Can I paint over existing semi gloss paint?

Experienced painters have one simple rule about painting over semi-gloss paint: don't do it unless you first prepare the old paint surface. If you don't adhere to this rule, you will likely find that your new paint will streak or flake—even if you apply a primer before applying your new paint.

Sanding Your Surface before Repainting

The only reliable way to prepare your semi-gloss surface for repainting is to lightly sand it. But, be sure that after sanding you wipe off any dust residue left from sanding. To be safe, test a small area first to see if you need to apply a primer after sanding.