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Building Tips and technical articles. => Paint and finishing => Topic started by: Ward Van Duzer on November 28, 2010, 11:15:29 AM
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What's your process of putting silkspan over sheeted wood? I often get a separation of the tissue from flaps, fuse, etc. on a totally finished plane. It really T's me off. It' is repairable, of course, pinholes, thin dope or CA...So what am I doing wrong?
I Normally apply 2-3 coats of nitrate, sand smooth, followed by wet tissue blotted semi dry, then diluted clear (not nitrate) smeared on with a 1 inch dope brush. Often rubbed in with a finger. Then a hot day on the field, BUBBLES!
HELP!
W-O :'(
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I normally apply 2 coats of dope, I use butyrate then a light sand. Then I put on another coat and let sit, right before I apply the silkspan I put on another coat. On sheeted I use full shrink since getting out wrinkles can be a pain.
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Ward, I cover wet over sheeted or open areas. Silkspan is probably the mot compliant material to cover with when its wet and the most annoying dry. Dope up well so the grain is sealed (not filled, just sealed) so you don't get any grain swelling. Then just cover as you would open bays, dope around the edges and pull smooth, then dope through after the span dries.
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I think if your base is Nitrate, you should use Nitrate to apply the silkspan. Making the transition to butyrate with the application of the silkspan might be your problem.
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After 2 or 3 coats of clear on the wood (sanded as needed), I use straight thinner, applied with a narrow brush to attach the tissue or silkspan to the sheeted surface. A bit of rubbing on stubborn areas may be needed...... "you gots to get it stuck good".
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I have to agree with Allan, I have read that Nitrate is used for adhering covering to the framework on full size aircraft as it has far better adhesion properties than Butyrate dope. I found this out to my cost too! When using Butyrate to stick tissue (modelspan) to the fuselage, despite giving the wood about 4 50/50 thinned coats, the tissue still bubbled-up after about 3 coats! Then when I masked off some colour, the tape pulled the whole lot off, down to the wood! Won't do that again!
Cheers Neville
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FWIW I've only ever used nitrate to attach silkspan to sheeted surfaces, and have never had a problem.
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When I apply silkspan or tissue over sheet, I put it on dry, and stick it down well around the edges. Then I water shrink it. When dry, I stick it down with thinner. First, this will allow you to put and keep the edges where you want them. Secondly, this will give you a smoother surface than the usual rub it down with thinner procedure.
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Ward-O,
I've done it both ways, but personally I never bother with using nitrate anymore. It's just another ingredient I don't need to spend money on in my opinion. I use 50/50 thinned butyrate for everything up until I'm ready for the color coats. With the bare wood sanded smooth and ready I put down two or three coats first, lightly sanding the "fuzz" off between coats but not cutting through the clear. I usually use a worn out piece of 220 for that. Then, wet or dry, I put down medium silkspan and brush (force) the clear through it to get it stuck down real good. I think the first coat when applying the silkspan is critical to it staying down well for the long term. Make sure you give it a good heavy coat and that you're getting it forced through the material, especially on any edges. After that, and a few more coats of the 50/50 clear, proceed with your normal finish build-up and you should be good to go. H^^
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I have to agree with Allan, I have read that Nitrate is used for adhering covering to the framework on full size aircraft as it has far better adhesion properties than Butyrate dope. I found this out to my cost too! When using Butyrate to stick tissue (modelspan) to the fuselage, despite giving the wood about 4 50/50 thinned coats, the tissue still bubbled-up after about 3 coats! Then when I masked off some colour, the tape pulled the whole lot off, down to the wood! Won't do that again!
Cheers Neville
Hi Neville,
Actually, fabric cement is used to adhere the fabric to the airframe on full-scale airplanes, and the cement is a different product compared to dope with a much greater peel and shear strength than dope has. The Ceconite covering process, which uses Dacron fabric, specifies the use of nitrate dope for the first coats on the Dacron fabric as the nitrate will better encapsulate the weave of the Dacron and thus give a better grip on the fabric for subsequent coats of dope.
When using the old grade A cotton for covering a full-scale airplane the only requirement for the dope is to use a fungicidal additive in the first coat of dope whether it be nitrate or butyrate.
Butyrate dope uses a more aggressive solvent system than does nitrate and will work just fine for adhering the silkspan to the underlying nitrate. However, I don't ever use nitrate on my models because I just don't see any need for it...it's easier to just stick to one dope system.
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Bill, according to the company I bought my Dope from, LAS Aerospace Ltd, here in England, fabric cement contains Nitrate, and on their website they actually say that Nitrate has better "stick" (they use that word!) properties, than Butyrate dope! I like the fuel-proof qualities of Butyrate.
Cheers Neville
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I have heard that some companies ship dope as 'industrial adhesive' and thus avoid hazmat fees. don't know this from experience.