Why exterior paint peels on New England houses, and the fix

Is peeling paint a paint problem or a moisture problem?

In most cases it is moisture. Paint fails where water gets between the film and the wood, swells the fibers and pushes the coating off. That is why peeling tends to show up in patterns: under windows, on the lower courses of a wall, beneath a bathroom, along the bottom of trim boards, or below a gutter that overflows. Paint that peels evenly across a whole sunny wall points more to age, poor prep or incompatible layers.

Looking at where and how the paint is failing tells you most of the story. Blisters that hold water, or peel down to bare wood, usually mean moisture from behind. Peeling between layers, where a newer coat lifts off an older one and leaves the old paint intact, points to adhesion problems such as latex over glossy oil or paint applied over chalk, dirt or salt film.

How does moisture from inside the house reach the siding?

Warm indoor air carries a lot of water vapor in winter. Showers, cooking, laundry, plants and people all add to it. In the older two-families and triple-deckers of Wollaston, North Quincy and Quincy Point, most built between about 1900 and 1930, there is rarely a vapor barrier, and many walls had insulation blown in years later. Vapor drifts outward, cools inside the wall and condenses on the back of the clapboards. When spring sun hits the wall, that water tries to escape through the paint and lifts it.

The signs are easy to spot once you know them: peeling clustered on the outside wall of a bathroom or kitchen, blisters that show bare wood, and siding that stays dark after rain. The fixes start inside. Bath and kitchen fans that vent outdoors, a working dryer vent and dehumidifying a damp basement all cut the load. On the outside, small siding vents or wedges can let some walls breathe.

What role do ice dams, gutters and caulk play on a Massachusetts house?

Eastern Massachusetts winters bring freeze-thaw cycles and, after a heavy snow, ice dams. Snow melts on a warm roof, refreezes at the cold eave and backs water up under the shingles. That water often runs down inside the wall cavity or behind the fascia, then shows up in spring as peeling along the top of the wall, on the soffits and around upper windows. Older capes in South and West Quincy with little attic insulation are classic ice dam houses. Clogged or sagging gutters do the same damage in every season, spilling water down the face of the siding.

Caulk is the smaller detail that fails most often. Joints where trim meets siding, the tops of window casings and the seams around corner boards open as the wood moves. Once a joint cracks, rain gets in on every storm, and a nor'easter drives it in sideways. The paint below starts to bubble. A repaint that does not rake out failed caulk and seal those joints with a quality elastomeric sealant is only painting over the leak.

• Peeling at the top of walls and soffits: look at ice dams and roof edges
• Streaks and peeling below one section: check that gutter run
• Failure at trim joints and window heads: open or missing caulk
• Soft wood under the peel: rot that needs repair before paint

What is alligatoring, and why do old oil layers cause trouble?

Many older houses carry decades of paint, and the bottom layers are often oil-based. As oil paint ages it keeps hardening and becomes brittle. Eventually it cracks into a scaly pattern that looks like alligator hide, and every new coat of flexible latex on top of it gets pulled apart as the old film breaks underneath. Painting over alligatored paint only buys a year or two before the new coat peels with it. We see it most on the sunny south walls and porch columns of century-old Quincy houses.

The fix is removal of the cracked layers on the affected surfaces, not more paint. That might mean thorough scraping and sanding, using an infrared paint removal tool at controlled temperatures, or replacing badly failed boards. Since most of these houses predate 1978, the old layers are presumed to contain lead paint, and the work calls for lead-safe practices: ground containment, misting, HEPA vacuuming and a careful daily cleanup.

How does a proper repaint fix the cause instead of the symptom?

A lasting exterior repaint follows a set order. First, find and fix the water source: clear gutters, have the owner's roofer repair flashing and roof edges where needed, vent the bathroom, replace rotted sills and trim. Next, wash the house to remove dirt, chalk and mildew, plus salt film on houses near Quincy Bay, then let the wood dry. Then scrape every loose edge, feather-sand the transitions so they do not show through, and remove alligatored areas.

Bare wood gets a primer matched to the surface, often an oil or alkyd primer on old weathered clapboard and a stain-blocking primer on cedar. Joints get fresh caulk. Two coats of a quality exterior acrylic finish the system. Timing matters too: paint on dry wood, after the morning dew has burned off, with temperatures inside the product's range and no rain expected before it sets.

When should a peeling Quincy house be repainted, and what does it cost?

In eastern Massachusetts the practical season for exterior painting runs roughly May through October. Late spring and September are often ideal, with milder days and lower humidity. Peeling that exposes bare wood is worth addressing within a season, because bare clapboards weather quickly and soak up water through a winter of snow and freeze-thaw, which makes the next repaint harder and can turn small problems into rot.

For planning, a full repaint with heavy scraping on a typical two-story Quincy house often runs in the range of $9,850 to $21,700, depending on size, height, how much old paint has to come off and how much carpentry is needed. Triple-deckers and large Wollaston Hill Victorians can run higher. These are typical ranges only, and the walk-through sets the real number. Call (617) 576-8235 any hour to set one up.