How to Paint Old Windows That Slide Up & Down

Remove window locks with a screwdriver and set them aside.

Mix trisodium phosphate, available at hardware stores, with water as directed on the TSP package. Scrub the painted window surfaces with TSP and a nylon brush to remove all traces of grime and dirt. Wipe off with a damp rag and let the windows dry completely.

Sand off the surface of the old paint with 100-grit sandpaper, making sure to remove the surface sheen from all painted surfaces.

Fill any gouges with wood filler, if desired, let dry and sand smooth.

Tape around the window trim and over the glass panes with painter’s tape.

Pull the top window sash all the way down, exposing the window frame at the top.

Paint the exposed window upper frame with a thin coat of wood primer, taking care not to pain inside the mechanical grooves in the window frame. Use a 2-inch angle paintbrush for the best results.

Paint the visible edge of the top window sash at the same time, since it is now in the bottom of the window frame.

Let the primer dry completely, return the top sash to the upper position and slide the bottom sash upward to expose the lower window frame. Brush on a thin primer coat on the exposed unpainted areas as you did before and then let the primer dry completely. Take care not to get paint in the grooves between the moving window parts and the frame.

Sand the primer coat with 120-grit sandpaper and add at least two thin coats of paint or enamel, in the same manner you primed the window. The trick is to let the paint dry as long as possible before moving the windows to prevent scratching up the soft paint.

Use a straightedge paintbrush to prime and paint the window trim and the windowsill. It’s easier to paint these areas after the moving parts of the window are finished.