Paint Cracks


Lakeside California
Right Side under wing from drumming . One spot about the size of a dime showing gray cloth
all from prop wash . Believe it’s Polycoat . Could be butyrate. what’s the steps to repair ? Can I use rejuvenator ?



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It might be ranthane or aerothane topcoat. A little MEK on a rag and rub it on inconspicuous spot. If the color rubs off it’s butyrate or polytone. Logbook should state.
The only way I got mine to quote cracking was to replace that chunk of fabric under wing tanks.
I see someone did that with the inspection hole area on yours. Might I recommend fabbing up a large rectangular inspection panel for that spot?
Makes working in there easier and cuts down on the drumming right there.
The thread I started on Stewart wingtips has pictures on how I did mine.

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In my opinion, and that's not worth much, you could probably use rejuvenator (if Butyrate) on the first picture. for the second and third (and first if polyfiber) I would wet sand the area out beyond the area of the cracks, repaint it either with a spraygun or those little Preval sprayers you can get at home depot. You don't necessarily need to get down to the fabric but feather it out like you would for any paint job and follow the manual for instructions as to mixing. Butyrate has to be thinned and polyfiber may have to be to spray properly. You SHOULD be able to look in the aircraft records and see what it was last covered with but I think it may be Butyrate as I think it is not polytone. As I recall Polytone has a pinkish base coat nor blue but that also could be the silver coat showing through and not the fill coat.
A.) determine what you have. B.) get and review the manual.
Look for an FAA Form 337 on covering the wings and see what it was covered in and painted with.
I have sanded spots like that before and then used an airbrush gun to touch it up. I got my airbrush in a craft store where they also sell cans of compressed air.

Pacer N3342Z
The finish is Randolphs Butyrate

The main question I have is concerning the area around the inspection rings. Is there anything that fills those cracks ? Kinda like bondo for a car? I know they make fill and Glaze . I did get the manual so Im about ready to take this on ( with my I/A watching. )
Nothing! the only way to do it right is to peel the finish off to remove the cracked areas then build it back up starting with Nitrate, then silver and finally color as specified in the Ceconite manual.
So i have Aerothane and a older recover job it has picked up a lot of small cracks at stress points.

My method for fixing small hairline cracks.
Sand down top layer of paint to open up the crack and inspect the silver to see if it is damaged. Spray silver in as needed, sand around cracks to help the new paint get some adhesion to the old stuff and blend a little better re apply paint layers with a paint brush pushing paint in to the cracks i have found sprayers do not seem to want to get paint in to the cracks it just builds up around the out side. Not as nice looking but good enough at 10ft and keeps the UV and water out.
If wings are the same read the Randolph covering book on rejuvenators. They put the plasticizers, flexible stuff back in the dope. Will take some time to make it look nice. I have used a small artist brush to fill in the cracks and my finger tip followed by several spray coats. You might consider doing this to fix the drumming.
I do not have the patience to try and repair fabric that has been top coated with anything other than dope. I have only known one person that is successful with these repairs. I have been known to just recover the piece rather than deal with the frustration of trying to make a silk purse out of pig skin. Especially on a customers aircraft. Cost to repair is exorbitant and never looks decent for any length of time. Once the cracks, flaking and ringworms start, they are not going to get better and you will chase them all over the aircraft. It can usually be traced back to improper recovery practices. Spraying on the first coat is a really common example of being lazy and poor workmanshIp. You just cannot get the fiber encapsulation needed on Dacron without brushing on the first coat. Then, poor workmanship is covered by a slick top coat.
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Maybe, maybe not. The proof is in the pudding. If the process is peeling, something has gone wrong. Too long between coats, contaminated surfaces, spraying the first coat, using expired materials and many other possibilities. Then, when you try to repair a covering that has other than a dope topcoat you spend hours very carefully sanding the surface to remove the topcoat. If you use most anything else to remove the paint, you have now introduced another contaminate and a new host of problems. In my opinion, the only correct way to repair this issue is to start all over again. I have had aircraft in the shop where I could actually peel the finish off to the fabric. Cotton was much easier to work with and delivered a much nicer finish with a lot less work. Dacron will last longer than it is safe for these old airframes.
Just read where you stated that your covering is butyrate dope. Makes a big difference in a successful repair. As Steve said, you can sand down to the first coats, use rejuvenator per the instructions and have a decent chance of success. You need to get down to the layer that is causing the poor adhesion. My issue is with non-dope topcoats.
I have no “peeling” just some cracks from drumming .

Maybe, maybe not

True , but I guess that if they didn’t do extremely good work they probably would not have been asked to Travel to Normandy for the d day anniversary where they did have to repair the tail feather on a DC 3 because of a tug clipping the tail while parked
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I have seen a lot of drumming and cracking in the area just behind the fuel tank even by very talented and well accomplished fabric people.
Talked to my I/A and he will be doing Steve ‘s repair . Did you have to open the cloth up to get the piece of aluminum in Steve ?

Let the sanding begin
Not trying to degrade anyones aircraft or work. I also have many Oshkosh, Sun and Fun and WAAAM trophy’s. If you do not explore the causes of the issue you are doomed to repeat the mistake. I am not buying into drumming is the root cause of the cracks. The PBY’s entire aft wing is fabric with some really big propellers beating the fabric to death. No cracks. The Early Corsair’s had fabric outer wing panels and controls surfaces. Over 400 MPH. No cracks The mustang, DC-3, DC-4, DC-6 all had fabric controls. No history of cracks. I am just trying to help solve the issue, not argue with you. If you are that sensitive to my advice, I’ll go work on my own Tri-Pacer’s issues. I surely do not want to put an opinion on this site that will upset someone’s feelings. God forbid that someone else’s diagnosis might be different.
Worked on all those warbirds you described less the DC4 and 6 along with lots of Cub, Super Cubs, Clippers, Pacers and Tri-Pacers. Even cover Rare Bears tail feathers. For whatever reason I have seen a lot of Short Wings with the inboard trailing edge cracked like the photos covered in almost all the processes.
What Steve said. My Clipper’s right wing top trailing edge repeatedly cracked the paint on the top trailing edge at the false spar. I finally removed the fabric from the rear spar to the false spar and from the butt rib out to the last tank bay rib.
I then recovered it with heavy weight fabric and several layers of tape at the false spar.
In the late 50s and early 60’s we put thousands of hours on EC121’s and C121’s with fabric covered rudders with no issues.


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Had a metalized PA-22 years ago, used it for banner towing. The underside of the left wing had half of the rivets wear, the holes around them crack, to the point where the skin lap under the tank was completely free. That’s when I sold the airplane. Even the metalized short wings have this problem. I’m sure a good prop balance would help, but it seems to be a recurring issue with these airplanes. It would be fun to tuft one and do some flights to see what the airflow actually does in different configurations and speeds.

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Seems to be a problem on big engines J3s, PA11, PA16, PA18-95 and PA22-108s with no flaps and the full span ribs as well. Even fixed a 150 hp Citabria with constant speed prop and no flaps with a broken trailing edge.
Still waiting for someone else to do this and realize that someone will be me .So here it
goes . I do have an I/A but he isn’t too forthcoming with info until I screw up . I have the correct manual .
First question
I need to remove the two inspection rings because the plastic rings are broken and missing pieces . I can do a new patch in the area ,cutting out both rings and starting over . Thoughts ?



The whole area . the rib stitching will be redone due to the rib repair



I had the same issue with partly broken inspection rings. I couldn’t tell exactly what paint I had on the wing. I tried first MEK to wash the paint off, but didn’t work. So I sanded the paint down to the silver coat and then used MEK to wash the area clean. That was a messy job. Then I cut the ripped fabric off and glued a new patch on. Repainted and new inspection rings. That was using Polyfiber process.

If you use the Steward system, you only need to sand the topcoat off. Then cut clean and glue a new patch on.

If we can get to the back side we score a line around the paint we want to remove, place a rag on the back side and soak with MEK. The MEK will soak through the fabric and we can peel the finish off.
Patched my ugly inspection rings on both wings . I’m ready to start painting A bit confused about how to proceed . Should I spray Rand O Proof only on the repaired areas and then silver over all , or Rand-o-Proof over all then all the other layers


Where you have virgin fabric, ie; no previous dope you will need to BRUSH on the rand-o-proof. Spraying the first coat will not encapsulate the fibers and you will be back to a finish that will peel off. Once you have a good coverage of the rand-o-proof, go to the rand-o-fill for several coats to give a sanding base for the final finish. They have pretty good instructions for patches in the consolidated manual.
Rand O Proof (nitrate) is the only thing that sticks to the raw fabric. I brush it on the raw fabric and then spray the silver over everything and feather sand to smooth at all before color.
perfect . That’s where I’m at .I have brushed nitrate into the patches and tapes I have applied . There are a few small spots where I used MEK because of paint cracking that might have small spots of bear fabric and I will brush those . What you guys have cleared up for me is I’m ready for Silver
This thread is probably pertinent for my question: Is MEK Substitute adequate for use on a Ceconite Randolf Dope coating?