A working season with edges
Paint goes on in minutes, but it takes days to become the tough film you are paying for. Outdoors, that film forms properly only when the air and the surface are warm enough, dry enough and not too hot. So an exterior repaint in Iowa City has a working season with edges at both ends, and much of the planning on a good job is about staying inside them rather than pushing past them to fill a calendar.
The Iowa City station's own figures
NOAA's current climate normals for the Iowa City station average 129.9 days a year with a low at or below 32°F, including 10.3 days with a low at or below 0°F. The same Iowa City normals average 24.2 days a year with a high of 90°F or more. Those are the station's figures as NOAA publishes them. This page doesn't turn them into dates or forecasts.
The humidity figures come from a different station. In an average year at Cedar Rapids, NOAA counts about 355 hours with the wet-bulb temperature above 73°F and about 1,124 hours above 67°F. Those are Cedar Rapids counts, not readings taken in Iowa City.
The cold edge
Most exterior paints and caulks print a minimum application temperature on the label, and many also want the air to stay above a floor overnight while the coat cures. A day whose low drops to freezing can spoil a coat applied that afternoon. The film may not knit together properly, and dew or frost settling on a surface that is still soft can leave it blotchy or weak. With 129.9 such days in the Iowa City normals, a careful painter keeps the outside of the house to the stretch when nights stay mild.
Ask which product is going on and what its label says about the lowest air and surface temperature. A good answer names the product and quotes the label, not "it'll be fine."
The hot edge
Heat brings different faults. On a sunny wall in a hot afternoon, paint can skin over before it levels, leaving lap marks where one pass dried before the next joined it. Siding in full sun can run much hotter than the air around it, and a coat rolled onto it may blister or flash. The usual answer is to follow the shade: begin on walls the sun has already left, and come back to the sunny ones once it moves on. A crew that plans its day around the sun has usually learned that lesson on a past job.
Damp air and drying
Wet-bulb temperature reflects heat and moisture in the air together, so those Cedar Rapids hour counts describe warm, damp hours. Water-based paint dries by giving its water up to the air, and damp air takes it back slowly. A coat that feels dry to the touch may still be soft underneath and not ready for the next one. On damp days a patient painter leaves extra time between coats, waits for morning dew to burn off before starting, and stops early enough that the last coat isn't still wet when evening dew settles.
Order of work on the outside
A sound exterior job usually runs in this order:
- wash the walls and let them dry fully;
- scrape loose paint back to a firm edge and sand the edges smooth;
- replace or repair soft trim before any primer goes on;
- spot-prime bare wood and repairs;
- caulk open joints once the primer allows it;
- apply the finish coats, top to bottom, following the shade.
Every step needs dry wood and suitable weather, which is why the season's edges matter so much. Our exterior painting page goes through each step in more depth.
What the schedule in a proposal should say
A written proposal for outside work should say more than a start date. Look for the surfaces to be painted and the preparation for each, the products by name and the number of coats, what happens if cold, heat or rain interrupts the job, and how long the crew waits after rain before painting a wall. A painter who writes those down is telling you how they handle the weather, not just promising to show up.
Iowa's registration rule
Iowa requires construction contractors who earn at least $2,000 a year from construction to register with the Department of Inspections, Appeals, and Licensing, and the department lists painters among the trades that must register. That is the rule as the department states it, and it's printed with its source below.