Exterior paint in the St. Croix Valley has a tough job. It bakes in July sun, gets soaked by spring rain and thunderstorms, and then spends months going through freeze-thaw cycles, snow and dry winter wind. A good exterior job here is about three things: preparing the surface so paint can grip, choosing products that flex and breathe, and painting when the weather actually allows paint to cure.
When to paint: the real limits
Our practical exterior season runs roughly from late spring through early fall. The calendar isn't the real rule, though. These are:
Temperature
Every exterior paint has a minimum application temperature on the label, and it applies to both the air and the surface. Many modern acrylic exterior paints allow application at lower temperatures than older products, but the temperature also has to stay above that minimum through the night while the paint starts to cure. A sunny 55°F afternoon followed by a 35°F night is a problem for many products.
Dew point and morning dew
If a surface is close to the dew point, moisture condenses on it. Paint applied to a damp surface, or paint that gets dew on it before it sets, can lose adhesion or develop surfactant leaching (sticky tan or brown streaks). In spring and fall, siding often stays wet until late morning and gets dewy again by evening, which shrinks the daily painting window. Many professionals wait for the surface to dry and stop early enough for the paint to set before the evening dew.
Sun and heat
Painting in direct hot sun makes paint dry too fast, which causes lap marks and poor adhesion. Pros "follow the shade," painting each side of the house after the sun has moved off it.
Rain and wind
Check the label for how long the paint needs before rain. Wind blows dust and debris into wet paint and speeds drying too much.
Wood moisture
Wood siding that has been soaked by rain needs time to dry before painting. A moisture meter takes the guesswork out of this.
Prep: what makes exterior paint last
Inspect first
Walk the house and note peeling areas, bare wood, rot, mildew, failed caulk and areas where water is getting behind the siding. Peeling in one area often points to a moisture problem: a missing gutter, a bathroom without ventilation, an ice dam or a downspout splashing onto the siding. Fix the cause first or the new paint will peel the same way.
Check for lead
Homes built before 1978 may have lead paint on siding, trim, windows and porches. Scraping and sanding it creates hazardous dust and chips. In Wisconsin, paid work that disturbs paint in pre-1978 homes must be done by certified lead-safe companies under the state's program. Read our lead-safe renovation guide before any scraping.
Clean
Siding collects dirt, chalk, pollen and mildew that paint won't stick to. Wash with a suitable cleaner and a soft brush or a low-pressure rinse. High-pressure washing can force water into siding and damage soft wood. Treat mildew with a mildew cleaner and rinse well. Let everything dry.
Scrape, sand and repair
Remove all loose and peeling paint. Feather sand the edges so they don't show through. Replace rotted boards or repair them with a two-part epoxy wood filler. Set popped nails and spot-prime them.
Prime
Prime bare wood, repairs and stains. Cedar and redwood contain tannins that bleed through latex paint as brown stains; use a stain-blocking exterior primer suited to those woods. Prime bare metal with a rust-inhibiting primer.
Caulk
Re-caulk gaps at trim joints, around windows and doors and where siding meets trim, using a high-quality exterior paintable sealant. Don't caulk the bottom edges of lap siding boards; those gaps let moisture escape.
Exterior painting step by step
- Inspect the house and fix moisture sources like gutters, downspouts and leaks.
- Test for lead on pre-1978 homes and set up lead-safe containment if needed.
- Wash the siding and trim, treat mildew, and let everything dry thoroughly.
- Scrape loose paint, sand edges smooth, and repair or replace damaged wood.
- Spot-prime bare wood, repairs, knots and stains with the right exterior primer.
- Caulk open joints at trim, windows and doors, leaving lap siding drip edges open.
- Paint the body of the house top to bottom, following the shade around the house.
- Apply a second coat after the recoat time on the label.
- Paint trim, doors and accents last.
- Clean up, remove containment carefully, and walk the house to touch up misses.
Choosing exterior products
Most exterior repaints today use 100% acrylic latex paint, which stays flexible, breathes and resists UV. Oil-based paints are still used on some metal and specialty surfaces, but they get brittle over time and can crack on wood that expands and contracts. Higher-quality paints generally contain more solids and better resins, giving better coverage and longer life.
Sheen for exteriors: flat or low-sheen finishes hide surface imperfections on siding; satin is common for siding and is easier to wash; semi-gloss or gloss is typical for trim, doors and shutters.
Color and heat: very dark colors absorb more heat. Some vinyl siding manufacturers restrict dark colors because heat can warp the siding, though some paint brands offer special heat-reflective formulas for vinyl. Check the siding manufacturer's guidance before choosing a dark color for vinyl.
Decks, porches and other surfaces
Horizontal surfaces take the most abuse. Painted porch floors need a porch and floor enamel; decks are usually better served with a penetrating stain, which wears away rather than peeling. Railings and stairs need regular maintenance. Fiber-cement siding usually comes factory-primed and takes acrylic paint well. Stucco and masonry need breathable masonry coatings.
How long should exterior paint last?
There's no single answer. Prep quality, paint quality, the substrate, sun exposure and how well the house sheds water all make a huge difference. South and west walls usually wear fastest because of sun. Washing the house regularly and touching up small failures early extends the life of a paint job considerably.