Can a Garage Foundation Shift?

Spalling

• Spalling is the deterioration of the foundation caused by poor concrete mixture. Inferior concrete has an inherent lack of strength, causing the foundation to crumble. In the 1930s, many garage foundations were made using dusty aggregate. This reduced the adhesive quality of the mix. Spalling does not necessarily indicate that immediate major repairs are needed. If the crumbling does not extend more than an inch below the surface, the foundation will remain sound. Proper drainage prevents spalling, which results from moisture and freezing.

Slab-On-Grade Foundations

• A too-thin foundation can cause shifting. This is a common problem with garages. A garage with a slab-on-grade foundation -- a thin slab with thickened edges serving as a floor/foundation for the structure -- is particularly susceptible to damage from seasonal ground freezing and thawing. Freezing expands the soil, pushing it, the foundation and the garage upward. With thawing, soil and structures resettle. Years of this rocking motion shift the foundation outward, putting pressure on the load-bearing edges of the slab. Improved drainage helps to alleviate or prevent the problem.

Soil Shifting

• The National Oceanic and Atmospheric Administration reports that the United States is experiencing longer dry spells than normal, followed by torrential rain. This trend began in the 1990s and continues through 2011. Such climatic change has had an adverse effect on clay and sandy soils. A drought causes clay soil to shrink. Floodwater makes the soil swell, causing foundations to bobble. The adhesive characteristics of sandy soil are also diminished, causing the soil to shift under the foundation, leaving voids.

Swelling of the Backfill

• Chemical reactions between pyrite-filled backfill and limestone cause soil to swell and foundations to buckle upward. The Quebec Consumer Protection Association explains that garage foundations are relatively thin with more backfill beneath them, making them susceptible to this phenomenon. Pyrite, an iron disulfide mineral, reacts with calcium carbonate in backfill material such as limestone, thaumasite, trona, thermonatrite and dawsonite. As a result, sulfuric acid is formed, causing rock to burst and soil to expand. If swelling and buckling are severe, the only solution is removal of the foundation and contaminated backfill.