Foundation & Concrete Crack Repair in San Antonio

What Crack Repair Covers

Crack repair is a range of work rather than a single service. At one end sits cosmetic filling, which addresses appearance. In the middle sits sealing, which excludes water. At the other end sits structural repair, which restores or reinforces the capacity of the material.

Cracks are also the most common reason homeowners first contact us about foundation repair in San Antonio, which makes the distinction worth getting right before any money is spent.

Those three are not interchangeable, and treating them as the same thing is how homeowners end up paying repeatedly for a repair that keeps failing. The method has to match both what the crack is and what it is doing.

Why Concrete and Masonry Crack

Concrete is strong in compression and weak in tension. Its tensile strength is a small fraction of its compressive strength, which is why it is reinforced with steel and why it cracks when pulled rather than pushed. Any force that puts a section of concrete into tension will eventually produce a crack, and that force can come from several places.

Curing shrinkage. Concrete loses volume as it cures. Shrinkage cracking appears early in a slab’s life, usually fine and irregularly distributed, and is not a movement indicator.

Thermal cycling. Materials expand in heat and contract in cold. In San Antonio the daily and seasonal swing is substantial, and masonry without adequate expansion joints accumulates stress.

Differential support. Where the ground beneath one part of a foundation moves relative to another, the structure is bent. Bending puts one face into tension and it cracks. This is the mechanism that connects cracking to foundation movement.

Shear failure. Where two sections are displaced in opposite directions along a plane, the result is a crack with displacement: one side sits proud of the other. This is a more significant observation than width alone.

Masonry behaviour. Brick veneer cracks through the mortar joints because mortar is the weaker material. That produces the step fracture pattern, diagonal through the joints, which is why stair-step cracking is the classic exterior observation.

Active Versus Dormant

This distinction decides almost everything about the repair.

A dormant crack has stopped moving. The conditions that created it stabilised, and it is now a static gap. It can be filled, sealed, or bonded, and the repair will hold.

An active crack is still changing, which means the underlying movement is ongoing. Any rigid repair applied to it will fail, either through the repair or immediately beside it.

Establishing which one you have takes time or takes measurement, and preferably both. Crack width monitoring over a wet and a dry season is the simplest method: mark the ends, date the marks, photograph with a scale, and compare. Elevation readings provide the other half of the picture, because a crack sitting above a flat floor profile means something different from the same crack above a measured differential.

We would rather tell you to monitor for six months than take payment for a repair that will not last.

Repair Methods

Epoxy injection

Ports are fixed along the crack, the surface between them is sealed, and epoxy is injected under pressure until it travels through the depth of the crack. Cured epoxy typically exceeds the strength of the surrounding concrete, so the crack ceases to be a plane of weakness.

Used for: structural restoration of dormant cracks in concrete. Not used for: active cracks, or where flexibility is needed.

Elastomeric polyurethane sealant

Injected or applied into the crack, polyurethane reacts with moisture, expands, and cures to a flexible solid. It excludes water and tolerates continued small movement without failing.

Used for: water exclusion, and cracks expected to continue moving seasonally. Not used for: restoring structural continuity.

Structural carbon-fiber staples

A slot is cut across the crack, the surface prepared, and a carbon-fiber staple bedded in epoxy so it ties the two sides together and resists further separation.

Used for: reinforcing against recurrence where the crack needs more than filling. Not used for: cosmetic work, or as a substitute for addressing the cause.

Mortar joint tuckpointing

Deteriorated mortar is cut out to a sound depth and the joint is repacked with new mortar matched to the original as closely as practical.

Used for: masonry joint failure where movement has stabilised. Not used for: walls that are still moving.

Non-shrink grout

Used to fill voids and re-establish bearing where material has been lost, rather than as a crack filler in its own right.

Surface filling

Flexible filler and paint for interior sheetrock cracking where the objective is appearance.

Used for: cosmetic finish on stable interior cracks. Not used for: anything described as structural. If a scope calls this a structural repair, that scope is wrong.

Moisture Conditions During Repair

This is a practical detail that determines whether a repair holds. Epoxy needs a dry, clean, sound substrate to bond. Polyurethane wants moisture, since that is what triggers its cure. Mortar needs the surrounding masonry appropriately dampened so it does not lose its water too quickly.

Getting this wrong produces a repair that looks fine on completion day and debonds within a year. Surface preparation and moisture conditions are part of the method statement, not incidental.

When a Crack Means More

Any of the following moves the conversation from crack repair to foundation evaluation:

• The crack is widening measurably between monitored checks.
• Displacement has appeared, with one side proud of the other.
• The same crack reopens after being repaired.
• Cracking is appearing in multiple locations rather than one.
• Cracking is accompanied by doors that have progressively worsened or floors that slope.
• A diagonal crack runs from a door or window corner and is growing.

In those situations, repeated cosmetic repair is money spent on a symptom. Foundation movement diagnosis through elevation measurement answers the underlying question, and the crack repair follows from that rather than preceding it.

After the Repair

Post-repair crack monitoring is part of doing this properly. Mark the repair, date it, and check it after a season. A repair that holds confirms the crack was dormant and the method was right. A repair that reopens is not a failure of workmanship, it is information: the movement is active and the question is a foundation question.

Either outcome is useful. Being able to tell them apart is the point.