Water is the variable to manage
Paint can fail from sun, from movement, from bad prep. In Brownsville, the variable most worth managing is water: in the air, on the surface in the morning, inside the wood and behind the film. The U.S. Department of Energy's Building America climate guide places Cameron County in the hot-humid climate region and IECC climate zone 2A, and the station figures below show what that looks like in hours.
What NOAA's Brownsville data shows
In an average year at Brownsville, NOAA counts about 3,783 hours with the wet-bulb temperature above 73°F and about 5,605 hours above 67°F. NOAA's engineering weather data for Brownsville also lists a 50-year basic wind speed of 130 mph (3-second gust at 33 feet), a 100-year rainfall rate of 4.5 inches per hour and about 1 freeze-thaw cycles in an average year. The wind and rainfall values are design figures for rare events. The humidity counts and the near-absence of freeze-thaw cycles are the parts that shape ordinary painting decisions: moisture is the steady pressure, and frost hardly enters into it.
Clean, kill, rinse, dry
Mildew and algae grow on damp, shaded paint, and new paint over them grows them back. Before any exterior coat:
- Wash with a mildewcide cleaner or the cleaner the paint maker names, then rinse thoroughly.
- Give the surface time to dry. Wood that has been washed can need far longer to dry out than it looks; a crew can check with a moisture meter against the label's limit.
- Trim back plants touching the walls, and fix gutters or sprinklers that keep a wall wet.
Inside, the same logic applies to bathroom ceilings, laundry rooms and closets on outside walls. Clean off any growth, dry the room out, and use a primer and paint suited to damp rooms.
Coatings that let moisture out
A paint film that traps water inside the wall will blister and peel. Breathable exterior acrylics allow vapor to pass, and many are sold with mildew-resistant additives. Thick elastomeric coatings can be useful on masonry and stucco but need a dry, sound surface; they're less forgiving on wood. Ask your painter why they've chosen a product for each surface. Our exterior painting page and the paint sheens and finishes guide explain the trade-offs.
Metal needs its own system
Steel railings, gates, security bars and light fixtures rust where the paint is broken. Repainting metal means:
- Removing loose rust and paint with a wire brush, scraper or sanding.
- Priming bare spots with a rust-inhibiting primer the same day, before flash rust starts.
- Topcoating with a paint made for metal.
Aluminum and galvanized steel need primers made for those surfaces; ordinary primer won't hold.
Timing coats around dew
Even on a dry day, surfaces can be wet early and late. Paint goes on after dew has dried and needs to set before it returns. Recoat times on the label lengthen in humid air. Ask the painter what hours they'll paint and how they'll check that the surface is dry before each coat.
Caulk for heavy rain
Heavy rain finds every open joint. Seal gaps at trim, windows, doors and penetrations with a paintable exterior sealant, and prime bare end grain. Leave weep holes and the bottom edges of lap siding open so water can drain out.
Inside the house
Air conditioning keeps indoor air drier, which helps paint dry and cure. Paint with the system running when you can, ventilate bathrooms and kitchens, and allow extra time before closing doors and windows on fresh trim. The interior painting page covers interior work room by room.
Questions for the painter
- How will you treat mildew, and how long will you let surfaces dry?
- Which primer and topcoat, and why for this surface?
- How will you prepare and prime metal?
- What will you caulk, and what will you leave open?
The pricing guide explains how these choices affect the price.