Stucco is a rigid skin over a building that moves. Houses settle, framing shrinks as it dries, and in this part of California the ground shifts more than most. So stucco cracks. That on its own is normal and not usually a problem.
What is not normal is a crack that comes back in exactly the same line after it has been patched. That means the patch was treating the symptom. Something behind the wall is still moving, or still getting wet, and it will keep opening the same seam no matter how good the patch is.
The two usual causes are water and a missing control joint. Water gets in at a failed flashing above — around a window head, at a roof-to-wall transition, or where a downspout dumps against the wall — soaks the paper and the lath, and the stucco lets go from the back. A missing or bridged control joint is the other: the wall has nowhere to relieve movement, so it relieves it through the weakest line in the field of the stucco, which is wherever the last patch was.
Which means fixing it properly starts by finding the water or the movement, not by mixing mortar. Once that is dealt with, the patch itself is mostly about matching: the browncoat has to be built back to the same plane, and the finish float has to match the surrounding texture. A patch that is structurally perfect but visibly the wrong texture still reads as a scar from the sidewalk, which for most people is the whole reason they called.
If a crack on your house keeps reopening, call (323) 243-7505 and we will come and look at what is actually causing it.
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