I have been spraying alkyd SI with HVLP for quite some time (mostly built-ins or furniture) and I always get great results. I thin with mineral spirits to about 40 secs using a Ford cup.
I recently sprayed a large room full of trim but the sheen is very low compared to what I normally see. The painted surface feels very smooth so I don't dust is the issue. I then sprayed a second coat (after sanding lightly with 320), with as little thinning as possible and spraying as thick as I dare. The flow out was excellent - like glass. The room took about 5 hours to spray (I'm dead on my feet when done). I run a fan in the doorway to get rid of overspray.
I have been racking my brain trying to figure out what would account for the noticeable difference compared to earlier work and the only explanation I can come up with is the cure temps. We recently started getting much lower overnight temps here. I know when I sprayed it was about 70 degs. I finished about 6:00 pm and the temps were about low 60's. I can't imagine indoor temps went much below 60 overnight. I did see a weird effect with the painted surfaces after 8 hours or dry time - many areas had a shiny, wet look surface but when I touched it, it disappeared. I have never seen this before.
I know that SI is chameleon like with regards to sheen. Sometimes I spray an object and it almost looks like semi gloss (seems like this happens when temps are 80+ and I'm spraying in direct sun), othertimes it's satin at best. Of course over time even unthinned, brushed SI seems to always go to a satin although it takes longer than 1 week IMO.
Anyone know how much of a factor temps are with regards to alkyd SI sheen?
I really wouldn't think on at 70 with no lower than 60 would make much difference.
I have seen a difference when using deeper colors- starts out ( and sometime stays) glossier. More resins needed to carry the color.
"It's better to come here with questions before you screw up than to come here after and ask how to fix them."- JS