Caulk and Paint: Which Joints to Seal, Which Caulk to Use, and When to Leave a Gap Open

Caulk is the cheapest part of a paint job and one of the most important: outside it keeps rain out of joints, and inside it closes the gaps that make trim look unfinished. Failed caulk is behind much of the peeling and rot we find on Matthews houses.

Choose a Paintable Sealant

Use a paintable sealant rated for the job: an interior acrylic or acrylic-latex caulk for trim gaps inside, and a high-performance exterior sealant for siding, windows and doors. Pure silicone is not paintable and belongs in tubs and showers, not on trim you plan to paint. Check the label for movement rating, exterior use and the time before it can be painted.

Where to Caulk Outside

• Window and door casings where they meet siding
• Corner boards and trim against siding
• Joints in trim boards (miters and butt joints)
• Around penetrations: hose bibs, lights, vents
• Nail holes on trim (or fill them with exterior filler)

Where Not to Caulk Outside

• The bottom edge of lap siding: water behind the siding needs to drain out.
• Weep holes in brick and drainage gaps above flashing.
• Gaps the siding maker says to leave open or flash instead.

Sealing those traps water inside the wall.

Where to Caulk Inside

• Where baseboards meet the wall
• Door and window casings against the wall
• Crown molding gaps
• Small corner cracks that are not structural

Not between baseboard and floor if the floor needs to move, and not as a fix for wide cracks that keep growing.

Old Caulk

Cracked, shrunken or peeling caulk should be cut out, not caulked over. New caulk needs a clean, dry joint and the right bead size. Very wide gaps get a foam backer rod first.

Frequently Asked Questions

How long before I can paint over caulk?

It depends on the product; many acrylic caulks can be painted within an hour or a few hours. Follow the label.

Why did my caulk crack after painting?

It was painted before it cured, the joint moved more than the caulk is rated for, or the bead was too thin.

Should I caulk the bottom of my siding?

No. Lap siding needs to drain at the bottom edge.

Is silicone caulk paintable?

Pure silicone is not. Use a paintable sealant on anything you will paint.

Caulk Is in Our Scope

Every exterior quote we write lists recaulking. See exterior painting or contact us.