Can I use this to spray latex paint without thinning on a popcorn ceiling?

Yes. Some latex paints will spray well with the Control Painter without thinning. The thickest latex paints will require some modification in order to spray better. 1 - Stir the paint/stain with a mixer in a drill until its creamy smooth, about 1 min per gallon 2 - Strain the paint/stain before it goes into the sprayer 3 - Add a flow agent, like Floetrol or Paint Easy (this is not a thinner) for latex paint – Penetrol for oil based 4 - Or you can thin, even as little as 5% can make a big difference, water for water based materials and mineral spirit for oil based material. Up to 20% is fine. Any one or all of these will help paint spray better.