Polished concrete flooring and what decides the finish

The floor

What polished concrete is

A polished concrete floor is produced by grinding a slab with diamond abrasives in a series of steps, treating it with a densifier, and refining it until it reaches the sheen that was specified. The result is concrete finished as concrete, not covered with a film.

Because nothing is applied over the top as a thick layer, the character of the floor comes from the slab: its colour, its aggregate, its joints and its history. Some of that is an attraction and some of it is a limit, and a good contractor will tell you which is which before you commit.

• It is a finish that is processed into the concrete, not applied to it.
• What the slab looks like beforehand strongly shapes what it can look like afterwards.

The process

Progressive refinement, step by step

Polishing works by refining the surface in stages. Each pass removes the scratches left by the one before it, using a finer abrasive each time, in the same way a piece of wood is sanded through coarse to fine paper. Skipping steps leaves scratches the next stage cannot fully remove.

The exact sequence differs between contractors and between slabs. As a general pattern, it looks like this.

• Coarse grinding removes any coating or surface layer, levels the floor and opens it to the depth the finish needs.
• Intermediate passes remove the coarse scratches and begin to refine the surface.
• Densifier is applied and allowed to react, typically after the early grinding steps.
• Finer resin-bonded abrasives then polish the surface through a series of higher grits.
• A protective treatment may be applied at the end, depending on the finish and the use.

Hardening

What densifier does

Densifiers are liquid treatments, commonly based on silicates, that soak into the concrete and react within it. The intended effect is a harder, denser surface that wears more evenly and creates less dust.

They are an important part of the process, but they are a part. A densifier cannot make a weak slab strong, and it does not by itself produce the finish. Ask which product is being used, when in the sequence it goes on, and what the supplier says about it.

Appearance

Aggregate exposure and sheen

Two separate choices describe how a polished floor looks. The first is how much of the concrete is cut away, which decides how much of the sand and stone shows through. The second is how fine the final polishing goes, which decides how much light the surface reflects.

Terms for both vary between contractors and published guidance, so a name alone is not enough. Ask for the finish to be defined in writing and shown on a sample, ideally on your own slab, before the whole floor is committed.

• Cream finishes cut little and leave mainly the surface paste, with little aggregate showing.
• Fine-aggregate finishes take the surface down a little further, so small particles of sand and stone start to show.
• Full-aggregate finishes cut deeper, so the larger stone is exposed across the floor.
• Sheen runs from a low, satin look to a mirror-like reflection, and each step up takes more passes.

Expectations

Cracks, joints and natural variation

A polished floor shows its concrete. Fine cracks, saw-cut and control joints, trowel marks, and changes in tone from one area to another are normal features rather than defects, and polishing generally highlights them rather than hides them.

Some of this can be improved. Cracks and joints are often filled, and repairs can be blended. Filled areas may still look different, and edges polished by hand rarely match the open floor exactly.

• Ask how joints and cracks will be treated, and whether they will still show.
• Ask how patches and edges will be blended, and what difference to expect.
• If you want a perfectly uniform floor, say so; a coating may be the better route.

Comparison

Polished concrete compared with epoxy and other coatings

Neither is better in every space. They are different kinds of floor, and the question is which set of trade-offs suits the building.

• A polished floor is the concrete itself, so there is no film to peel or delaminate; a coating forms a film that can fail if it was not bonded properly.
• A coating can add colour, pattern, texture and a seamless, chemical-resistant surface; polished concrete shows what the slab already has.
• A coating can disguise some slab imperfections; polishing tends to reveal them.
• Polishing has no cure time, but it is a slower sequence of passes, and densifiers and protective treatments have their own timings.
• Polished concrete is not impervious. Spills and acids can mark it, so exposure matters.

Upkeep

Maintenance considerations

A polished floor is generally straightforward to keep clean, but it is not maintenance-free, and the right routine depends on the finish and the way the space is used.

• Regular dust-mopping and cleaning with products suited to polished concrete.
• Avoiding acidic or harsh cleaners that can etch the surface.
• Matting at entrances to keep abrasive grit off the floor.
• Wiping up spills promptly, especially acidic ones.
• Asking what protective treatment is used and whether it needs renewing over time.
• Asking about traction, because a high-gloss floor can be slippery when wet.

Before the work

What a contractor evaluates first

Whether a slab is a good candidate is a judgement that should be made on site.

• The strength and surface condition of the concrete, and whether it is dusty or soft.
• The age of the slab, the history of the floor and how it was finished.
• What is on it now, including coatings, adhesive and stains.
• Cracks, joints, patches and the likely depth of aggregate near the surface.
• The finish you want, and whether the slab can realistically reach it.
• Edges, columns and fixed items, and how they will be handled.

Checklist

Questions to ask when comparing proposals

Polished concrete proposals can look alike on paper while describing very different finishes.

• What aggregate exposure and what sheen are being proposed, in writing?
• Is a sample available, ideally on your own slab?
• What sequence of steps is planned, and where does densifier go on?
• What protective treatment is proposed, and what upkeep does it need?
• How will cracks, joints and patches be treated, and will they remain visible?
• What happens if the slab turns out not to suit the finish?
• What is excluded, and how would a change in scope be priced?

Next step

What to include when you request an introduction

Epoxy Pro Leads is an independent education and contractor-introduction resource. We are not the installer, we do not employ crews, and we do not price, specify or inspect your floor.

When you send a request we read the details, and where it is a fit we pass it to one contractor who works in your area and takes on that kind of project. Submitting a request does not commit you to anything.

• Whether the slab is new or existing, and what is on it now.
• Approximate area, and what the space is used for.
• The look you have in mind, and whether you want a uniform floor or are comfortable with natural variation.
• Anything known about cracks, patches, stains or moisture.
• Your timing, and any period the space cannot be closed.