A downspout split this stucco foundation skirt. This Old House shows the repair

The segment is part of Season 25, Episode 5, posted by PBS on Oct. 29 and put on YouTube by This Old House on Oct. 31. The homeowner, Will, bought the house a year ago. McCullough said he blames bad drainage whenever he sees damage like this: in winter the water sits in the pan, freezes and pops the stucco. From the crawl space he found the skirt carries no load, because two concrete piers hold up the porch. Daylight through the stucco showed water was getting in, the wire lath had rusted brittle, and the wood slats behind it were worn out.

Demolition exposed the original two-coat job: a lighter, lime-rich coat for grip, then a darker Portland cement coat. The crew reframed with pressure-treated lumber. Redoing it the old way would mean galvanized lath plus a scratch coat and a brown coat, each needing about three days to cure, McCullough said. Exterior-grade cement board arrives already cured. He tucked it under the bottom row of shingles, which is padded out so runoff kicks clear, cut it with a diamond blade on a grinder hooked to a HEPA vacuum, and fastened it with the screw the board maker specifies, since other screws can crumble the board.

He sponged the board wet first because it pulls water out of the mix, troweled on Portland cement, sand and water with a bonding agent already added, and buried fiberglass mesh tape over the joint between the pier and the board. To match color he analyzes a chip of the old material and uses the same ingredients instead of dye, which won't weather the way the original did. PermaBase's exterior guide for its board calls for corrosion-resistant screws no more than 8 inches apart and 4-inch alkali-resistant mesh tape in every joint.

The downspout now empties into a pipe that will go underground with two gutters when the driveway is redone. Will's homework was to dampen the new stucco whenever it looked dry over the next day or two.