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#1
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Epoxy over Gel coat troubles
I am repairing a fibreglass hull that has quite a few hairline cracks
and deep gouges over the hull. I sanded the hull using 180 grit wet & dry and cleaned out the gouges using a small grinder. The hull has been left to thoroughly dry for a few weeks after a good cleaning, and then wiped over with acetone. I have applied some epoxy resin over a small ares to test, the idea was for the resin to weep into the hairline cracks and gouges to seal them before applying any required filler. I used a roller to apply the resin to the hull and it looked good for a couple of minutes, then it all went wrong. The resin formed hundreds of little globules/islands and no amount of brushing or using a roller would give me a smooth even coat. What has happened??? Regards Bruce |
#2
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On Sun, 27 Feb 2005 19:13:58 -0800, b.stevens wrote:
I am repairing a fibreglass hull that has quite a few hairline cracks and deep gouges over the hull. I sanded the hull using 180 grit wet & dry and cleaned out the gouges using a small grinder. The hull has been left to thoroughly dry for a few weeks after a good cleaning, and then wiped over with acetone. I have applied some epoxy resin over a small ares to test, the idea was for the resin to weep into the hairline cracks and gouges to seal them before applying any required filler. I used a roller to apply the resin to the hull and it looked good for a couple of minutes, then it all went wrong. The resin formed hundreds of little globules/islands and no amount of brushing or using a roller would give me a smooth even coat. What has happened??? I'm not sure. Did the epoxy cure or not? It sounds like you kept messing with it after it started to cure. Aren't you glad you just did a small test area? Can you use a slower epoxy mixture? Also, why didn't you use an epoxy fairing compound or primer instead of resin? I don't think painting a boat with resin is a normal procedure, but I could be wrong. Regards Bruce --Mac |
#4
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wrote in message oups.com... I am repairing a fibreglass hull that has quite a few hairline cracks and deep gouges over the hull. I sanded the hull using 180 grit wet & dry and cleaned out the gouges using a small grinder. The hull has been left to thoroughly dry for a few weeks after a good cleaning, and then wiped over with acetone. I have applied some epoxy resin over a small ares to test, the idea was for the resin to weep into the hairline cracks and gouges to seal them before applying any required filler. I used a roller to apply the resin to the hull and it looked good for a couple of minutes, then it all went wrong. The resin formed hundreds of little globules/islands and no amount of brushing or using a roller would give me a smooth even coat. What has happened??? Regards Bruce ##** Hello Bruce, I've done an fair amount of Epoxy repair and the problem you describe sounds like gassing which happens when some type chemical evaporates through the epoxy layer. Also any kind of silicone contaminate will cause similar problems. I usually wipe down any surface with white vinegar and then wash with soap and water before applying resin.Hope this may help. Rey |
#5
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Thanks, for all the advise so far. I did'nt think of surface tension as
being a problem. I can try another band but what type ??. I know the resin had not started to cure before the problem started and as far as I can tell the surface is pretty clean. Gassing might be present, but this would give little bumps correct. Bruce |
#6
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On Mon, 28 Feb 2005 16:58:14 -0800, b.stevens wrote:
Thanks, for all the advise so far. I did'nt think of surface tension as being a problem. I can try another band but what type ??. I know the resin had not started to cure before the problem started and as far as I can tell the surface is pretty clean. Gassing might be present, but this would give little bumps correct. Bruce If it was caused by beading of the epoxy, then maybe just adding some kind of filler to the epoxy you've got would help. In any event, it would be a good experiment. If you have done this kind of thing before, then you will have your own ideas about how much filler to add to the resin. If you haven't done this kind of thing before then let me just say make sure you add enough filler to get a substantially thicker texture, otherwise the results of the experiment may be inconclusive. If you want to be really scientific about it, you could prepare 2 or 3 different mixtures with differing amounts of filler, and see whether any of them bead up on you. As I said elsewhere, you may want to just get an epoxy primer and use that. --Mac |
#7
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we deal with this all the time. there are two solutions: 1 is to change
the surface energy of the epoxy by adding a fisheye preventer, or wetting agent, which you can get from an automotive paint store. 2, is to add cabosil (colloidal silica) , to thicken the epoxy until it wont bead up. it often makes sense to put on an unthickened coat (which will seep into cracks much better) and then follow immediately with a thickened coat, which will not bead up. good luck. Dick Pereli |
#8
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Bruce,
It sounds like you are making more work for your self than you need to. If the repair is above the waterline, any good quality marine polyester filler(3m premium) is the product of choice for the gouges. As for the stress cracks in the gelcoat, it is necessary to find our what is causing the crack or the repair will comeback the second the stress is applied to that area. Repairing stress cracks around stanchions, is worthless unless you beef up the bottom side of the stanchion...even then there is no guarantee that the crack will come back. Paul was correct in suggesting the addition of a thickening agent for the stress crack. The pooling is the result of surface tension and adding any wetting agent not approved by the manufacturer is a very bad idea. There is no telling what kind of chemical reaction is going to occur. I always use epoxy below the waterline and polyester above..mainly because of cost. Good luck Bruce -- Shield Finishes and Nauticoat Marine Finish Systems www.shieldfinishes.com |
#9
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#10
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On Mon, 28 Feb 2005 17:56:32 -0600, "Reynaud" wrote:
wrote in message roups.com... I am repairing a fibreglass hull that has quite a few hairline cracks and deep gouges over the hull. I sanded the hull using 180 grit wet & dry and cleaned out the gouges using a small grinder. The hull has been left to thoroughly dry for a few weeks after a good cleaning, and then wiped over with acetone. I have applied some epoxy resin over a small All acetones are not created equal. Many sold to the consumer have numerous impurities that cause problems. I use a solvent wash (Interlux 202 ) with good results. Other manufacturers have similar products. I pay the extra money because of problems with what is sold by the mass market stores. Also 180 grit is a little fine for a pure epoxy coat. I would use 120 grit. 180 to 220 grits are for finish primers and color coats. Check the manufacturers recommendations for the particular product that you are using. Hairline crack filling is not straight epoxy's strong point, it is usually much to viscous for that. Epoxy primers are what you use for hairline cracks, then use an appropriate filler for the dings and imperfections that primer can't cover. If there are numerous problems then start with a high build primer. Note: Any proper surface prep most often involves multiple coats of primer and filler with sanding in between until the surface is ready for the finish primer and color coats. JJ ares to test, the idea was for the resin to weep into the hairline cracks and gouges to seal them before applying any required filler. I used a roller to apply the resin to the hull and it looked good for a couple of minutes, then it all went wrong. The resin formed hundreds of little globules/islands and no amount of brushing or using a roller would give me a smooth even coat. What has happened??? Regards Bruce ##** Hello Bruce, I've done an fair amount of Epoxy repair and the problem you describe sounds like gassing which happens when some type chemical evaporates through the epoxy layer. Also any kind of silicone contaminate will cause similar problems. I usually wipe down any surface with white vinegar and then wash with soap and water before applying resin.Hope this may help. Rey James Johnson remove the "dot" from after sail in email address to reply |
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