Part 2: How I applied the paint
I had the good fortune of working for an employer with a temporary excess of warehouse space, which they let me use to apply the fabric and paint. This would have been really difficult in my crowded and dusty shop. I made special sawhorse caps lined with felt for resting the wing panels on. In the back of the photo you can see me setting up a spray booth with PVC tubing and plastic sheeting (worked fine for me, but be sure to read the caveats in Sid Lloyd's Fabric Covering and Painting page. 2/9/03 note: See photos of my new metal conduit version here). The booth had a roll-up flap for a door on the wall by my left arm, and was vented by a common window fan and furnace filters taped into the opposite wall. Don't worry about using a spark-free fan, because latex vapors are not flammable! (Non-flammable, inflammable, non-inflammable -- don't get me started. It won't burn, dammit.)
I'll never regret taking the time to build this "rotisserie" for holding the fuselage. On the front you can see a plywood disc with a lock-pin hole every 45°. The fuselage could be rotated to the best working angle for the task at hand and then locked in place with the black handled pin (not being used in photo). This made a potentially back-breaking job about as effortless as it could be.
After applying the fabric, tapes and reinforcing patches with Poly-Tac and heat-tautening with an iron per the Stits instructions, I applied the color paint directly to the bare fabric with no Poly-Brush and no UV barrier (see Part 1). But first I scrubbed the material with a mild detergent -- this may be a critical step IF your material has any glycol residue in it from the extruding/weaving process. Some builders say it's an issue, others say it isn't. I didn't care to take chances.
I used Sherwin-Williams Acrylic Latex Interior/Exterior High Gloss Enamel (this was in 1995, so the name and/or product may have changed by now). The creamy-white paint for the wings and tail feathers was thinned with water for use in a standard Binks-type spray gun (didn't have an HVLP gun at the time). I don't remember how much I thinned it... maybe 20-30% water, but don't hold me to that. I just thinned it until it had a viscosity similar to oil-based enamels I was familiar with. The first coat should be applied heavily enough so it will soak into and around the fabric fibers, but not so heavy that it soaks through too much and starts running on the back side of the fabric. Allowing the paint to soak in and wrap around the fibers gives you the mechanical bond with the plastic (polyester) fibers which will assure a durable, non-flaking finish. Latex paint will not establish a good chemical bond with plastics -- polyester included -- so a mechanical bond is important.
The thinned paint, especially being very lightly-colored, builds slowly and has a difficult time hiding contrasting features below (such as those hideous black stamps Stits puts on the fabric every few feet). I tried to get by with two coats, but it just wasn't enough. The third coat gave an acceptable opacity and a nice semi-gloss sheen. Sure, I could have added more coats, but I was concerned about the weight of the airframe and wanted to keep it as light as possible.
Many people recommend adding Floetrol, a latex retarder, to help the paint lay out flat before it gets tacky. I'm reasonably sure that Floetrol (mixed per the instructions) gave me headaches. I would spray a panel and these greasy-looking splotches would appear, and the paint would flee the area. After trying several times, having to wipe the fresh paint off immediately before it dried that way, I stopped using the Floetrol and the problem went away. But other people seem to have good results with it (it's mentioned favorably in the 12/01 Kitplanes article "Maximum Paint Job, Minimum Cost"), so I don't know what to say. It seems telling that the Sherwin-Williams clerk tried to discourage me from buying it, but I had been told to use it and by golly I was gonna use it.
I brushed two coats of red onto the fuselage. The brain cells that stored what kind of brush I used are dead or dying, but if I had to guess I'd say that I tried foam brushes but switched to a high-quality bristle brush because of brush stroke problems at the edges of the foam brush. I think I do remember that the first coat (whether sprayed or brushed) should be thinned slightly so that penetration into the fabric fibers is assured. I probably applied a slightly-thinned first coat of red, and then a full-strength second coat. When brushing, the pressure from the brush helps force the paint into the fabric, so it may not need to be thinned as much as a first coat sprayed on. You can peek at the back side of the fabric while you're painting and see what kind of penetration you're getting. I am not aware of anyone using latex paints over fabric that has first been sealed with Poly-Brush -- if you know anything about doing this I'd love to hear about it. My gut feeling is that the latex won't get a decent chemical OR mechanical bond to the Poly-Brush, and is likely to start peeling long before the fabric is ready to be retired. I hear about lots of builders mixing and matching primers, color coats and clear coats from different systems and/or manufacturers, but I consider this an extremely risky practice. There are a lot of unsuccessful (blistering, peeling, etc.) aircraft paint jobs out there to give creedence to this opinion, too. A homebuilt airplane represents a HUGE investment of life energy and money; therefore I don't think it is worth it to mix and match different kinds of paint and risk ruining the whole thing. (See 5/11/02 update below)
I had to use careful and consistent brushing technique to keep brush strokes to a minimum on the red surfaces. The red was a more substantial paint, and two coats produced a very satisfactory opacity, although the black Stits stamps could still be seen if you looked closely in good light. If you looked closely with a glare you could see some slight unevenness in the paint's surface (brush strokes), but you had to be looking for them. I've heard a lot of favorable comments about using rollers to apply the paint, but I didn't have enough confidence in them to try it. The Kitplanes article mentions the use of Floetrol to allow the paint to flatten out after rolling.
I remember wet sanding the paint between coats (probably with 400) to knock down the little fuzzies that got in the paint despite my precautions with the booth (I sprayed the walls and floor of the booth with water before painting, to keep dust down and also to raise the humidity level and hopefully retard the paint some.) You can bear down on the sandpaper over unsupported stretches of fabric, but be extremely careful over ribs and other frame members -- you'll sand through the fabric in a heartbeat if you're not careful. I also remember lots of little corners on the pinked edges standing up a bit after each coat of paint. These can be ironed back down, as heat seems to melt both the latex and the underlying Poly-Tac and allows it to re-bond.
Personally, even though I am a perfectionist in many ways, I'd much rather be "up here" with a good paint job than "down there" still trying to achieve (and pay for) a perfect paint job. Also, I was soooo tired of the project by the time I got to the painting that I simply didn't have the time or motivation to labor unnecessarily over the paint. Notice the lack of masked trim colors. K.I.S.S.!
If you haven't been there already, Part 1 of this article discusses some pros and cons of using latex for aircraft paint, as well as a description of an accelerated aging test I conducted on Stits Polyfiber with the Sherwin-Williams paint.
Paul Yarnall sent the following message to Tandem Talk:
I'm very interested in the long-term success of the latex paint over the Cecofill, and hope that Paul will stay in touch and let us know how it performs over the years. This seems like an ideal solution if the latex paint will stay firmly attached to the Cecofill through years of temperature/humidity cycles. We also need to know if spilled gasoline and/or oil will have any deleterious effects on the bond between the two components. I'm hoping that it works great, Paul.
Paul sent the following additional details about his experiences with AFS products and latex paints.
(ed. note: The CecoFill bottle says "For best results we recommend spraying." It does later say that it can be brushed or rolled, though.)