Why this skill matters

The water ratio and the bonding adhesive. Two things most concrete guides mention but don't emphasize. Two things that determine whether a repair lasts.

Concrete is the most durable residential construction material — properly placed, it outlasts every other material in the house. The failures are almost always installation failures: too much water weakened the mix, the bonding adhesive was skipped on a repair, the form boards weren't level, the curing phase was skipped. These aren't subtle professional skills. They're straightforward steps that produce durable results when followed and failed repairs when skipped.

The water-to-cement ratio is the single most important concrete variable. Standard pre-mixed bags are designed to be mixed with a specific amount of water. Adding more water — because it makes the concrete easier to work — reduces the final strength by a predictable amount. A mix with double the specified water loses approximately 40% of its design strength. The concrete looks similar, but the mechanical properties that make it durable are diminished.

Post-setting is probably the most common homeowner concrete application. Fence posts, mailbox posts, and equipment supports all go in concrete. The difference between a post that's plumb after a decade and one that leans in three years is the depth of the hole (below frost line), the hole-to-post diameter ratio, and whether the post was braced while the concrete cured. All three are specified in this page — because all three are commonly skipped.

What you should be able to do

L1 Household Basic

Mix pre-bagged concrete to the correct consistency — thick oatmeal, not soup

Apply concrete bonding adhesive before any patch application

Patch a spalled or cracked concrete surface with vinyl concrete patcher

Cure fresh concrete correctly — cover and keep moist for 3–7 days

Identify the correct concrete repair product for each situation

L2 Capable Homeowner

Set a fence or mailbox post — correct hole depth below frost line, post plumb, braced while concrete cures

Build, level, and square form boards for a small slab

Screed, float, and edge a small concrete slab

Tool control joints in a slab to direct cracking to predictable locations

Caustic hazard: Uncured concrete has a pH of 12–13 — comparable to strong lye. Prolonged skin contact causes chemical burns that aren't immediately painful (the damage happens before the sensation registers). Wear nitrile or rubber gloves for all concrete work. If concrete gets in the eyes: flush immediately with large amounts of water for 15–20 minutes and seek medical attention.

Products and their correct applications

The right product for the job — concrete, mortar, and repair compounds are not interchangeable.

Pre-mixed concrete (Quikrete, Sakrete)

Contains portland cement, sand, AND aggregate (gravel). For structural applications: post footings, slabs, and any application requiring strength. The aggregate is what makes it concrete. Available in 50# and 80# bags; 80# bags are more economical but harder to handle. One 80# bag = approximately 0.6 cubic feet of cured concrete.

Vinyl concrete patcher (Quikrete Concrete Patch)

A polymer-modified mortar designed to bond to existing concrete. For repairing spalled surfaces and filling cracks. Requires bonding adhesive under it. Available pre-mixed (more expensive) or in dry form. Minimum effective thickness: ¼"–½". Don't use standard concrete mix for surface patches — the aggregate prevents proper thin-application bonding.

Concrete bonding adhesive — the most important product on this list

Applied before any patch, repair, or new concrete placed against old concrete. Brush onto the clean dry surface and allow to become tacky before placing the patch. Without this product, new concrete doesn't bond reliably to old concrete and delamination is common. Not optional for any repair application.

Hydraulic cement

Sets in 3–5 minutes even in contact with flowing water. For active water seepage through foundation cracks, basement walls, and below-grade applications. Not for general patching — the fast set time makes it impractical for surface work, and it doesn't bond as well as vinyl concrete patcher in dry applications.

Concrete sealers (silane/siloxane penetrating type)

Applied to sound, cured concrete to reduce water absorption and protect against freeze-thaw spalling and deicing salt damage. Apply every 3–5 years to exposed concrete (walkways, steps, patios). Apply to completely dry concrete in temperatures above 50°F. Not a substitute for patching — seal only after all cracks and spalls have been repaired.

Common concrete problems — causes and diagnosis

Most concrete surface failures trace to installation, not material.

Surface spalling — repairable with patcher

The top surface breaks away in flakes or chips. Cause: freeze-thaw cycling of water that entered through surface cracks, deicing salt damage (salts lower the freezing point and deepen the freeze-thaw cycle), or inadequate curing when originally placed. Fix: vinyl concrete patcher over clean, bonding-adhesive-primed surface. Seal with a penetrating sealer after repair to prevent recurrence.

Control joint cracks — normal, don't repair

Concrete cracks as it cures and in response to temperature cycles — this is inevitable and expected. Control joints (tooled or sawed into slabs) direct this cracking to specific predictable locations. A slab that cracks at its control joints is performing correctly. These cracks can be filled with a flexible polyurethane caulk if water infiltration is a concern, but they don't require patching.

Delaminating patch — failed previous repair

A previous repair that has separated from the surrounding concrete. The most common cause: bonding adhesive was not applied before the original patch. Fix: remove the failed patch completely by chipping until the edges are firmly adhered. Clean the area. Apply bonding adhesive. Patch again. A patch applied over a delaminating patch produces a third layer of delamination.

Heaving, tilted slabs, or widespread cracking — structural issue first

Slabs that have lifted, tilted, or cracked across their full surface (not at control joints) indicate a subgrade problem: expansive clay soil that swells when wet, inadequate compaction of the fill below the slab, or tree root heaving. Patching the surface without addressing the subgrade produces repeated failures. Identify the cause before any repair — in many cases, the slab must be removed, the subgrade corrected, and a new slab placed.

Leaning fence post

Causes: hole too shallow (above frost depth, so freeze heave shifted the post), concrete volume too small relative to the hole (inadequate bearing), or post not braced while concrete cured. Fix: excavate around the post, remove old concrete if present, re-dig to correct depth and diameter, reset with fresh concrete, and brace until cured.

Step-by-step procedures

Four procedures. The bonding adhesive step applies to every repair — it's never optional.

L1

Mixing concrete correctly

The consistency check — the most important thing to get right before placing any concrete. Mix in a container, never on the ground (soil contamination weakens the mix). A wheelbarrow works for larger batches; a 5-gallon bucket works for patches.

The slump test: After mixing, pile some concrete on a flat surface and press down with the flat of the trowel. The concrete should hold its shape without spreading. If it flows outward: too much water. If it crumbles: too little water, or add just a few drops more at a time.

1Put on gloves and eye protection before touching concrete. Concrete work is sustained skin exposure — wear nitrile or rubber gloves throughout.

2Pour the dry concrete mix into the mixing container first. Make a depression in the center. Add approximately ¾ of the specified water amount into the depression — not all of it.

3Mix from the center outward, incorporating the dry material into the water. Work all the way to the bottom of the container — dry material hiding at the bottom of a wet-looking batch is the most common mixing error.

4Assess the consistency. Test by dragging a finger through the mix. It should leave a clean furrow that holds its shape. Add remaining water a tablespoon at a time until this consistency is achieved. Stop adding water when it's workable — resist the temptation to add more "to make it easier."

5Work in batches sized to what can be placed and finished in 30–45 minutes. Concrete begins setting as soon as water is added — a batch that sits while the previous batch is being placed may have stiffened past workable consistency. Don't add water to revive stiffened concrete — it weakens the mix.

L1

Concrete patching — spalls and cracks

The procedure for surface spalling repair, crack filling, and step edge repair. The bonding adhesive step is what separates patches that last from patches that delaminate. Do not skip it.

1Prepare the surface: Remove all loose concrete with a hammer and cold chisel. Any material that moves, crumbles, or sounds hollow when tapped must come out — it's not bonded and will continue to delaminate under the patch. Wire brush the surface. Vacuum out all dust.

2For cracks: widen to at least ¼" and undercut the edges (wider at the bottom than the top) with a cold chisel. This mechanical key prevents the patch from being lifted out of the crack by traffic or freeze-thaw.

3Apply bonding adhesive. Brush onto the clean, dry surface covering the full patch area and 1"–2" around it. Allow to become tacky — typically 20–30 minutes. Don't skip this step.

4Mix vinyl concrete patcher to peanut butter consistency. Apply while the bonding adhesive is still tacky. Press firmly into cracks and depressions with a margin trowel. Minimum thickness: ¼" for surface repairs, ½" for structural bearing repairs.

5Strike flush with the surrounding surface and feather the edges. Don't leave a ridge at the patch boundary — water pools against ridges and accelerates the next failure.

6Cure: Cover with plastic and keep the patch moist for 24–48 hours. Concrete patcher loses water faster than standard concrete because of the thin application and large surface area. Early drying reduces strength and bond.

L2

Setting a post in concrete

Fence posts, mailbox posts, and small structure supports. Depth below frost line is the most commonly skipped specification — and the reason posts lean after 3–5 years in freeze-thaw climates.

Frost depth by region: Northern Minnesota, Wisconsin, Michigan: 42"–48". New England, Northern Plains: 36"–42". Mid-Atlantic, Pacific Northwest: 24"–30". Southeast, Southwest: 12"–18". Check your county's frost depth — it's often in the local building code.

1Dig to correct depth and diameter. Depth: local frost depth + 6" (the extra 6" provides concrete bearing below the frost heave zone). Diameter: 3× the post diameter — 4×4 post needs 12" hole, 6×6 needs 18" hole. Use a clamshell digger (manual) or power auger.

2Add 6" of coarse gravel at the hole bottom. Tamp firmly. This drainage layer prevents the post base from sitting in water — wood post bases rot, and the water-saturated concrete below the post is the most vulnerable area for freeze heave.

3Set the post. Brace it with two 2×4 diagonal braces attached to ground stakes at right angles to each other — one brace holds the post plumb in one direction, the other holds it plumb in the other. Check plumb in both directions with a level before pouring.

4Mix concrete to a workable (not wet) consistency. Pour around the post in 6"–8" lifts, tamping each lift with a rod or stick to remove air pockets. Don't pour too fast — the concrete needs to consolidate against the hole walls.

5Slope the concrete top away from the post: build up slightly against the post face and taper down toward the hole edge. This directs water away from the wood-concrete interface — the point where rot and freeze damage concentrate.

6Leave braces in place 24–48 hours minimum. Concrete at the bottom of the hole sets slower than the top because of lower temperature and less air exposure. The post must not be disturbed until the entire column is set.

L2

Pouring a small slab

For equipment pads (generator, AC condenser, hot tub), shed floors, doorsteps, and similar applications under about 50 square feet. Larger than this and bag concrete becomes impractical — order ready-mix.

Preparation — forms and base

1Excavate to 4" depth (6" in freeze-thaw climates for exposed slabs). Add 2" of compacted gravel. Compact the gravel — a plate compactor is ideal; a hand tamper works for small areas. An uncompacted gravel base settles unevenly and causes the slab to crack.

2Install 2×4 form boards at the slab perimeter. Level the forms: set each board level with a 4-foot level and secure with 2×4 stakes driven every 18"–24". All form tops should be at the same height — this is the finished slab elevation. Square the form: measure corner to corner diagonally — if the measurements are equal, the form is square.

Placing, screeding, and finishing

3Pour concrete starting at one end. Use a hoe or shovel to roughly level the concrete across the form. Don't overwork — overmixing concrete in the form brings excess water to the surface, which weakens the surface layer.

4Screed: Work a straight 2×4 across the form tops in a sawing (back-and-forth) motion, advancing toward you at about 1" per pass. The screed rides on the form tops and levels the concrete to the form height. Move excess concrete ahead of the screed; fill low spots by pulling concrete from adjacent high areas.

5Float: Work a float in large circular arcs across the surface to smooth the screed marks and further consolidate the concrete. A magnesium float is easier to use than wood. The floating also pushes coarse aggregate slightly below the surface.

6Wait for bleed water to disappear. Fresh concrete bleeds water to the surface — a sheen visible on the surface. Finishing before this disappears traps the water under the surface layer, creating a weak, dusting layer that fails quickly. When the sheen is gone and footprints leave a firm impression about ¼" deep: time to finish.

7Edge, joint, and final finish. Edge: run an edging tool along the form boards to round the corners. Joint: tool control joints across the slab every 8–10 feet (for slabs over 10 feet in one dimension) using a jointing tool. Broom finish: drag a broom across the surface in one direction for texture and traction. Or steel trowel for a smoother finish.

8Cure: Cover with plastic sheeting immediately. Mist the surface with water daily for 3–7 days. Remove forms after 24–48 hours. Allow 7 days before loading with equipment. The 28-day cure period is when concrete reaches full design strength — don't rush loading the slab.

Emergency and seasonal application

Three scenarios where concrete skills prevent compounding damage.

Step or walkway safety hazard

A cracked or heaved concrete step edge is a trip hazard — potentially a severe one. Emergency: use an angle grinder to chamfer the sharp edge, eliminating the trip hazard. Permanent repair: patch with vinyl concrete patcher over bonding adhesive within the same season. Don't leave cracked edges untreated through a winter — freeze-thaw cycles accelerate the deterioration.

Pre-winter concrete sealing

Apply a penetrating silane/siloxane concrete sealer to all exposed concrete walkways, steps, and patios in late fall after all patch work is complete and cured. This reduces water absorption during the freeze-thaw season. Sealer applied over spalled or cracked concrete seals in moisture — address all damage first, then seal the repaired surface.

Post reset after storm or heave

A fence post that leaned or heaved from freeze-thaw needs to be reset correctly — straightening the post without fixing the depth and diameter issue produces the same failure again in 3–5 years. Excavate, remove old concrete (or the post if severely rotted at the base), dig to correct depth and diameter, reset with fresh concrete, and brace. This is a half-day project done correctly.

Mandatory section

When to call a concrete contractor.

Surface patching, post-setting, and small slabs are well within homeowner territory. Several concrete situations require professional equipment, structural expertise, or scale.

Structural concrete — footings, foundations, retaining walls

Structural concrete is engineered: the mix design, rebar size and placement, and footing depth are specified by an engineer based on loads, soil conditions, and local code requirements. Homeowner-mixed concrete without engineering design for load-bearing applications may meet code or may not, and there's no way to verify strength after placement without destructive testing.

Slabs over 50–100 square feet

Bag concrete for a large slab is physically impractical — a 10'×10'×4" slab requires roughly 45 bags. Ready-mix concrete (ordered by the cubic yard from a concrete supplier) is more economical and delivers concrete that's mixed to consistent proportions. Ready-mix requires being ready to place, screed, and finish a full load (typically 1 cubic yard minimum) before it begins setting — usually with a crew of 2–3 people.

Driveways and reinforced slabs

Driveways carry vehicle loads and require 5"–6" slab thickness, rebar or mesh reinforcement, proper base preparation, and usually permits. Decorative stamped or colored concrete requires specialized tools, pigment, release agents, and sealing — the technical window for applying these finishes is narrow and requires experience. Both are typically contractor work.

Slab demolition and removal

Breaking up an existing slab requires a jackhammer or electric demolition hammer, which can be rented — but the debris requires a dumpster or a truck with significant haul capacity. A 10'×10' slab generates approximately 4,000 pounds of rubble. This is renting equipment and dumpster territory, not impossible for a homeowner, but worth evaluating against the cost of a contractor with a skid steer and dump truck.

Practice project

Patch one spalled or cracked area this season.

Time: 2–3 hours. Cost: $25–$40 in bonding adhesive and vinyl patcher. Outcome: the full patching sequence completed on a real surface, with a durable result if the bonding adhesive step was followed.

1.

Walk every concrete surface on the property — walkways, steps, garage floor, driveway. Look for spalling, edge chips, and cracks. The step edges are the most common failure point: they take direct impact from foot traffic and are exposed to freeze-thaw on multiple faces.

2.

Buy concrete bonding adhesive, a 10-lb container of vinyl concrete patcher, and a margin trowel. Total: $25–$40.

3.

Address one damaged area following the procedure. Clean, chisel, brush, bond, patch, cure. This teaches the sequence in a low-stakes context before tackling larger damage.

4.

Inspect 24 hours later: press a thumb firmly on the patch. It should feel hard and not compress. Inspect the edges: no gaps between the patch and surrounding concrete. If either is wrong, address before the next freeze cycle.

Next project: Set a 4×4 post for a garden stake, small gate post, or mailbox — whatever applies to the property. This teaches the depth, bracing, and concrete-sloped-away-from-post skills at small scale before a full fence installation.

Recommended resources

Books, resources, and the credential.

Books and manuals

Quikrete, Sakrete, and other pre-mixed concrete manufacturers publish free project guides on their websites covering post-setting, small slabs, and patching with specific product instructions. These are more practically useful than general concrete textbooks for homeowner applications.

Concrete, Masonry, and Brickwork (DOD Technical Manual TM 5-742) — a public domain document covering concrete fundamentals at a depth appropriate for general application. Available free online from multiple sources.

Free resources

YouTube — This Old House concrete and masonry series: clear technique demonstrations for patching, post-setting, and small slab work with consistent attention to the preparation steps most guides skip.

Local frost depth: check your county or state building code, or the ASHRAE climate map. Also searchable by ZIP code at several frost depth databases maintained by civil engineering resources.

Community college masonry and concrete programs — see your state's Learning page.

The credential

ACI (American Concrete Institute) offers certifications for concrete field testing, flatwork finishing, and concrete construction inspection. These are professional credentials used in commercial construction. No credential is required for homeowner concrete patching, post-setting, or small slab work. General contractor license is required for permitted structural concrete in commercial contexts.