How to Paint Interior Window or Door Case Moldings

Painting interior window trim

The Spruce / Margot Cavin

Project Overview
  • Working Time: 1 - 2 hrs
  • Total Time: 1 - 2 days
  • Yield: One window or door case molding
  • Skill Level: Beginner
  • Estimated Cost: $20 to $50

Painting interior trim moldings is one secret to freshening up a room with little cost or effort. There are two main reasons why you may want to paint your interior trim—the first is existing trim that has become beaten-up, dinged, and discolored over the years. The other common scenario is that you have installed trim that is primed but unpainted and is in need of the finishing coat. In either case, the painting process requires about the same amount of work. Along with baseboards, the outer trim moldings of a window or door—called case moldings—are very often painted.

What Is Case Molding?

Case molding is a particular type of trim molding that fits flat against the wall to "encase" a window or door unit and hide the joints where the unit meets the wall. Case moldings come in many styles, but many are simple one-piece ranch or colonial moldings that are 2 to 3 inches wide, mitered at the corners of the window or door. Case moldings are often stained and varnished, but they are also often painted, sometimes to blend in with the wall, other times to offer a contrasting color. Case moldings are usually finished to match the baseboards and other wood trim within a room.

Before Getting Started

Repainting case moldings that were already previously painted is a fairly easy job that involves light patching and perhaps some light sanding before applying a fresh coat of paint. It becomes a little more involved if you are applying paint for the first time to trim that has a stained and varnished finish. It's entirely possible to paint varnished wood trim, but it's important to first thoroughly clean and sand the woodwork to scuff the gloss that can prevent paint from adhering. And when painting varnished wood, applying a good primer is a must—you can often omit this step when you are repainting trim that already has a paint finish.

Wood trim is usually fairly easy to paint, but remember that not all window and door trim is made of wood. If you have vinyl or polystyrene case moldings around your windows or doors, mention this fact when purchasing the primer and paint. And remember that if your windows or doors themselves have vinyl sashes or inner frames, the manufacturer may caution against painting these inner moldings. It's usually still fine to paint the outer case moldings, but inner window or door frames made of vinyl usually are not meant to be painted. The reason? Vinyl expands and contracts quite a bit in response to weather changes, and paint may interfere with the weather-proofing of the unit. If you do choose to paint the inner frames of vinyl windows or doors, consult a painting specialist for recommendations on what type of paint to use.

What Is Cutting-In?

Achieving professional-quality sharp edges when painting along the edges of wood trim (called "cutting in") is often done with the assistance of painter's tape to mask off the edges where casing trim meets the walls or inner frames. At least, this is a common method used by amateurs. But professional painters—and many experienced amateurs—often do this work by free-handing, omitting the taping process entirely. In the hands of a skilled painter equipped with an excellent angled trim brush, cutting in by hand may produce better results than masking. The choice is up to you, but when you first learn to paint wood trim, it's probably best to mask the edges using painter's tape.

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Supplies needed to paint interior window trim
The Spruce / Margot Cavin

What You'll Need

Equipment / Tools

  • Scrubbing sponge
  • 1 2-inch trim paintbrush
  • Scissors
  • Putty knife (if needed)
  • Utility knife (if needed)

Materials

  • Drop cloth
  • 1 1/2-inch painter's tape
  • Wood filler (if needed)
  • 120- and 220-grit sandpaper
  • Primer
  • Interior trim paint, gloss or semi-gloss
  • Clean cloth or tack rag

Instructions

  1. Mask Off the Trim


    Cover the floor beneath the window or door with a drop cloth. Then, use painter's tape to mask the case molding on both edges—the junction with the inner window or door frame as well as with the surrounding wall. It works best to cut the ends of the tape at 45-degree angles and to overlap the ends of both pieces. Where possible, try to use a single long piece of tape to cover these edges.

    Tape one side of interior trim
    The Spruce / Margot Cavin
    Tape right side of trim interior
    The Spruce / Margot Cavin
  2. Clean the Woodwork

    Use a damp sponge and clear water to scrub dirt from the trim. A coarse scrubbing sponge can be useful here if the trim is very grimy. But do not use detergents, which can leave residue that will interfere with the paint bond.

  3. Repair Damage to Trim

    If there are nail holes, gouges, splinters, or other damage to your moldings, fill these areas by applying wood filler with a putty knife. Make the repair as flush as possible to the surrounding trim. Let the wood filler dry completely before moving on to sanding. (Large repair areas may need to dry overnight.)

    Tip

    Very small holes can be filled with lightweight spackling compound rather than wood filler. Spackling compound usually dries in a matter of an hour or so, but it is not suitable for filling large gaps.

    Fill in window trim holes
    The Spruce / Margot Cavin
    2:51

    Watch Now: How to Fill Nail Holes in Trim

  4. Sand the Trim

    Use sandpaper to smooth out repair areas and to lightly scuff the surface of the trim molding. Giving the surface some "tooth" will help the primer and paint adhere.

    A good sanding is especially important if you are painting varnished wood. Here, begin with 80- or 120-grit sandpaper, then move to a 220-grit paper for final sanding. With previously painted wood, a light sanding pass with 220-grit paper is usually sufficient.

    After sanding, wipe the trim and surrounding walls free of dust with a clean dry cloth or tack cloth.

  5. Prime the Trim (Optional)

    Applying a paint primer is not always necessary, but it is a good idea if you are painting wood that was varnished, or if you are applying latex paint over a previous coat of oil-based paint. But if you are painting trim moldings that have already been painted with latex paint (which is often the case), then primer is usually not necessary.

    Primer application is done exactly like standard paint application. The choice of what type of brush to use is yours, but most people find that a 1- to 2-inch nylon/polyester trim brush, either square cut or angled, works well for painting window and door case moldings. Square-cut brushes tend to paint faster, but angle brushes can be more precise and are a good choice for more intricate moldings, or where you are applying paint right up to a glass edge.

    The best technique for most people is to hold the brush like a pencil or pen, applying the paint with long, slow strokes. Always "keep a wet edge" by drawing the brush from wet to dry areas. This prevents you from applying paint over areas that have just dried, which can leave lap marks. And you should paint relatively quickly, which also prevents lap marks.

    Allow the primer to dry completely before moving to the next step. Depending on weather conditions, this can require as little as an hour or as much as several hours.

    Paint window trim that faces room
    The Spruce / Margot Cavin
  6. Apply First Coat of Paint

    After the primer dries, apply the first coat of paint, using the same technique used for priming. Most people find it best to begin with the inner portion of the molding, painting all around the portion of the molding that is nearest the window or door unit.

    Next, paint delicate outer edges that adjoin the wall surfaces. Because you've got painter's tape applied, you can run the brush right over the tape (just don't go beyond it). Be careful not to slop too much paint over the tape. Otherwise, the dried paint will not separate easily when it's time to remove the tape.

    Conclude by painting the wider surfaces that face the interior of the room. Allow the paint to dry completely (one hour to overnight, depending on conditions).

  7. Apply Second Coat (If Needed)

    After the first coat of paint has dried, inspect the coverage to make sure the first coat has adequately covered the moldings. Where necessary, you can now apply a second coat of paint.

    When painting with a glossy paint (standard when painting wood trim), some professionals like to very lightly sand the first coat, which provides some "tooth" that helps the second coat adhere. If you do this, make sure not to over-sand, and make sure to wipe the molding free of dust before applying the second coat.

  8. Remove the Painter's Tape

    Let the paint thoroughly dry. Remove the painter's tape only after the paint is dry. Do not try to remove the tape while wet. But it's also not wise to allow the paint to fully cure and harden before removing the tape, as sometimes the dried paint will peel away from the molding. Some tape manufacturers recommend waiting until the paint is fully dry to the touch, but no more than about 24 hours, before removing the painter's tape.

    Peel the tape away in a smooth, constant motion. The tape is strong enough to slice through one or even two layers of paint (beyond that, the tape itself might tear). If the tape does not cleanly cut through the paint, use a sharp utility knife to slice the paint film before pulling off the tape.

    Remove painter's tape from window trim
    The Spruce / Margot Cavin

Painting Trim Before Installation

When installing new trim around a door or window, you'll have the option of either painting the pieces first—placed on drop cloths or laid over sawhorses—or waiting until after you've cut and nailed up the trim pieces. Pre-painting is often the approach of professional trim carpenters.

But even in the hands of a skilled professional, there will always be some touch-up work required after the primed and painted trim pieces are nailed into place. Nail holes will need to be filled, sanded, and painted. And some scuffing and marring are almost inevitable during installation. Still, pre-painting can be a time saver if you are trimming out many doors and windows at the same time.

But if you are installing trim for a single window and door, pre-painting doesn't really save you that much time. As a compromise position, you might consider priming the pieces before installation but wait for the final painting until after the trim moldings have been nailed into place.

Article Sources
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  1. How to Paint Interior Trim. Sherman Williams.