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#1
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Odd epoxy/gelcoat problem
I've done many repairs with epoxy and covered them with gelcoat, with no
problems with curing or adhesion. However, I'm having a problem on one particular boat. I did a structural repair on a kayak with epoxy and fiberglass cloth (nothing special about it), but for some reason, the gelcoat didn't want to cure where it was over the epoxy (I'm using finish gelcoat, so air exposure is not the issue). I removed it and allowed the epoxy to cure for an extra couple of days under heat. When I re-applied the gelcoat, ~75% of it cured fine. However, I still have three small spots that won't cure properly where it's over the epoxy. Where it's applied over other gelcoat, it cures fine. It's been ~2 weeks since the initial repair was made, so I'm confident that the epoxy is well cured. I've tried using denatured alcohol, lacquer thinner, acetone and MEK to clean the epoxy surface, but the gelcoat still won't cure properly in these three spots. I'm using the same products that I've used successfully many times before. The only clue to the problem is that the uncured gelcoat takes on a slightly yellow-greenish cast. Any ideas? |
#2
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The Gougeon folks suggest cleaning the dreaded amine blush with amonia and
water. Have you asked the vendors of either of the prducts? "Brian Nystrom" wrote in message ... I've done many repairs with epoxy and covered them with gelcoat, with no problems with curing or adhesion. However, I'm having a problem on one particular boat. I did a structural repair on a kayak with epoxy and fiberglass cloth (nothing special about it), but for some reason, the gelcoat didn't want to cure where it was over the epoxy (I'm using finish gelcoat, so air exposure is not the issue). I removed it and allowed the epoxy to cure for an extra couple of days under heat. When I re-applied the gelcoat, ~75% of it cured fine. However, I still have three small spots that won't cure properly where it's over the epoxy. Where it's applied over other gelcoat, it cures fine. It's been ~2 weeks since the initial repair was made, so I'm confident that the epoxy is well cured. I've tried using denatured alcohol, lacquer thinner, acetone and MEK to clean the epoxy surface, but the gelcoat still won't cure properly in these three spots. I'm using the same products that I've used successfully many times before. The only clue to the problem is that the uncured gelcoat takes on a slightly yellow-greenish cast. Any ideas? |
#3
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Brian Nystrom wrote:
I've done many repairs with epoxy and covered them with gelcoat, with no problems with curing or adhesion. However, I'm having a problem on one particular boat. I did a structural repair on a kayak with epoxy and fiberglass cloth (nothing special about it), but for some reason, the gelcoat didn't want to cure where it was over the epoxy (I'm using finish gelcoat, so air exposure is not the issue). I removed it and allowed the epoxy to cure for an extra couple of days under heat. When I re-applied the gelcoat, ~75% of it cured fine. However, I still have three small spots that won't cure properly where it's over the epoxy. Where it's applied over other gelcoat, it cures fine. It's been ~2 weeks since the initial repair was made, so I'm confident that the epoxy is well cured. I've tried using denatured alcohol, lacquer thinner, acetone and MEK to clean the epoxy surface, but the gelcoat still won't cure properly in these three spots. I'm using the same products that I've used successfully many times before. The only clue to the problem is that the uncured gelcoat takes on a slightly yellow-greenish cast. Any ideas? Yes - I think you got lucky the other times. Gelcoat is NOT supposed to cure when applied over epoxy (i.e. the conventional wisdom)! Evan Gatehouse |
#4
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Jim Conlin wrote:
The Gougeon folks suggest cleaning the dreaded amine blush with amonia and water. I've never noticed any blush with this epoxy. With all the scraping and chemical cleaning I've done, it's hard to believe that there could be anything left on the surface. Have you asked the vendors of either of the products? I have, but haven't received a reply yet. |
#5
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Evan Gatehouse wrote:
Yes - I think you got lucky the other times. Gelcoat is NOT supposed to cure when applied over epoxy (i.e. the conventional wisdom)! My experience has been that the "conventional wisdom" is simply wrong and epoxy manufacturers agree. Once epoxy cures completely, it's inert, so it shouldn't matter what you put over it unless it specifically reacts with the epoxy chemically. I've used this particular combination of epoxy and gelcoat successfully many times (literally from the same cans) and have used other epoxies with this gelcoat, so I know from experience that it works quite well. Something has gone wrong this time, but I can't figure out what it is. One suggestion I've been given is contamination in the epoxy or gelcoat. That's possible, but I'm not sure what could have contaminated it. |
#6
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Brian Nystrom wrote:
Evan Gatehouse wrote: Yes - I think you got lucky the other times. Gelcoat is NOT supposed to cure when applied over epoxy (i.e. the conventional wisdom)! My experience has been that the "conventional wisdom" is simply wrong and epoxy manufacturers agree. Once epoxy cures completely, it's inert, so it shouldn't matter what you put over it unless it specifically reacts with the epoxy chemically. I've used this particular combination of epoxy and gelcoat successfully many times (literally from the same cans) and have used other epoxies with this gelcoat, so I know from experience that it works quite well. Something has gone wrong this time, but I can't figure out what it is. One suggestion I've been given is contamination in the epoxy or gelcoat. That's possible, but I'm not sure what could have contaminated it. Is it possible that the epoxy mix was rich in one or the other of the components, some of which permeates the epoxy, and which cannot cure without it's required co-component? Might adding a little of the other cause it to set up to the point where it actually becomes "inert?" Might it then work better with the gelcoat as you would expect? Or would it be better to remove the epoxy, recoat it with a more careful mix of epoxy, then finish? If one of the epoxy components has been around for a while is it possible it has become "corked", that is, oxodized to the point where it is not still the epoxy part you bought? Almost everything oxidizes over time. I have had old polyester resin gum up, it seems to set up slowly with air, humidity, or UV, sometimes. MEK is an oxidizer. Have you done a subsequent test to see if this leftover old epoxy will still set up under normal conditions? It sounds like a contamination problem, you sure the dog didn't pee in your mash, or summat? Terry K |
#7
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Check the expiration date on the gelcoat. It sounds like the mekp is not
curing the entire batch. Bruce -- Shield Finishes and Nauticoat Marine Finish Systems www.shieldfinishes.com "Terry Spragg" wrote in message ... Brian Nystrom wrote: Evan Gatehouse wrote: Yes - I think you got lucky the other times. Gelcoat is NOT supposed to cure when applied over epoxy (i.e. the conventional wisdom)! My experience has been that the "conventional wisdom" is simply wrong and epoxy manufacturers agree. Once epoxy cures completely, it's inert, so it shouldn't matter what you put over it unless it specifically reacts with the epoxy chemically. I've used this particular combination of epoxy and gelcoat successfully many times (literally from the same cans) and have used other epoxies with this gelcoat, so I know from experience that it works quite well. Something has gone wrong this time, but I can't figure out what it is. One suggestion I've been given is contamination in the epoxy or gelcoat. That's possible, but I'm not sure what could have contaminated it. Is it possible that the epoxy mix was rich in one or the other of the components, some of which permeates the epoxy, and which cannot cure without it's required co-component? Might adding a little of the other cause it to set up to the point where it actually becomes "inert?" Might it then work better with the gelcoat as you would expect? Or would it be better to remove the epoxy, recoat it with a more careful mix of epoxy, then finish? If one of the epoxy components has been around for a while is it possible it has become "corked", that is, oxodized to the point where it is not still the epoxy part you bought? Almost everything oxidizes over time. I have had old polyester resin gum up, it seems to set up slowly with air, humidity, or UV, sometimes. MEK is an oxidizer. Have you done a subsequent test to see if this leftover old epoxy will still set up under normal conditions? It sounds like a contamination problem, you sure the dog didn't pee in your mash, or summat? Terry K |
#8
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Terry Spragg wrote:
Brian Nystrom wrote: Evan Gatehouse wrote: Yes - I think you got lucky the other times. Gelcoat is NOT supposed to cure when applied over epoxy (i.e. the conventional wisdom)! My experience has been that the "conventional wisdom" is simply wrong and epoxy manufacturers agree. Once epoxy cures completely, it's inert, so it shouldn't matter what you put over it unless it specifically reacts with the epoxy chemically. I've used this particular combination of epoxy and gelcoat successfully many times (literally from the same cans) and have used other epoxies with this gelcoat, so I know from experience that it works quite well. Something has gone wrong this time, but I can't figure out what it is. One suggestion I've been given is contamination in the epoxy or gelcoat. That's possible, but I'm not sure what could have contaminated it. Is it possible that the epoxy mix was rich in one or the other of the components, some of which permeates the epoxy, and which cannot cure without it's required co-component? Might adding a little of the other cause it to set up to the point where it actually becomes "inert?" Might it then work better with the gelcoat as you would expect? Or would it be better to remove the epoxy, recoat it with a more careful mix of epoxy, then finish? If one of the epoxy components has been around for a while is it possible it has become "corked", that is, oxodized to the point where it is not still the epoxy part you bought? Almost everything oxidizes over time. I have had old polyester resin gum up, it seems to set up slowly with air, humidity, or UV, sometimes. MEK is an oxidizer. Have you done a subsequent test to see if this leftover old epoxy will still set up under normal conditions? The epoxy was carefully mixed (it's a 1: 1 ratio, so it's hard to screw up) and it set up just fine, so I don't think there's anything wrong with it in that regard. It sounds like a contamination problem, you sure the dog didn't pee in your mash, or summat? I transfer the epoxy from the original cans into catchup bottles for easier handling when mixing small batches. The stuff I used for the repairs has been in those bottles for a few months. Although I can't think of anything that could have contaminated it, it's a possibility. |
#9
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Bruce on horizon wrote:
Check the expiration date on the gelcoat. It sounds like the mekp is not curing the entire batch. The odd thing is that it cures fine wherever it's over other gelcoat. I have had this can for a while, so it could possibly be age related. I could try another tube of MEKP, as I have a couple that haven't been opened. I'll give that a shot tonight. |
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