semi-gloss paint over semi-gloss
It depends on the paint you have on the wall, and the paint you want to put over it.
By rights, if you have a semigloss oil or latex paint, you should really sand it down before applying an oil or latex paint, respectively, over it. That is, sand down a semi-gloss oil before repainting with oil, sand down a semi-gloss latex before repainting with latex. Ditto for gloss.
Non-ditto for anything under semi-gloss. Paint over satin oil based paint with oil based paint, paint over satin latex paint with latex paint. No sanding required.
However, if you have a semigloss oil based paint, and you want to paint over it with a latex, then you definitely need to sand it down before applying your latex paint. Otherwise it won't stick!
Did you sand down the substrate paint before painting over it?
And, was the substrate an oil based paint, and did you paint over it with a latex?
Sanding will make all the difference in the world when it comes to adhesion of one paint to another. If you don't roughen the surface of the substrate to increase it's surface area, you can't expect to have very good adhesion of latex paint to oil based paint. (and, vice versa, really)
Last edited by Nestor_Kelebay; 08-11-2008 at 02:10 AM.