NOAA's Portland figures, as published
NOAA's engineering weather data for Portland lists a 50-year basic wind speed of 110 mph (3-second gust at 33 feet), a 100-year rainfall rate of 2.3 inches per hour and about 78 freeze-thaw cycles in an average year. The same data counts, in an average year at Portland, about 74 hours with the wet-bulb temperature above 73°F and about 495 hours above 67°F.
These are station figures, not readings from your street, and they describe the weather, not your house. Below is how each one bears on a painted exterior.
The freeze-thaw count and a paint film
About 78 times in an average year, the air at the Portland station crosses the freezing point. A sound paint film shrugs that off. A cracked one doesn't: water creeps into the crack, freezes, widens it, thaws and creeps further. Over time that's how a hairline break at a board end turns into a flake, then a bare patch. On an exterior repaint, that is where the money goes first:
- board ends and butt joints, where cracks start;
- window sills and the bottom rail of each sash, which hold standing water;
- the lowest course of siding, which takes splash and snowmelt;
- trim that meets a roof, deck or step.
Wind, rain rate and the seams of the house
The 50-year basic wind speed and the 100-year rainfall rate are design figures for rare events. They aren't forecasts. For a painter, they're a reminder that wind-driven water reaches places a gentle shower doesn't, so the seams of the house matter as much as the faces of the boards. Ask the painter how they'll treat:
- vertical joints between trim and siding, which usually get caulked;
- the gap under each lap of clapboard, which usually stays open so the wall can drain;
- nail heads that have rusted or popped;
- any split board that can't hold paint.
The wet-bulb hours
The wet-bulb temperature combines heat and moisture in the air. NOAA's count of about 495 hours above 67°F at Portland is a measure of muggy hours in an average year. Humid air slows how fast water-based paint gives up its water, and evening dew can settle on a coat that hasn't set yet. That's why a careful crew watches the clock in late afternoon and may stop earlier than you expect. Ask how they decide when the last coat of the day goes on.
Wood, shingles and trim
Painted clapboard, stained or painted shingles and trim all age differently. Shingles that were stained may not take paint well without preparation, and a switch from stain to paint is hard to undo. Trim usually carries a glossier finish than the body, which sheds water and cleans more easily; the sheen guide explains the trade-offs. If a deck or fence is part of the plan, the staining page covers it.
What the Maine Attorney General says
The Maine Attorney General says Maine does not license or regulate home contractors. That puts the weight on what you and the painter write down. Get the scope, the products, the number of coats and the preparation in writing before work starts.
Questions for an exterior bid
- Which areas will you scrape, and how far?
- Which joints will you caulk, and which will you leave open?
- What primer goes on bare wood, and on any repaired boards?
- What happens to the schedule if rain or dew comes in?
- How will you protect plantings, walkways and windows?
- Is cleanup of chips and debris included each day?
The exterior painting page has more on washing, scraping and priming.