chalk Paint
The only time it's acceptable to mix water in the paint is when you're using a deep or ultra deep base paint to reduce its stickiness, which is rare with new paint technology. Dark primary colors are composed almost entirely of tint that makes it very hard to work with without adding water. (You never use a sprayer and need to thin paint.?) If i was still in the industry I'd take the time to make a better article than this. Take this for a grain of slat. Use a reputable painter or someone you know you can trust or has been referred to you by someone you trust. I wouldn't hire anyone I had to watch like a hawk to make sure they're not screwing me.
To paint a large section without leaving lap marks, roll the nearly dry roller in different directions along the dry edge, feathering out the paint as you go. After completing the entire length of the wall or ceiling, move to the next section and paint over the feathered edges. For the second coat, apply the paint in the opposite direction. This crisscrossing paint application sharply reduces (if not eliminates) lap marks.
