Flexible Polyurethane on Stable Cracks, Foam-Lift Plus Seal When the Slab Has Moved.

Exterior concrete cracks aren't basement cracks. The driveway, sidewalk, patio, garage floor, and pool deck all live in a tougher environment: direct sun cycling the slab surface temperature each summer day, repeated freeze-thaw cycles each winter, vehicle and foot load that flexes the slab, and de-icing salt that attacks both the concrete and any rigid repair compound in it. The right repair on exterior concrete cracks is rarely the same product or sequence that works inside a basement, and the diagnosis comes before the price. Epp Foundation Repair's concrete repair team has repaired exterior cracks across the four-state territory since 1994, and the first thing the inspection answers is whether the crack is the problem or whether the crack is the symptom of soil movement below the slab. An exterior crack quote that prices only the crack is a product quote. That works on a stable, cosmetic, surface-tension crack. It doesn't work on a crack that's opening because the slab dropped on one side. The crack can reopen because the underlying movement hasn't been addressed. Epp's standard practice is to diagnose first, install a crack monitor if movement is questionable, and quote either a sealing scope, a foam-lift-plus-seal scope, or an honest new pour when the slab is end-of-life.

This is the single biggest mistake on exterior crack repair. Epoxy cures rigid, which works inside a basement where the wall is temperature-stable and movement-free. Outside on a driveway in the Midwest, the same epoxy can crack because freeze-thaw expansion and contraction move the slab, the epoxy can't flex with the movement, and the bond fails at the concrete face. Flexible polyurethane sealants cure soft enough to absorb the freeze-thaw cycling, elastic enough to recover after compression, and UV-stable in formulations rated for exterior exposure. Epp uses flexible polyurethane on stable cosmetic exterior cracks, period. Epoxy is the wrong product outside, and Epp will say so. ## Where This Page Fits, and Where the Foundation-Crack Page Fits

This page covers exterior cracks in driveways, sidewalks, patios, garage floors, pool decks, and other above-ground exterior slabs. The companion page on structural foundation crack repair covers cracks in foundation walls. The page on basement crack repair covers leaking basement wall cracks. If the crack is in a slab you can see from outside the house, this is the right page. If it's in a foundation wall, basement floor, or stem wall, one of the others is.

There are three categories after inspection. Cosmetic stable crack. Hairline to 1/10 inch wide, no offset across the crack face, no settlement of the slab on either side, no nearby cracks indicating a broader problem. Right scope is flexible polyurethane sealing. Clean the crack, install a backer rod if the crack is wide, gun in the sealant, tool the surface flush. Settlement-driven crack. Crack with offset. One side has dropped relative to the other, the crack is wider at the surface than at depth, the slab on the lower side is noticeably below grade. Sealing the crack alone fixes nothing because the soil is still moving. Right scope is foam-lift to restore the slab, then seal the crack with flexible polyurethane. End-of-life concrete. Multiple structural cracks on a single slab section, crumbling edges, widespread surface spalling, or structural cracks with active movement. Sealed or lifted end-of-life concrete can fail again. Right scope is full replacement. Epp removes the failed slab, corrects the base, and pours new concrete on prepared ground.

A crack monitor is a small glass or plastic gauge. It gets installed any time the on-site inspection can't definitively call a crack stable or moving. For example, the homeowner reports the crack getting wider over the last year, secondary cracking has appeared nearby, or the slab has visible offset that might be settling further. The monitor is bonded across the crack and re-measured over time before injection or sealing is committed. Sometimes a monitored crack reveals enough movement to shift the diagnosis from "seal" to "foam-lift first then seal," or from "foam-lift first then seal" to "replace." The wrong repair on a moving exterior crack can reopen.

Every exterior crack has a cause underneath it, such as frost heave at an expansion joint, hydroconsolidated loess under the slab where a downspout has been discharging, tree root pressure lifting the corner of a sidewalk panel, or apron-to-street settlement at the lowest point of a driveway. Sealing the crack without addressing the cause is putting a band-aid on a structural problem. Epp identifies the cause on the inspection and tells the homeowner what needs to change: extending the downspout, root-pruning the tree (arborist scope, not Epp), or re-grading a drainage swale (landscape scope, not Epp). Epp then quotes the lift-and-seal or seal-only scope contingent on the cause being addressed. Sealing lasts longer when the cause is corrected.

A crack gauge is a thin plastic strip with progressively wider lines printed on it. Held against the crack, it reads the width. A hairline crack is held closed by surface tension against most water entry. Sealant there is cosmetic, not waterproofing. A crack wide enough to admit water but narrow enough that flexible polyurethane fills it cleanly is the typical sealing target. Wider cracks need a backer rod (closed-cell foam pushed into the crack to limit the depth of sealant) before sealing. The widest cracks are usually settlement cracks or end-of-life concrete and get a different scope entirely. Crack length, depth, offset, and surrounding slab condition all factor into the diagnosis alongside width.

Inspection, monitor if needed, scope decision. Crack measured for width with a gauge, length tape-measured, offset noted with a straightedge across the crack face, surrounding slab inspected for nearby cracks or settlement indicators. Crack monitor installed if movement is questionable and re-measured over time. Scope decided as seal-only, lift-and-seal, or removal and a new pour. Surface prep. Crack cleaned with a wire brush, compressed air, and (on contaminated cracks) a chemical concrete cleaner to remove loose concrete, prior failed sealant, dirt, oil, and salt residue. A clean crack face is what the sealant bonds to. Contaminated faces fail at the bond regardless of product quality. Backer rod if needed. Wider cracks get a closed-cell foam backer rod sized to crack width and pushed in below the surface plane. The rod limits sealant depth (efficient material use), provides a bond-breaker so the sealant flexes properly, and ensures the sealant adheres only to the two crack faces rather than three. Sealant injection or gunning. Flexible polyurethane sealant applied via cartridge gun for narrow cracks or pump dispenser for longer runs. Sealant slightly overfills the crack to allow tooling. Tooling with a metal spoon or rubber spatula presses the sealant against both crack faces, removes air voids, and finishes the surface flush or slightly recessed. Cure and final inspection. The polyurethane sealant needs time to cure before the slab carries foot and vehicle traffic. Homeowner walks the work with the installer before sign-off. Foam-lift first if settlement-driven. When the diagnosis was lift-and-seal, the polyurethane foam injection happens first (separate scope, separate process), the slab is lifted, and then the crack is sealed with flexible polyurethane. Both scopes are done in the same site visit when access allows.

Epp seals stable cracks and lifts settled slabs. Here are three scenarios where crack repair is the wrong scope. End-of-life concrete. Multiple structural cracks, crumbling, and spalling mark an end-of-life slab; removing the slab and pouring new concrete is the right scope. Cosmetic complaints disguised as cracking. Paint failure on a painted driveway, salt-spalling on the surface, staining or discoloration. These aren't crack problems and aren't Epp's scope; they are mason or decorative concrete contractor scope. Surface resurfacing. Worn or rough concrete surface that the homeowner wants to look new is not a crack repair scope; it is decorative concrete overlay contractor scope. Epp says so on the inspection. Sealing a crack with rigid epoxy on exterior concrete in this climate is also the wrong scope. It gets done because the homeowner asked for epoxy. Epp explains the chemistry, declines to use epoxy where it will fail, and offers the flexible polyurethane scope instead. Same goes for sealing a hairline crack too narrow to admit water. Epp will tell them.

Nebraska, Iowa, and northern Kansas exterior slabs see repeated freeze-thaw cycles each winter, with surface temperatures swinging from below freezing overnight to above freezing by midafternoon. Each cycle works existing cracks open and admits the meltwater that becomes the next cycle's frost wedge. Flexible polyurethane sealant absorbs that cycling; rigid epoxy doesn't. Missouri and southeastern Kansas see fewer freeze cycles but more thermal cycling. Direct sun on a driveway can swing the surface temperature widely on a July day, expanding and contracting the slab. The same chemistry logic applies: flexible product survives, rigid product fails. De-icing salt across the territory attacks both the concrete (creating spalling and surface scaling) and any non-UV-rated polyurethane (degrading the sealant over time). Epp specifies UV-stable polyurethane formulations rated for direct sun and salt exposure on every exterior crack repair.

Epp seals stable exterior cracks, lifts settled slabs adjacent to cracks, and pours new concrete where a slab has reached end of life. There are three adjacent scopes Epp does not perform. Decorative resurfacing, stamped overlay, or staining. That is decorative concrete contractor scope. Tree root removal or pruning when roots caused the crack. That is arborist scope. Re-grading the surrounding landscape or installing a French drain to fix drainage causes. Landscape contractor and Epp's own drainage scope respectively. Drainage work is on Epp's basement-waterproofing pages, not exterior crack repair.