About Soft Stucco

Stucco is made with Portland cement. Cement is not concrete but rather an ingredient of concrete (the glue). Cement gets hard through a chemical reaction that only happens when it is wet called hydration. Stucco is applied in a thin coat, 3/8th of an inch thick and thinner on texture coats. It usually dries out quickly, without staying wet long enough for it to get hard (cure). Therefore the stucco must be wet down until it gets hard. This is called water curing.

Water curing should occur shortly after application (first few days). Once hydration begins when first mixed with water it must be completed sooner rather than later. The more time that elapses the less hard the stucco can become and at some point no amount of water will cause it to cure (after several weeks).

Unfortunately, all too often water curing is not being done and the result is soft stucco. Soft stucco erodes, cracks, buckles, is prone to bird holes, allows paint or synthetic finish to peel and has little strength to withstand shock and abrasion. This is the number one cause of stucco failure and takes no more than a little time and a water hose to prevent.

Lack of hydration failure may not become evident for many years after application (even 10+). Only after the paint breaks down, chalks and allows more water to penetrate does erosion begin.

Often professionals will proclaim there was too much sand in the mix and that is why the stucco is soft. This is highly unlikely. If someone has told you that, you may want to find a more knolagable consultant. It is almost always a lack of hydration and or sulfate attack. Most stucco contractors do not understand this chemistry.

Sulfate attack is the breakdown of cement due to sulfates (salts) activated by water. This is usually more isolated to areas exposed to prolonged moisture. Such as foundations, planters, retaining walls and the bottom of block walls where the ground stays wet; but over time on soft stucco that is being penetrated with water the salts break down what little strength the cement had.

If you think you have soft stucco contact T.G.A Painting for a consultation. Our Owner has 40 years experience in wall construction, 30 as a licensed stucco contractor.

During hydration crystals are forming, inter locking, forming a synthetic rock.

The cement should cure for 4 weeks. That means it should not be painted or have synthetic finish applied before that time frame. If it has not been sufficiently water cured stucco should not be coated even if 4 weeks has passed.

Opinion. Failure has become more prominent in the last couple of decades because of fly ash. Fly ash is a byproduct of burning coal and seems to be being added to cement products more often.

Fly ash when added to Portland cement can add strength and resistance to sulfate attack. However, it slows curing. That means it takes longer and more water to cure cement products with fly ash. In hot dry Arizona, stucco was not being water cured properly to begin with. Fly ash makes water curing even more critical.

Hearing rules about stucco needing to be wet down 3 (or however many) times are meaningless. It is all relative. Wetting a wall in 112 degree, low humidity weather in the sun is not the same as wetting a wall in humid low temperatures in the shade. When wetting stucco, it needs to be saturated enough that it pernitrates to the lath. What matters is how long the stucco remains wet. Stucco must be wet as many times as it takes to get hard, that may be once or 5+ times.