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Southern Polyurethanes Forum
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Short answer is there are drawbacks. The good ones that work are expensive $2K or more. They don't spray high solids clear well. The warm air that it produces affects how the clear lays out. Same with urethane primers. The warm air accelerates things and it doesn't lay down well at all. They are OK for epoxy primer and basecoat. For the cost of a good one, you would be well on your way to outfitting your shop with a good air compressor and proper spray gun. I've been working in the Industry for 30 years and I've never seen a shop that uses one.