Concrete Flatwork Inspection

Per IRC R506.1, concrete slab-on-grade floors shall be a minimum 3.5 inches thick and placed on compacted earth or granular fill. Subgrade soil must be compacted to a minimum 95% Standard Proctor density (ASTM D698). A vapor retarder of minimum 6-mil polyethylene or equivalent shall be placed between the base course and concrete per IRC R506.2.3, with joints lapped a minimum of 6 inches. A minimum 4-inch-thick base of clean graded sand, gravel, or crushed stone must be provided per IRC R506.2.2.

1. Verify subgrade soil has been proof-rolled and compacted to 95% Standard Proctor — request density test reports per ASTM D698

2. Confirm a minimum 4-inch granular base course is placed and uniformly graded per IRC R506.2.2

3. Inspect vapor retarder installation — verify minimum 6-mil thickness, 6-inch lap at joints, and sealed penetrations per IRC R506.2.3

4. Check for standing water, soft spots, or organic material on the subgrade surface

5. Verify the subgrade is graded to correct elevation and slope per plans, with no areas of fill exceeding engineered limits

- Inadequate compaction causing differential settlement and slab cracking

- Missing or damaged vapor retarder allowing moisture migration through slab

- Organic material or topsoil left beneath granular base

- Uneven subgrade creating variable slab thickness and stress concentrations

- Granular base not meeting gradation requirements or insufficient thickness

Per ACI 318 Chapter 20, minimum concrete cover for reinforcement in slabs cast against and permanently exposed to earth is 3 inches; for slabs not exposed to weather or earth contact, minimum cover is 3/4 inch. Welded wire reinforcement (WWR) per ASTM A1064 shall be positioned at mid-depth or upper third of slab per ACI 302.1R. Rebar splices must maintain a minimum 40-bar-diameter lap length per ACI 318 Section 25.5. Reinforcement must be supported on chairs or bolsters to maintain specified cover.

1. Verify reinforcement type and size match structural drawings — typical residential flatwork uses 6x6-W1.4xW1.4 WWR or #3 rebar at 18 inches on center

2. Confirm reinforcement is supported on chairs or bolsters at correct height to maintain specified cover per ACI 318 Chapter 20

3. Check that WWR sheets are lapped a minimum of one full mesh spacing plus 2 inches per ACI 318 Section 25.4

4. Inspect rebar for excessive rust, scale, oil, or coatings that would reduce bond per ACI 318 Section 26.6.1

5. Verify dowels and tie-ins to adjacent structures are placed per plans and properly positioned

- Reinforcement left lying on vapor retarder instead of supported on chairs (no cover achieved)

- WWR pulled up after concrete placement without proper initial positioning

- Insufficient lap at WWR sheet joints causing discontinuous reinforcement

- Wrong reinforcement size or spacing relative to structural plans

- Rebar chairs spaced too far apart allowing reinforcement to sag between supports

Per ASTM C94, ready-mixed concrete shall be discharged within 90 minutes or before 300 drum revolutions after water is added to the mix. Slump shall be within the specified tolerance per ASTM C143 — typical flatwork slump is 4 inches plus or minus 1 inch per ACI 302.1R. Air content for exterior flatwork exposed to freeze-thaw cycles shall be 5% to 8% per ACI 318 Table 19.3.3.1. Minimum compressive strength for residential flatwork is 2,500 psi per IRC R402.2, though 3,500 to 4,000 psi is typical for driveways and exterior slabs. Concrete temperature at placement shall be between 50 degrees F and 90 degrees F per ACI 305R and ACI 306R.

1. Review batch tickets for each truck — verify mix design, water-cement ratio, admixtures, and batch time per ASTM C94

2. Perform slump test per ASTM C143 at point of placement — reject loads outside specified tolerance

3. Measure air content using a Type B pressure meter per ASTM C231 for exterior flatwork

4. Check concrete temperature with a thermometer — verify it is between 50 degrees F and 90 degrees F at time of placement

5. Observe placement procedures — concrete should not be dropped more than 5 feet and must be consolidated with vibration per ACI 302.1R

6. Verify no water has been added to the truck beyond batch-ticket quantities per ASTM C94

- Excess water added on-site to increase workability, reducing strength and increasing shrinkage

- Concrete arriving outside the 90-minute discharge window per ASTM C94

- Missing or inadequate air entrainment for exterior slabs in freeze-thaw environments

- Concrete placed at temperatures below 50 degrees F without cold-weather protection per ACI 306R

- Segregation from excessive drop height or improper chute placement

Per ACI 302.1R, finishing operations shall not begin until bleed water has dissipated from the surface. Bull-floating or darbying must be completed promptly after strike-off. For interior slabs requiring floor coverings, surface flatness and levelness shall meet minimum FF 25 / FL 20 per ASTM E1155 for conventional construction, or FF 35 / FL 25 for moderately flat floors. Exterior flatwork shall have a broom finish or equivalent non-slip texture. The slab surface shall not deviate more than 1/4 inch in 10 feet when checked with a straightedge per ACI 302.1R for standard flatwork.

1. Observe that finishing does not begin while bleed water is still present on the surface — working water into the surface causes scaling and dusting

2. Check flatness with a 10-foot straightedge — maximum gap of 1/4 inch for standard flatwork per ACI 302.1R

3. Verify exterior surfaces have a broom finish or textured surface for slip resistance per ACI 302.1R

4. For interior slabs, confirm FF/FL measurements meet specified values per ASTM E1155 within 72 hours of placement

5. Inspect for trowel marks, chatter, discoloration, or surface defects indicating improper finishing technique

- Finishing over bleed water causing surface scaling, dusting, and delamination

- Adding water to the surface during finishing to ease workability, weakening the surface layer

- Over-troweling exterior surfaces creating a slippery finish instead of proper broom texture

- Insufficient flatness for floor covering installation causing visible imperfections

- Premature finishing in hot or windy conditions causing surface crusting over wet concrete below

Per ACI 302.1R, contraction joints (control joints) shall be spaced at a maximum of 2 to 3 times the slab thickness in feet — for a 4-inch slab, maximum joint spacing is 8 to 12 feet. Joints shall be cut to a minimum depth of one-quarter the slab thickness per ACI 302.1R and IRC R506.1. Joint panels should be approximately square, with a length-to-width ratio not exceeding 1.5 to 1 per ACI 302.1R. Saw-cut joints must be cut within 4 to 12 hours of placement depending on conditions, before random shrinkage cracking occurs. Isolation joints must separate flatwork from fixed structures such as columns, walls, and utility penetrations per ACI 302.1R.

1. Verify joint spacing does not exceed the maximum ratio of 2 to 3 times slab thickness in feet per ACI 302.1R

2. Measure control joint depth — must be a minimum of one-quarter the slab thickness

3. Check that joint panels are approximately square with a length-to-width ratio of 1.5 to 1 or less

4. Confirm isolation joints are installed at all intersections with fixed structures — columns, walls, steps, and utility penetrations

5. Inspect saw-cut timing — joints must be cut before random cracking initiates, typically within 4 to 12 hours of finishing

- Joint spacing too wide causing uncontrolled mid-panel cracking

- Joints cut too shallow to initiate a proper crack beneath the cut

- Irregular or L-shaped panels creating stress concentrations and re-entrant corner cracks

- Saw cutting delayed too long after placement resulting in random cracking

- Missing isolation joints at columns or walls causing restraint cracks radiating from fixed points

Per ACI 308R, concrete flatwork must be cured for a minimum of 7 days at temperatures above 50 degrees F to achieve adequate strength and durability. Acceptable curing methods include water curing (ponding, misting, or wet burlap), plastic sheeting, or liquid membrane-forming curing compounds conforming to ASTM C309. Curing compounds shall be applied at the manufacturer's recommended rate, typically 200 square feet per gallon per ASTM C309. Evaporation retarders may be applied to the surface during finishing in hot, windy, or low-humidity conditions when the evaporation rate exceeds 0.2 lb/ft2/hr per ACI 305R.

1. Verify curing method is applied immediately after finishing — no exposed concrete surfaces should be left unprotected

2. If using curing compound, confirm it meets ASTM C309 and is applied uniformly at the specified coverage rate

3. For water curing, check that wet coverings remain continuously moist for the full 7-day minimum cure period per ACI 308R

4. Monitor ambient and concrete temperature — curing must maintain concrete above 50 degrees F for at least 7 days per ACI 306R

5. In hot weather, verify evaporation retarder is applied when conditions exceed 0.2 lb/ft2/hr evaporation rate per ACI 305R

- No curing method applied, causing rapid moisture loss, surface crazing, and reduced strength

- Curing compound applied over bleed water or at insufficient coverage rate, providing incomplete protection

- Wet burlap allowed to dry out during the curing period, creating intermittent curing and surface discoloration

- Curing not maintained for the minimum 7-day period, resulting in reduced surface durability

- Cold-weather protection removed too early, allowing concrete temperature to drop below 50 degrees F