Zinc Chromate in 2005?

[mhorowit]

I'm looking at a 60 year old Tcraft. She was originally primed with
zinc chromate. If I need to remove some fabric to get at some rust, is
there any reason I shouldn't use ZC as a primer? After all, the last
application seems to have lasted 60 years!
Are there any concerns about any of the Dacron-based covering
processes adhereing to the ZC? - Mike

PS - My A&P loves the two part epoxy primer, but why should I bother if ZC has a good track record?

[Ray36048]

Re: Zinc Chromate in 2005?

Most fabric glues will lift the ZC and then you will get rust. The epoxy primers are far better on the steel parts than the ZC. Remember these airplanes were recovered every 7 to 10 years with grade A cotton. Use the epoxy and let it cure for at least 72 hours before you apply any glue over it.

[mhorowit]

Re: Zinc Chromate in 2005?

Most fabric glues will lift the ZC and then you will get rust. The epoxy primers are far better on the steel parts than the ZC. Remember these airplanes were recovered every 7 to 10 years with grade A cotton. Use the epoxy and let it cure for at least 72 hours before you apply any glue over it.

Ray - I had thought I'd heard about an incompatibality between glue and ZC, but I've seen several ships covered using the Ceconite process (from the mid-70's) with a ZC primer. That's 35 years, so it must not be a terrible incompatibility! Am I incorrect in what I'm observing? - Mike

[Carl Ellis]

Re: Zinc Chromate in 2005?

My former 1977 F-19 is ceconite covered. The tubing appears to be painted with ZC. Fabric is original.

[Forrest Barber]

Re: Zinc Chromate in 2005?

If that F-19 is original then that is not "Ceconite." ( that is a process) WE used our own "Taylorcraft" process which used Dacron fabric straight from the mill. I have the process here, will look up and reprint. ( Basically it was a Randolph Dope Nitrate, Butyrate build up with silver added and finished in Randolph Butyrate dope.)
The stick on was done with Super Seam Cement. The first coat was 1 qt. of Super Seam added to one gallon of nitrate dope & one gallon of thinner. A FEW ships used Razor-Back)

Yes we used Oakite soak after welding , then Zinc Chromate. If the "dope" & ZC are all encapsilated then it works if there is a fracture in teh coating then you get air & rust.

[mhorowit]

Re: Zinc Chromate in 2005?

If the "dope" & ZC are all encapsilated then it works if there is a fracture in teh coating then you get air & rust.

Forrest - please find below a collection of punctuation marks. Feel free to scatter them throughout your e-mails. - Mike



.,.,.,.,.,.,.,.,.,.,.

[mhorowit]

Re: Zinc Chromate in 2005?

If the "dope" & ZC are all encapsilated then it works .

Could someone please explain what's getting encapsulated ? - Mike

[Ray36048]

Re: Zinc Chromate in 2005?

Poly Fiber manual clearly states the glue will lift single part primers and tells you to use only epoxy. My experience with the epoxy is very good. I know of 2 gliders that were revcovered at least 8 years ago using Poly Fiber with epoxy primers. These sit outside in all kinds of weather. The tubing looks excellent. In my opinion, I would only use the modern epoxies when restoring and fabric aircraft.

The standard test to determine old primer types is to rub it with a rag soaked in MEK, single part primers will come off, epoxy will not.

[VictorBravo]

Re: Zinc Chromate in 2005?

When I owned a J-3, we went to Clyde Smith "the Cub Doctor" seminar on maintenance. He showed us an original 1940 film of a factory tour. They were priming the fuselages with a GARDEN HOSE pumping out liquid Zinc Chromate!

The reason this lasted for 60 years is probably because there was a good, thick layer of this goop that was fliowing into all the nooks and crannies in the welded clusters. The Cub Doctor said that all these people who are spraying on the primer or powder coating are doing themselves a dis-service because spray does not get into the small crevices as well.

It is OBVIOUS to me, that the best way in 2005 would be to use 2 part epoxy because it definitely sticks better and will withstand solvents, but the right way is to brush it on and poke the bruch into all the weld clusters. This would also be a lot safer, since the vapors of the primers are very toxic. It also avoids any EPA or airport painting restrictions because there is no spray.

Bill

[Robert Lees]

Re: Zinc Chromate in 2005?

Keep up, Mike, try this thread

[mhorowit]

Re: Zinc Chromate in 2005?

Keep up, Mike, try this thread

I'm getting old I guess. Thanks - Mike

[mhorowit]

Re: Zinc Chromate in 2005?

WE used our own "Taylorcraft" process which used Dacron fabric straight from the mill. I have the process here, will look up and reprint. ( Basically it was a Randolph Dope Nitrate, Butyrate build up with silver added and finished in Randolph Butyrate dope.)

When Forrest says "WE", to whom is he referring?

When I first got introduced to fabric covered a/c (in this forum), it was stressed that there was a process for covering, and specific brands of chemicals to be used; frustrated me because if there was a generic butyrate dope, I didn't see the need to use Brand 'X' only; but I eventually came around and understood why. Now Forrest mentions "our own 'Taylorcraft' process".

Anyone got any background? Did he go to the effort to have an STC approved? - Mike

[Carl Ellis]

Re: Zinc Chromate in 2005?

When Forrest says "WE", to whom is he referring?

I always assumed he has a mouse in his pocket.

- Carl -

[mhorowit]

Re: Zinc Chromate in 2005?

I always assumed he has a mouse in his pocket.

- Carl -

Well, my initial thought was Kelly-belle, the beagle, but a mouse is a possibility.- Mike

[Forrest Barber]

Re: Zinc Chromate in 2005?

I belong to many tribes , that last WE was of course, Taylorcraft Aviation, they are the only ones to produce the F-19. Owned by Charles & Dorothy Feris, I did the final inspection on all aircraft and test flew most of them after ser# 74. This "Taylorcraft" process was the approved process for the F-19, F-21, F21A, and most of the F-21B's.....IF using Poly Fibefr then of course use their recommendations.
Encapsulate ; to enclose in or as if in a capsule.
IF you use the blanket method on the fuselage then we ( Al & Forrest Barber)used to dope a strip of tape to the longerons with nitrate and IT would try to lift the ZC, but would all melt together and encapsulate the ZC and dope & tape as a unit.
The envelope method is not as critical, just shrink her and dope her.

Go ahead and use the epoxy primer, God help the next person to cover the ship, I agree that will be about 30-40 yrs down the road but it will happen, maybe just an accident. My 43533 needs recovered, but all tests good and the tubes are very weill preserved, she was done in 1969.....just looks crummy , never did wash her , just flew her a lot.

There was a time in bars that WE is the mouse too
Kelli has never smelled dope, I did my last about 6 yrs ago..nitrates do build up and I have them in my lungs.

I would suggest that you follow the advise of the Mechanic that will be doing the job....