Dope. How do I know when I have enough on Silkspan?

[Marty Hammersmith]

     I have a 90% Challenger that I covered in medium silkspan and brushcoated with butyrate dope from the first few coats. How do I know when I have applied enough coats to properly seal the silkspan. I added a flattening agent to the dope as I'm going for a flat finish, not gloss. I have at least 3 full coats brushed on and it's ready for spray coats.

[Dan McEntee]

     I have a 90% Challenger that I covered in medium silkspan and brushcoated with butyrate dope from the first few coats. How do I know when I have applied enough coats to properly seal the silkspan. I added a flattening agent to the dope as I'm going for a flat finish, not gloss. I have at least 3 full coats brushed on and it's ready for spray coats.

   Hold it up to the light at an angle and look at it for uniformity and any holes. This is called "candling" There are some good Windy videos on The Walt Brownell Channel on YouTube specifically on applying dope. You usually look for an even gloss and shine when doing this, but there shouldn't be too much difference using flat dope. Check out the videos. But if you only have three coats on, and you haven't mentioned any sanding in between, I imagine you could use a couple more. Even if you aren't going for a front row 20 point finish.
   Type at you later,
   Dane McEntee

[Dave_Trible]

In most cases depending on the brand and how much the dope was thinned,  four to six clear coats.  You only need the flattening on the last top coat of clear.  The rest is wasted.  Thats the last coat AFTER the color is applied-final coat.

Dave

[Marty Hammersmith]

     I need clear? Why is that different than color butyrate? I wasn’t planning on using clear at all.

[Dave_Trible]

Clear makes the structure of the finish but without as much weight.  Color pigment is really heavy.  I will usually apply four to six clear coat.  Then if I am wanting a good finish I wet sand the clear with #600.  You can skip this if you want.  Then air brush just enough color to cover, add trim then two or three clear top coats for protection and shine.  If I intend to wet sand and polish that will require considerably more top clear so as not to go through the color while sanding.  The clear is the basis of the finish and usually costs a little less than that much color as well.

Dave

[Dennis Toth]

Marty,
The "clear" is clear butyrate dope not "auto clear" that some use for top coat. The usual approach is to thin it 60/40 (thinner/dope) for the first two coats then go to 50/50 (just use up what you already mix then switch over). This fills the fiber grain and tightens the covering. Most wind up with about 6 coats of clear before going to color. After color butyrate let it gas off several days then spray on two coats of clear butyrate to seal the color. Then you could do the auto clear top coat.

Best,   DennisT 

[Ken Culbertson]

When your wife stops making comments and starts making threats!

Ken

[Paul Smith]

     I need clear? Why is that different than color butyrate? I wasn’t planning on using clear at all.

Clear is less expensive and not as heavy as color.   I use at least six coats of clear, and even more if the covering needs to shrink more. 
Then I spray on the absolute minimum of color needed to trim out the model.

A model done in all color will be overweight.

[Ken Culbertson]

     I need clear? Why is that different than color butyrate? I wasn’t planning on using clear at all.

That would be a mistake.  Colors, some more than others, even white, are considerably heavier than clear.  What you intend to do with the finish matters.  If it is to be a rubbed contest finish you want as much clear over the color as possible and follow some of the real experts on front row finishes.  But, if what you want is a nice light good finish, then use 5-6 coats of 50/50 thinned with a very light sanding 600 grit or higher on each coat after the second, then one coat of either light gray, white, or silver to block color differences.  As little color as it takes to cover. Now, as much clear on top of that as you want to wet sand off.  The purpose of the light sanding between coats is to avoid the need for a heavy filler or primer coat.  The sanding dust fills the small imperfections so don't use a tack rag or vacuum, just bed sheet rags before each coat to take the dust off of the surface not the dust in the cracks.  If you are brushing the final clear then don't thin it as much and add some retarder so that it will flow better, and DON'T do it on a humid day!

Then there is always MonoKote.

Good luck - Ken

[Air Ministry .]

Tradition was you sprayed 20 coats thinned to blazes , one a day ( preferably two days apart ) .

BUTRATE will PULL , if it hasnt ' gassed off ' between coats . So take your time . They can twist detroit style wings for YEARS  . till finally its all ' dried  ' .

So do em real thin & thinned . The Sheen , even reflected , shows its ' sealed ' . But depth of finish is whatyerafter .

[fred cesquim]

When your wife stops making comments and starts making threats!

Ken

that´s pure science! 

[Paul Taylor]

Windy has several videos on painting.
He answers your question here about 10 mins in.

https://youtu.be/-ZXUil-61VQ?si=miWAZUDgFeA8wNrS

[Peter in Fairfax, VA]

When your wife stops making comments and starts making threats!

Ken

Ken,

I even managed to upset myself with dope smell on my latest project, silkspan over a fuse, replacing plastic film.  The basement bathroom exhaust fan just didn't get it done.  At the moment, I'm waiting for 60 degree F weather, trying to be patient to get my favorite flyer, a Pathfinder, ready for the field.  Ultimately, I'll probably brush on a coat of color, white, some Friday night and fly Saturday. 

I'm sure my style of building combat planes as a teen didn't prepare me for a front row finish.  Same with Carl Goldberg Stuntman 23 projects flown on Lehigh Lane at age 11 or so.

Peter

[Ken Culbertson]

I don't remember the sidewalk!  Ah, the memories.

Ken

[Doug Moisuk]

Usually in the neighborhood of 6 coats, brushed and sprayed. Light sanding between coats then a coat of dope and filler, usually baby powder and sand it all off and asses the finish. If your not satisfied another coat of dope and filler, repeat until your happy. Then sand filler off and spray with silver or grey. It will show every imperfection. Sand the silver off. Fix the imperfections and spray with silver. Repeat until you are satisfied or sick of it and apply bace colour coat.