why primer is pealing from a F/G cowl
05-21-2015, 03:11 PM
#1
why primer is pealing from a F/G cowl
Hi all I have run into something I have never had happen, and I am assuming it is my fault. but hear goes.
Received new cowl, washed it with soap and warm water, wiped it down with D/alcohol, let it dry for a day in heated shop.
Then I sanded it with 220 W/D as wanted to have matched color with the plane, Wiped it down again with D/A primed it with Dupli-color primer. as I was not quite ready to paint the bird yet let it sit till I could get the dummy engine mounted in side the lip, with that done I managed to drop it and it landed on the back edge, and big pieces of the primer popped off, Didn't think much of it so started to feather the edges, and more popped off.
So the question is what did I do wrong ?
I have done cowls over the last 30 + years with the above steps and never had this problem.
Cheers Bob T
Received new cowl, washed it with soap and warm water, wiped it down with D/alcohol, let it dry for a day in heated shop.
Then I sanded it with 220 W/D as wanted to have matched color with the plane, Wiped it down again with D/A primed it with Dupli-color primer. as I was not quite ready to paint the bird yet let it sit till I could get the dummy engine mounted in side the lip, with that done I managed to drop it and it landed on the back edge, and big pieces of the primer popped off, Didn't think much of it so started to feather the edges, and more popped off.
So the question is what did I do wrong ?
I have done cowls over the last 30 + years with the above steps and never had this problem.
Cheers Bob T
05-22-2015, 01:59 AM
#2
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Two ideas come to mind. First contamination of either the soap or denatured alcohol or you sprayed the primer on to thick and/or left it sit to long to the point it oxidized.
I watch all the custom garage shows and see them completely remove all paint down to bear metal the plaster the car with bondo then and, then next spray a whole lot of primer on and over the bondo, then sand, then paint.
I took an autobody class at my local community college when I was 16, 37 years ago, to get my POS's dents out and to use the spray booth and back then you learned how to use body tools to get the dents minimized and used as little as bondo as possible.
Primer can be a PINA if not covered with a sealer right away or painted right away.
When i need to use primer for metal I use a primer-sealer as the first coat and usually use either a metal etching primer with a hardener. If no metal etch is needed I still use a 2 part primer, primer paint and hardener as the first filler layer.
The gray lacquer primer is great for fast filling, but very porous, and oxidizes really fast if left for a couple of days before final sanding for paint.
Point is unless the cowl needed filling for pinholes or the cloth weave it's the best surface for paint. For me I'll spray 2 or three coats of primer then try to sand most of it back off so as not to add weight but to fill.
My experience is that primer isn't very flexible either as you have just mention by it popping off after a drop, another reason to sand as much off as possible.
Why are you using Denatured Alcohol instead of Prep-All or another brand that's specifically for that purpose?
Hope you figure it out as it would suck to have the finish coat just flake off in flight.
I watch all the custom garage shows and see them completely remove all paint down to bear metal the plaster the car with bondo then and, then next spray a whole lot of primer on and over the bondo, then sand, then paint.
I took an autobody class at my local community college when I was 16, 37 years ago, to get my POS's dents out and to use the spray booth and back then you learned how to use body tools to get the dents minimized and used as little as bondo as possible.
Primer can be a PINA if not covered with a sealer right away or painted right away.
When i need to use primer for metal I use a primer-sealer as the first coat and usually use either a metal etching primer with a hardener. If no metal etch is needed I still use a 2 part primer, primer paint and hardener as the first filler layer.
The gray lacquer primer is great for fast filling, but very porous, and oxidizes really fast if left for a couple of days before final sanding for paint.
Point is unless the cowl needed filling for pinholes or the cloth weave it's the best surface for paint. For me I'll spray 2 or three coats of primer then try to sand most of it back off so as not to add weight but to fill.
My experience is that primer isn't very flexible either as you have just mention by it popping off after a drop, another reason to sand as much off as possible.
Why are you using Denatured Alcohol instead of Prep-All or another brand that's specifically for that purpose?
Hope you figure it out as it would suck to have the finish coat just flake off in flight.
05-22-2015, 04:00 AM
#3
Roguedog
Thanks for your comments and will take them into account, But like I said above I have been using these steps for a long time, the only difference was the brand of primer and the primer seams vary lite (weight wise) and was recommended by a fellow at one of our local body shops
Cheers Bob T
Thanks for your comments and will take them into account, But like I said above I have been using these steps for a long time, the only difference was the brand of primer and the primer seams vary lite (weight wise) and was recommended by a fellow at one of our local body shops
Cheers Bob T
05-22-2015, 08:55 AM
#4
Best to wash with soap and water, then use prep solvent, and dry with clean cloth before and after sanding. I say before because there could be traced of release media left on the cowling surface, some are water based, some are not. So sanding prior to a good cleaning with both cleaning methods could result in a contaminated surface, hence peeling primer..:
Bob
Bob
05-22-2015, 12:45 PM
#5
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Roguedog
Thanks for your comments and will take them into account, But like I said above I have been using these steps for a long time, the only difference was the brand of primer and the primer seams vary lite (weight wise) and was recommended by a fellow at one of our local body shops
Cheers Bob T
Thanks for your comments and will take them into account, But like I said above I have been using these steps for a long time, the only difference was the brand of primer and the primer seams vary lite (weight wise) and was recommended by a fellow at one of our local body shops
Cheers Bob T
Ditch the new primer and go back to the previous or try a different brand.
Regards
05-23-2015, 02:40 PM
#6
Thanks guy's for the help.
The problem now is trying to match the primer color it's lite and cant seem to find anything close so may just try the stuff again, as the blue I am using really changes with the primer color. but I am not in a hurry so will keep looking in a few more places S/W and wally world next
Cheers Bob T
The problem now is trying to match the primer color it's lite and cant seem to find anything close so may just try the stuff again, as the blue I am using really changes with the primer color. but I am not in a hurry so will keep looking in a few more places S/W and wally world next
Cheers Bob T
06-12-2015, 05:46 PM
#7
well it is time for an update, Could not find a primer any ware near the color of the Dupli-color laqure primer, found same brand in a rattle can that is a bit darker, so wet sandes the cowl started to show cloth, and painted it with the rattle can stuff, and it has stuck, so now sanding the bird and will give it a coat of the rattle can primer. so all is good but most likely will not get done till next fall. Gotta go flying
cheers Bob T
cheers Bob T
