Polished or washed terrazzo: choosing a finish

Polished and washed terrazzo are not two products. They are two ways of finishing the same poured tile, and the decision is made after the mix is chosen, not before. A specifier who understands what happens in the last hour of the pour can put the right surface in the right room without guessing.

One tile, two endings

Both finishes start identically. Crushed stone is blended into a pigmented cement matrix, poured into a mould over a backing layer, pressed and left to cure. The aggregate runs through the full depth of the wearing layer in both cases, which is why neither finish can wear off.

What differs is how the cement skin on the face is dealt with.

Polished

The cured tile is ground back mechanically in stages, from a coarse head down to progressively finer ones. The grinding cuts straight through the top of the aggregate, so each chip is sliced flat and reveals its section. A grout coat fills the pinholes that opening up the matrix exposes, then the surface is honed and polished until stone and cement sit in one continuous plane.

The result is flat, reflective and easy to read. It is the finish that shows a chip grade honestly, because you are looking at the stone in section rather than in silhouette.

Washed

The face of the green tile is washed before the cement has fully set. The thin layer of matrix over the aggregate is taken away, and the stone is left standing proud with the matrix sitting just below it. Nothing is cut. You see the natural face of each piece of stone, rounded or fractured as it was crushed.

The surface is matt, textured and quieter in colour, because you are seeing unpolished stone. The same mix will always look a little softer washed than polished.

Slip resistance is a finish decision

This is the practical reason the distinction exists.

A polished floor is a flat plane. Wet, it behaves like any flat polished floor. A washed floor has relief across its whole surface, and that relief keeps a water film from forming an unbroken layer under a shoe. That is the mechanism, and it is the reason washed terrazzo goes outside and around water while polished terrazzo goes inside and dry.

Two cautions worth writing into a spec.

• Do not accept a slip number from a photograph or a brochure. If a slip classification is a contractual requirement on your project, it has to be tested on the actual finish, in the actual format, with the sealer you intend to use. Ask for the sample and test it.
• Test it wet, on site, at the fall you have drawn, with the footwear the building will actually see. A pool surround used barefoot and a service corridor walked in hard soles are different problems.

Where each belongs

Polished is for dry, internal, high traffic floors that want to be read as a single continuous surface. Lobbies, retail floors, offices, corridors, stair treads inside the envelope, reception counters and wall linings. It is also the right choice when the aggregate is the point, because polishing is what makes a size 3 grade legible from standing height.

Washed is for anywhere water lands. Bathrooms and shower floors, kitchen and utility areas, pool surrounds, terraces, courtyards, external steps, and the transition strip at an entrance where rain is walked in. It is also worth considering purely visually, on a large external area where a polished floor would throw sun back into the building.

Ramps and level changes

A ramp is the case where the two finishes most often need to meet. The usable rule is simple. The ramp itself and its landings take the washed finish. The flat floor at either end can take polished. Draw the change of finish at the head and foot of the ramp, on a line, so it is a deliberate detail rather than something the tiler resolves on the day.

Stair nosings deserve the same attention. If the flight is external, or the treads collect water blown in from an open stairwell, the whole tread wants the washed finish rather than a strip of it.

Wet rooms

In a bathroom, the tempting move is a polished floor to match the walls. Resist it, or at minimum keep the shower tray and the area within the splash zone washed. The visual break can be turned into the drawing rather than hidden. A washed field with a polished border reads as intentional, and the two finishes in the same code share a base colour and an aggregate, so they belong together even when the texture changes.

Maintenance

Polished terrazzo shows scuffs and grit scratches the way any polished surface does, and it is renewable in exactly the same way: it can be ground and repolished in place. That is a real advantage over any surface with a printed or applied face.

Washed terrazzo holds dirt in its relief more readily and wants regular washing rather than dry buffing. It does not scuff visibly, and it does not need repolishing, because there is no polish to lose. On an external terrace this is usually the deciding argument.

Both finishes take a penetrating sealer rather than a film. A film sitting on top of a washed surface fills the relief that the finish exists to provide, which defeats the specification.

What to ask for

Send the code and the room. Ask for the same code in both finishes if the project has wet and dry areas, because seeing them next to each other is the only reliable way to judge how far apart they read. Then decide where the line between them falls, and draw it.