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Author Topic:   Gel Coat Patch Paste Won't Cure Over Epoxy

69boo307 posted 03-16-2009 04:51 PM ET (US)
I purchased some Spectrum Color matched patch paste to repair screw holes on my Striper. I filled the holes with epoxy, plain old two-part stuff from the hardware store. Let that dry for about a week, then scuffed it with 220 grit and scrubbed it thoroughly with soap and water. I've since made four attempts to apply the patch paste, and it will not cure over the epoxy! Not even after a week. It was applied in 80-degree weather. It cures fine anywhere but over the area where the epoxy is. I'm at my wits end with this stuff. I'm going on about four weeks with repairing a few screw holes. I've read all the stuff about the Amine blush and removing with soap and water. I've done all that, ad-nauseum. At this point removing the epoxy would require making a much larger wound than was originally there. Any suggestions?
thanks,
Brian
jimh posted 03-16-2009 07:32 PM ET (US)
Try post-curing the epoxy by using a heating gun to warm it. Then repeat your cleaning attempts. Use some acetone to clean, then soap and water.
The "hardware store" epoxy might be part of your problem. Next time use WEST System epoxy.
Ritzyrags posted 03-16-2009 07:36 PM ET (US)
You may want to consider this;
I think that you should remove all the patching material that will not harden first.
Next clean the area thoroughly with acetone and take a step back to consider.
I think that your problem could be one of two thing;
1- Your MEK is not doing the job it was designed to do.
You will remember to use 10 to 12 drops of fresh liquid per ounce of Spectrum product.
And to follow the directions to the letter.
2-If the epoxy does argue with the Polyester gel paste;
Give the epoxy a barrier coat of primer.
I have had great success with the Duratec 1041 grey surfacing primer to isolate epoxy repair prior to re gel coating.
Check it out.
69boo307 posted 03-16-2009 08:06 PM ET (US)
I had not thought of primer, that sounds like a promising solution. I havn't needed to use an ounce of the paste at once, the areas that I'm patching are no bigger than a dime and not deep. Just a small 'dollop' on the end of a kitchen knife does the trick. In the different attempts I made I have used between 2-5 drops of the hardener.

Tom W Clark posted 03-16-2009 08:30 PM ET (US)
You are probably using too much catalyst. Too much catalyst results in the patch paste not hardening. It seems odd; more should be better, right? Wrong. That the most common error with the patch paste.
I doubt the epoxy has anything to do with the gel coat patch paste hardening or not. Adhesion to the epoxy AFTER the gel coat has hardened is another matter but not what we are discussing here.
Newtauk1 posted 03-16-2009 09:03 PM ET (US)
"It cures fine anywhere but over the area where the epoxy is"
It appears 69boo307 is mixing the paste correctly based on this statement. I would lean towards the base epoxy as the culprit. Perhaps grinding the repair down a bit and applying a coat of polyester resin(and hardener) would also work as a primer. Polyester resin is cheap.
69boo307 posted 03-17-2009 07:43 AM ET (US)
Thanks for the suggestions. I have some high quality automotive primer (pro quality stuff, not Advanced Auto rattle can stuff), that I might try over the epoxy.
Yes, I successfully patched some scratches on the bottom of the hull that involved no epoxy, with the same 'batch' of patch paste I used on the screw holes. That part came out great, it would take a very close inspection to know that there was any work done there. The patch paste is a shade lighter than my original gelcoat, probably just due to weathering.
SIM posted 03-17-2009 08:42 AM ET (US)
I don't know what brand Epoxy you are using, but I would have to agree with Jim. If you use West system epoxy for a repair and want to cover that repair with polyester gel-coat, the epoxy must be washed with water and sanded before applying gel-coat. If you don't, the blush from the epoxy hardener can prevent the gel-coat from "kicking". The blush feels to the touch like a slimy coating after the epoxy kicks.
Since I am posting this on the CW forum, some of you may be waiting for an explanation as to why this happens. Sorry.......I'm just a application guy. I'll leave the explanation as to why it won't to our resident chemists. :^)
Andy
Blackduck posted 03-17-2009 08:44 AM ET (US)
The best way out for you is to remove some of the new epoxy, and re- fill with System 3 SB 112, surfboard epoxy. This is the only type of epoxy that gelcoat will bond to reliably every time. With other types of epoxies, heating and washing with soapy water does not always work, and I wouldn't waste any more time on any other ways out of this little jam.
andygere posted 03-17-2009 10:06 AM ET (US)
Using epoxy to fill screw holes is a bit of overkill, and it's a different matrix than the Spectrum patch paste (which is a polyester resin matrix). Drill out the epoxy and use polyester resin thickened with chopped glass fiber or cabosil. You can put the patch paste on as soon as it reaches the "green" stage, and will get a chemical bond between the poly resin and the patch paste. You can buy it polyester resin premixed with chopped glass in a UV cure paste. If there's not enough direct light to cure it, a few drops of MEKP will get it to catalyze. http://www.solarez.com/products/
If the Spectrum is hardening on your mixing palate but not in the holes, there's some problem with the epoxy you used. I'm inclined to agree with Tom, if it's amine blush, the Spectrum would harden but not bond, and eventually your plug of patch paste would fall out.
Paint Legend posted 03-17-2009 10:30 AM ET (US)
SIM is correct polyester gelcoat doesn't adhere well to epoxy for some odd reason (even properly prepared). One of my customers makes smaller racing sailboats and they make a special boat with kevlar and epoxy and over several years most if not all of the gelcoat delaminated from the epoxy/kevlar.
Most plastic boat now-a-days are built with Vinylester Resin, this is what many of the boatyards I frequent use for repair as well. It's better than Polyester and not quite as good as Epoxy from what I've been told.
Good Luck!
Tom
69boo307 posted 03-18-2009 09:54 AM ET (US)
Thanks again for the wealth of advice. It sounds like I'm just wasting my time messing with this epoxy that I used or trying to cover it up. I've already wasted WAY too much time on what should be a simple repair.
I picked up some fiberglass resin, just a can of it with a tube of hardener, for about $11. My plan is to just take the Dremel and grind/drill out as much of my epoxy as I can without making the holes much bigger, the re-do the areas with the fiberglass resin instead, followed by the patch paste again.
Does this sound like a reasonable plan?
tedious posted 03-18-2009 03:22 PM ET (US)
Is it safe to assume polyester resin is compatible with the foam inside Whalers? I know polyester will destroy styrofoam.
Tim
L H G posted 03-18-2009 05:11 PM ET (US)
There are only two reasons I can think of for using Epoxy resin for boat repair:
1. It will not be receiving a top coat of gelcoat, such as when you are repairing stripped out screw holes, such as under a rail base, and the re-installed fitting will cover the polished epoxy surface. I recommend this method for repairing rail mounts.
2. when the boat, or repair, is being painted, instead of being gelcoated. This would apply to either bottom paint areas, or a new Awlgrip/Imron total boat paint job.
Otherwise use polyester resin, such as Evercoat #27. Works very well.
jimh posted 03-18-2009 09:27 PM ET (US)
There is one important reason for using epoxy to make boat repairs: it is a much better adhesive and forms much stronger secondary bonds than polyester resins.
Tom W Clark posted 03-18-2009 09:33 PM ET (US)
There is no question but that epoxy forms a stronger secondary bond than polyester resin, but if one material is three times as strong as need be and the other only twice as strong, there is nothing to be gained by using the material with greater adhesion.
For minor screw holes and little imperfections, epoxy is not necessary and can cause added expense and other problems as described in this thread.
Newtauk1 posted 03-19-2009 12:18 AM ET (US)
No good reason for epoxy on this repair. Epoxy is more of a problem.Use polyester like Boston Whaler does.
Ritzyrags posted 03-19-2009 12:51 AM ET (US)
I have personally used a product called;
3M Marine High Strength Repair Filler.
It is a "Unique Vinyl Ester Formulation"
Contains fiberglass strands to restore strength when repairing and bonding fiberglass.
Cures fast.
Easy to use, pre-mixed formulation.
For above and below the waterline.
http://img13.imageshack.us/my.php?image=olympusphotos347.jpg
Now this product will make sure that the damages will be permanently repaired.
69boo307 posted 03-19-2009 12:15 PM ET (US)
I ground out most of the epoxy and got the fiberglass resin put on last night, and it was nicely cured this morning, so today I will sand it a little and re-try the patch paste. Here's hoping it will 'take' this time. I'll have to post photos of the final result after all this :)
TransAm posted 03-19-2009 02:00 PM ET (US)
Never had a problem with gelcoat over west system epoxy, even before I knew to wash the amine blush off.
69boo307 posted 03-24-2009 09:49 PM ET (US)
Here are some photos of the finished product. The successful method was finally using the fiberglass resin to fill in the holes, and the patch paste on top.
Go easy, it's my first gelcoat repairs. There were 4 screw holes in each of these photos, you can see some discoloration where the patch paste is slightly different than the original gelcoat. I've sanded these with 1500 grit paper, but I havn't yet done a final polish and wax over it.

http://picasaweb.google.com/lh/photo/ KbpK0hu_WOZ9jbRXMEWA3g?feat=directlink
http://picasaweb.google.com/lh/photo/ 6WAqBaIfkIn9ul8MfzrNGw?feat=directlink
http://picasaweb.google.com/lh/photo/ 3dkcaNtbQocqcZSujqvFTw?feat=directlink

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Author	Topic: Gel Coat Patch Paste Won't Cure Over Epoxy
69boo307	posted 03-16-2009 04:51 PM ET (US) I purchased some Spectrum Color matched patch paste to repair screw holes on my Striper. I filled the holes with epoxy, plain old two-part stuff from the hardware store. Let that dry for about a week, then scuffed it with 220 grit and scrubbed it thoroughly with soap and water. I've since made four attempts to apply the patch paste, and it will not cure over the epoxy! Not even after a week. It was applied in 80-degree weather. It cures fine anywhere but over the area where the epoxy is. I'm at my wits end with this stuff. I'm going on about four weeks with repairing a few screw holes. I've read all the stuff about the Amine blush and removing with soap and water. I've done all that, ad-nauseum. At this point removing the epoxy would require making a much larger wound than was originally there. Any suggestions? thanks, Brian
jimh	posted 03-16-2009 07:32 PM ET (US) Try post-curing the epoxy by using a heating gun to warm it. Then repeat your cleaning attempts. Use some acetone to clean, then soap and water. The "hardware store" epoxy might be part of your problem. Next time use WEST System epoxy.
Ritzyrags	posted 03-16-2009 07:36 PM ET (US) You may want to consider this; I think that you should remove all the patching material that will not harden first. Next clean the area thoroughly with acetone and take a step back to consider. I think that your problem could be one of two thing; 1- Your MEK is not doing the job it was designed to do. You will remember to use 10 to 12 drops of fresh liquid per ounce of Spectrum product. And to follow the directions to the letter. 2-If the epoxy does argue with the Polyester gel paste; Give the epoxy a barrier coat of primer. I have had great success with the Duratec 1041 grey surfacing primer to isolate epoxy repair prior to re gel coating. Check it out.
69boo307	posted 03-16-2009 08:06 PM ET (US) I had not thought of primer, that sounds like a promising solution. I havn't needed to use an ounce of the paste at once, the areas that I'm patching are no bigger than a dime and not deep. Just a small 'dollop' on the end of a kitchen knife does the trick. In the different attempts I made I have used between 2-5 drops of the hardener.
Tom W Clark	posted 03-16-2009 08:30 PM ET (US) You are probably using too much catalyst. Too much catalyst results in the patch paste not hardening. It seems odd; more should be better, right? Wrong. That the most common error with the patch paste. I doubt the epoxy has anything to do with the gel coat patch paste hardening or not. Adhesion to the epoxy AFTER the gel coat has hardened is another matter but not what we are discussing here.
Newtauk1	posted 03-16-2009 09:03 PM ET (US) "It cures fine anywhere but over the area where the epoxy is" It appears 69boo307 is mixing the paste correctly based on this statement. I would lean towards the base epoxy as the culprit. Perhaps grinding the repair down a bit and applying a coat of polyester resin(and hardener) would also work as a primer. Polyester resin is cheap.
69boo307	posted 03-17-2009 07:43 AM ET (US) Thanks for the suggestions. I have some high quality automotive primer (pro quality stuff, not Advanced Auto rattle can stuff), that I might try over the epoxy. Yes, I successfully patched some scratches on the bottom of the hull that involved no epoxy, with the same 'batch' of patch paste I used on the screw holes. That part came out great, it would take a very close inspection to know that there was any work done there. The patch paste is a shade lighter than my original gelcoat, probably just due to weathering.
SIM	posted 03-17-2009 08:42 AM ET (US) I don't know what brand Epoxy you are using, but I would have to agree with Jim. If you use West system epoxy for a repair and want to cover that repair with polyester gel-coat, the epoxy must be washed with water and sanded before applying gel-coat. If you don't, the blush from the epoxy hardener can prevent the gel-coat from "kicking". The blush feels to the touch like a slimy coating after the epoxy kicks. Since I am posting this on the CW forum, some of you may be waiting for an explanation as to why this happens. Sorry.......I'm just a application guy. I'll leave the explanation as to why it won't to our resident chemists. :^) Andy
Blackduck	posted 03-17-2009 08:44 AM ET (US) The best way out for you is to remove some of the new epoxy, and re- fill with System 3 SB 112, surfboard epoxy. This is the only type of epoxy that gelcoat will bond to reliably every time. With other types of epoxies, heating and washing with soapy water does not always work, and I wouldn't waste any more time on any other ways out of this little jam.
andygere	posted 03-17-2009 10:06 AM ET (US) Using epoxy to fill screw holes is a bit of overkill, and it's a different matrix than the Spectrum patch paste (which is a polyester resin matrix). Drill out the epoxy and use polyester resin thickened with chopped glass fiber or cabosil. You can put the patch paste on as soon as it reaches the "green" stage, and will get a chemical bond between the poly resin and the patch paste. You can buy it polyester resin premixed with chopped glass in a UV cure paste. If there's not enough direct light to cure it, a few drops of MEKP will get it to catalyze. http://www.solarez.com/products/ If the Spectrum is hardening on your mixing palate but not in the holes, there's some problem with the epoxy you used. I'm inclined to agree with Tom, if it's amine blush, the Spectrum would harden but not bond, and eventually your plug of patch paste would fall out.
Paint Legend	posted 03-17-2009 10:30 AM ET (US) SIM is correct polyester gelcoat doesn't adhere well to epoxy for some odd reason (even properly prepared). One of my customers makes smaller racing sailboats and they make a special boat with kevlar and epoxy and over several years most if not all of the gelcoat delaminated from the epoxy/kevlar. Most plastic boat now-a-days are built with Vinylester Resin, this is what many of the boatyards I frequent use for repair as well. It's better than Polyester and not quite as good as Epoxy from what I've been told. Good Luck! Tom
69boo307	posted 03-18-2009 09:54 AM ET (US) Thanks again for the wealth of advice. It sounds like I'm just wasting my time messing with this epoxy that I used or trying to cover it up. I've already wasted WAY too much time on what should be a simple repair. I picked up some fiberglass resin, just a can of it with a tube of hardener, for about $11. My plan is to just take the Dremel and grind/drill out as much of my epoxy as I can without making the holes much bigger, the re-do the areas with the fiberglass resin instead, followed by the patch paste again. Does this sound like a reasonable plan?
tedious	posted 03-18-2009 03:22 PM ET (US) Is it safe to assume polyester resin is compatible with the foam inside Whalers? I know polyester will destroy styrofoam. Tim
L H G	posted 03-18-2009 05:11 PM ET (US) There are only two reasons I can think of for using Epoxy resin for boat repair: 1. It will not be receiving a top coat of gelcoat, such as when you are repairing stripped out screw holes, such as under a rail base, and the re-installed fitting will cover the polished epoxy surface. I recommend this method for repairing rail mounts. 2. when the boat, or repair, is being painted, instead of being gelcoated. This would apply to either bottom paint areas, or a new Awlgrip/Imron total boat paint job. Otherwise use polyester resin, such as Evercoat #27. Works very well.
jimh	posted 03-18-2009 09:27 PM ET (US) There is one important reason for using epoxy to make boat repairs: it is a much better adhesive and forms much stronger secondary bonds than polyester resins.
Tom W Clark	posted 03-18-2009 09:33 PM ET (US) There is no question but that epoxy forms a stronger secondary bond than polyester resin, but if one material is three times as strong as need be and the other only twice as strong, there is nothing to be gained by using the material with greater adhesion. For minor screw holes and little imperfections, epoxy is not necessary and can cause added expense and other problems as described in this thread.
Newtauk1	posted 03-19-2009 12:18 AM ET (US) No good reason for epoxy on this repair. Epoxy is more of a problem.Use polyester like Boston Whaler does.
Ritzyrags	posted 03-19-2009 12:51 AM ET (US) I have personally used a product called; 3M Marine High Strength Repair Filler. It is a "Unique Vinyl Ester Formulation" Contains fiberglass strands to restore strength when repairing and bonding fiberglass. Cures fast. Easy to use, pre-mixed formulation. For above and below the waterline. http://img13.imageshack.us/my.php?image=olympusphotos347.jpg Now this product will make sure that the damages will be permanently repaired.
69boo307	posted 03-19-2009 12:15 PM ET (US) I ground out most of the epoxy and got the fiberglass resin put on last night, and it was nicely cured this morning, so today I will sand it a little and re-try the patch paste. Here's hoping it will 'take' this time. I'll have to post photos of the final result after all this :)
TransAm	posted 03-19-2009 02:00 PM ET (US) Never had a problem with gelcoat over west system epoxy, even before I knew to wash the amine blush off.
69boo307	posted 03-24-2009 09:49 PM ET (US) Here are some photos of the finished product. The successful method was finally using the fiberglass resin to fill in the holes, and the patch paste on top. Go easy, it's my first gelcoat repairs. There were 4 screw holes in each of these photos, you can see some discoloration where the patch paste is slightly different than the original gelcoat. I've sanded these with 1500 grit paper, but I havn't yet done a final polish and wax over it. http://picasaweb.google.com/lh/photo/ KbpK0hu_WOZ9jbRXMEWA3g?feat=directlink http://picasaweb.google.com/lh/photo/ 6WAqBaIfkIn9ul8MfzrNGw?feat=directlink http://picasaweb.google.com/lh/photo/ 3dkcaNtbQocqcZSujqvFTw?feat=directlink