Microcement and polished concrete are finishes, not floors

There is a short answer about seamless floor finishes and a useful one, and they are not the same. What follows is the useful one.

The material is millimetres thick

Microcement is a polymer-modified cement applied in coats a few millimetres thick over an existing surface, which is why it can go over tiles without demolition. Because it is so thin, it has no capacity to bridge movement, and anything that moves underneath will telegraph through.

This is why the same product looks flawless in one installation and crazed in another with no difference in the tin. Substrate preparation, priming and reinforcing mesh account for most of the difference between the two outcomes.

Cracking is normal and needs to be discussed in advance

Fine hairline crazing appears in many microcement installations and is generally cosmetic, particularly on floors over timber or over underfloor heating. Larger cracks follow substrate movement, joints in the base and doorway thresholds, which is why movement joints have to be carried through the finish. A contract that does not state what level of cracking is acceptable produces a dispute rather than a repair.

People who are troubled by any crack should choose a jointed material such as tile instead, because the seamlessness is the whole point and the risk.

Poured resin and polished concrete are different again

A structural polished concrete slab is the concrete itself, ground and sealed, and behaves like the slab because it is the slab. A poured resin floor is a thicker applied layer with more elasticity and a very different appearance, warmer to the touch and usually more uniform. These are frequently confused in specification, and their costs, thicknesses and substrate requirements are not comparable.

Room to room, a polished concrete floor generally has to be planned before the slab is poured, because the aggregate and the finish are decided then.

The sealer does the work

Cementitious finishes are porous and rely entirely on their sealer for resistance to water, wine, oil and cleaning products. Penetrating sealers keep a natural matt look and offer less stain protection; film-forming sealers protect better and can scratch and show wear. Sealers are consumable and need reapplication on a schedule that varies with traffic, and skipping it is how a floor stains permanently.

Ask specifically what sealer is being used and what its maintenance cycle is, because this is where satisfaction is decided.

Where it works best

Walls, splashbacks, shower enclosures and small bathroom floors are lower-movement applications where the material performs very reliably. Large open floors over timber joists are the hardest case and the one that most often disappoints. Over a solid, dry, stable slab with correctly detailed joints, a microcement floor can be excellent for many years.

The quieter point is that it also adds almost no height, which is why it is the usual answer where a new floor cannot raise the level.

Taste is not the argument here; how a room performs is.

Cost, applicator and repair

The material cost is a minor part of the price; it is a skilled hand-applied finish and the labour and the applicator's experience dominate. Repairs are difficult to make invisible because the finish is trowelled and mottled, so a patch usually reads as a patch.

Ask to see completed floors that are at least two years old rather than photographs taken on handover day. A material warranty means little without an installation warranty, since almost all failures are installation-related.

The takeaway

Judge the applicator, not the product, and agree in writing what cracking is acceptable.

Buy slowly. The gaps are not a problem.