11.3 Flooring, Tile, and Acoustical Ceilings
Key Takeaways
- Test concrete moisture before resilient flooring: ASTM F2170 RH (typically 75-85 percent max) is more reliable than ASTM F1869 calcium chloride MVER (3-5 lb).
- Thinset coverage must reach 80 percent dry / 95 percent wet; large-format tile (over 15 inches) needs medium-bed/LHT mortar to limit lippage.
- Estimate tile area plus waste: 10 percent straight-lay, 15 percent diagonal or large-format; always round up to full cartons.
- NRC measures in-room absorption; CAC measures sound blocked between rooms; high NRC does not provide speech privacy.
- Seismic Design Categories D-F require ASTM E580 heavy-duty grid, bracing wires, compression posts, and two-wall attachment with perimeter clearance.
Flooring, Tile, and Acoustical Ceilings
This Division 09 group covers resilient flooring, ceramic tile, and suspended acoustical ceilings. Reference standards include the Tile Council of North America (TCNA) Handbook, ANSI A108/A118 (installation and materials), ASTM F710 (concrete moisture for flooring), and ASTM E1264 (acoustical ceiling classification). Sequence matters: most finish flooring goes in late to avoid damage.
Concrete substrate moisture (ASTM F2170, F1869)
Resilient flooring and adhesives fail when the slab is too wet. Two tests dominate:
- ASTM F2170 — in-situ relative humidity (RH) probes: acceptance is typically 75 percent to 85 percent RH maximum per the flooring manufacturer.
- ASTM F1869 — calcium chloride MVER: limit often 3 to 5 pounds per 1,000 square feet per 24 hours.
A standard slab needs roughly 28 days of cure before testing. The exam trap: passing a calcium chloride test does not guarantee an RH pass — RH is the more reliable indicator and manufacturers increasingly require it.
Tile setting methods and mortar
Thinset (dry-set / modified, ANSI A118.1 / A118.4) is the standard bond mortar; trowel notch size is matched to tile size so coverage reaches 80 percent (dry) / 95 percent (wet or exterior). Large-format tile (any side over 15 inches) requires a medium-bed or LHT (large-and-heavy-tile) mortar to prevent lippage.
Membranes: ANSI A118.10 waterproofing and A118.12 crack isolation. A trap: omitting a crack-isolation membrane over a control joint telegraphs cracks straight through the tile.
Tile takeoff scenario
Estimate tile quantity by area plus waste:
- Field area: 30 ft x 20 ft = 600 square feet.
- Waste factor: 10 percent straight-lay, 15 percent diagonal/large-format.
- Order: 600 x 1.10 = 660 square feet.
For grout and thinset, follow coverage charts; coverage drops with larger trowel notches. Always round up to full carton/box quantities — partial cartons are not sold.
Acoustical ceiling performance (ASTM E1264, E1414)
Suspended acoustical tile is rated by two distinct numbers — do not confuse them:
| Metric | Measures | Better when |
|---|---|---|
| NRC (Noise Reduction Coefficient) | Sound absorbed within the room | Higher (toward 1.00) |
| CAC (Ceiling Attenuation Class) | Sound blocked between rooms over a wall | Higher (35+ for privacy) |
A tile can have high NRC but low CAC, allowing speech to pass over a partition through the plenum. Open-plan offices want high NRC; private offices need high CAC.
Suspension grid and seismic
The main runners and cross tees form the grid; perimeter wall molding supports the edge. In Seismic Design Categories D, E, and F, ASTM E580 requires heavier (intermediate/heavy-duty) grid, wall attachment on two adjacent walls with clearance at the opposite two, splay/bracing wires every 12 feet, and compression posts. Ceilings over 144 square feet require lateral bracing in higher seismic categories.
A private office needs speech privacy from the adjacent room over a partition that stops at the suspended ceiling. Which acoustical ceiling property is most important?
A floor measures 30 ft by 20 ft and will receive straight-lay tile with a 10 percent waste factor. How much tile should be ordered?
Flooring Types and Substrate
Match flooring to the substrate and moisture. Resilient (LVT, VCT, sheet vinyl) needs a flat, dry, clean substrate — concrete slabs are tested for moisture (ASTM F2170 RH probe; F1869 calcium chloride MVER) before installing, or adhesives fail. Hardwood must acclimate and is not placed on damp slabs. Carpet over pad or glue-down. Subfloor flatness (e.g., 3/16 in over 10 ft) is critical for thin resilient products that telegraph defects.
Tile Setting and Movement
Tile is set in thinset mortar over cement backer board or a crack-isolation/uncoupling membrane (never directly over untreated gypsum in wet areas). Wet areas require a waterproof membrane behind/under the tile. Movement (expansion) joints are required in tile fields (e.g., interior every 20–25 ft, perimeter at walls) per TCNA — omitting them causes tenting/cracking. Grout after the thinset cures; seal natural stone.
Acoustical Ceilings
Suspended acoustical tile ceilings (ACT) hang on a suspension grid (main runners + cross tees) from wires to the structure above; tiles drop into the grid. The grid must be level and braced (seismic clips/wires in seismic zones). NRC (Noise Reduction Coefficient) rates sound absorption (higher = more absorptive); CAC rates sound blocked between spaces. Maintain clearance above for ducts/lights and access to plenum equipment.
Common Exam Traps
- Trap: Installing resilient flooring on an untested wet slab (adhesive failure).
- Trap: Tile over regular gypsum in a shower. Use backer + waterproofing.
- Trap: Omitting tile movement joints (causes tenting).
- Trap: Confusing NRC (absorption) with CAC (blocking between rooms).
Before installing glue-down resilient flooring on a concrete slab, what must be verified to prevent adhesive failure?
Transitions, Slope, and ADA Floor Rules
Where two floor finishes meet, a transition strip bridges the height difference; ADA limits abrupt level changes to 1/4 in (or 1/2 in beveled) and caps accessible-route slope at 1:20 (steeper becomes a ramp at max 1:12). Wet rooms slope the finish floor to the drain (commonly 1/4 in per ft in showers). Tile flatness and lippage (edge-to-edge height difference) are controlled with leveling systems. The exam ties trip hazards and non-compliant transitions back to these accessibility limits.
Tile Layout, Sizing, and Estimating
Lay out tile from balanced center lines so cut tiles at opposite walls are equal and no sliver cuts appear at sightlines; dry-lay to confirm before setting. Estimate by area plus waste: ~10% for straight (grid) layouts, 15% or more for diagonal/herringbone patterns and rooms with many cuts. Worked example: a 12 ft x 15 ft room = 180 SF; at 10% waste order about 198 SF of tile, plus thinset and grout by coverage. Order all tile from the same dye lot to avoid shade variation.