I do not know if butyrate will melt into the nitrate the same way it would melt into a previous coat of butyrate.  I can only suggest testing it by trying it on a scrap wing.

Nitrate has better adhesive properties but I have used butyrate to attach Polyspan and Thermalspan.  If the framework has several coats of butyrate clear on it and you give the butyrate enough time to dry thoroughly after sticking down the covering everything should be OK.  If you try heat shrinking before allowing enough time for the butyrate to dry you might break the adhesive bond and end up with a problem.

I was in a bit of a hurry some years ago and when applying the heat to shrink the material I could hear faint "snapping sounds."  I bet that was the loosening of the adhesive bond and the covering was coming loose. 

I've not had any issues with butyrate over nitrate putting on my polyspan.  Just can't do it the other way.  My now defunct Ringmaster used that method and the polyspan survived the crash better than the wing structure.  New Ringmaster will be finished for this weekends GSCB OTS contest.

Guys,
If polyspan is applied with Nitrate dope then finished with Butyrate (Sig, Brodak's) does the Butyrate melt in the top layer of the nitrate like it does to other Butyrate coats or just glue itself on top of it?

Seems if it just glues on top any break in the surface could cause the two separate.

Can you use all Butyrate to adhere the polyspan?

Best,  DennisT

Hi Dennis,

Butyrate will adhere extremely well to nitrate as the solvents in butyrate soften the nitrate and blend the nitrate/butyrate interface.  Nitrate is extremely flammable and was used in the very early days of fabric covering on airplanes, in fact nitrate in the twenties and thirties was available in colors as butyrate was just being introduced. 

Butyrate was developed due to the extreme flammability of nitrate - butyrate, while it will burn & sustain combustion is much less explosively flammable than nitrate.  I have peeled a sheet of the nitrate dope off of a test piece, put it in a metal pan on the floor in the middle of my hangar and put a flame to it.  A foot square piece of nitrate was completely gone in less than a second.

Also, butyrate has more than enough adhesion to use when applying polyspan, silk, or silkspan.