Painting a nice, straight line on trim or between walls and ceilings is known as "cutting in" by professional painters. This page contains tips for painting trim molding using masking tape to form a straight, cut-in line with the wall and some best practices for painting features like doors and windows.
Before you begin make sure your trim is primed with a color close to the finish color. This will make it possible to cover with one finish coat and make the whole job go easier. If it's not primed or the color is very different from the finish color you are using, apply a first coat before proceeding.
If you're using alkyd or oil paint, let it dry for 12 to 24 hours and lightly sand before proceeding. If you're using latex paint, let it dry according to the label instructions but don't sand between coats.
When the first coat on the trim is dry, paint the walls. Start by brushing a 2 inch band of paint around the trim, letting it overlap onto the molding a bit. Avoid getting gobs of paint on the trim, but be sure to completely cover the seam between the molding and the wall. Follow with the roller work. Do as many coats as needed to get good coverage on the walls and let the final coat dry for about a week before attempting to mask.
Use delicate masking tape to form a straight line on the wall surface as close to the trim as possible without sticking it to the molding bead itself. Use several short lengths of tape to control exactly where it sticks and oerlap the ends of each piece a bit.
Load the brush lightly with a quality latex or alkyd paint and apply a thin coat overlapping the tape slightly. To prevent bleeding under the tape use a light brush to leave only a thin coat along the seam. Work along one wall at a time and remove the tape right away.
Pull the masking tape off as soon as possible and before the paint can dry to minimize the chance of pulling the new paint off with the tape. Pull it slowly and at a sharp angle to minimize the chance of peeling the wall paint. Watch for peeling and, if necessary, run the point of a putty knife along the edge of the tape to break any paint film.
Painting the trim first, so it can be masked to paint the walls, can produce a sharper line between the colors, but it can also be a bit more difficult to do when painting baseboards and other molding with thin edges. Taping this small strip, and getting a straight line, can be a bit tricky and require close attention to get a crisp line between paint colors.
Brush the molding with a good, thick coat of paint, at the edge overlap onto the wall slightly, but avoid leaving thick paint in the seam between the wall and trim. If your trim paint will take two or more coats to cover, do as many coats as necessary and let the final coat dry completely before taping. If you're using an oil paint it should dry sufficiently overnight, if you're using latex let it dry for about a week.
Mask the trim using several short strips of tape, overlapping the ends of each piece a bit. Press the tape tightly to the trim using a clean putty knife, pushing down while pulling along. Make sure the tape is flat with no bubbles or gaps between it and the molding.
If you need to do more than one coat for good coverage on the walls, brush near the trim but avoid touching the tape as much as possible until applying the last coat. On the final coat, paint along the trim using a lightly filled brush, overlapping the tape slightly. Avoid applying excess paint that would bleed under, but be sure to completely cover the seam.
Pull the tape slowly and at a sharp angle, watch for peeling. To minimize the chance of peeling, it's a good idea to do the final coat on one wall at a time so you can remove the tape immediately, this is especially true if you're using a shiny paint. If the paint starts to come away with the tape, run the point of a putty knife lightly along the edge to break the paint film.
Doors between rooms are either completely flat surfaces or they have one or more raised-panel. Modern doors with faux panels pressed into the MDF and old doors with multiple panels built in can be hard to paint without leaving brush and drag marks in the finish. These marks occur when the brush touches partially dry paint as you try to blend the different parts of the door together. Use the technique here to get a smooth paint finish on raised-panel doors.
The parts of a raised-panel door are pictured here and include the rails, stiles and panels. The door rails are the cross members, including the top and bottom as well as the cross pieces dividing the middle. The stiles are the pieces that run vertically, including the small pieces between the panels and the two long pieces on the sides. They run from top to bottom of the door to tie the rails, center stiles and panels together. The panels are the inset squares or rectangles. In old doors the panels are separate pieces of wood that fit into a groove cut along the edge of the rails and stiles.
These door panels are designed to float in the frame as the wood expands and contracts with the moisture and temperature changes in the surrounding atmosphere. Over time this movement can cause the paint film to crack along the border of the panel. Many people make the mistake of caulking these cracks, but the best way to fix this problem it to fill the gap with more paint, not caulk. Caulking the crack will only create a cracking caulk problem that will be more unsightly than cracking paint. If you have cracking caulk around the panels in your raised-panel door, you should scrape it off before repainting.
Remove the door handle to make painting easier. Prep the door for painting by sanding with 120 sandpaper. Start at the top and sand each segment of the door. If you're repainting over latex paint, sand very lightly, being too rough with the surface will cause the paint will curl up, not flake off. Brush or vacuum the dust off the door, use a tack cloth to thoroughly wipe the surface for the best finish. This is a particularly good idea if you're using an oil, alkyd or high-gloss paint because these will show any dust in the dried finish.
Start at the top when painting raised-panel doors and paint all of each part, i.e. all panels then all rails and then all stiles, before moving to the next. Work quickly to finish each part so the paint doesn't dry before you can do the adjoining parts.
Start with the panels then do the rails and small inner stiles together. Finish by painting the long, outer stiles. Along with the outer stiles also do the edge of the door. If you are only painting one side of the door, paint the edge that shows from the side when the door is open. For example, if you're painting the outside of a door that opens into a room, paint the edge with the hinges.
Brush the panels, pushing the paint into the corners and edges around the edge. Let the paint overlap onto the surrounding rails, stiles and the center of the panel. Next do the center of the panel, applying the paint with back and forth strokes to cover it completely and then smooth the coat out by stroking up and down with a semi-dry brush. Let the paint overlap along the edge and finish the panel by brushing along the border several times with a semi-dry brush to pick up all the excess paint. Runs will develop at the corners of the panels if all the excess paint is not removed.
Do all the panels and then go back to the top and paint the rails and short, center stiles. Blend these two parts together by painting the short stile first with vertical strokes smoothing out the lap marks from the panel while overlapping onto the rail. Paint the rail next with horizontal strokes and blend the lap marks from the stiles and panels into the horizontal strokes on the rail.
Move down the door painting these interior pieces until all the rails and small inner stiles are done. Return to the top and paint the edge and down the two side stiles to finish the door. Blend all the overlap-marks from the rails, panels and edge into the vertical strokes on the outer stiles.
Paint windows starting at the top, inner most parts, and work out. For the window pictured here that would be the mullion molding around the glass in the upper sash. From there work out to the sash frame, then the case molding and finally, the sill and apron.
Work each facet of the window, applying the paint first to completely coat it and then immediately brushing it out along lengthwise to smooth the coat. Let the paint from each part overlap onto the adjoining part a little and then paint it next. Blend the parts together like this, painting each to overlap onto the next and then brushing that section along its length.