My paint
>guy tells me that using a slower hardner really won't help
>as they are primarily used for hotter temps. He also argued
>strenously against using any sort of thinner or other
>material to thin the mixture as he claimed that the
>clearcoat adhesion would be severely compromised.
Wrong. Wrong. Wrong. Wrong.
I do not want to sound like a "poopy head" (family oriented site), but most guys who work in paint stores are just that, paint salemen. They are not PAINTERS. My good friend Bill Wilson is a PAINTER, actually he is MASTER PAINTER, and we have thinned various clears as much as 100% with absolutely no ill effects (especially adhesion). Bill has been doing it for decades, on cars and airplanes alike.
Reducers promote flowout, especially slow reducers. Slower hardners also promote flowout. The only reason you would use a fast hardener with poor flowout would be for SPOT JOBS and those jobs you want to deliver to the customer tomorrow.
I have seen absolutely no advantage to faster hardeners, as I do not mind waiting a few days after shooting clear to assemble my plane. The faster hardeners as promoted by most body shop supply stores are designed for fast drying properties because in the body shop business TIME IS MONEY!!!! You do not want to shoot a bumper and wait two days to buff it. You want to buff it and deliver it in the morning. Period.
Most of what is said about adhesion is bull- "mooky stinks" or simply misinformation by poorly informed folk. The FASTER the clear dries the MORE I WOULD WORRY ABOUT ADHESION!!!
Get yourself some "all over" or "premium" clear with an "all over" hardener. The slower the better I say... avoid anything that says "fast" or "spot repair" or "panel repair". They simply do not work as well (orange peel, buggers, snot balls, overspray marks, etc). Long and short, use a clear that is designed to shoot an ENTIRE CAR not repair panels and try to shoot between 60 and 70 degrees if possible. Cold is better than hot.
More from the FM article:
"The clear I am currently using is the Matrix MS-42 2 to 1 premium urethane clear, with the MH006 hardener, or the MH008 hardener in hot weather. All of the major paint companies offer a “premium” 2 to 1 clear. You could substitute PPG or Dupont, and in particular PPG’s bargain line of paints called Omni has a very nice 2 to 1 clear that is very suitable to our application. I have also used 4 to 1 clears, including Chromaclear and Valspar and they behave exactly the same as each other. I like the 2 to 1 clears better. When I first started using the clears myself, Bill Wilson happened to give me the Matrix clear, as it was a sample from a sales rep. I would have normally been using Valspar brand, because that is what Bill uses, but I took home the Matrix clear and that is what I have been using ever since. In fact, I have grown to really love the Matrix clear, as it performs wonderfully and is priced very reasonably, at nearly half the cost of Chromaclear.
I thin (or reduce) the clear coat from 33% (2-1-1) to 100% (2-1-3) depending on what I am planning to shoot. I typically shoot at close to 100% reduction or slightly less. I use Omni medium, slow, or super-slow urethane reducer depending on the temperature. I use the Omni reducer because I have found that it is IDENTICAL to the PPG urethane reducer that I was using before, and the Omni costs about one-fourth as much (it is also what my local shop carries). A gallon of Omni reducer costs less than $20 and can be used in the primer also. Feel free to use whatever brand urethane reducer you want, as I am sure they are extremely similar.
The real function of the reducer in the clear is to give the modeler a chance at a light clear coat. We are painting model airplanes after all not cars, so a thick heavy coat of clear, (while desirable) is not practical. Urethane auto clears are “high solids”. High solids content simply refers to the fact that there is actually more material in the can and less solvents (epoxy, for example would be considered 100% solids-as it loses no weight as it cures). This has been the trend in auto paints for years, resulting from enormous pressure from the EPA. Dope clear for example, is typically a 10% solids and 90% evaporating solvents, so it would take 6 times as much dope clear to equal a 60% solids auto clear (it also takes much more time to gas off). The urethane reducer used in the clear serves to stretch the material into a thinner coat, resulting in a reasonable weight. The reducer can also serve help the clear flow and flash a little slower if the hardener is a little fast, as most spot repair hardeners often are. The slower the clear dries the more it will lay out typically, but it will also serve to allow more “trash” to stick to the wet surface, especially if you are painting in your garage. Everything is really a compromise in the end.
I have been doing pretty well with using “one slower” reducer when thinning the clear if a slow hardener is not available. So, for example, if the temperature calls for medium reducer (70 deg.-80 deg.) I use the slow (80 deg. -90 deg.). Don’t get cute and think that using a super slow reducer when it is 60 degrees will result in a finish that looks like a mirror. Most likely you only succeed in trapping the solvents in the first coat and “popping” the surface with the second, which will result in a bunch of tiny little air bubbles to appear in the surface.
3 oz of clear, 3 oz of reducer for a total of 6 oz in the gun will do a Nobler sized plane if the overspray is kept to a minimum. The result will typically be a 1.5 oz clear coat (see note). The first coat is shot semi-gloss, the second is shot a little wetter. Allow 10-15 minutes in between to let the reducer gas off out of the previous coat. Don’t try to fix all the orange peel until you give the material 10 minutes to flow, you might be surprised how much it will. The 2 to 1 clear is just so much easier to shoot and seems to not want to run if "stacked" like the 4 to 1 clears. Not to mention the shine is at least triple."
