What Is a Block Foundation Wall?

If you’re planning to build a home with a basement, your contractor will likely begin with a block foundation. You might be wondering what this is and whether it’s the most durable foundation material.

Read on to discover answers to these and other related questions, along with effective waterproofing methods for repair.

Block foundation walls are constructed by stacking and mortaring blocks called concrete masonry units (CMUs). An initial block layer is built on a concrete footing, and subsequent layers are stacked to reach the desired height.

Standard concrete blocks and compressed stabilized earth blocks are made from materials like limestone or sand mixed with concrete. Regardless of the material, all block foundations require a waterproofing strategy to prevent water leakage, especially in areas with high precipitation.

Block foundations have a relatively recent history in the U.S. compared to traditional materials like brick or stone.

Concrete blocks gained popularity in the early 20th century, marked by Harmon S. Palmer’s 1900 invention of a machine for manufacturing hollow concrete blocks. These lighter, easier-to-transport blocks became practical construction materials. Their affordability and ease of use led to their widespread adoption for foundation walls and below-grade construction.

• Strength and Durability: Block foundations support substantial weight. They are resistant to fire, termites, and rot, making them a durable foundation choice.
• Cost-effective: Block foundations are generally less expensive and require less labor than poured concrete due to pre-made blocks and quicker assembly.
• Ease of Construction: Block foundations are easy to construct, and some have an interlocking capability that requires no curing, saving project time.
• Versatility: Block foundations are easily stackable and suit various foundation types, including basements, crawl spaces, and slabs.
• Insulation: Some blocks provide insulation, improving home energy efficiency. Block foundations can also be filled with insulation material for enhanced performance.

• Leak-prone: If not properly sealed, mortar joints between blocks can allow water infiltration, leading to basement moisture, mold growth, and foundation damage.
• Less Lateral Strength: Block foundations are less resistant to lateral pressure from soil or water compared to poured concrete, which can cause bowing walls and cracking, especially in high-water table areas.
• Less Design Flexibility: Block foundations offer less design flexibility due to their modular shape, limiting them to straight walls and basic corners, which may be a drawback.
• Aesthetics: Exposed block foundations may look less finished, requiring additional covering or treatments if appearance is important.
• Maintenance: Depending on the size of the cracks, mortar joints may require repointing to maintain waterproofing. Impacts or settling can also damage block foundations.

1. Water Infiltration

Moisture and hydrostatic pressure are critical concerns for foundation integrity. Damage occurs in these ways:

Moisture

Moisture penetration occurs when water seeps through cracks in mortar joints or gaps between blocks, eroding the mortar and weakening the structure. Freeze-thaw cycles worsen this issue.

Hydrostatic Pressure

Poor drainage or high water tables increase the hydrostatic pressure caused by water in the surrounding soil pushing against foundation walls. Standing water and high water tables, particularly near lakes or ponds, can intensify this problem. Over time, hydrostatic pressure allows water infiltration and leaks, attracts pests, and promotes mold growth.

2. Settlement and Pressure

Block foundations, though strong, are susceptible to damage from movement, including:

Foundation Settlement

Foundation settling occurs when the soil beneath the foundation fails to support it properly. This is caused by poor soil compaction or changes in moisture content.

Oversaturated expansive soil softens and causes foundations to sink, while dry soil shrinks, cracks, and fails to provide support. Poorly compacted soil leaves air pockets, compromising structural integrity and allowing foundations to sink into weak soil.

Lateral Pressure

Lateral pressure from soil or water pushing sideways against the foundation walls can also cause bowing or cracking, particularly if the foundation lacks proper reinforcement. Proper drainage around the foundation is crucial to reduce hydrostatic pressure from water accumulation.

• Wall Anchors: Address bowing or leaning walls with wall anchors. These reinforcements involve steel plates on both sides connected by a tightening rod that straightens the wall.
• Carbon Fiber Reinforcement: This method repairs cracks and reinforces block foundations by bonding carbon fiber sheets to the interior or exterior wall surface, providing added strength and preventing further damage.
• Wall Crack Repair: Monitor hairline cracks less than 1/8 inch and fill them with high-quality sealant if they worsen. Patch larger cracks with hydraulic cement or epoxy to prevent water infiltration and further damage.
• Foundation Piers: Helical piers, slab piers, and push piers address the foundation settlement that causes wall damage. Foundation piers transfer the structure’s weight to a more stable soil layer.

Apply Exterior Waterproofing Membrane

High-quality waterproofing membranes applied directly to the exterior foundation walls are crucial. This barrier prevents moisture seepage through the block walls.

Perimeter Drain Tile System

Drain tiles installed around the foundation perimeter collect groundwater and redirect it away from the basement, reducing hydrostatic pressure and preventing water from entering through cracks or gaps.

Backfilling and Compacting

Backfilling and compacting the trench around the foundation after installing drain tiles ensures proper drainage and prevents voids that could collect water.

Basement Waterproofing Methods

Basement waterproofing solutions like vapor barriers, interior drainage systems, sump pumps, and dehumidifiers ensure the area remains dry. This approach prevents the moisture and humidity that cause damage like efflorescence, mold, and rot.

Concrete block foundation walls are popular in Virginia, Maryland, and D.C. homes because they are affordable, easy to construct, and durable. If you’ve noticed bowing walls, damp walls, or other damage, contact JES Foundation Repair for a free inspection. We’ve been protecting homes for over 20 years. Let us to safeguard yours.