How to Apply Caulking for HardiePlank Before Repainting

Rinse the siding off, using a garden hose with a spray nozzle set to a light spray. Aim at the top of the house and allow the water to roll down the wall and avoid pressure washers. Pointing up at the siding or using high-pressure spray can force water behind the siding, causing moisture damage, while pressure washers may also damage the siding.

Fill a large bucket with tap water. Add a squirt of dish detergent or all-purpose household cleaner. Substitute bleach, at a ratio of one part bleach to three parts water maximum, for the cleaner if mold, mildew or stubborn stains are present. Bleach is a harsh cleanser and may remove any natural mildicides (factory added mold and mildew cleaners).

Scrub the siding with a cloth, sponge or car wash brush, dipping into the cleaning solution and spreading generously. Work from the top of the house, down. Allow the cleaning solution to remain on the surface at least 15 or 20 minutes. Mix more cleaning solution as needed.

Rinse the siding completely, again aiming the spray down and working from the top of the house downward. Scrub at persistent spots as you rinse, following with another squirt of water to complete. Air dry the siding for two or three days to ensure all moisture has evaporated.

Dig the old caulk out of every seam using a stiff putty knife or even a utility knife. Look underneath the bottom edge of the siding, especially around doors and windows, along with vertical seams between the siding and corners or edge trim. Anywhere the siding adjoins another surface material, you will find caulking.

Load a caulk gun with a tube of exterior-grade permanently flexible caulk suitable for HardiePlank and the trim surfaces. Twist the tube in place to lock inside the caulk gun. Cut the tube's tip at a 45-degree angle, about 1/2 inch from the tip, for proper installation.

Line both sides of visible seams around windows and doors with masking tape to guide the caulking. Leave about a 1/16-inch-gap where the caulk will go; this provides a neat appearance when complete.

Squeeze a bead of caulk into each seam on your exterior wall. Concentrate on filling the opening gap, not necessarily the cavity; caulk expands slightly and will fill the cavity easily.

Wipe away any excess caulk as you work, using a damp, soft cloth. Remove the tape when finished. Allow the caulking to dry 24 to 48 hours before painting over it.