Terrazzo
Summary
Terrazzo is aggregate chips set in an epoxy resin or portland cement matrix, poured in place between divider strips or precast into tiles and stair units, then ground, polished, and sealed. It has very long life and design freedom for airports, schools, and lobbies, but system type sets thickness, weight, crack tolerance, cost, and slab preparation.
Cols
Terminology
- Epoxy (resinous matrix) terrazzo: thin-set system with epoxy binder; most common today
- Cementitious terrazzo: portland cement matrix; bonded, monolithic, or sand cushion systems
- Sand cushion: cementitious system on a sand bed and isolation sheet; isolates the topping from slab movement
- Bonded / monolithic: cementitious topping bonded to a structural slab, or placed integrally with it
- Divider strip: zinc, brass, aluminum, or plastic strip separating colors and controlling cracks
- Control joint strip: double strip placed over slab joints
- Precast terrazzo: factory-made tiles, treads, risers, and bases
- Aggregate: marble, granite, recycled glass, mother of pearl
- Crack isolation membrane: flexible layer under epoxy terrazzo to bridge slab cracks
- NTMA: National Terrazzo and Mosaic Association
Standards
Thicknesses
| System | Typical thickness | Weight |
|---|---|---|
| Epoxy thin-set | 1/4 in. to 3/8 in. | About 3 psf |
| Bonded cementitious | 3/8 in. to 1/2 in. topping over underbed | Heavier; varies with underbed |
| Sand cushion cementitious | Thick system with underbed and sand bed | Heaviest, up to about 30 psf for cement systems |
Test standards
- NTMA technical guide specifications for each system
- ANSI A326.3 or manufacturer data for slip resistance
- ASTM F2170 and F1869: slab moisture limits for epoxy systems
Materials
- Epoxy resin matrix: wide color range; thin and light; needs dry, stable slabs
- Portland cement matrix: traditional; heavier; tolerates more slab moisture
- Aggregates: marble, granite, glass, shell
- Divider strips: zinc and brass common; aluminum and plastic for lower cost
- Membranes: crack isolation and moisture mitigation under epoxy systems
- Precast pieces: stairs, base, and wall panels matching poured floors
Detailing
- Locate divider strips over slab control joints and along design lines
- Recess slabs for cementitious systems; epoxy systems need minimal depression
- Test slab moisture before epoxy terrazzo; specify mitigation if needed
- Use crack isolation membrane where slab cracking is expected
- Coordinate precast stair treads and base with poured floor colors
- Specify sample panels and a mockup for color and aggregate distribution
Uses
Specific uses
- Airports and transit stations
- School and university corridors
- Hospital lobbies and public spaces
- Government buildings and courthouses
- Retail and corporate lobbies with custom designs
Pros and cons
Pros
- Service life measured in decades
- Seamless, low-maintenance, and easy to clean
- Custom colors, patterns, and logos
- Recycled glass and stone aggregates
Cons
- High first cost
- Cracks reflect from slabs without isolation
- Long installation time; specialty installers only
- Cementitious systems are heavy
Manufacturing and cost
Construction
- Substrate prepared; membranes and divider strips installed
- Matrix and aggregate mixed, poured, and troweled; cured
- Ground with progressively finer abrasives, grouted, polished, and sealed
Main manufacturers and suppliers
Trade association: National Terrazzo and Mosaic Association.
Typical costs
- Poured terrazzo, installed: $20 to $60 per sq ft, epoxy and custom patterns toward the high end
- Precast terrazzo tile, installed: $25 to $60 per sq ft
- Labor and substrate prep: about 40 to 60 percent of installed cost
Sources
- University of Houston: 09 66 13 resinous matrix terrazzo specification, https://www.uh.edu/facilities-services/departments/fpc/master-specs/09-66-13-resinous-matrix-terrazzo.pdf
- Houzz: making floors terrific with terrazzo (thin-set weight), https://www.houzz.co.nz/magazine/make-your-floors-terrific-with-terrazzo-stsetivw-vs~32026189
- Flooring Clarity: terrazzo tile cost per square foot, https://www.flooringclarity.com/terrazzo-tile-cost-per-square-foot-pricing-factors/
- NTMA: technical resources, https://ntma.com/
- Wikimedia Commons: Terrazzo entryway.jpg, by Ned Hartley (CC BY-SA 4.0), https://commons.wikimedia.org/wiki/File:Terrazzo_entryway.jpg