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Wing glassing help

Old 07-04-2020, 01:50 PM
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bluetomcat74
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Default Wing glassing help

Hi all. I've built and decided to glass the airframe of a top flite p51. Sanded the wing surface to a decent finish then applied cloth and resin. Then once cured applied a second coat of resin as per instructions. Once cured I have sanded back the shine and any high spots but have noticed the top layer of resin has started to peel in places. Unfortunately it's on the top side of the wing. I used 80grit paper as per instructions. Do I now reapply more resin to the affected area and sand back or apply automobile body filler and sand back to a finish. I don't have any pics but imagine having sun burn and having the unavoidable painful peeling . It's looks terrible!!
Old 07-04-2020, 05:13 PM
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speedracerntrixie
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I'm going to venture that you used polyester resin ( smells really bad and uses MEKP as a hardener ). If so most polyester resins contain wax that comes up to the surface when curing. Failure to remove the wax between coats will create adhesion issues. I'm afraid that if I am correct in what you used, the only fix is to remove what has been applied and start over. First step though is to verify what product it is that you used.
Old 07-05-2020, 12:28 AM
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bluetomcat74
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Thanks for the quick reply. I used a reputable resin supplied by fighteraces.co.uk A very reputable company with a great instruction booklet available. L285 skinning resin. I applied the resin in warm/hot conditions (for the UK!) Outside temp was around 26c and in my shed it was probably closer to 28c. Would this have affected the cure? Although due to work commitments it has been over a week since it's cure before sanding.
Old 07-05-2020, 05:44 AM
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speedracerntrixie
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Ok L285 is an epoxy resin made by MGS which is regarded as a top shelf product. I did have a similar issue with it once curing very brittle on some CF landing gear I made. Even with the help of the a Distributor Aircraft Spruce we were unable to verify the exact cause. I would normally set my molds out in the sun for cure so I'm thinking that we both may have experienced curing the resin at too high of a temp. Unfortunately your fix will be the same as I suggested earlier, remove what you have already done and start over. The other thing I found about MGS resins is that they are mix sensitive, the ratios need to be very accurate.
Old 07-05-2020, 08:32 AM
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bluetomcat74
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Great thanks for the explanation. I'll sand back as far as I can then re-apply where the problem areas are. Thanks very much👍
Old 07-06-2020, 11:18 AM
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RCFlyerDan
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Originally Posted by bluetomcat74 View Post
Great thanks for the explanation. I'll sand back as far as I can then re-apply where the problem areas are. Thanks very much👍
Sand the whole plane where the second coat was applied. Donít be fooled to think there wonít be further issues elsewhere, and they usually show up when painting. Also, as a suggestion, down grade your sand paper to 220. 80 is too aggressive for fine tuning the surface. I prefer 220 wet to eliminate the dust. And, to be inside in the A/C. Try to stop before you get to the balsa. If you do, no issues, just apply a small patch. Or do the whole area.
I prefer using a 4:1 Laminating Epoxy thinned with another 1. So, 4:1:1 mix.
Old 07-06-2020, 11:25 AM
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bluetomcat74
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Hi RCFlyerDan Thanks very much for the info. I have been in contact with Phil at Fighteraces.co.uk today to discuss. Seems as it was my first time glassing i may have put too much resin onto the first coat. This may have created a waxy resin where I was unable to "key/scratch" when sanding down for the second coat. Or it simply could have been a set of contaminated brushes. But the first suggestion makes more sense. You are correct, the advise was to sand down as far to the cloth as i can using a finer grade paper then reapply the second coat. Phil said the wings will probably be overweight which is unfortunate but not a complete writeoff!!

Thanks again guys. I will update you all on my progress.

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