It depends on the pattern more than the size. Fine, evenly distributed hairline cracks are common and often just the finish coat responding to curing and temperature movement. What deserves attention is a crack that runs diagonally from a window or door corner, a crack wide enough to admit water, or cracking concentrated in one area — those suggest movement in the structure behind or water getting into the assembly. The reliable test is whether the wall around the crack still sounds solid when tapped; hollow means the stucco has debonded and the repair area is larger than the visible crack.

It means the stucco has separated from the substrate behind it and is no longer bonded — that section is effectively a shell. It usually happens because water got behind the stucco and broke down the bond, or damaged the lath or sheathing supporting it. Hollow areas will eventually crack and fall away, and they are a strong indication that moisture has been in the wall for a while. Sounding the whole elevation, not just the area you noticed, is how the true extent gets established before any repair is quoted.

In most cases, yes, though it takes matching both the texture and the plane. Stucco repairs are built up in coats rather than smeared on in one pass, and the final coat has to be worked to the same texture as the surrounding wall — float, sand, dash, and smooth finishes all look completely different under raking afternoon light. Colour is the other variable: patched stucco cures at a slightly different shade, so on a painted wall the cleanest outcome is repainting the full elevation rather than spot-painting the patch.

Because those are the places water concentrates. Window and door openings need flashing to divert water out of the wall assembly, and when that flashing is missing, incorrectly lapped, or has failed, water runs behind the stucco and works outward — which is why cracks and staining so often start under a sill. At the base of a wall, the usual causes are grade or paving built up against the stucco, or splashback from a hard surface, both of which keep the bottom of the wall wet. Repairing the stucco without correcting those details resets the same failure.

Breathable, masonry-appropriate coatings can be fine; film-forming waterproof sealers usually are not. Stucco needs to release moisture that gets into the wall, and a coating that blocks vapour traps water behind the finish, where it breaks the bond and freezes. That is a common route to hollow, debonded stucco on Pennsylvania homes. If the wall is already showing staining or hollow areas, coating over it hides the symptom and accelerates the underlying problem — the repair has to come first, and the water has to be given a way out.

K&S Masonry Restoration is based in Brookhaven, PA and works throughout Delaware County and the Philadelphia suburbs, including Philadelphia, Havertown, Springfield, Drexel Hill, Chester, Wayne, Radnor, and Ardmore, plus Montgomery and Chester Counties. If you are unsure whether your address is in range, call (610) 990-1379 and ask — it is a quick answer.