but at the same time using it and having problems 6 months later is even less acceptable :blue: .

I would like to hear from I-Boaters that have actual experience with this situation please. As always, I appreciate all information. Ondarvr, where are you? :)
 

Woodonglass

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Well I'm not a PRO like ondarvr but, I've messed with a bit of resin now and then....:D;)

No need to use any glass or mix an entire quart. Using the metric system pour out 60cc of resin (1/4 cup)and use 10 cc of MEKP (2 teaspoons) and mix for 45 secs wait 30 to 45 mins and see if it kicks. Your resin will prolly NOT be the problem it's usually the MEKP that goes bad first and quickest. I've had resin that's a year old that kicks off fine with Fresh MEKP!!!
 
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gm280

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I have to agree with WOG and his recommendations. Just try a little sample test and you will see. If it works with the sample test, it will work with larger amounts as well. I actually had some sitting around for a few years, and I tried a little test with the equally old MEKP. It didn't work, I even tried to step up the percentage of MEKP, still no kicking. I even bought some new MEKP. and it still never setup. So it went in file 13 container. Then I found another few year old polyester resin and the MEKP for it too. It didn't work, but I tried the newer MEKP hardener and WaLa, solid as a rock in about 35 minutes... So all that to say, just try it...
 

Rickmerrill

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Just like you i figured something bad could happen down the road until I looked at the paperwork from usc (they guarantee the resin for 3 months and the mekp for 2 months). Then it said if it was older than that to mix a test batch and see if it hardens before doing a large layup. I figure they wouldn't say that if there were any other gotchas.
 

Daniel1947

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Yeah, I figured I would get a reply from that "old dumb Okie!" LOL, thanks Mike, Rick and gm280. I guess my main concern was that if it hardened in the cup, would there still possibly be a problem doing the layups with the cloth. One of those "well it worked there....wonder why the motor fell off" moments :confused: :facepalm:. Might just go get a fresh bottle of MEKP to be safe, it is cheaper than the resin.

I consider your opinion a real close 2nd to Ondarvr Mike. And as always....thanks everyone....Have a great Turkey day everyone.
 

jc55

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Hmmm. I didn't know that about the MEKP. I have a one gallon bottle I've been using for about a year with new resin.
 

Woodonglass

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WOW a Gallon of MEKP!!! I've never, ever had a Gallon of MEKP!!! Why so Much??
 

jc55

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On my first boat, I bought a 5 gallon "sample" pail that came from the supplier's rep. He cut me a deal on a gallon of Hi-Point MEKP since it wasn't included in the resin.

I had one "misfire" recently where 500mL of thickened PB didn't kick. I had to remove it all and start over. Haven't had a problem since but curious about the MEKP now.
 

ondarvr

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The standard shelf life is 3 months, but it doesn't go from good to bad on 90+1 days. The difficult part for the manufacturer is that each batch made will age slightly different, plus will be handled and stored differently. So the shelf life is based on a somewhat conservative guess as to how long it will still be in spec. By in spec, they mean the gel time and viscosity will still be in a certain range, normally for GT around a 5-8 minute window, and the gel time normally drifts longer, so a 20 minute gel time product could have an 18-25 minute window to be in spec. At 90 days the GT should not be longer than 25 minutes.

Viscosity tends to become lower for a period of time as the thixitropes (typically Silica, Cabosil and such) become less effective. After a somewhat unpredictable time frame the resin will begin to crosslink (gel) on it's own and the resin will become thicker again until it solidifies.

In a manufacturing plant the viscosity and gel time can be critical for production purposes, falling out of the correct spec can slow production and cost a great deal of money even though it may still make a good product. This may not effect a guy doing a small repair at all, or if it does it still may not be a big deal.


I have seen resin and gel coat still do what it's supposed to do at one year old, and I've seen it bad at one week of age, so a generic "how long is polyester good" question isn't easy to answer. It can also depend a great deal on the container it's stored in. Steel containers are best, plastic pails can allow styrene to escape and this may change how the product works, anything that is translucent or transparent will allow UV rays to penetrate and may start the gelling process sooner. If the container has never been opened it has better chance of being good too.

At some point the resin will get to where it doesn't crosslink very well, so the physical properties will suffer, knowing this time frame is almost impossible unless you test it in a lab. So what do you do?

In the lab it's tested in a 100 gram mass and catalyzed at around 1.2 - 1.5% (it may vary by resin). The math is easy with the metric system, 1.5% would be 1.5cc's, and in a test like this I will normally use 2% (2cc's) just to speed things up. You won't easily be able to repeat the lab results because they have a controlled environment at 77F, so the actual time you get won't be the same anyhow.

If it gets hard in 30 minutes or so it is probably OK to use. The temperature will effect the Gel time a great deal though, going up in temp 15*F will about cut the gel time in half, going down 15* will about double it (the actual number of degrees is around 18*, but 15 is easier to work with and will be very close.). You need to work this into your testing.

Most builders won't use a product after its shelf life, or will do some testing to ensure it will still work, they can't risk the possibility of the product failing in some way.

This was a long winded way of saying, test it and see, it's up to you to be comfortable with the results.
 
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Flukinicehole

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I have 3 gallons of resin left over from the last fiberglass project I did back in 2005 I believe. Could have been 04 or 06 .....either way. Three years ago I redid a hatch cover on my boat and used the resin and hardener with no problem. Just yesterday I did a test batch with the new hardener I just got for my new project and it kicked in 30 minutes at around 58 degrees. Although I would not use this in construction I will use it to build my electronics box for the ttop. The resin was separated in the can but I just mixed it up and mixed up about 4 ounces to see what would happen. I was very surprised to see it kicked.
 

gm280

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Yes Fluk, I also had some that I know for certain was a few (okay maybe even five or more yo) in my semi-temp controlled shop. It was a quart-sized metal can inside my metal chemical/flammable cabinet. And once I purchased some new (newer) MEKP from a local auto parts store (not knowing how many years that was there), it also kicked perfectly. So I also test things like that before discarding. But I would never use that for some serious laminating structural building of any project! Just my warped thinking.
 

Daniel1947

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So, looks like the consensus is: Yes....No....Maybe....Probably. :facepalm: Actually it looks like I should mix a sample batch (which I already figured I would) see if it kicks. If it kicks I can consider it is safe to use for all areas of repair (PB, sealing the wood, tabbing, etc.) If it doesn't kick with the older MEKP, I should get a new bottle and see if it kicks. If it does than I can use it for all areas of repair (PB, sealing the wood, tabbing, etc.) If it still doesn't kick, I should discard the resin and purchase new, which I will need to do anyway as I know I don't have enough. Thanks Wood, Ondarvr, Rick, gm280, JC55, and Fluckinicehole, and everyone else. Have good turkey day everyone. :D
 

Flukinicehole

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So, looks like the consensus is: Yes....No....Maybe....Probably. :facepalm: Actually it looks like I should mix a sample batch (which I already figured I would) see if it kicks. If it kicks I can consider it is safe to use for all areas of repair (PB, sealing the wood, tabbing, etc.) If it doesn't kick with the older MEKP, I should get a new bottle and see if it kicks. If it does than I can use it for all areas of repair (PB, sealing the wood, tabbing, etc.) If it still doesn't kick, I should discard the resin and purchase new, which I will need to do anyway as I know I don't have enough. Thanks Wood, Ondarvr, Rick, gm280, JC55, and Fluckinicehole, and everyone else. Have good turkey day everyone. :D

Glad we could help....:laugh:.
 

GT1000000

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After reading through the entire thread, I, too, have come to the unerring conclusion that a test batch is always the best to determine if the resin and MEK are still viable...
I have to whole heartedly agree with ondarvr, that plastic containers give a shorter life span than metal and that an un-opened container is the best bet...metal doesn't allow UV { that's not to say that heat may not be a factor...}, to get to the chemical make up of resin and un-opened containers don't allow regular atmosphere to contaminate and denigrate the contents.
If within reasonable limits the resin goes from a semi-liquid viscous state to a total and complete solid state after the addition of MEK-P within a certain time frame, given the correct conditions for curing, then you can do it...:D
Happy Turkey day...Dan
 
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