DIY Concrete Slab Patio Extension: Sod to Sealer
- Staff Desk
- 2 hours ago
- 7 min read
Transforming a muddy, unused strip of lawn into a durable, low-maintenance concrete slab doesn’t have to be a mystery. This blog walks through the entire build of a 12-ft by 22-ft slab poured in three manageable sections, covering planning, excavation, drainage, base prep, forming, reinforcement, mixing, finishing, curing, and cost control.
Project snapshot
Footprint: 12 ft × 22 ft (≈ 264–270 sq ft poured in three ~90 sq ft sections)
Use case: Hardscape connection between an existing patio and a fence, replacing an awkward grassy area prone to mess and runoff
Pour strategy: Three separate placements to keep quality high and workload reasonable
Thickness: ~4–4½ in concrete with reinforced dowels between sections and into the existing slab
Base: #57 crushed stone, plate compacted
Finish: Broom texture with clean edged perimeter
Curing: Acrylic cure & seal immediately after brooming, then covered; rain the following day aided moisture retention
All-in cost target: ~$1,900 (rentals + gravel + rebar + 171 bags of concrete + tools + forms)
Plan the slab with water in mind
Concrete works best when the site and drainage plan are set before the first shovel goes in. This build sits between a patio and a fence and naturally collects water during storms. The design choices reflect that:
Positive slope: Aim for about 1½ in of fall from the patio edge toward the fence across the slab width. Confirm with a rotary laser or builder’s level.
Under-slab drainage path: A 4-in SDR35 drain line set in gravel (acting like a mini French drain) escorts groundwater to a lower discharge point.
Future-proofing: Conduit sleeves under the slab preserve the ability to pull low-voltage or power in the future without cutting concrete.
Movement joints where needed: Slab sections are doweled together and into the existing patio for alignment, but the interface with the sidewalk is isolated by compressible joint material to let that edge move independently.
Tools, rentals, and materials
Rentals (one to two days is typical):
Sod cutter – optional, but it keeps stripped turf intact and speeds grading later.
Concrete cutoff saw – for clean joints in the existing sidewalk and tie-in points.
Mini excavator – compact machine for tight access; also handles tree removal and sidewalk breakup.
Hammer drill – for dowel holes in existing concrete.
Plate compactor – non-negotiable for consolidating the stone base.
Materials:
Concrete: 80-lb premix bags; 57 bags per ~90 sq ft section (≈ 171 total).
Aggregate base: #57 crushed stone (angular, ¾–1 in).
Rebar: ½-in for dowels; ⅜-in grid across the slab; tie wire.
Formwork: Straight 2×4s or 2×6s, stakes, and form oil.
Drain line: 4-in solid SDR35 with gravel surround.
Conduit sleeves: Rigid or schedule 40 PVC in two sizes.
Jointing: Expansion foam for the sidewalk interface.
Finishing: Bull float, magnesium float, edger, broom, long handles/poles.
Cure: Acrylic cure & seal suitable for exterior flatwork.
Step 1: Strip turf and cut concrete cleanly
Sod removal: Cutting turf in 1¼-in thick, shovel-length strips keeps pieces manageable and reusable elsewhere. This avoids mixing root mats into the excavation spoils.
Sawcut tie-ins: Use a sharp blade and steady feed with a concrete saw to create straight, square edges where the new slab meets the old. Smaller segments are easier to haul and dispose of.
Step 2: Excavation and rough grading
Target depth: Enough to accommodate the base, finished slab thickness, and slope. Depth will vary because existing grade rarely sits perfectly flat.
Protect native subgrade: Avoid over-digging; the compacted native layer is stronger than freshly disturbed soil.
Material handling: In tight yards, an excavator plus a garden trailer behind a lawn tractor can be more practical than a larger skid steer. Multiple passes may be required; don’t rush compaction to save a trip.
Step 3: Utilities and drainage under the slab
Conduit trench: Two different-size conduits set below subgrade allow future pulls without saw-cutting. Backfill and compact the trench carefully to avoid later settlement.
French-drain concept: The 4-in solid SDR35 line sits in compacted gravel, sloped to daylight. Gravel around the pipe encourages water beneath the slab to migrate toward the trench and exit.
Backfill choices: Use gravel around drains for permeability; use soil around conduits if standing water near the conduit is undesirable. Compact both.
Step 4: Base rock, laser checks, and compaction
Place #57 stone to roughly 2–4 in, feathering depth to correct minor excavation variances.
Set slope with a rotary laser: Mark “to grade” dots across the field for reference.
Compact: A plate compactor locks angular stone together; a properly compacted bed will feel surprisingly solid underfoot. Don’t skip this.
Tip: #57 is ideal under slabs because the fractured faces interlock under vibration. Rounded river rock doesn’t compact as well.
Step 5: Forms, dowels, and rebar
Formwork
Use 2× lumber with staked support and set the top of the forms to finished elevation and slope. Treat the form faces with oil to ease removal.
Doweling
Drill the existing patio edge and epoxy or drive ½-in rebar dowels at even spacing. These hold transitions flush and reduce differential movement.
Isolate the sidewalk edge with foam expansion material instead of dowels, creating a planned movement joint where conditions demand it.
Rebar layout
Set ⅜-in bars perpendicular to the dowels and tie intersections with wire.
Keep steel in the lower ¼ to ⅓ of the slab using small rocks or chairs. Steel on the subgrade doesn’t help; steel too high can telegraph.
Why rebar over wire mesh? Mesh often ends up at the bottom if not chaired and lifted properly during placement. Tied rebar can be positioned correctly before the pour and left alone.
Step 6: Mixing strategy that keeps quality up
Bag-mixing a 12×22 slab is possible when broken into three pours of ~90 sq ft each:
Mixer choice: A continuous-feed mixer with a bag breaker and water dial keeps output steady.
Crew flow: One person loads mix and monitors consistency; another rakes and places.
Output reality: Expect about 1 hr 15–20 min of continuous mixing per 1.25–1.33 yards (~57 bags).
Consistency control: The first few minutes after starting or restarting can run too wet or too dry. Catch off-spec material in a bucket, adjust by hand, and fold back in later.
Step 7: Placement, screeding, and finishing
Placement & screed
Place from far to near, keeping the head of concrete just ahead of the screed.
Use a straight 2× as a screed board riding the forms; go slow and let the blade saw back and forth to cut highs and fill lows.
Initial bull float (immediately after screed)
A bull float levels ridges, fills voids, and brings up paste (“cream”). This sets the stage for a uniform finish.
Edge early
Run an edger once around while the slab is still plastic to create clean borders. It’s easier now than later.
Mag float at set
When a test touch allows only slight fingertip indentation, use a magnesium float to close pinholes and refine the plane. Avoid overworking; the goal is paste consolidation, not burnishing.
Broom texture
Pull a broom consistently in one direction to add traction and disguise minor tool marks. Brooming also standardizes appearance across pours.
Final edge pass
One last edging after brooming creates a crisp framed border that looks intentional and professional.
Step 8: Curing and weather protection
Cure & seal: Spray an acrylic cure & seal immediately after brooming. This locks in moisture for a stronger cure and reduces dusting. Initial appearance can look blotchy; coverage is what matters.
Shade and cover: Tent with tarps to reduce heat and evaporation, especially in hot weather.
Rain bonus: Light rain after sealed placement can actually assist curing if the surface film is intact.
Jointing and movement strategy
Between new sections: Doweled interfaces help all sections act together.
At sidewalk: A compressible expansion joint decouples the slab from another mass that may move differently.
Saw cuts vs. hand tooling: For small sections with strong perimeter definition and consistent doweling, many builders rely on edges and natural shrink patterns. If saw-cut joints are desired, cut at the right window (once the slab supports the saw but before random cracking).
Edges, posts, and “don’ts” with floating slabs
Don’t tie a floating slab to structure (awning posts, fence posts, house foundation). Posts get their own footings and are isolated from the slab with joint material.
Perimeter solutions: A temporary 2×10 can hold grade at high sides; later, a cast curb or masonry edging can finish the look and help manage runoff.
Real-world cost breakdown (target ≈ $1,890)
Equipment rentals: ~$425 (excavator, cutoff saw, sod cutter, hammer drill, plate compactor)
#57 stone: ~$150
Rebar & ties: ~$85
Concrete: 171 bags of 80-lb premix @ $5.15 ≈ $880
Finishing tools: ~$300 (economy bull float + quality edger/mag float)
Forms, stakes, consumables: ~$50
This DIY approach avoided truck minimums, scheduling constraints, and short-load fees, while keeping quality high by splitting the work into three controlled placements.
Quality checkpoints that matter
Slope verified with laser before concrete day.
Base compaction that feels firm underfoot.
Rebar position in the lower third, tied and supported.
Dowels in clean holes at the patio tie-in; isolation foam at the sidewalk.
Consistent mix; catch initial off-spec discharge and re-blend.
Finish timing: bull float immediately, mag float at the right set, broom once, edge twice.
Cure immediately, then shade; protect from pets, kids, and sprinklers.
Common mistakes to avoid
Skipping compaction: Loose base leads to settling and cracks.
Overworking the surface: Too much troweling can seal in bleed water and cause scaling.
Mesh on the dirt: Reinforcement only works when it’s in the slab, not under it.
Tying to structural posts: Creates stress fractures during seasonal movement.
No allowances for water: Without slope and a drainage path, flatwork fails faster.
Performance add-ons
Full French drain along the upslope side to intercept runoff before it hits the slab.
Perimeter curb or edging to contain stone mulch and direct sheet flow.
Surface treatments later: Decorative overlays, tiles, or coatings can refresh appearance after a few seasons of service.
When to phase the work
Breaking the slab into three pours is a smart call for homeowners. Each section (~90 sq ft) can be placed, finished, and cured without rushing, and skills improve with each round. The mix equipment can run continuously for about 75–80 minutes per section without shutting down, which keeps consistency and productivity high.
Safety quick list
Eye, ear, and respiratory protection around saws and cement dust.
Gloves and sleeves for cement exposure.
Stable footing and two-person lifting protocols for 80-lb bags.
Keep cords, hoses, and tools out of the discharge and walk paths.
Respect pinch points on compactors and mixers.
The bottom line
A 12×22 concrete slab can be planned, poured, and finished to pro-level standards by a small team in phases, provided the fundamentals are respected:
Drainage and slope come first.
Base compaction is non-negotiable.
Rebar and dowels are positioned with intention.
Finishing happens at the right moment, not the convenient one.
Curing begins immediately and continues with protection.
With a realistic budget of about $1,900 and smart sequencing, an awkward strip of grass becomes a durable, clean, and usable extension of outdoor living space—ready for furniture now and future upgrades later.
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