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Answers

Which terrazzo system goes into a commercial building?

A sand-cushion cement system if the floor can take 25 to 30 pounds per square foot and there is three inches of height to fill. Epoxy if it cannot — at 3 to 4 pounds it goes on a suspended floor, over a renovation, and around an old slab with cracks in it. The finish does not decide this. The structure does.
Six terrazzo processes, drawn to one scaleEach column shows the layers of one terrazzo process. Precast and cement-bound are thick; epoxy is thin; porcelain is a fired body. Dimensions are published ranges, not our measured figures.substratePrecast20 mmsubstrateCement-based12 mmsubstrateEpoxy5 mmsubstratePoured10 mmsubstrateLiquid3 mmsubstratePorcelain9 mmSections drawn to one scale from published ranges. Our measured figures are listed separately.
The six processes drawn to one scale. Layer thicknesses are published ranges.

The figures, and where each one comes from

System Topping Total build-up Weight, lbs/sq ft Where it goes
Sand cushion cement 1/2 in 3 in 25 to 30 ground-floor commercial, slab on grade
Bonded cement 1/2 in 2-1/4 in 18 to 22 interior and exterior, recessed slab
Monolithic cement 1/2 in 1/2 in 5 to 7 directly bonded to a flat slab
Epoxy 3/8 in 3/8 in 3 to 4 upper floors, renovations, chemical exposure

Why the processes are not interchangeable

A commercial floor is a forty-year decision, and the number that decides it is usually not the one a designer asks about. A sand-cushion floor carries a reinforced underbed, an isolation sheet and a sand layer between the topping and the slab. That assembly is what gives it the deepest grinding reserve — it can be taken back twice over its life — and it is also what makes it impossible to add to a building that is already built, because the three inches have nowhere to come from. Epoxy gives up the reserve and gets back a floor that weighs a seventh as much, can be bonded over a cracked slab, and tolerates the cleaning chemicals a hospital or a food plant throws at it.

What these figures are, and what they are not

The weights and build-ups are from the NTMA Terrazzo Systems Reference Guide, given in inches and pounds per square foot. ⛔ Those figures are the association's systems, not our products: we supply precast, cement-bound, epoxy and poured material, and we have not published a dead-load figure for any floor we have supplied. Ask us for what we hold and we will say so. ⛔ We do not quote a deflection figure for cement-bound floors: the number in general circulation could not be traced to a standard and is not reproduced here.

Measured data sheets and test reports

If you are specifying this

These are the forms we actually supply for this question, with production photographs where we have them:

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