When painting wood, the optimal situation is to paint primer on top of clean, bare wood, and then to lay down your paint on top of the primer. That's optimal; the world is not optimal. Paint chips and peels and fades, and before you know it, you need to put down a second, third, or fourth coat. Stripping off the original layers of paint is not usually an option.
So here are some tips on painting successive coats of paint:
- Problem: Dirty surface. Answer: Don't use Pine-Sol or soap. Instead, use an ultra cheap powder found at any hardward store called TSP. Mix it with water, and wipe down with a sponge. Removing grease, dirt, and dust will do wonders to help paint stick to previous coats. TSP looks and sounds like wickedly toxic stuff; and yes, while you do want to take precautions, it's not the horrifying experience you might expect it to be. It's always good to have a box of TSP on hand.
- Problem: Latex paint over oil-based paint. Answer: It can be done. When laying down latex over oil-based paint, make sure that you wipe down with TSP. Of course, any peeling paint needs to be stripped off, too.
- Problem: Painting on a shiny surface. Answer: Use a fine sandpaper to scuff the surface. You will be using a sandpaper in the #180 to #100 range, and applying only minimal pressure while sanding (thought you'd like to hear that!).