dope lifting with tape!!

I recently used .2 carbon veil attatched with SIG dope and filled it with 5 coats of clear followed by two coats of clear mixed with zinc stearate from Randy.. Sanded smooth and applied two coats of silver wet sanding between coats to get a nice surface.I then shot the whole plane white for a base. This whole thing was allowed to dry for two weeks before I got a chance to put colors on it.Then when I masked it off for the first color using green 3m fineline tape, the white and silver came off with the tape. Three weeks of finishing and four months of building are out the door!!! My question is this, was it the zinc stearate that caused this? That is the only thing that I used that was different. Also can it be fixed. I should probably go back to using talc!! It fills better anyway. I suppose it's my fault for trying something on a good plane before testing it.

Thanks for any replies.

Danny

It's probably the darn Sig dope itself. I have had highly variable results with it and while some people seem to have no trouble with it, I'm not one of them.
Can the mess be fixed?- yes, but probably not without a LOT of effort.
If I were you, I'd go to Brodak or Randolph next time around...

The green fineline tape is VERY tacky. Switch to the blue fine line--it is much more friendly to the paint.

I also use very narrow blue tape for the edge and only "seal down" the very edge. Then I go over it with the easy release tape and masking plastic. So only the very edge of the tape is sealing.

FWIW

Good advice, but I've had Sig dope come off when I was using drafting masking tape- which has even less tack.

And I thought that I was the only one who had the problem with drafting tape!
Sig dope appears to be very critical (at times) to the amount and type of thinner used, and the wetness of the coats. (??)
Bill

Silver has a bad habit of separating, or delaminating. Sig silver seems to be the worst.
IF your coats are not *wet* enough, the chemical bond is poor.
I would submit that the silver did not bond very well to the substrate.
It can be fixed! I have learned to live with this happening at times, but I hate it! Sand and refinish the spots.
HTH
Bill

I would suspect the Sig dope is the culpret. I have used a lot of sig dope in the past with great results. But a couple of years back, I had an awfull time with paint lifting, with and without tape. After pulling out a lot of hair, I checked around and found that sig has reformulated to meet EPA regs and as a result their product just isnt the same. One question to you. How much thinner are you using? I is very important to thin your dope about 2:1 ( two parts thinner to one part dope) this allows the material to penetrate the wood and previous coats to allow for better adhesion. I have been using Randys AeroFiller for a couple of years now with exellent results. I am however using it with Brodak dope. Good luck, Larry NorCal Circle Jerks.

My
>question is this, was it the zinc stearate that caused this?

I don't think so. I use about 5 times as much zinc stearate as you are supposed to in Polycrylic and have never noticed any adheasion problems.

Dope relies heavily on melting the previous coat for adhesion. Can be a tricky proposition...

Join the club..

I think it's the silver dope. Dope has enough problems with adhesion and shrinkage as it is, and metallics are often a problem. Although silver is great as a blocking coat and it clearly shows all flaws, it is poor for adhesion.

And I wouldn't bet that any brand other than SIG will be any better in silver or metallic..

Notice a lot of folks using "polar gray" as a blocking undercoat? Adhesion properties are one reason.

[photo not recovered: 3e69bb3870f12ad5.jpg]

"Where subtlety fails us we must simply make do with cream pies."

>Join the club..
>
>I think it's the silver dope. Dope has enough problems with
>adhesion and shrinkage as it is, and metallics are often a
>problem. Although silver is great as a blocking coat and it
>clearly shows all flaws, it is poor for adhesion.
>
>And I wouldn't bet that any brand other than SIG will be any
>better in silver or metallic..
>
>Notice a lot of folks using "polar gray" as a blocking
>undercoat? Adhesion properties are one reason.
>
>[photo not recovered: 3e69bb3870f12ad5.jpg]
>
>"Where subtlety fails us we must simply make do with cream
>pies."

I've had Sig peel or flake off of a white base coat- NO metallics...

>Join the club..
>
>I think it's the silver dope. Dope has enough problems with
>adhesion and shrinkage as it is, and metallics are often a
>problem. Although silver is great as a blocking coat and it
>clearly shows all flaws, it is poor for adhesion.
>
>And I wouldn't bet that any brand other than SIG will be any
>better in silver or metallic..

Could be a combination of things, but silver dope is notorious for poor adhesion. I haven't looked at a Windy tape in a long time, but I beleive that he uses it as a reveal coat, then sands it all off.

>I recently used .2 carbon veil attatched with SIG dope and
>filled it with 5 coats of clear followed by two coats of
>clear mixed with zinc stearate from Randy.. Sanded smooth
>and applied two coats of silver wet sanding between coats to
>get a nice surface.I then shot the whole plane white for a
>base. This whole thing was allowed to dry for two weeks
>before I got a chance to put colors on it.Then when I masked
>it off for the first color using green 3m fineline tape, the
>white and silver came off with the tape. Three weeks of
>finishing and four months of building are out the door!!! My
>question is this, was it the zinc stearate that caused this?
>That is the only thing that I used that was different. Also
>can it be fixed. I should probably go back to using talc!!
>It fills better anyway. I suppose it's my fault for trying
>something on a good plane before testing it.
>
>Thanks for any replies.
>
>Danny

Danny,

The silver is your culprit in this case. My business, for the past 20 years or so, has been the restoration of full-scale classic and antique airplanes with my shop being located on Chino Airport in Chino, California. Practically all of the airplanes that we restore are fabric covered with doped finish.

In the course of restorations I have used "Certified" brand dopes, Randolph dopes, Sig dopes, and Poly-Fiber brand dopes. I typically mix my own silver using clear butyrate dope and aluminum paste so that I can control both the ultraviolet blocking characteristics and the adhesion characteristics of the silver coats. By the way, for Grade A cotton cover the FAA specifies the use of silver pigmented dope as a UV blocker and the other FAA certificated covering processes (using primarily polyester fabric) in their Supplemental Type Certificates also specify the use of silver dope as a UV blocker. So, I have had to learn to deal with the characteristics of silver dope.

When mixing silver dope Randolph specifies no more than 5 1/2 ounces of aluminum paste per gallon of unthinned butyrate dope; "Ceconite" process specifies no more than 4 ounces of aluminum paste per unthinned gallon of butyrate dope and states that "Use of more aluminum powder per gallon will probably result in peeling".

I use Randy's zinc stearate with Sig dopes on my models and have had no adhesion problems doing so. Zinc stearate is not the problem if you follow directions.

Another thing that I do to assure adhesion when a doped surface has been drying for more than a week is to (just prior to spraying on subsequent coats) spray a couple of light coats of straight butyrate dope thinner to soften the existing dope surface. The coats of thinner should not be wet but rather just damp (wet will be glossy and damp will be just short of glossy), so it does not run. This will allow the maximum chemical adhesion of the following coats of butyrate dope.

Sig silver may not be the best to use for silver undercoats as it is pigmented sufficiently for a topcoat, which is a little too much for best adhesion as an undercoat. Other than that one thing, I find Sig dopes to be high quality, consistent from batch to batch, and well pigmented.

All this being said, for my models I do not use silver as a filler/undercoat. I use Sig Polar Grey which does two things: 1) it eliminates the issue of adhesion which can arise with the use of silver dope and 2) Polar Grey provides a better undercoat uniforming color for most dope colors which tend to be somewhat translucent.

Another point which was addressed in another post in this thread is the type of tape to use. I do use "3M" blue vinyl tape for taping most of my color separation lines as it has just enough tack. The "3M" green "fine line" tape does have much more tack and is less flexible for taping curves...I don't use this.

One other thing that I suggest is to spend the money to get a roll of "3M" yellow impermiable masking paper (if you want the part number send me an email) to mask for color on your airplanes. You can get a roll with enough material on it to give you a lifetime supply for about $15 and it is so much better than trying to use newsprint (the worst material for masking as the ink can transfer and the paper allows vapors to migrate through to the underlying doped surface) or "butcher paper".

Keep trying as finishing is not learned in a really short time but it is worth learning.

LAST EDITED ON Oct-27-03 AT 04:04 PM (CST)
 
The latest bubbling and peeling problems I have had were over a Sig "Polar Grey" undercoat.
NO silver or any other "metallic"- just straight Sig dope...

John

I've found Sig dope can be tough to use.
I like polar gray as my blocker coats over Silv.
When removing your tape & stencils use a hair dryer to warm up the tape glue & dope. The tape will come off much better. I learned the hard way. Ted Fancher gave me the tip on the hair dryer.
Go ahead & fix your paint problem areas. It wont take long compared to the time you already have invested.
Photo is a problem I ran into 2 years ago using Sig dope.

"I feehul yur payne!"...

>The latest bubbling and peeling problems I have had were
>over a Sig "Polar Grey" undercoat.
>NO silver or any other "metallic"- just straight Sig dope...
>
>John
>
>

John,

It's hard to figure why you have had so many problems with Sig dope; I have had virtually no problems with the product over the years, both on full size airplanes and on my models. There is a lot more to dope and fabric than just the product.

>
>John,
>
>It's hard to figure why you have had so many problems with
>Sig dope; I have had virtually no problems with the product
>over the years, both on full size airplanes and on my
>models. There is a lot more to dope and fabric than just
>the product.

Bill,

This is absolutely correct. However, I don't seem to be the only one lately who is having this "problem", so I suggest a re-examination of the product might just be in order.

Just this weekend, someone told me that Sig has changed from pigments to dyes in some of their colors in response to EPA oversight. He said the dyes were definitely inferior, and said reds, oranges, and yellows (and maybe other colors) were affected. Has anyone else heard this?

LAST EDITED ON Oct-27-03 AT 08:20 PM (CST)
 
Hi Guys,
I'm not an expert finisher but I will share some I have learned. When putting down your first coats of clear over the wood to seal it, usually 2 or 3 coats before the silkspan. I was told to mix 1/2 clear to 1/2 thinner. In a lot of cases especially if the wood grain is dense you need to thin the dope even more than this so it will penetrate the wood properly for a good grip. I didn't and it pulled the trim up with the paper and all the under coats with it down to the wood, this was with low tack tape.

In spite of comments otherwise, I've never been impressed with SIG dope when it comes to coverage. It simply lacks pigment. White, yellow, red have always had terrible coverage in my experience. It appears that the Brodak dope has better coverage and more pigment.

For color coats, I use Dupont Lucite lacquer (auto paint), which covers beautifully, adhere well, cure quickly, shrink very little, and are more consistent and easier to apply. Yes, with more PIGMENT, they are heavier than dope, however, when I can get great coverage in only two coats, the weight penalty is small. And they are available in about a zillion colors. Disadvantages include not being fuel proof, and somewhat greater "surface tension" effects - masked edges do not lie as flat as dope does.

Clear dope top coat, rubbed out - beautiful. Fuel proof (sorta).

[photo not recovered: 3e69bb3870f12ad5.jpg]

"The rule is perfect: in all matters of opinion are adversaries are insane." -Mark Twain

>In spite of comments otherwise, I've never been impressed
>with SIG dope when it comes to coverage. It simply lacks
>pigment. White, yellow, red have always had terrible
>coverage in my experience. It appears that the Brodak dope
>has better coverage and more pigment.
>
>For color coats, I use Dupont Lucite lacquer (auto paint),
>which covers beautifully, adhere well, cure quickly, shrink
>very little, and are more consistent and easier to apply.
>Yes, with more PIGMENT, they are heavier than dope, however,
>when I can get great coverage in only two coats, the weight
>penalty is small. And they are available in about a zillion
>colors. Disadvantages include not being fuel proof, and
>somewhat greater "surface tension" effects - masked edges do
>not lie as flat as dope does.
>
>Clear dope top coat, rubbed out - beautiful. Fuel proof
>(sorta).

Larry, automotive lacquer is definitely nice to paint with and I have used it in the past; however, it is no longer available here in California so we no longer have the zillions of colors that were available.

Although Sig is only one of the brands of butyrate dope that I use I really don't find it to be deficient in pigment, even in the white. When I finish up with the Polar Grey Sig undercoat I make sure that the Grey is uniform in color and then put two coats of white over it. The white is really white and the other colors (red, yellow, blue, etc.) on the white really stand out. I don't own stock in Sig or even know anybody there but I am just not having the problems with the product that some of the guys out there seem to be having. I do find that Randolph color dopes are more viscous as shipped and do require more thinner, but when thinned they do not seem to have any greater pigment density than Sig, Certified, or others. Just my observations over the past 20 years or so.