This is a follow-up on the original question of putting clear dope over water based stain. I expanded the test to include some “dope over” combos we might encounter in trimming techniques, repairs, or new planes with film wings and doped / covered fuselages.
   I was also interested in using the “Windex method” of adding film trim (numbers, designs, . . .) except over doped surfaces prior applying a clear dope finish coat over the entire plane. (obviously can’t use trim solvent!). After some thought, the test was expanded to add the following:
Monokote (True Red) – (Coded “M”)
Ultrakote (Bright Yellow) – (Coded “U”)
Brodak Kolar Kote (White) – (Coded “B”)
Coverite trim film (Blue) – (Coded “CT”)
Monokote trim film (Missle Red) – (Coded “MT”)
plus the original test;
Minwax Rosewood Water Base Stain

 The first pic shows the test block – a pine 1 x 2 sanded with 220, with panels of each of the films in addition to the stain. All films were applied to the raw sanded wood. The three coverings were ironed on, instead of Windexed on, since it is bare wood. That shouldn’t affect the test, as the concern is adhesion of dope to the film, not the films to the substrate. The second pic shows the codes under each patch. Nobody is going to use dope over a large area of film, so the question is, do we get good enough adhesion to be comfortable with small dabs of trims and overlap areas?
   The dope was clear Brodak thinned exactly 50-50, not that that is an ideal finish clear. But I figured any final clear of choice would bond to the Brodak, making it a reasonable choice for these “next layer” tests.
   The stain was rubbed on, allowed to stand for 3 minutes, then rubbed off. I applied the first coat of dope about 12 hours after the stain application. Following coats of clear were added over a three day period, for a total of 6 coats of clear. Light sanding and tack rag between each coat, 400 after coats 1 and 2, 600 after coats 3, 4, and 5.
   Each of the covering films was roughed up with 400 prior to doping, although I think Scotchbrite is preferred(?), but I didn’t have any handy. I figured 400 was good enough for a test.  I first thought the trim films were known to be dope compatible and were included in the test more as comparative controls than a test. Then, on second thought, I was less sure so sanded the top half (only) of the trim films also. The sanding line is the inked line in the pics. Prep-Sol and tack rags on all films before the first coat.
   I’ll do the tape pull adhesion tests on 2/19, having finished the final coat on 2/12. I’ll add some other details at that time.

Larry Fulwider

The results in a nutshell:

1.) Don’t ever dope over Coverite trim film
2.) Doping over water based stain is no different than doping over bare wood
3.) Monokote trim is totally dope compatible, with no need to rough it up

Tape Pull Results / Methodology:

The first tape pull was a frosty back generic brand “Magic Tape” – the “invisible” kind you can write on. Tapes in this category do not have an overly aggressive adhesive, but are used as an adhesion standard for testing book covers and other graphic arts coatings. The “tape adhesion test” is a serious rub down, followed by a quick snap up, not back. Results are judged more by the amount of coating or paint picked up by the tape – by looking at the tape – than by the appearance of the test material after the pull.

First Pull PASS, No dope transfer to tape:
Stain
Brodak sanded
Ultrakote sanded
Monokote Trim sanded
Monokote Trim not sanded

First Pull Acceptable, Slight dope transfer to tape:
Monokote Film sanded
Coverite sanded

First Pull Fail:
Coverite not sanded

The second pull was a generic brand similar to Scotch 610, a more aggressive adhesive;
Second Pull PASS, No ADDITIONAL dope transfer to tape:
All except for Coverite

Second Pull Fail:
Coverite sanded
Coverite not sanded
A picture of the Coverite patch is shown after the second pull. The dope pulled off, and areas outside the tape are lifted up around the edges showing the general lack of bonding throughout.
   
The third pull with hinge tape was redundant; More dope came off the Coverite, and no other patches were affected any further.

(The bubbles seen in the Monokote to the right of the Coverite are not an issue. The aggressive tape pulled some of the films away from the bare wood, which has nothing to do with the dope to film adhesion.)

Larry Fulwider