Brick piers that extend both above and below grade face a unique challenge: the portion buried in soil is constantly exposed to moisture that can lead to mortar deterioration and damp over time. Without proper waterproofing, water migrates from the surrounding soil into the brick masonry, weakening the mortar joints and compromising the structural integrity of the entire pier. This comprehensive guide explains the correct methods for waterproofing brick piers below grade, drawing on proven techniques recommended by masonry experts to extend the life of your brick piers for decades.
Understanding Why Brick Piers Need Below-Grade Waterproofing
Brick masonry is a porous material by nature. The clay bricks themselves absorb moisture, and the mortar joints between them create capillary pathways that water can follow. When a brick pier is buried below grade, the surrounding soil acts as a constant moisture reservoir, pressing water against the masonry surface 24 hours a day, 365 days a year. This persistent exposure creates conditions that lead to accelerated deterioration if left unaddressed.
Above-grade portions of brick piers do not require waterproofing because they are exposed to air and sunlight, which allow them to dry out naturally between rain events. In fact, sealing above-grade brickwork can be counterproductive, trapping moisture inside the masonry rather than letting it evaporate. The critical distinction is that below-grade masonry never gets a chance to dry, making waterproofing essential for this section.
The rate of mortar deterioration is directly influenced by the length of time the brick masonry remains wet. Laboratory studies conducted by the Brick Industry Association have shown that continuously saturated mortar can lose up to 50 percent of its compressive strength within a decade, compared to mortar that experiences normal wet-dry cycles. This makes below-grade waterproofing not just a cosmetic concern but a genuine structural necessity.
Building codes in most jurisdictions recognize this requirement. The International Building Code (IBC) specifies that foundations and below-grade masonry must be protected from moisture penetration, though the exact method is left to the designer or builder. Understanding these code requirements helps ensure your waterproofing approach meets or exceeds minimum standards.
The Science of Mortar Deterioration and Rising Damp
When cement mortar in brick piers remains saturated for extended periods, several chemical and physical processes begin to degrade the material. The most significant is the dissolution of calcium hydroxide, a key component of hydrated Portland cement. Over time, water slowly leaches this compound out of the mortar, leaving behind a more porous and weaker matrix. This process is accelerated in acidic soil conditions, which are common in areas with high rainfall or decaying organic matter.
Rising damp is a related phenomenon that affects brick piers even above the grade line. When the below-grade portion of a pier is saturated, capillary action draws moisture upward through the brick and mortar, sometimes reaching several feet above the soil line. This rising damp keeps the above-grade portion of the pier wet for prolonged periods, extending the zone of potential deterioration far beyond the buried section. The visible signs include dark staining, efflorescence (white salt deposits), and flaking or spalling of the brick surface.
Freeze-thaw cycles compound the problem dramatically. Water trapped in saturated brick masonry expands by approximately 9 percent when it freezes. In cold climates, this expansion creates internal pressures that can crack bricks, pop mortar joints, and eventually cause sections of the pier to delaminate. A single winter season can cause more damage to an un-waterproofed brick pier than a decade of normal weathering above grade.
The following table summarizes the key differences between above-grade and below-grade brick pier conditions:
| Factor | Above Grade | Below Grade |
|---|---|---|
| Moisture exposure | Intermittent (rain only) | Continuous (soil contact) |
| Drying potential | High (air and sun exposure) | Minimal to none |
| Freeze-thaw risk | Moderate | Severe when saturated |
| Mortar deterioration rate | Slow (normal weathering) | 2-5x faster without protection |
| Typical lifespan of properly built pier | 50-100+ years | 15-30 years without waterproofing |
| Waterproofing required | No (leave exposed) | Yes (essential) |
Step-by-Step Waterproofing Process for Brick Piers
The standard waterproofing approach recommended by the Brick Institute of America involves two distinct layers: a cement parge coat and a foundation sealer. This dual-layer system provides both a physical barrier and a waterproof membrane, addressing the unique challenges of below-grade brick construction.
Step one is to prepare the brick surface. Remove all loose mortar, dirt, and debris from the below-grade portion of the pier using a stiff wire brush. If there is existing efflorescence, clean the surface with a mild muriatic acid solution (one part acid to ten parts water) and rinse thoroughly with clean water. Allow the surface to dry for at least 24 hours before proceeding. This preparation ensures the parge coat bonds properly to the brick and mortar.
Step two is applying the parge coat. Mix one part Portland cement with three parts clean, fine sand by volume, then add water until the mixture reaches a stiff but workable consistency similar to thick mortar. Apply this mixture to the below-grade section of the pier at a minimum thickness of 3/8 inch (approximately 10 mm). Use a trowel to press the parging firmly into the brick joints and create a smooth, uniform surface. The parge coat should extend from the top of the footings to approximately one to two inches above the finished grade line to ensure complete coverage of the below-grade zone.
Step three requires patience: let the parge coat cure for at least seven days. During this curing period, keep the parging moist by lightly misting it with water once or twice daily, especially in hot or windy weather. Proper curing allows the Portland cement to fully hydrate, developing maximum strength and adhesion. Rushing this step can lead to cracking or delamination of the parge coat, compromising the entire waterproofing system.
Step four is applying the foundation sealer. Once the parge coat has fully cured, brush or roll on a coat of black foundation sealer (asphalt-based or rubberized) over the entire parged surface. These sealers are available by the bucket at most hardware stores and home centers. Apply the sealer from the top of the footings to just above grade, covering the same area as the parge coat. A single coat is typically sufficient, but two thin coats applied 24 hours apart provide more reliable coverage. Allow the sealer to dry completely before backfilling around the pier.
Long-Term Maintenance and Inspection of Waterproofed Brick Piers
Even with proper waterproofing, brick piers require periodic inspection to ensure the protective system remains intact. The most vulnerable area is the transition zone at the grade line, where the waterproofing ends and the exposed brick begins. Over time, soil settlement, landscaping activities, or erosion can expose previously waterproofed sections or create pathways for water to bypass the protection.
Inspect your brick piers at least once per year, preferably in the spring after the freeze-thaw season has passed. Look for signs of deterioration including cracked or spalling bricks, deteriorating mortar joints, white efflorescence deposits, or any dampness on the above-grade portion of the pier during dry weather. These indicators suggest that the waterproofing system may have failed and needs repair.
If you discover damage to the waterproofing, the repair process depends on the extent of the problem. Minor cracks in the parge coat can be patched with hydraulic cement after exposing the affected area. More extensive damage may require excavating around the pier, removing the old parging and sealer, and reapplying the full two-layer system. In extreme cases where the brick or mortar has deteriorated significantly, partial rebuilding of the pier may be necessary before re-waterproofing.
Proper drainage around the base of brick piers also plays a critical role in long-term performance. Ensure that the soil slopes away from the pier to direct surface water elsewhere rather than pooling at the base. Installing a French drain or perforated pipe at the footing level can further reduce soil moisture content in areas with poor drainage or high water tables. Good site drainage complements below-grade waterproofing and significantly extends the service life of brick piers, keeping them structurally sound for 50 years or more with minimal maintenance.