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Q.The stucco siding on my client’s recently remodeled home has developed some small cracks. My stucco sub wants to patch them with plastic stucco cement and then prime the walls with latex mortar primer, but I’m afraid the problem will resurface. Is there a better way to fix hairline cracks?

A.Ron Webber, a veteran plastering contractor in Orange, Calif., responds: I do not recommend using plastic stucco cement — actually a blend of portland cement, silica sand, lime, and fillers to increase plasticity — for patching. It has a high water content and develops a lot of very small shrinkage cracks as it dries, which can cause a patch to break apart prematurely. A better approach is to repair dead hairline cracks — where the stucco is stable and the cracks don’t change size or reappear — by dusting them with premixed, pigmented stucco. I pour dry stucco powder into a cup, then use a dry 1-inch brush to dab the powder into the cracks. Immediately after dusting, I brush any excess off the edges (to prevent buildup) and blend in the patch. Moisture from the night air will help the cement set up overnight.

This technique is quick and easy and gives me a better color match than a wet-mortar repair. Dusting allows me to blend the patch in with the existing texture; simply filling in the cracks tends to leave a telltale “snail trail” of different stucco textures.

If the cracks are live and reappearing, you will have to take more extreme measures. For larger cracks, I mix up a stucco fog coat (pigmented stucco without the sand) and inject it into the crack with a large syringe. (I moisten the area around the crack with water beforehand.) I use a small chip brush as needed to brush away the excess buildup and mist the patch as it dries; this helps harden the cement and makes the mineral pigment more stable.

If the cracks are too small, though, the fog coat won’t penetrate them very well and the patch won’t be as strong. To avoid this, you can dig out the cracks, moisten the area around them, and then squeeze the wet stucco into the cracks. It helps to brush some diluted acrylic admix into the cracks to help with adhesion. You might need to scrape back some of the finish coat and retexture the stucco, but matching an existing texture is a repair that requires good hands. Again, misting water onto the patch as it dries helps a lot.

While I’ve seen other plasterers fill cracks with urethane caulking, it’s not a method I use. Pigmented acrylics and urethanes might closely match the stucco when they are dry, but when it rains and the walls are wet, every patch will show up. This is because portland cement stucco absorbs water and darkens, while acrylics and urethanes don’t. Of course, if the walls are painted, then the color difference won’t be as obvious when it rains.