how about: when I do painting, I wear a hat. If this is wrong, then when you say, 'let's do some painting' is painting a verb or a noun indicating a painting?
Let's make a painting. ( A painting is an art work created with a brush and paints.) The room needs painting, and I need a project. So let's do some painting. (Painting - a noun - refers to an activity. )
When I paint, I wear a hat. (Paint is a verb here.)