The joints are where paint fails first
Walk around almost any house that needs repainting and look at where the damage starts. It's rarely the middle of a wall. It's at the joints: where trim meets siding, where boards butt end to end, around window and door heads, at corners and along the bottom of the walls. Those are the places water gets behind the paint, and once it's behind, the film lifts. That's why a lot of the work in an exterior repaint is sealing, not painting.
NOAA's Sioux City figures
NOAA's engineering weather data for Sioux City lists a 50-year basic wind speed of 90 mph (3-second gust at 33 feet), a 100-year rainfall rate of 3.8 inches per hour and about 73 freeze-thaw cycles in an average year. In an average year at Sioux City, NOAA counts about 354 hours with the wet-bulb temperature above 73°F and about 1,138 hours above 67°F. These come from the station that carries the city's name, as NOAA gives them.
The rainfall rate is a design figure for intense rain, the kind that drives water at every gap. The freeze-thaw count is the number of times, in an average year, that water caught in a joint can freeze and thaw. Together they explain why sealing gets so much attention.
What a sealing pass covers
Before finish coats, a painter should work around the house joint by joint:
- cut out caulk that has cracked, shrunk or pulled away, rather than smearing new over old;
- fill deep gaps with backer rod first, so the sealant isn't too thick to flex;
- prime bare wood at the joint before sealing, so the caulk has something to grip;
- run a neat bead that bridges the gap and bonds to both sides;
- tool it smooth so water runs off instead of sitting on a ledge.
Gaps that should stay open
Not every gap is a mistake. The bottom edge of lap siding, the small slots at window flanges, and weep holes in brick or trim are there so water can drain. Sealing them traps moisture behind the wall, which can push paint off from the inside. Ask the painter which gaps they plan to leave open, and why. A confident answer is a good sign.
Matching the sealant to the gap
Painter's caulk is fine for small, stable joints indoors. Outside, where joints move with heat, cold and moisture, a paintable exterior sealant rated for that movement lasts much longer. Around windows and doors, the sealant should be paintable and compatible with the frame material. Ask for the product names in the proposal, not just "caulk as needed."
Timing around damp hours
Sealants and paints both need a dry surface and a chance to set up. Wet-bulb temperature combines heat and moisture, so the Sioux City hour counts above describe warm, damp hours. On days like that, dew can linger on north walls and shaded trim well into the morning, and a bead laid on a damp joint may not bond. A careful crew waits for surfaces to dry, gives sealant the time its label asks before painting over it, and plans the shaded sides for later in the day.
Water that isn't from rain
Some paint failures come from inside the house. Moist air from a bathroom without a working fan, a laundry room or a crawl space can work outward through a wall and blister paint from behind. If peeling keeps returning on one wall, especially above a bathroom or kitchen, that's worth raising. Paint can't fix a moisture source, but the right painter will point it out.
How Iowa's rule describes the trade
The Iowa rule that defines construction for contractor registration (871 IAC 23.82, used by Iowa Code 91C.1) lists painting and wall covering contractors, including house painting, as construction. That definition is quoted as the rule words it.
Questions for an exterior proposal
- Which joints will be cut out and resealed, and which only touched up?
- Which sealant and which paint, by name?
- Which gaps will be left open to drain?
- How will you handle a wall that's still damp in the morning?
Our exterior painting page explains the rest of an outside job, and the surface preparation guide covers priming and repairs.