How to Replace Caulking on the Outside of Your House

Caulk and other sealants safeguard your house against rain and snow at vulnerable points such as cracks and open joints, wherever flashing and other approaches can't do the job. Keep the weather outside where it belongs by making sure your exterior caulking stays in good shape.

Sealing joints around windows and doors

Scrape out old caulk using a painter's five-in-one tool, a stiff putty knife or another similar tool.

Use a putty knife to scrape off any caulk that remains on the surface or walls of the joint.

For very dry, stubborn caulk, use a caulk softening and removal chemical, such as 3M Caulk Remover, as directed by the manufacturer.

Allow the cleaned joint to dry for a day or more unless the product is approved for wet applications.

Press an open-cell foam backer rod into joints wider than 1/4 inch (6 mm) or deeper than 1/2 inch (12 mm) so the joint is about half as deep as it is wide. Never fill a deep joint. Doing so wastes caulk and makes a good, permanent bond less likely.

To avoid getting caulk on adjacent surfaces, apply painter's masking tape. While this may not be practical for large areas, it's an option for highly visible areas or for surfaces that caulk might ruin.

Cut about 3/8 inch (1 cm) off the caulking cartridge's nozzle at a 45-degree angle with a utility knife. The goal is to get a hole 3/16 inch (5 mm) across to produce a bead of that diameter.

Press the caulk into the joint, adjusting both the rate of application and the amount of pressure to apply enough caulk so you slightly overfill the joint. Some experts say it's better to push rather than pull, but you can achieve excellent results either way.

Smooth the joint with a wetted fingertip or smoothing tool.

Sealing joints in other locations

For masonry chimney and siding joints, always use backer rods and choose a caulk that is designed to adhere to masonry and that matches the color of the cement grout. Mask the chimney; caulk won't easily come off porous surfaces.

For horizontal joints between a house and concrete slabs, such as those in a patio, walk or driveway, always use a backer rod. Self-leveling polyurethane sealants, although very messy to work with, offer superior protection.

For joints between a foundation and the wall above it, use expanding foam. The gap here is often too difficult to access with the tip of a caulking tube. The foam expands to fill the gap and better seal against air infiltration and pests.

Caulking tips

If you plan to paint, use paintable caulk. Paint does not bond well to silicone caulk.

Caulk may not adhere to paint or stain that contains wax, stearate, silicone, or paraffin-based oil. Verify the compatibility of your caulk and paint.

Caulk bonds best when gaps are between 3/16 inch (5 mm) and 1/2 inch (12 mm) wide, when they are as half as deep as they are wide, and when the caulk adheres only to the joint walls (not to the bottom or rear surface).

Do not caulk the joints between aluminum or plastic siding and windows or doors. The channels provide the necessary seal.

Clear silicone caulk does not bond well with unfinished cedar siding, shingles and trim. Use a copolymer rubber-based clear sealant, such as Lexel (available from Sashco Sealants, www.sashcosealants.com).

The primary purpose of exterior caulk is to keep water out. Caulking for energy efficiency also requires that you seal wall penetrations indoors.

Caulking guns with a thumb-activated quick-release trigger are easier and less messy to use.

Caulking guns with an open frame are easier to keep clean than the partially enclosed type.

Ideally, the hole in the tip of the caulk tube should be as wide as the gap you're filling. A smaller hole is OK but slower; a larger one makes a mess.

Wrap the end of a partially used caulking tube in plastic and secure it with a rubber band to prevent caulk from drying out in the nozzle.

Things You Will Need

  • Caulk Softening And Removal Chemical
  • Expanding Foam
  • Open-cell Foam Backer Rod
  • Polyurethane Sealant
  • Painter's Masking Tape
  • Utility Knife
  • Exterior Caulk And Gun
  • Painter's Five-in-one Tool Or Stiff Putty Knife
  • Smoothing Tool


  • Most sealants don't bond to wet surfaces and bond better to primed wood than bare wood.
  • Keep paper towels and a wet cloth or sponge handy to clean your smoothing finger and wet it for the next task.
  • A finger is easy to use for smoothing and it's always handy. On rough or splintered surfaces, however, use an ice-pop stick, a caulk-smoothing tool, metal flashing or an old putty knife cut or ground to a suitable shape.
  • Seal any gaps between dissimilar materials (foundation and wall, chimney and siding) and along the perimeter of penetrations (wire, pipe, vent, fan, air conditioner, mail slot and so forth). Fill cracks in the exterior siding and trim.