Can terrazzo be laid over an existing floor?

Sometimes, and the sand-cushion system is never one of the answers. It needs three inches of build-up, and a finished floor has no three inches to give. What is available is epoxy at three-eighths inch, precast tile, or a coating — and the one thing you must establish first is whether the slab under you has cracks.

The six processes drawn to one scale. Layer thicknesses are published ranges.

The figures, and where each one comes from

Option	Build-up	On an existing slab?
Epoxy	3/8 in	yes, and it can take a crack membrane
Precast tile	the tile	yes, fixed like any tile
Bonded cement	2-1/4 in	only if there is a recess to be found
Sand cushion cement	3 in	no

Why the processes are not interchangeable

NTMA puts the problem plainly: cracks in an existing floor will telegraph straight through monolithic or bonded cement terrazzo. Both are ground together with the slab, so a crack below becomes a crack in the finish at the same line, and no amount of preparation prevents it — the cement and the slab move as one piece and the weakness is shared. Epoxy does not have that failure mode because it is flexible and can be laid over a crack-resistant membrane, which no cement system accepts. So the real question on a refurbishment is not what the new floor looks like; it is what the slab underneath is doing.

What these figures are, and what they are not

The inability to add a sand-cushion system to a finished floor and the crack-telegraphing behaviour are both from NTMA guidance. ⛔ That NTMA also states no crack membrane is compatible with cement systems, so we do not suggest one for a cement topping. ⛔ We have not inspected a slab and we are not offering an opinion on any specific floor: substrate condition is established by testing on the site.

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:

Send a specification Ask for a sample