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 between 40°F and 140°F surface temperature in a single summer day, 50-plus freeze-thaw cycles each winter, vehicle and foot load that flexes the slab thousands of times a year, 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 3/4 of an inch on one side. The crack will reopen within a year 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 with roughly 7,000 to 12,000 psi tensile strength. Wonderful inside a basement where the wall is temperature-stable and movement-free. Outside on a driveway in the Midwest, the same epoxy cracks within 3 to 5 winters because freeze-thaw expansion and contraction cycle the slab 0.005 to 0.010 inch per cycle, the epoxy can't flex with the movement, and the bond fails at the concrete face. Flexible polyurethane sealants cure to a Shore A hardness of 25 to 40. 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. 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.

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 wider than 1/4 inch, 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 to grade, then seal the now-closed crack with flexible polyurethane. End-of-life concrete. Multiple structural cracks (5 or more on a single slab section), crumbling edges, surface spalling covering 40 percent or more of the area, structural cracks 1/4 inch or wider with active movement. Sealing or lifting end-of-life concrete buys 2 to 4 years before re-failure. 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 and 20 minutes of installer time. It gets installed any time the on-site inspection can't definitively call a crack stable or moving. The homeowner reports the crack getting wider over the last year, secondary cracking has appeared nearby, the slab has visible offset that might be settling further. The monitor is bonded across the crack and re-measured at 30, 60, and 90 days before injection or sealing is committed. About one in five exterior crack inquiries gets a monitor first in Epp's practice, and roughly one in eight monitored cracks 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 reopens within 12 to 18 months. The monitor pays for itself the first time it changes a diagnosis.

Every exterior crack has a cause underneath it. Frost heave at an expansion joint. Hydroconsolidated loess under the slab where a downspout has been discharging for 10 years. Tree root pressure lifting the corner of a sidewalk panel. 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), re-grading a drainage swale (landscape scope, not Epp). Then quotes the lift-and-seal or seal-only scope contingent on the cause being addressed. Sealing without cause correction is a 12 to 24 month repair. Sealing with cause correction is a 10 to 15 year repair.

A crack gauge is a thin plastic strip with progressively wider lines printed on it. Held against the crack, it reads the width to the nearest 1/64 inch. A crack under 0.020 inch wide is held closed by surface tension against most water entry. Sealant is cosmetic, not waterproofing. A crack 0.020 to 0.060 inch wide is the typical sealing target. Wide enough to admit water, narrow enough that flexible polyurethane fills it cleanly. A crack 1/16 to 1/4 inch wide needs a backer rod (closed-cell foam pushed into the crack to limit the depth of sealant) before sealing. A crack wider than 1/4 inch is usually a settlement crack or end-of-life concrete and gets 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; re-measured at 30, 60, and 90 days. 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. Cracks wider than 1/4 inch 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. Polyurethane sealant skins in 30 to 60 minutes and reaches initial cure in 24 hours. Slab can be walked within an hour and driven on within 24. Final cure to full elastic recovery takes 7 days. Homeowner walks the work with the installer before sign-off. Written warranty documents crack location, width, depth, products used, and any cause-correction recommendations. 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 lifts to grade, the crack closes mechanically as the lift restores the slab geometry, and then the now-closed crack is sealed with flexible polyurethane. Both scopes are done in the same site visit when access allows.

The honest part. Epp seals stable cracks and lifts settled slabs. Three scenarios where crack repair is the wrong scope. End-of-life concrete. Multiple structural cracks, crumbling, spalling. Sealing or lifting end-of-life slabs buys 2 to 4 years; 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. 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. Decorative concrete overlay contractor scope. Epp says so on the inspection. Also wrong scope. Sealing a crack with rigid epoxy on exterior concrete in this climate. 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 narrower than 0.020 inch. Epp will tell them.

Nebraska, Iowa, and northern Kansas exterior slabs see 50-plus freeze-thaw cycles each winter, with surface temperatures swinging from below 0°F overnight to above 32°F by midafternoon for 60 to 90 cycles between November and March. Each cycle works existing cracks open 0.005 to 0.010 inch 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 from 40°F at dawn to 140°F at midafternoon in July, expanding and contracting a 12-foot slab section roughly 0.02 inch per cycle. Same chemistry logic. 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 in 3 to 5 years). 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. Three adjacent scopes Epp does not perform. Decorative resurfacing, stamped overlay, or staining. Decorative concrete contractor scope. Tree root removal or pruning when roots caused the crack. 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.

Exterior concrete crack repair from Epp Foundation Repair runs across these anchored components. Inspection and quote: no-cost on-site visit, Customized Repair Estimate within 48 hours, scope decision (seal, lift-and-seal, or a new pour) included. Customized Repair Estimate after on-site inspection reflects your scope. Epp Foundation Repair is BBB A+ accredited and a two-time BBB Integrity Award winner (2011 and 2016). Recognition tied directly to declining to seal end-of-life concrete that needs replacement, declining to use rigid epoxy on exterior slabs where flexible polyurethane is the correct chemistry, and installing crack monitors before committing to repair when movement is questionable.