A complete CSI Section 09 66 23 keeps the bidders honest and the install clean. An incomplete one creates RFIs, change orders, and color-match disputes that cost the project weeks. Use this as a checklist against your current spec.
1. System and references
Open the section with the NTMA technical specification number that matches your system, by exact reference number:
- NTMA TM-1 — Sand-cushion cementitious terrazzo (2-1/2" thick over isolation membrane).
- NTMA TM-2 — Bonded cementitious terrazzo (5/8" thick).
- NTMA TM-3 — Monolithic cementitious terrazzo (1/2" directly bonded).
- NTMA TM-4 — Thinset cementitious terrazzo (3/8" over cement underlayment).
- NTMA TM-5 — Polyacrylate-modified cementitious (3/8", interior only).
- NTMA TM-6 — Epoxy terrazzo (3/8", interior only).
Cite by number. 'NTMA standards apply' is not enforceable. 'Furnish and install monolithic terrazzo per NTMA TM-3' is.
2. Divider strips
Specify metal type, gauge, depth, and exposed face width. Defaults that often need updating:
- Metal: white alloy zinc (most common), brass (premium), aluminum (rare, restoration only).
- Top gauge: 14-gauge typical for epoxy systems; 16-gauge acceptable for residential.
- Anchor: L-shape with 1/2" leg minimum, set into substrate adhesive.
- Exposed face: 1/8" standard, 1/4" available for high-design accent dividers.
- Pattern: shown on drawings, not described in spec — divider layout is design intent.
3. Aggregate
Specify aggregate by type, size, and source. 'Marble chips' is not a spec.
- Aggregate type: marble, granite, quartz, recycled glass, mother-of-pearl, or named blend.
- Aggregate size: #0 (small) through #4 (large) per NTMA aggregate sizing.
- Color blend: by approved sample, ratio identified to the supplier (e.g., 60% Bianco Carrara, 30% Verde Alpi, 10% Nero Marquina, all #2 size).
- Glass aggregate post-consumer content: specify minimum percent for LEED MR credit.
4. Performance test reports (submittals)
Require manufacturer test data in the submittal package:
| Standard | What it measures | Acceptable result |
|---|---|---|
| ASTM C501 | Abrasion resistance (Taber) | Class A (lowest wear) |
| ASTM E84 | Surface burning characteristics | Class A (Flame ≤ 25, Smoke ≤ 450) |
| ASTM C97 | Absorption and density | <0.25% absorption typical |
| ANSI A326.3 / ASTM C1028 | Dynamic coefficient of friction (slip) | DCOF ≥ 0.42 wet for level interior |
| ASTM G21 / G22 | Fungal and bacterial resistance | No growth (healthcare projects) |
| ASTM F1869 / F2170 | Substrate moisture (not the system) | Per epoxy tolerance |
5. Sustainability and IEQ
If the project is pursuing LEED or WELL certification, require contributing documentation in submittals:
- Environmental Product Declaration (EPD) per ISO 14025.
- Health Product Declaration (HPD) per HPD Open Standard.
- Recycled content statement (pre- and post-consumer percentages).
- VOC content per SCAQMD Rule 1168 or CDPH Standard Method v1.2.
- Regional materials documentation if pursuing MR credit.
6. Installer qualifications
The clean approach is to require NTMA contractor-member status and a documented installation history at the project's scale and system type. Do not sole-source by manufacturer — that exposes the owner to the manufacturer's pricing without a competitive bid.
Recommended language: 'Installer shall be a current contractor-member of the National Terrazzo & Mosaic Association (NTMA) with documented installation of [system type] terrazzo on a minimum of three projects of comparable size and scope within the past 5 years. Submit project references with substrate type, square footage, and owner contact information.'
7. Mock-ups and samples
- Lab samples: 8"×8" minimum, 3 samples of each color/aggregate blend.
- Field mock-up: 4'×4' minimum, in approved location on the project, including divider strip, full system thickness, and final finish.
- Approval: architect and owner sign before production pours.
- Retention: mock-up remains in place as the standard of comparison through final acceptance.
8. Substrate and slab tolerance
Reference the substrate tolerances the system actually requires:
- Epoxy terrazzo: ASTM E1155 FF35/FL25 minimum; tighter for restoration.
- Cementitious bonded: substrate must be sound, free of curing compounds, and roughened to CSP-3 minimum.
- Cementitious sand-cushion: substrate condition tolerant — sand/membrane absorbs minor variation.
- Moisture: ASTM F1869 ≤ 3 lb and ASTM F2170 ≤ 75% RH for epoxy; not required for cementitious.
9. Warranty
Standard warranty language is 1 year for installation defects, 5 years for delamination, and 10 years pro-rated for material defects. Manufacturer's extended warranty is available on most epoxy systems when a moisture-mitigation membrane is installed by a manufacturer-approved applicator.
10. What does NOT belong in the spec
- Brand-specific color names without 'or equal' language (limits competitive bid).
- Dimensional details that should be on the drawings (divider layout, edge profiles).
- Maintenance procedures (those belong in Division 01 closeout requirements).
- Substitution language that allows polished concrete (a different system, not an equal).
Frequently asked
What if our project requires a system NTMA doesn't cover?
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Polyaspartic, urethane, and MMA flooring are not NTMA systems. They have their own manufacturer specifications. Don't try to fit them into 09 66 23 — write a separate Section 09 67 23 (resinous flooring) or 09 96 23 (high-performance coatings).
Is NTMA membership a real differentiator?
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Yes. NTMA contractor members are vetted on installation history and complete continuing-education requirements. The trade has a tail of unqualified installers, so the membership check is real risk management for the owner.
How long should bidders have on a terrazzo spec?
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10 business days minimum for a competitive bid on a complete spec. Aggregate sourcing, color matching, and shop drawings need time. Short bid windows produce bid coverage gaps that become change orders.