White trim serves as a visual baseline to the rest of the room's color scheme, adding snap to even lightly-pigmented walls and furnishings. Whether you're painting unfinished new wood or repainting antique wood trim, the key to an attractive paint job is proper surface preparation.
Ventilate the room. Clean previously painted or varnished wood trim. Sponge it down with trisodium phosphate or a TSP substitute. Wipe off the wood trim with a slightly wet sponge to remove any TSP residue. Allow the trim to dry.
Smooth the trim using a small square of 180-grit sandpaper on any rough or noticeably uneven portions of previously painted or stained wood. Do not sand to the extent of stripping off the old finish. Use the sandpaper to rub out any splinters or significant surface irregularities on unpainted wood.
Remove the sanding dust with a tack cloth.
Spread wood putty into any deep cracks or indentations in the wood, using a putty knife. Allow the putty to dry completely, then sand it down to a smooth finish level with the adjoining wood segments. Clean off the sanding dust with a tack cloth.
Affix painter's tape to any wall, floor or ceiling surface that adjoins the wood trim.
Apply white pigmented shellac primer to the wood trim, using a synthetic fiber paintbrush. If the trim previously was painted with a high-gloss enamel paint or stained and varnished with a high-gloss polyurethane, apply a water-based bonding primer instead. Allow the primer to dry thoroughly for two to three hours or as indicated on the label.
Brush on a coat of acrylic latex paint in the desired sheen -- semi-gloss or gloss are standard for trimwork -- using a high-quality synthetic filament brush. Allow the paint to dry thoroughly for two to three hours or as indicated on the directions.
Apply a second coat of the acrylic latex paint. Wait one to two days before removing the painter's tape.