Why chinooks and freeze-thaw wreck exterior paint in Calgary.

A chinook arch appears over the foothills, the wind shifts to the west, and the wall of your house goes from -18°C to +8°C before lunch. The cladding, the fasteners and the paint film all expand at different rates. Paint is the thinnest and least forgiving of the three, so the stress concentrates at its weakest points: edges, seams, fastener heads, and any place the film is already thin.

Meanwhile, snow sitting against the north foundation or in a soffit line melts. That water follows gravity and capillary action into hairline cracks, lap joints and end grain. When the temperature drops again overnight — and in Calgary it usually does — the water expands about nine percent as it freezes and pushes the coating away from the substrate from behind.

Do that thirty times a winter for four winters and you get the failure pattern every Calgary painter recognises: intact paint across most of a wall, and blistering or sheet peeling on the south and west elevations and around every window sill.

Acrylic stucco, which covers a large share of Calgary homes built between roughly 1975 and 1998, is porous and moves with the wall behind it. It handles chinooks well when it is sound and coated with something breathable, and badly when it has been sealed with a film that traps moisture inside.

Wood — cedar shakes, fir trim, older fascia and any painted deck rail — is the most freeze-thaw sensitive material on the house because it absorbs water directly. Fibre cement (Hardie and similar) is the most stable and the most forgiving to repaint. Vinyl and aluminium siding move a lot dimensionally, so they need coatings formulated to flex and a colour no darker than the manufacturer's heat limit.

The difference between a repaint that lasts four years and one that lasts ten is almost entirely what happened before the first coat. Pressure washing to remove chalking, scraping and feather-sanding every failed edge, spot-priming bare substrate, and filling cracks with a flexible sealant rather than rigid filler are the four steps most commonly skipped by the cheapest quote in your inbox.

Moisture content matters more here than most homeowners expect. Painting a wall that read 18% moisture in the morning because snow melted against it the day before guarantees a bond failure by spring, no matter how good the paint is.

On fibre cement with good prep, eight to twelve years is realistic. On sound stucco with a breathable coating, seven to ten. On wood siding or heavily exposed south-facing elevations, five to eight, with trim often needing attention sooner than the field.

If your last repaint failed inside four years, the paint was almost certainly not the problem. Either it went on over damp or chalky substrate, or the cracks underneath were never repaired.