This post could easily be part of the Open Forum, the Finishing forum, or the Classic forum. I am sure that all will not agree and that is OK:

I want to thank everyone who has been following the construction and recent problems of my “Sea Vixen”.

I now know that the problems have not been caused by poor silk span, or the grain direction of the silk span.  Last night I took another look and promptly put another hole in a wing tip. The covering practically shattered to the touch! It is incredibly brittle!

It seems that the last stages of the project have certainly been snake bit. From cracks in the fillets, to a crack in the spray gun cup lid causing drips, to the super brittle covering.  It is time to strip the entire covering and finish, and fix it. Unfortunately, this means I will miss VSC 2009, but I will be well prepared for 2010 with both a Classic and a new OTS airplane.

My major disappointment is letting Jack Sheeks down for this year.

Now for a discussion on want went wrong and hopefully we can all learn from it.

I have followed many of the finishing procedures that I have used in the past, including the medium silk span on the I-beamer. Unfortunately some of the newer materials obviously are not compatible. I used nitrate dope to apply the carbon fiber on the wood areas because nitrate fills faster. I also used the Nitrate over the fillets. Then instead of using Butyrate over the Nitrate I went right to the auto primer. This is when the headaches started.

I had small cracks develop in numerous places on the airplane, and major cracks in the fillets. I then used thin CA in the cracks and after numerous tries, I got most of the cracks fixed, but not all. Then, I continued while trying to meet a deadline. Can you say “Haste makes waste”?

Then after applying base coat colors, I had 2 splits in the covering, in the leading edge area, develop while the airplane was sitting over night. I repaired these splits and continued to apply some of the graphics. Then when I removed some of the aluminum foil that I use to prevent over spray getting into places that I don’t want it, I discovered the very large split in the from leading to trailing edge in the lower wing covering.

After many discussions with several people, we now know that all the problems were caused by the Nitrate dope, with no Butyrate dope applied over it. The Nitrate is not compatible with the modern materials we use for fillets. In this case it was SuperFil. But the same result will probably happen with AeroPoxy. The Nitrate also is not compatible when using auto primer over it without Butyrate over the Nitrate. The solvents in primer and the base coat further exasperate the problem.  Simply put, the brittleness was caused by having both no butyrate and not enough butyrate dope under the auto primer.

Synopsis:    1) Never use Nitrate over the modern fillet materials.
      2) Auto primer and base coats cannot be used directly over Nitrate.
      3) Butyrate Color dope can be used over Nitrate
      4) Haste makes waste

Thankfully I had not applied clear coat, and the auto base coat will wipe off easily with denatured alcohol. I will be able to re-cover the airplane, probably using poly span, and then finish the project. The only thing lost is time, but big lessons have been learned.

I want to publicly thank Bill Byles, John Miller, and Ralph Wenzel for their concern and valuable inputs. Friends all! The Stunt community is full of wonderful people.
 

Man, I knew there was a reason I wasn't using nitrate.   

Sorry for your problems. Finishing problems can be a real nightmare. i hate it when that happens.

Robert,

There are many people who say that they are using butyrate directly under and over Polyspan with no problems.

WHOA Pete, you are not getting off that easy.  Post some pix of that Ryan!

BTW I thought Superfil was an epoxy-base product - meaning its a shock that either nitrate or butyrate affect could it.  Did you thin it wi acetone?

Tom, Dennis, (and others):  Thanks for that clarification.  On closer inspection, it is in fact a slight (and easily fixed) adhesion problem  The filet itself does not exhibit any softening, I leaped to the wrong conclusion after reading the original post...sorry 'bout that, my bad.  As far as leather fillets, they worked well in this application, but as you mentioned, are not suitable every design. They do not lead themselves to varying contours, or sharp corners and I feel do not strengthen the wing/fuselage joint as well as epoxy based products.  As for photos...well, I'm "on the road" so it'll be a few weeks but they will get posted. 

Tom,

I didn't say polyspan.  I said polyester fabric.  I haven't used polyspan yet and may try it with butyrate, I don't know.  The stuff I'm using comes from Brodak  It's polyester fabric, woven like silk.  So far, I've used a large package of it.  It ( this is also in the manual from Randolph dope products) along with Stitts and the other one for full scale aircraft must be applied and encapsulated with nitrate.  I have some lighter poly fabric to try and I will get some polyspan when I get to Brodak next month.  Other than that I'm afraid I can't help.  I haven't used any automotive finishing products on a model other than body putty.  I do know that when I thought I'd get slick and spray the nitrate on the polyester fabric instead of brushing it on the fabric and encapsulating it, the sprayed butyrate started eating holes in the nitrate down to the fabric and then the holes started expanding.  I finally got it useable but not pretty.

And I'm sorry for your problems.  The cure is a lot of work.

Bob

Ty,

I will not be using colored silk or silkspan etc. I will be matching the colors of the Royal Navy Sea Vixens.

Hi Tom,

I am sorry that I am so late on this, but I fonally got to it.

I always use a flex additive in my automotive lacquers.  I forgot who told me to do that, but it is a necessity for some of those lacquers.  Duplicolor has the flex additive added in their products, as far as I know.  My Spacehound, built in '97 has had splits all over it in the wing covering.  I used PPG mixing base white lacquer, but no flex additive.  It is as brittle as it can be.  But, since then I have not really experienced any problems that I can relate to the auto lacquers.  I do shoot on Sig Lite coat to seal everything before I apply anything else.  And everything in the substrate is Sig or Randolph's Nitrate.  I especially like the Randolph's non tautening tinted Nitrate!  A big thanks to Mr. Robin Hunt for that one back in about '93.

I hope all comes out great this time with the Vixen, it will be gorgeous!

Say *HI* to Linda!
Bill <><