Caulking and sealing in Tacoma to keep rain out of your walls

Most exterior joints that face the weather should be sealed: where vertical trim meets siding, around the sides and tops of window and door casings, at corner boards, along the joints in fascia, and around penetrations like hose bibs, dryer vents, electrical boxes and light fixtures. These are the places where wind-driven rain gets into a wall. On fiber cement siding, the joints at trim and openings are usually caulked, while butt joints between planks depend on the installation method and flashing behind them.

Some gaps should stay open. The bottom edge of lap siding, where one board overlaps the next, lets water that gets behind the siding drain out. Caulking those horizontal laps traps moisture and can cause rot. Weep holes at the bottom of window frames and in brick also need to stay clear. The underside of some window head flashing should be left open for drainage. Knowing the difference is a big part of this work. Our siding painting jobs always include checking these drainage paths.

Putting new caulk over old, cracked caulk is a common shortcut, and it rarely lasts. The new bead sticks to the failing caulk underneath instead of to the wood, siding or window frame, and when the old layer lets go, the new one goes with it. We cut out old caulk with knives and scrapers, clean the joint of dirt, mildew and loose paint, and let it dry fully. In Tacoma's damp months, that drying step can take time, especially on shaded walls.

Joint shape matters too. A good caulk joint sticks to two sides, not three, so it can stretch as the materials around it move. In deep or wide gaps, we push in a foam backer rod first, which controls the depth of the bead and keeps the caulk from bonding to the back of the joint. Very wide gaps, often from shrinking trim or old rot, may need repair first. Our wood rot repair work handles those before the joint is sealed.

Not every caulk belongs outside. Cheap acrylic caulk shrinks, cracks and loses flexibility fast in weather. For exterior joints, we use high-performance sealants that stay flexible through temperature swings, stick well to wood, fiber cement and metal, and accept paint. Many can be applied in cooler temperatures and handle light moisture better than standard caulk, which helps in shoulder seasons. For joints that will not be painted, like around some vinyl windows, we choose color-matched sealants.

Pure silicone caulk is great in some places, like bathroom fixtures, but most kinds cannot be painted, so we rarely use it on painted exteriors. Older homes built before 1978 may have lead paint along the trim edges where caulk is being removed. On those homes, cutting and scraping use lead-safe methods, with ground plastic and careful cleanup. Homes near salt air in Ruston and Dash Point need sealants that hold up to the extra exposure, and we check those joints more often.