Applying dope and filler for a glass smooth finish

The key is to first cover the entire airplane with silkspan. Use a medium grade silkspan for everything. It takes less dope than the heavier grade and fills better than the lighter grade. Cover the open bays, the solid parts, the fuselage, everything. Sand the surface well before covering. Then apply a couple coats of clear, apply the silkspan, a couple more coats of clear, then a light sanding overall. THEN you apply the talc sealer. Approximately 1/3 clear, 1/3 talc, and 1/3 color is a good mix.(The color can be Polar Grey, Silver, Black, or whatever you plan to use for your base.)

Brush the talc sealer on heavy over everything EXCEPT for the open bays. The silkspan will follow the dips of the grain of the wood somewhat, and what you are planning on doing is filling those dips where it shows the grain. The open bays will have no grain pattern in them.

Once the dope is dry (with SIG this may take a week. With Brodak you can sand the next day) you need to sand the filler off except for what fills the grain. You sand until you get down to the grain streaks. Then you stop. Done right, you will add very little weight (less than an ounce) and end up with a glass smooth surface.

Now EVERYONE, after applying the first coat and sanding, will find a few imperfections that still need filling. Go back and brush more filler in these areas, wait the appropriate amount of drying time, then sand these areas again. Once you are sure it is perfect, give the whole plane a light coat of silver or Polar Grey, hold it up to the light, and blush. Then go back and fill the spots that you still missed, sand, and lightly spray those areas again.

When the base is absolutely perfect, go ahead and paint your colors. With a light coat of Polar Grey or silver underneath, you have applied a blocking coat where the entire subsurface will be even, and all colors--even white and yellow--will cover with less dope build up. This keeps the entire finish lighter. You should add no more than 6 to 7 ounces total on a plane the size of a Nobler when going from bare wood to completed finish including the top clear coats.

When painting the color coats, back mask. That means masking off the areas that do not get that color coat. That way you do not build up one color on top of another. Put on just enough color to cover. Then put on clear over the top of this. And, if you buff the clear out afterwards, you will have a mirror finish that can take you to the front row of the Nats. (well, at least the front half.)

No, it doesn't go on in a day or a week. But, even if you aren't a contest flyer, it will give you a finish that you will be proud of, and one that can be easily touched up if a ding does happen.

When you take it out to the field, someone is bound to ask you, "Is that airplane made of plastic?"

"No," you will say, "it is silkspan and dope."

"REALLY?"

That's what makes it worth while.

As to the primer, some people do use this, but it doesn't fill as well. There is a filler type of primer that is made to fill small scratches, but the dope/talc mix will fill greater voids in one application. (That still doesn't mean you won't have to go back for small "fixes".) It is usually better to stick with the same product from beginning to end, however, and that is why a dope filler of some kind would be best. You could, also, use corn starch. And the zinc Stearite (sp?) that Randy Smith sells works extremely well, too.

I called John Brodak to discuss a problem of not being able to sand the White Primer DRY (he said he wet sands it). In our conversation, John mentioned that they have developed a "sanding sealer" though he wasn't sure if it was to the stage where they were actually shipping it or not. You would have to call sales to find out.

I did not get a clarification of the difference in application between the "primer" and the "sanding sealer", but I certainly would be interested in trying the sanding sealer.

Sig Sanding Sealer and good ole "talc and dope" are still my favorites.

Cheers,

Your explanation is very good. I am in the process of finishing my Sig Skyray .35 and this is a usefull topic for me. I am not trying for a "Front Row" finish on this plane as it is the first .35 size plane I have ever built. But I am trying out some of the suggestions I am learning from the BBS. I have covered the wing and fuselage with medium silkspan and two coats of dope. Your explanation said to apply the talc/dope filler on the fuselage but what about the open bays of the wing? Do I apply it to those areas as well? What about the tail? should I cover them with silkspan and apply the talc/dope mixture to them as well? I have not assembled the wing into the fuselage yet but the silkspan is on them. Should I use the talc/dope filler now or should I assemble the wing and tail to the fuselage and then fill it?

Thanks,
Kurt

Where there are wood surfaces under the paper, you use the fillercoats. Although I never bothered where it was only above cap strips, and certainly never when cap strips were omitted, over plain ribs.

Kiwi

Granted, you can't get that "plastic" look with silk that you can get with silkspan. Most of us don't get that look even with silkspan!

Now, gang, how would you modify Leonard's lessons for silk instead of silkspan? How much of a weight penalty do you pay? I am trying 5 momme.

In the fully competitive world, I am sure silkspan wins. But for us 'tweeners, good silk finishes are right more durable, almost as light (maybe not!), probably easier to apply, and danged near as pretty.

With today's dope the brittleness is gone. So silk is back in as a medium. But so is silkspan. Silkspan no longer shatters in a crash. It isn't brittle, it isn't hard to manage, you have to really work at it to punch a hole in it. (You spent a lot of hours building this airplane, use a little common sense in caring for it. Don't throw it in the back of your pick up and then throw the shovel on top.)

Now, if the airplane is built light and you cover it with silk, when you crash the silk may hold, the structure may crumple, and you may just end up with a bag of crumpled balsa inside. If you covered it with silkspan and crash, it will simply shear leaving the major structure intact and a relatively simple repair. (Been there, done that.) So the argument can go either way.

If you just put a couple of coats of clear on it, silk--silkspan, probably doesn't make a lot of difference. If you go for a glass smooth finish, silkspan builds up very little additinal weight. I would hate to think what would be added with silk. But I guess the joy of silk is to see the weave, etc. underneath. I guess it is all a matter of what you want, but don't fear silkspan because you think it will make your plane weak and hard to care for. Build just enough structure to accomplish the job and you will be surprised as to how much additional strength and stiffness are added by silkspan alone.

Well, darn you, you just might be right. I gotta think on this a little. I guess my prejudice comes from hauling a bunch of combat ships and rats in a Mini-Cooper in the early 60s. I went the light silkspan route and often flew combat with quick Ambroid patches due to damage suffered in transportation or small children. So, I settled on silk and nylon as the only way to go. Had nothing to do with crashes. Then, at the 65 Nats, the silk plane survived a crash that I thought the silkspan guy would not have survived. Pure prejudice.

I have no small children now, and the transportation problems are minimal compared to the old days. I never thought about the difference in flexibility of modern finishes vs the old ones.

It takes me 24 hours to make any decision, but I think you might have changed my mind.

Hmm, I always put filler over the open bays. I've found, for me at least, that it is good at filling those little corners where the paper meets the edges of the wood. Seems to give a smoother transition from open bay to wood. Also fills any little paper tweaks. Almost all of it ends up on the floor, but that little bit in the corners seems to help.

What kind of sandpaper do you use? Also, is there any advantage, do you think, to spraying filler vs. brushing it on?

Also, if I'm reading correctly, some are using the terms sanding sealer and filler interchangibly. To me, sanding sealer is the stuff you sand most of off between coats. Filler is for uneven areas and dings, and is a much thicker consistency...although sanding sealer Is a filler coat...hmmm.

As for auto primer, it of course works, but lighter stuff is available. I only tried auto primer once. I was using a brush and it didn't work worth a hoot for me. I think most who use it successfully are spraying it. Anyone had success using a brush?

I just need to decide if I need a blocking coat before I start putting on color.

Awhile ago, there was an extensive discussion on using Acrylic Polyurethane and Catalyzed Polyurethane auto paint. Someone mentioned using clear Acrylic Polyurethane as a clear coat. I know it make repairs difficult, but was there any consensus on that?

People talk about “automotive primer” and feel that it is a generic term, but when it comes to dope they are very particular, making minute distinctions between brand and type (What kind of filler to use, etc). I feel that this is mistake, and I will never make that mistake again.

My latest plane will use basecoat/clearcoat so our local auto paint (and every kind of paint for that matter) guru Bill Wilson, said to use automotive primer. He said any brand will do (I disagree-back to that in a minute) and you do end up with a mostly gray plane. You need some primer for adhesion. The secret to basecoat/clearcoat is that the color coats have effectively no weight (unlike dope and lacquer) but also do not FILL at all (unlike dope and lacquer-Note: I used no Primer or filler on my last lacquer plane, I just wet sanded the white after sealing the paper with clear, the white worked like primer). So, on a Basecoat/clearcoat paint job, all of the FILLING is done with the FILLER. Bill had a handout at our Dallas Stunt Symposium that outlined the weights of each coat, and he said primer coat was about 2 oz. That seems about right.

I tested some auto primer, because I too have had problems with it in the past, and not just on airplanes, cars too! Long story short, not all auto primers are alike, even the lacquer types are different. Some do not “flake” well, but prefer to be wet sanded. These types are more likely to “shine” when sanded. K & B primer is like that. It is much more difficult to be “aggressive” with these types of primers, and as a result they tend to get heavy, quick…

I must shorten this story, I tire of typing…

Evercoat primer/surfacer is a dream to use, and is not heavy. It fills super fast and can be completely removed with 180 paper (dry) in no time (if you just don’t like it). It can also be feather sanded for a super thin, flat gray coat with 320. It really seems to love Brodak clear and silkspan. It dries to a totally dull finish so that tells me that it is very similar to Basecoat in that it has very little FILM STRENGTH (unlike dope) so that could explain why it is so light. It is much easier to use than dope, and I just put it on with a brush and it is sandable in 10 MINUTES! It absolutely fills like MAD. Only one coat is required over open bays (I thin 1/3-less coats). This plane has one coat sanded all of the way down with 180 grit, and a second coat sanded FLAT with 320 (dry). The brush marks actually help because they act as a GUIDECOAT. When the brush marks are gone, it is FLAT.

I would not recommend the Maurhyde primer that I tried. It sanded very slowly and did not “powder” well. It was an old can though. Ditzler is good but is extremely pricey at $35 a quart. The Evercoat was $12 a quart.

The main ingredient in Evercoat primer/surfacer is TALC.