- What is Sulfate?
- When and where do symptoms of sulfate attack show up?
- How many buildings are affected by sulfate damage?
- What do the Building Codes say about sulfates in the soil?
- What are builders required to do to determine if sulfates are in the soil on which they want to build?
- What happens when sulfates get into concrete?
- What's the worst that can happen?
- Do all builders comply with the code requirements?
In the past several years it has become increasingly obvious that the foundations of many homes and other buildings in certain regions of California and Arizona are slowly and irreversibly being destroyed by a white, powdery substance called sulfate. It's an unpredictable, pernicious agent that seeps into the foundation of a home or building. Some areas appear to have higher levels of sulfates than others, but much of California and Arizona has soils of a marine origin containing measurable levels of sulfates. Because sulfates can destroy the structural integrity of a foundation and undermine a buildings long-term performance - and construction strength - property owners with sulfate problems are filing construction defect lawsuits in increasing numbers to recover damages. Some of the most commonly asked questions about sulfates are answered below.
Sulfate is a naturally occurring mineral salt compound. Soil deposits are often rich in gypsum, and are laced with gypsum veins. Gypsum is a form of calcium sulfate (CaSO4). Sulfate deposits in soils with a marine origin are also high in sodium sulfate (NaSO4) and magnesium sulfate (MaSO4). When the soil becomes wet from irrigation or rainfall, the sulfates dissolve into the water and seep into porous (that is, less dense) concrete. The sulfate eats away the cement "paste" that holds the concrete together. Once the deterioration starts, the damage to the concrete cannot be reversed.
Sulfate damage typically appears in the form of hairline cracks called "etching," or white, powdery stains referred to as "efflorescence". The first place to look is on the garage floor or driveway, or along the exterior foundation. As the sulfate attack worsens, other parts of the home's or buildings foundation will show signs of efflorescence and etching. It can also appear on patios, driveways, swimming pools and other so-called "hardscape". However, not all white powder is sulfate. If you are suspicious and want to know for sure, a geotechnical firm can take a sample from your home and analyze it.
Possibly tens of thousands of homes, apartments, condominiums, and commercial buildings along the coastal and inland areas of California and Arizona are built on sulfate laden soils that can, under certain conditions, destroy the concrete foundations. One expert said sulfate cases could cost the Southern California homebuilding industry - or more precisely, their insurance companies - as much as the Northridge earthquake.
Since 1979, Building Codes have required that a special Type V cement be used in high-sulfate soils, and that a lower water-to-cement ratio be used to mix the cement to maintain a proper level of density in the concrete after curing. Dense concrete retards groundwater from seeping in; it's the water that carries the sulfates. According to most code, the ratio of water-to-cement in high-sulfate soil conditions should be no more than 0.45. However, in many cases that we have investigated, the ratio is more like 0.65 to 0.70, or 50% more than the maximum allowed by code. The result is concrete with a loosely interconnected pore structure, and therefore not dense enough.
Before beginning construction, builders are required to conduct soil tests that measure sulfate content. Reports on such tests should be on file with local building departments or environmental management agencies. If a housing project is newer, the builder may still retain a copy of the report. Ask to see it.
As the sulfate infiltrates concrete, it combines with the C-S-H, or concrete paste, and begins destroying the paste that holds the concrete together. As sulfate dries, new compounds are formed, often called ettringite. These new crystals occupy empty space, and as they continue to form, they cause the paste to crack, further damaging the concrete. The concrete weakens and the paste continues to separate and crack. Consequently, the concrete becomes increasingly permeable, allowing in more and more water filled with sulfates. Over time the process accelerates dramatically. The excess water content also begins to rust away the anchor bolts that tie the home's structure to the foundation.
Eventually, the concrete foundation disintegrates and turns to rubble. This condition, coupled with the rusting structural ties and anchor bolts, puts a building and its occupants at greater risk from earthquakes, high winds, and other destructive forces of nature. According to the National Association of Home Builders, the useful life of concrete should be about 150 years; however, left unattended, sulfate attack can cut that life span to 15 years or less.
Certainly, many builders comply with code sulfate requirements. However, concrete used in construction of potentially tens of thousands of California and Arizona homes built on high-sulfate soils since the mid-1980s do not meet Building Code standards, creating a defect that can result in the concrete's decomposition. One reason is that contractors and suppliers of concrete ignored the code requirements. Compounding the problem, those contractors who poured concrete at building sites frequently mixed in additional water to make the concrete less thick, which resulted in quicker and easier installation.