Buyer education
Polished Concrete Floors, And What People Mean By Them
Polished concrete is the most misused phrase in floor specification. Three completely different floors are sold under it, at three very different prices, and only one of them is actually a polished slab.
What true polished concrete is
A genuinely polished concrete floor is the structural slab itself, mechanically ground with progressively finer diamond abrasives, densified with a chemical hardener and honed to the chosen level of sheen. Nothing is added on top. The finish you see is the concrete, and the aggregate exposed at the surface is whatever was in the mix.
That last point is the one people underestimate. Grind deeper and you expose more and larger aggregate, which changes the look completely. If a particular appearance matters, the concrete mix and the placement have to be designed for it from the beginning. It cannot be decided once the slab is down.
The two things frequently sold under the same name
Power floating is the process of trowelling a fresh slab to a smooth, closed surface with a mechanical float. The result can look excellent and costs a fraction of grinding and polishing, but it is not polished concrete and it will not have the same clarity or aggregate exposure.
Thin overlays are the other one: a cementitious topping applied over an existing floor to give a concrete appearance where the slab beneath is unsuitable. These are legitimate products, and microcement is one of them, but describing them as polished concrete confuses a coating with a slab.
- Polished concrete
- The slab itself, ground, densified and honed
- Power floated
- Fresh slab trowelled smooth, no grinding, no aggregate exposure
- Thin overlay
- A topping over an existing floor, a few millimetres thick
What has to be true for a real polished slab
You need a slab of adequate thickness and quality, poured with polishing in mind, with no services buried at the depth the grinding will reach. You need enough programme to grind and hone in multiple passes with a great deal of dust extraction. And you need to accept the crack control joints, which are structural and are not going away.
On new build this is entirely achievable when the decision is made early. On a refurbishment it usually is not, because the existing slab was never intended to be a finish, may be patched, may hide services and may be at the wrong level. That is precisely the gap that thin overlay finishes exist to fill.
- Decide before the slab is poured, not after
- Coordinate mix design and aggregate with the intended exposure level
- Keep services out of the grinding depth
- Accept and design in the crack control joints
- Allow programme and dust extraction for multiple grinding passes
If a project is a refurbishment and somebody is quoting polished concrete, ask whether they mean grinding the existing slab or applying an overlay. The two are not comparable.
Living with the finish
A densified and sealed polished slab is extremely hard-wearing, which is why it is the default in warehousing, showrooms and large retail. Domestically the reservations are usually comfort and acoustics rather than durability: it is cold underfoot without underfloor heating, and a large hard floor is acoustically lively in a room with little soft furnishing.
It is also permanent in a way a coating is not. Changing the appearance later means grinding again, and you cannot make the aggregate go back. Anyone specifying it for a home should be confident they want that surface for a very long time.
Polished concrete questions
Work out which floor you are actually being offered
Before comparing prices, establish whether each quote is for grinding a slab, floating one or applying an overlay. If your project is a refurbishment, a thin overlay is often the realistic route and we can tell you whether it suits your floor.