stunthanger.com
Building Tips and technical articles. => Paint and finishing => Topic started by: Pat Johnston on March 29, 2021, 04:34:27 PM
-
I've been finishing my Bearcat 617 with Brodak Dope. I have several coats of Nitrate as a base coat then covered it all with polyspan. When putting on the acetate silver, the finish resembled a fine tree bark pattern. This conditioned skipped the canopy and L/G wheelpants which are fiberglass. Those two are smooth as can be.
Has anyone discovered compatibility issues with Brodak acetate over Brodak nitrate? What do I do now?
Pat Johnston
patsplans@yahoo.com
-
What is acetate silver? Typical model airplane dope is a butyrate dope. If it is truly an acetate paint that may be the issue. Some have problems with butyrate if the nitrate isn't left to gas off enough. It seems like any of today's dope may be a crap shoot some tines! Check what you are using again.
Type at you later,
Dan McEntee
-
Yeah, what's "acetate" silver?
-
Sorry, I goofed up. The silver is Brodak silver (acetate butyrate, I believe). Essentially all Brodak products.
I may just put it aside to let it gas off really well and start building my Epiphany Twin.
Pat
-
People have been putting butyrate over nitrate with no problem since the Dead Sea was sick, and some times I wonder if the problems that do occur from time to time are a matter of something being mislabeled, or just a quality issue from the manufacturer. Todays products certainly are not the same as what they were back in the day, and if you are from that time period, you do as you did then and expect the same result and when you don't get that you don't have any way of pinning the reason down unless you have a chemical analysis lab at hand!! I think that is why some have gone t using stuff for full size aircraft and doing what they need to do to deal with the costs like splitting it u with friends and such. If you let it sit for a week or two, and use the same paint, let us know the results?
Type at you later,
Dan McEntee
-
Sorry, I goofed up. The silver is Brodak silver (acetate butyrate, I believe). Essentially all Brodak products.
I may just put it aside to let it gas off really well and start building my Epiphany Twin.
Pat
I think I got a glimpse of your Epi'-Twin plan some time ago. If that's what I saw, it looks like a good one. I hope you do a series of build posts.
John Miller
-
Hi Pat,
Butyrate should go ovef nitrate without any problems. I haven't seen what you described in a long time. Tbe last was jn the 60's wben Aerogloss was changing their formulations and an Ares l was buildjng sudenlly had the pajnt that looked lime alligator hide. I'x suggezt testing on a piece of scrap to see if maybe there was some contamination introduced. Could be in the spray gun or the container where it was mixed. You migbt sanding an area on the bottom and sprayi g with some rejuvenator. Brodak usex to sell it. I think Randolph still does.
-
Pat,
Just curious why you would use Nitrate dope?
Thanks
CB
-
Pat, I've had issues as your describing when I thinned the coats too much that were going over the nitrate. It looked great when it went on, minutes later it started to crater the base coat. My only explanation is that the top coat flashed off trapping in the solvents which attacked the underlying coats. I was also brushing and not spraying.
Fixing it for me was a bit of a pain, I ended up using red spot putty which I squeegeed on over the bad areas. I had enough clear coats on not to worry about sanding through and I wet sanded the areas with 320 finishing with 400.
-
Pat,
Just curious why you would use Nitrate dope?
Thanks
CB
Apparently it's supposed to bond better to the polyspan than butyrate Charles.
-
I've never figured out any real reason to ever use nitrate, ever. D>K
-
Thanks, guys. I’ll let it gas off for a while then get back to it. Some parts look Okay, some not so much. I’ll get back on this thread when I make more progress.
Pat
-
I have several reasons as to why I use nitrate. Nitrate base coats essentially work with almost any paint combination you choose to use. I also find it builds and dries faster than butyrate. It dusts off essentially in a hour without loading the paper. I also found it not to blister when it comes to intersections such as vertical stab to fuse or wing planking to fuse. I've had butyrate form blisters in these areas. Nitrate works better with synthetic coverings which I use a lot. In addition, I use a lot of water based finishes and you can't use butyrate under them due to the top coat just shedding off of it. These are my reasons and experiences so I'm quite certain others have their reasons.
-
Look up some explanations from Bill Byles, and noted full scale aircraft finisher, who is a member of Stunthanger. Nitrate is used on full size aircraft finish applications. Think of it as a sort of primer. It comes in tautening and non-tauteing types. Free flighters use it for rubber powered models and gliders because it is supposed to be a bit lighter, and not fuel resistant, which you do not need on rubber models and gliders. It adheres better when applying covering with dope, and fills faster during build ups. On full scale coverings, they use a tinted non-tautening nitrate to apply the pinked strips over rib stitching and such to make sure it's held down securely, and it's tinted so you can see where you have been with previous coats.. Then at a certain point the butyrate comes in for final build ups and colors. Silver is applied under the colors as a anti UV measure, I do believe, and like on a model can show you where any blemishes or trouble spots may be so they can be addresses. The silver makes a good under coat for almost any color also.
The whole process can be done from start to finish in butyrate alone as Ty points out. The same can be said of Nitrate if you are building an electric model and are weight conscious and don't need a fuel resistant finish, just don't pit you model aroud anyone with an IC powered airplane that likes to run his engine in the pits!!
Type at you later,
Dan McEntee
-
Pat,
I would first let it gas off for a while longer. Next apply a coat of Butyrate clear, let it gas off a week before the silver. Mix the silver really well, scrap the bottom of the can to get it all, then mix again. Silver should be 40/60 reducer/paint to have enough base clear to adhere the silver pigment. Before over coating test a small spot with 400 wet paper and see if it sand or gums. If sands well sand rest flat if not give it another week. When in doubt look at the YouTube Windy Brodak videos.
Best,