Unbeatable for strength and durability, stucco provides protection from extreme weather with minimal maintenance. In fact, in some climates it's reasonable to expect 50 years of beauty and duty from properly applied stucco. What can cause a stucco application to fail, though, are careless workmanship and skimping on important preparation details. Here are a few key areas where it's smart to slow down and do it right.

Substrate

No amount of lath will make up for structural movement if stucco is applied over an unstable substrate. If there's any sign of green or wet lumber in the frame, you can be sure there will be problems with your stucco as the studs dry and the building moves.

Ingredients

Fresh cement, clean sand, and clean water are essential. If the Portland cement is old or has been exposed to moisture, it may be partially hydrated. If there are lumps or "rocks" in the sack, throw it away and get fresh cement.

If the sand doesn't meet ASTM (American Society for Testing and Materials, also called ASTM International) specs for plaster, don't use it. Dirty sand (sand with clay, silt, or excessive fines in it) will make it hard to predict the amount of water required for a workable mix and make quality control difficult. Dirty sand also greatly increases the likelihood of cracking for similar reasons. Excessive salts in the sand make stucco "bloom" or effloresce.

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