"Painting" Stuff with Thinner/Mineral Spirits?

You shouldn’t ever reduce a paint by more than the manufacturer recommends. It dilutes the solids too much and then the paint solids can’t bond together properly. This means a coat that won’t bond and adhere to the surface properly either. Multiple coats of this thinned out material won't bond to each other well either.

It’s a recipe for premature failure and peeling of the paint.