Polished concrete

Polishing runs the slab through progressively finer diamond grits, with a chemical densifier applied partway through that reacts with free lime in the concrete to harden the surface from within. The result is a floor whose wear surface is the concrete itself.

The honest tradeoff

The advantage is permanence: no delamination, no hot tire pickup, no UV ambering, because there is no film. The disadvantage is that you get the slab you have. Polishing reveals aggregate, colour variation, old stains and repairs rather than hiding them. Some people want exactly that. Others are surprised by it.

Grit levels and gloss

Polishing is a sequence, and where you stop determines the finish. Each pass uses progressively finer diamonds, and the industry describes the result by the final grit and the measured gloss.

Higher grit costs more because each pass is a full pass over the whole floor. Going from 400 to 1500 roughly doubles the labour. It also shows more — a mirror finish reveals every undulation in the original pour.

Aggregate exposure

How deep you grind determines what you see. This is decided at the first pass and cannot be undone.

• Cream finish. Minimal removal; you see the cement paste surface with almost no aggregate. Cleanest and most uniform look.
• Salt and pepper. Removing a few millimetres exposes the fine sand aggregate. The most popular choice and the most forgiving.
• Full aggregate. Grinding deep enough to expose the large stone. Dramatic and very much a design statement, but it demands a slab with well-distributed aggregate — and you find out whether you have one only after you start.

Densifiers

Partway through the grit sequence, a chemical densifier — usually lithium, sodium or potassium silicate — is applied. It reacts with free calcium hydroxide in the concrete to form additional calcium silicate hydrate, the same compound that gives concrete its strength. The surface becomes measurably harder, less porous, and takes a better polish.

This is not optional in a proper polish, and it is the step most often skipped in a cheap "polished concrete" quote that is really just grinding and sealing. A ground-and-sealed floor looks similar for about a year, then the sealer wears through in traffic paths.

Maintaining a polished floor

Polished concrete needs different maintenance from a coated floor, and getting it wrong is the most common reason a good polish stops looking good.

• Dust mop frequently. Grit is the whole problem. On a polished floor it acts as lapping compound underfoot and dulls the sheen in traffic paths.
• Neutral cleaner only. Anything acidic etches the surface; anything alkaline leaves film. pH-neutral, always.
• No wax or acrylic sealer. People apply these thinking they protect the floor. They build a soft film that scuffs, then has to be stripped — and stripping chemicals attack the densified surface underneath.
• Burnish periodically. A high-speed pass with a fine pad restores sheen without regrinding. Every one to three years depending on traffic.

Where polishing beats coating, honestly

Three situations where we would recommend polish over a coating without hesitation. A space with very high moisture emission, because there is no film to lift. A warehouse with heavy forklift traffic, where the wear surface being the slab itself means there is nothing to chip at joint edges. And any client who genuinely wants a concrete aesthetic rather than a decorative one.

Everywhere else, a coating usually gives more — colour choice, stain resistance, hiding power over a slab that has seen some life. We do both and have no preference between them.

Common questions