Clear Dope over Silkspan--coats?

Question concerning dope application.

I'm doing a clear dope finish on a wing applied over dyed silkspan. Using Brodak clear and their thinner. brush finished so far and expect to put final coats on by spray.

I've got about 12 coats on with 400 sanding at two intervals. I'm still getting print-thru of the silkspan pattern. I'm using about 15-25% thinner to get brushing consistency ok.

Relatively light brush marks--it levels well on test surfaces and the silkspan over wood areas. Its the open bays that are grainy.

How many coats should I expect to apply?

THanks

You may need more thinner, Curt. Cut it about 50%. I have a feeling that you are getting brush marks all the way down to the bottom and not really getting any buildup. Just lay the dope on and let it flow. Don't overwork it or you will be back to the bristles cutting right on down to the base.

If you flow it on, it should build up in a couple of coats. When you have sealed it and are able to level it and get it shiny, you should have sufficient coverage. Anything additional is up to you. (Do you want to buff it out? If you get heavy handed with the buffing compounds, you will need more.)

For a more complete buildup, alternate your application of the clear, if you're not already doing so. That is, one coat spanwise, one coat chordwise, ad nauseum.

And isn't it nauseating when, after 12 coats even, that you're still up close and personal with the 'span? As Len says, let it flow. Get a little sloppy even, get that big 1" Sig brush (you do use a largish, thick 'ol brush, natch?) full of paint, and have at it. Watch for drips and runs, of course, and tip the stuff out by lightly running the brush tips every so often through the just-applied application, in order to smooth things out.

I don't think your thinner % is excessive, especially after 12 coats, but, yes, try the clear neat.

Hey, do you put your dyed 'span on when the dye is still wet? It actually works.

Currell, I don't know if you have used Brodak dope, but the stuff is really too thick right out of the can even for brushing. That is why I suggested thinning it more. About 50-50 works well. And the thinner dope will flow better so the brush marks don't show and you will get better build up sooner.

Now, if you are using SIG or something else, then maybe try it straight out of the can.

Yes, I flow it on and work from a wet edge--just like varnish or awlgrip. I cant tell you how many acres of bright work I've done in my life of yacht maintenance!!! I try to get it on right without going back over it more than a second or two since that will lead to brush marks. My test pieces do not show any brush marks so I'm pretty sure the mix is flowing properly. I'll just keep going and light sanding till it wont show the span pattern.

Is there a feel for how much I might have to use on a Twister wing?? I'm probably at about 1/2Qt right now and same amt of thinner.

And yes, this was my first try with the dyed span--at, I believe Leonard's recomendation, I went right from the dye vat, rinse, then apply. It worked great and I have a really cool looking custom yellow translucent wing. I've got some PPG DAR acrylic enamel for the fuse and tail group and will overcoat with clearcoat.

Leonard, I might try my hand at rubbing this one out--just to see how it works. I seem to have developed a deft hand at being able to safely sand with 320 or 400 over the open bays and ribs etc without going through.

Thanks for the input.

If you a planning to rub / buff out. I'd leave the 320/400 grit paper in your drawer. On the open bays and wood, I'd take my time and wet sand with 1200. Selectively on bad areas over wood maybe 600 ( But I seldon have the never ) . Let the Brodak cure at least a week. The longer it is left to cure/gas off the easier it sands off and surprizingly easily. When using 600/1200 or even 1500, I wet sand.

Brushes, visit a hobby shop that also carries a good selection of art brushes. I use 3/4" or 1" Floquil brush, you'll see a significant improvement over the brushes SIG sells. You pay a bit more but if you keep your brushes clean and look after them, they are an investment. Also, to protect your brush investment, see if they have small cans of artist brush soap/conditioner. When you clean out your brushes with thinner just finish the job with a bit of brush soap. Leaves the brush brissels soft for the next project.

I do use a sable art brush 3/4 or 1"--they are nice and one of the only ways to really lay down smooth coatings.

I wouldn't try to buff out 320/400 grit. I use it to level off the high spots as the build up progresses. after final coat then a 600 or 800 wet then buff. or like you suggest, 1000 or 1200.

I have also noticed that it sands alot easier after it is cured for a week or more. Like the old days painting cars with lacquer--drive the 57 chev around in gray primer for a summer before final coats!!

THanks

Curt: You used the term "print thru" of the silkspan pattern. Peculiar term, at least to me. You're still seeing texture, maybe feeling it, even, right?

Are you absolutely sure that the parent texture of the 'span still is apparent at the surface, even after 12 (count 'em) 12 ever lovin' coats? The mind boggles...Please take another look.

You'd think that the surface would be smooth by now. And I don't see how the surface you started out with, be it silkspan served straight up, dyed silkspan put on wet, dyed silkspan put on dry, with big brushes, little brushes, rolled on, heck, applied with a trowel, even, whatever...man, you oughta be done painting.

WElll... I will take a closer look--maybe use a eyepiece. But I can take a piece of polished aluminum sheet, and apply a sample area the size of a wing bay with the mixture I'm using on the wing, with the same brush. Same temp same stroke,etc, and the sample will come out dead-smooth--minimal brush or overlap marks etc. THe same area on the wing will appear kind of blotchy and mixed dull (shiny now over the LE and solid areas). If I were spraying, I'de almost call it orange peel. but a little sharper and smaller.

Print thru is a term I carried over from the composites experience. If one builds a glass or other fiber reinforced epoxy or polyester panel without proper fabric layering, and then apply a finish, as the material continues to age (long term curing ie weeks and months) the reinforcement fabric pattern will "print thru" to the finsh layer. It can be micro smooth to begin with then look like a wicker basket after a month. dark colors are especially prone to this. it is caused by the lay-up physically shrinking microscopically in the "hollows" of the woven material. so most cosmetic lay-up schedules include heavy fiber content woven materials then a "barrier layer(s) of non-directianl or flat weave uni or bi directional materals to isolate the finsih side from the shrinkage problem.

This is much more of a problem when female molding is emplyed with the final finish achieved through the molding process. As opposed to a post-finished, formed-over-male-mold technique when the finish can be improved prior to final coating application.

Also, vacuum and autoclave or similar hi temp curing processes are less of an issue.

Anyway, I'll look closer this PM. It is getting better.

Curt --

Currell is right. This smells of fish. Do you suspect you are seeing something other than just a silkspan pattern? Gee whiz, we could never finish even 5 momme silk! I would suggest a 7x to 10x magnifier as about right for "seeing" this problem. Too much or too little magnification can hide / distort a problem.

We are anxious for you to find the "final answer" and share it with us.

Gentlemen:

Well I looked closely at the surface last evening. and watched a small area as it dryed (VERY exciting!) its difficult to estimate the depth of this effect but I would guess that it would be 95% filled with one application of dope/filler. My painting experience says this is the result of very low solids content in the dope. The area goes on smooth and brush marks flow out almost completely--after about 5 minutes, it appears that the surface is shrinking down and getting mottled. It remains very glossy.

Anybody think theres any problem putting a couple of coats of Sig lite over the Brodaks then final coating with Brodaks again?

Also, I guess I just thought of this, I'm might try a different quart. Perhaps I got a odd batch or something.

In all other respects though, it appears and applies as previous quarts have. But I havent ever used it to build up a totally clear finish.

It is getting better tho--the blotchy areas are getting smaller.

I'll let you all know how it goes.

This doesn't sound right at all. Brodak dope has a lot more solids than does SIG, and this is why you do need to use more thinner with Brodak. But, yes, I suppose it is possible, as with anything, that you got a bad can. If you did, John will replace it.

One question here, did you use Brodak thinner? Just trying to cover all bases. You could use SIG over Brodak or the other way around since they are both Butyrate, but they use different thinners and the thinner is the key. Problems could, therefore, develop with grip, if it doesn't dig in enough, or melt down, which occurs when the top layer eats all the way down to the bottom. SIG dopes (and thinners) take longer to dry and you can smell them while they continue drying for a week or more.

Yes--I'm a firm believer in staying "in the system" with paints and thinners. I've only used the Brodak thinner for this.

You sure are right about the smell of the Sig stuff!

putting in a couple Sig coats, on more thought, I probably wont do. It was before I thought about trying a different quart.

Just another thought, Should I be stirring or mixing this clear in any way before use? I havent done that except once a while ago but the bubbles were so bad I quit. I just stir the thinner into the cup prior to application.

Stir, yes, do stir. Any dope, paint, whatever, can settle out if allowed to sit. We, normally, have a tendency to just think of the colored pigment as settling out. But if you have any dope or paint that has been sitting around for a while, the thinner can actually rise to the top and be skimmed off leaving the thicker stuff at the bottom--even if it is clear. Shake the can or stir well before taking the clear out. Then add thinner as needed in order to get to brushing consistency.

Did you, or has anybody else, checked weight gains for each coat of clear dope? I did when I was building A-2 (F1A) Gliders, and found that the first coat on tissue was the only one that added a significant amount of weight. It was Nitrate, and I don't think that fact would matter a lot, but am not 100% sure. Emil Kovak had a Jameson last year with clear on silk, and it was like plastic. I was told 30 coats, but don't know if it was Brodak or if it was brushed or sprayed. Also, foam brushes are supposed to work well on fabrics like silk...has anybody here tried them? Steve