How to Caulk a Window Inside

Caulking the inside of a window seals the gap between the window trim and the wall, stops interior drafts, and gives the window a clean finished look. It's a different job from exterior caulking — here's how to do it right.

Why Caulk the Inside of a Window?

• Seals the gap between window trim (casing) and the drywall or plaster
• Stops cold air that has infiltrated the wall cavity from entering the room
• Creates a clean, finished appearance before painting
• Prevents insects from entering through gaps in the trim

Interior vs. Exterior Caulk: Key Difference

Interior window caulking uses paintable latex or siliconized latex caulk — not pure silicone. Pure silicone can't be painted, which is fine for exterior joints but not for interior trim that you want to paint over. Siliconized latex gives you the flexibility of silicone with the paintability of latex.

What You'll Need

• Paintable latex or siliconized latex caulk (white)
• Caulk gun
• Painter's tape
• Damp cloth
• Rubbing alcohol

• Bates Caulking Gun 10:1 No Drip — smooth, controlled application; no-drip mechanism prevents mess on interior surfaces
• Caulking Tool 5-in-1 Silicone Finishing Kit — finishing pads for smoothing interior caulk beads cleanly

Step 1: Identify the Gaps

Look at the joint between the window trim (casing) and the wall. There's often a gap of 1/8"–1/4" that needs filling. Also check the joint between the window sill and the wall below it.

Step 2: Clean the Surface

Wipe the joint area with rubbing alcohol and let dry. Remove any dust, paint chips, or old caulk residue.

Step 3: Apply Painter's Tape

Apply tape on both sides of the joint — on the trim and on the wall. This is especially important on interior work where you want clean lines against painted surfaces.

Step 4: Apply the Caulk

Cut the nozzle small (1/8"–3/16") — interior gaps are usually smaller than exterior ones. Apply a thin, continuous bead along the joint. For very small gaps, a tiny bead is all you need.

Step 5: Smooth with a Damp Finger

Smooth the bead immediately with a damp finger. For latex caulk, plain water works perfectly. Wipe excess caulk off your finger with a damp cloth as you go.

Step 6: Remove Tape and Clean Up

Remove painter's tape while the caulk is still wet. Wipe any smears immediately with a damp cloth — latex caulk cleans up easily with water when wet but is much harder to remove when dry.

Step 7: Paint Over When Dry

Latex caulk is paintable in 1–2 hours. Paint over it to match the trim or wall color for a seamless finish.

Interior Caulking Locations Around a Window

• Trim-to-wall joint on all four sides
• Window sill-to-wall joint
• Any gaps in the trim miters at corners
• Gap between the window frame and the trim (if visible)