# Floating Slabs: What They Are and Repair Costs > A floating slab is a concrete slab foundation poured directly on grade without traditional footings. Learn how it works, when it cracks, and what repairs cost. Canonical: https://foundationrepairlab.com/floating-slab/ Last updated: 2026-11-09 A floating slab is a concrete foundation poured directly on prepared soil without traditional footings underneath. The slab “floats” on the ground, with its weight and the building’s load transferred to the soil through the slab surface and a thickened perimeter edge. This article explains how floating slabs work, when they fail, and what repairs typically cost. ## What Is a Floating Slab? A floating slab is a monolithic concrete slab-on-grade foundation. Unlike a pier-and-beam or basement foundation, it has no crawl space and no continuous footing running beneath the entire structure. Instead, contractors excavate and compact the subgrade, add a gravel or sand base, place reinforcement such as rebar or wire mesh, and pour concrete that thickens at the edges to form a shallow grade beam. The thickened edge, usually 12 to 18 inches wide and deep, carries most of the perimeter load. The interior slab, often 4 to 6 inches thick, distributes floor loads across the soil. Floating slabs are common for garages, room additions, sheds, and some single-story homes where soil conditions are stable and frost depth is shallow. ## How Floating Slabs Differ From Other Foundations Floating slabs lack the deep bearing elements found in pier-and-beam or basement systems. A pier foundation transfers loads to piers that extend below the active soil zone. A floating slab relies entirely on near-surface soil support. That makes it cheaper and faster to install, but more vulnerable to soil shrinkage, expansion, and poor compaction. Because there is no crawl space, plumbing and electrical lines are typically embedded in or beneath the slab. Leaks under a floating slab can be difficult to access and may contribute to soil softening and slab settlement. ## When Floating Slabs Crack Cracks in floating slabs usually come from soil movement beneath the slab. Expansive clay soils swell when wet and shrink when dry, creating differential support. Poorly compacted fill settles over time. Tree roots can draw moisture from one side of the slab, causing that edge to drop. Crack width matters. A crack up to 1/16 inch is generally cosmetic. A crack at 1/8 inch or wider should be monitored. If a crack shows vertical displacement—one side higher than the other—or if doors and windows begin to stick, the slab may be undergoing structural movement. Wall movement beyond 2 inches in an attached structure is a strong signal that the foundation needs professional evaluation. ## Repair Options and Costs Repair costs depend on the method, the size of the slab, and the extent of movement. All figures below are estimates. ### Slab Lifting Slab lifting raises settled sections back toward level. Mudjacking pumps a cementitious grout under the slab and costs $3 to $8 per square foot. Polyurethane foam injection costs $5 to $15 per square foot and is lighter and faster curing. For a 400-square-foot garage slab: - Mudjacking: 400 sq ft × $3 = $1,200 to 400 sq ft × $8 = $3,200 - Polyurethane foam: 400 sq ft × $5 = $2,000 to 400 sq ft × $15 = $6,000 Mudjacking typically lasts 5 to 15 years. Polyurethane foam is more expensive per square foot but often requires smaller injection holes. ### Piers When soil support is inadequate, piers transfer the load to deeper, more stable bearing strata. Push piers cost $1,000 to $3,000 each. Helical piers cost $700 to $2,500 each. A typical residential pier job ranges from $6,000 to $30,000 depending on pier count, depth to bearing, and access. For example, if an engineer specifies eight helical piers at $1,500 each: 8 × $1,500 = $12,000 If the same job uses push piers at $2,000 each: 8 × $2,000 = $16,000 Pier installation usually requires exterior excavation or interior floor breaks, which adds to cost and disruption. ### Crack Repair Non-structural cracks can be sealed with epoxy or polyurethane injection. Carbon fiber straps cost $400 to $1,200 each and are used to stabilize cracked foundation walls, not typically the slab itself. Wall anchors cost $500 to $1,500 each and apply to bowed basement or crawl space walls, not floating slabs. ## What a Full Repair Job Might Cost Average foundation repair runs $4,000 to $15,000. Major structural work can reach $20,000 to $40,000. Full slab replacement ranges from $40,000 to $150,000 depending on square footage, demolition, and site access. Restoration of finishes after structural repair typically adds 10 to 25 percent of the structural repair cost. For a $10,000 pier job: $10,000 × 0.10 = $1,000 $10,000 × 0.25 = $2,500 Expect an additional $1,000 to $2,500 for drywall, flooring, and paint repairs. ## When to Replace Instead of Repair Replacement is generally considered when more than one-third of the slab has failed structurally or when repeated lifting no longer holds the slab level. If repair costs approach replacement cost, or if the slab is undermined by plumbing leaks or expansive soil that cannot be stabilized, replacement may be the more durable option. Replacement requires demolition, hauling, new subgrade preparation, and a new pour. It also means moving utilities and temporarily relocating occupants if the slab supports a living area. ## Inspection, Permits, and Warranties Start with a structural engineer or qualified foundation inspector. An engineer inspection costs $400 to $1,500 and typically has a lead time of 1 to 2 weeks. Permits vary by city and county and typically take 1 to 3 weeks to approve. Pier warranties are often lifetime and transferable. A warranty transfer fee usually runs $100 to $500. Slab lifting methods do not carry the same long-term structural warranty because they address symptoms, not necessarily the underlying soil condition. ## Choosing a Repair Path Measure first, method second, price third. Crack width and displacement, pier count, depth to bearing, and unit price should drive the decision. A floating slab with a single 1/8-inch crack and no displacement may only need sealing and monitoring. A slab with multiple cracks, visible tilting, and sticking doors likely needs piers or lifting. Get a written scope that specifies the repair method, material quantities, pier locations if applicable, and total cost before signing any contract. [Learn more about overall foundation repair pricing](https://foundationrepairlab.com/foundation-repair-cost/) [See cost details for pier-and-beam systems](https://foundationrepairlab.com/pier-and-beam-foundation-repair-cost/) [Read about crack repair pricing](https://foundationrepairlab.com/foundation-crack-repair-cost/)