Ok, just want to say a few things about wet film thickness versus dry film builds and the addition of thinners to the ready to spray mix. Let's look at the Cardinal stuff mentioned. It has 11% solids by volume as packaged, not a high solids coating by any stretch. So if you are hanging 5 mills wet you are going to net just over half a mill dry per coat. That means at least 9-10 coats to bring the film up to 5 mills before buffing ( my suggested minimum), depending on surface texture you may need another mill for level sanding. Now Cardinal's literature does not mention thinning, the product is basically packaged RTS, small amounts of thinner or retarder may be needed for environmental conditions like high temp/humidity but generally speaking these adjustments will be far less than 10% added to the product. So let's say we reduce a bit due to high temp, 10% even, we have lowered our dry film build slightly. We will now net half a mill less every ten coats so instead of the 5 mills we had previously at 10 coats we now have 4.5 mills, so we will need at least one more coat to get the same film. Now let,s thin out at the 2:1 as mentioned, that's a reduction of 33%. Now we are only applying about .35 mill dry film per coat, so now we need to spray out at least 15 coats to get our dry build. With an average flash between coats of 30 minutes those extra coats with all that thinner mean another 2.5 hrs. in the booth, more exposure ( lots of these chemicals absorb directly through the skin) and the kicker is we have increased our dry time to buff out, it will take more time for the extra solvents to escape. So how long does it take to sand out a guitar? How much longer to sand out a little more texture? Bet it's less than the 2.5 hrs we just mentioned. The extra solvents can also have an effect on things like the pore fill. Every coat you spray actually wets all the product on the instrument all the way down to bare wood, the more solvent or the more aggressive it is the more pronounced the effect ( those who use acetone, take note). This constant re-wetting can cause the oil base pore fill to swell and then shrink causing the pores to reappear on the final finish a few weeks out, it takes time for all that extra solvent to work back out. Even 30 days out without any extra solvents we may be only 95% dry, at a week you may 90% or 85 %, there is no way of knowing but that means that the coating will still shrink. So those who spray and measure rather than measure their wet films will need to think about that, 5 mills at a week may only actually be a little over 4 in the end ( 3 mills is about the bare minimum for a functional lacquer coating). And we haven't even talked about the environmental impact of all the extra solvents.... That's the real reason they are making these products harder and harder to get ( in some cases unobtainable) by non industrial users. Industrial users can still buy anything we want in any quantity as long as our equipment and methods are compliant. Hopefully some of you find this info helpful as this topic comes up fairly regular.
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What I found out is that I'm laying my coats down at 5 mils wet. I'm using Behlen's instrument lacquer and I'm thinning it 2:1. The results are turning out great! The 5 mils that I'm spraying is at the max of what I would lay down. I'm just on the verge of runs, but I'm not getting any. Laying down 10 mils at 2:1 you would have nothing but runs. Just my observation on what I'm spraying now. Hopefully that helps with your Cardinal lacquer.
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