stunthanger.com
Building Tips and technical articles. => Paint and finishing => Topic started by: Jim Oliver on November 11, 2016, 04:58:19 PM
-
I have had two occasions with Sig dope spider webbing or crazing as/when it dries, only over open bays covered with silk span and only when brushed with thinned Sig clear (don't have spray capability). Once when I covered with colored Sig silkspan using Sig clear only and once with white (natural color) silkspan which had been doped with Sig gray and then had Sig Flatcoat brushed on to give flat finish.
All thinner and retarder are Sig products.
What am I doing wrong??
-
it sounds like you either built up the layers to fast, not enough dry time, or to much retarder prevented it from drying quickly enough.
I would normally say it sounds like laquer over enamal but since you used all SIG products, I would have to say its likely just to much to fast,,
-
The base gray had dried for several months and crazed with the first brushed coat of Flatcoat............
-
No contamination in my case....wonder if it's because of the time lapse between color and clear??
Also can't understand why it only happens on covered open bays and not on sheeted areas that have been covered with the same finish n~
-
No contamination in my case....wonder if it's because of the time lapse between color and clear??
Also can't understand why it only happens on covered open bays and not on sheeted areas that have been covered with the same finish n~
Jim,
I believe Ty might be on to something? Not sure though.
Also, and I know you're experienced with the use of dope products, but do you sand the open bays?
I put no paint over shine. I always scratch the surface up.
Charles
-
Charles,
Any sanding of bays is very light wet with very fine paper before rub out, but in this case little if any due to flat warbird finish.
Gonna have to do some sanding to smooth the ridges/cracks from the crazing:(
-
You would be wise to remove all of the material that crazed, its very likely that the problem is in the lower layers and sanding then repaint will not solve it.
I am curious how much retarder you used..what temp was it when you painted, humidity, etc,,
-
Charles,
Any sanding of bays is very light wet with very fine paper before rub out, but in this case little if any due to flat warbird finish.
Gonna have to do some sanding to smooth the ridges/cracks from the crazing:(
Jim,
Not sure if you have looked into it yet but the 2K clears are available in semi-gloss and flat.
Charles
-
You would be wise to remove all of the material that crazed, its very likely that the problem is in the lower layers and sanding then repaint will not solve it.
I am curious how much retarder you used..what temp was it when you painted, humidity, etc,,
I don't use much retarder but can't give an exact percentage. I apply dope in A/C shop so temp is mid 70* with ~40% humidity.
-
Thanks for all the replies.
After some experiments, it seems that I applied the clear too heavily in both cases (Flatcoat and gloss). I used a full brush as I normally would do but for some reason it didn't work.
When I finished applying Flatcoat with a "dry" brush I got no spiderwebbing n~
-
Jim, you might have some luck with this old trick. Try a test patch of clear dope thinned 50-50, with a tablespoon of castor oil added to a quart of thinned dope. It will take at least a week to dry, but can restore flex and a plastic feel to even the worst cracked and crazed dope finish. The castor makes the top coat seep down into the cracks and meld the entire finish back together. This was a pretty well known fix for Aerogloss 50 years ago. It wasn't dope, but acrylic lacquer and was way too stiff for open bay work.
-
Is there another "plasticizer" than castor oil? Seems to me there is something to use on the new plastic bumper covers and such. Don't know if it would work with butyrate dope. Mark? D>K Steve
-
Here's an approach that is very much the more extreme mode of fixing. Start over! That is to say, start over with the finish in the effected area's. Many moons ago I started a repair to a crashed Twister.
The wing was salvageable, other than some holes punched in the silk-span covering. Throwing caution to the winds I bought a gallon of cheap hardware store (Canadian Tire) lacquer thinner and a couple rolls of paper towels. I soaked the wing in the thinner in a controlled fashion and in very short order had the wing down to it's base layer. I had somewhat expected that the remaining tissue might begin to lift off the surface, this did not happen at all. Attached is a picture of the wing in a new fuselage with the open bay silk-span panels that survived the crash. With care you can control where you apply your efforts and protect other area's you wish to save. I think total time to get the wing down to base was maybe about an hour or so. It sure beat careful sanding around the area's.