Flat paints are normally used in low-traffic areas such as closets or ceilings. Flat finishes also stain easily and are difficult to clean, whereas a semi-gloss paint can be washed and does not absorb moisture, preventing mildew growth in high-moisture areas such as bathrooms or kitchens. Semi-gloss paints apply over flat finishes with little difficulty. Gloss finishes, though, will show more imperfections than flat ones, so repairing any imperfections is necessary before you begin to apply semi-gloss paint.
Repair with the spackle any imperfections in the paint, such as holes from wall hangings, deep scratches or chips. Put on the latex gloves and use your fingers to apply the spackle to the damaged areas. Smooth the spackle onto the area and remove any excess. To cover large damaged areas, use the spackle spreader. Wait for the spackle to dry.
Sand down any high points or roughness in the spackle so that it is smooth and even with the painting area. Run your hand across the surface. It should feel flat and smooth. If it does not, continue sanding the area.
Wash the area with soap and water. Remove any dirt or dust so that you have a clean surface on which to apply primer and then paint.
Primer only the spackled area, using a paintbrush. Primering will give your painted finish an even look, where you will not see the previously damaged areas. It is not necessary to primer the whole area. The flat paint will hold your new semi-gloss finish. Wait for the primer to dry before continuing.
Paint the gloss paint over the flat paint. Use brushes to paint corners or small, hard-to-reach areas. Rollers are best used on large, flat surfaces. Work evenly, one section at a time in an up and down motion. Wait for the paint to dry before handling the surface.