Microcement Flooring and Walls: Substrates, Cracking, Sealers and Wet Areas

What microcement is, and what it is not

Microcement (also sold as microtopping or micro-concrete finish) is a thin, hand-trowelled finish made from polymer-modified cement, very fine aggregate and pigment. It is applied in several coats, typically building up to only a few millimetres in total, then sealed. The result is a seamless, mineral, concrete- like surface on floors, walls, stairs and counters, without the weight, time or cost of a new concrete topping.

That thinness is both the attraction and the risk. Microcement can go over an existing sound floor, which makes it popular for office, retail and hospitality refurbishment. But it cannot bridge movement. The common misconception is that it is "a concrete floor in a tub". It is a decorative finish, and it shows every crack, joint and weakness in what lies beneath it. The cost of getting it wrong is a feature floor with a map of hairline cracks, or a shower that leaks because the sealer was treated as waterproofing.

Suitable and unsuitable substrates

Whatever the substrate, the screed or slab beneath must be sound, dry and flat to the tolerance the system asks for. Where a floor needs smoothing first, a self-levelling underlayment is often laid before the microcement coats.

Joints, movement and cracking

Microcement cracks for predictable reasons:

• Structural and movement joints in the slab: these must be carried through as joints in the finish. See movement joints
• Cracks in the slab or screed: treated and, where the system specifies, bridged with a reinforcing mesh in the base coat
• Changes of substrate, such as screed meeting old tiles or a board meeting masonry: meshed and, where movement is likely, jointed
• Application faults: coats too thick, drying too fast in heat or draughts, or insufficient time between coats

A floor with many joints is better finished with joint lines planned as part of the design than with an attempt to hide them, which usually ends in cracks.

Sealers and wet areas

The sealer, typically a water-based polyurethane or similar system chosen by the manufacturer, gives microcement its stain and water resistance. It is also the part that wears, and it is renewed periodically.

In showers, wet washroom floors and around basins, microcement is laid over a waterproofing membrane, with the membrane detailed at drains, upstands, wall junctions and pipe penetrations. Floors that get wet also need a slip-resistant finish, usually by adding an anti-slip additive to the sealer. Wet areas drive more of the services and detailing than their size suggests; see why wet areas drive the services.

Microcement compared with epoxy and polished concrete

For workshops, stores and industrial bays, epoxy flooring is the more appropriate choice. Polished concrete suits new slabs designed for it from the start.

Some microcement and levelling products are declared against EN 13813, which classifies screed materials by binder (CT for cementitious) and declared properties such as compressive and flexural strength. A declaration describes the material as tested; it does not tell you whether the floor build-up is right for the space.

Common mistakes

• Treating the sealer as waterproofing in showers and wet floors.
• Laying over hollow tiles or a weak screed. The finish cracks and lifts over them.
• Ignoring slab joints to get a "seamless" floor; the joint appears anyway, as a crack.
• Rushing coats in a hot, ventilated space so the material dries too fast.
• Acidic or bleach cleaners that strip the sealer.
• Specifying it for forklift or trolley-heavy areas where an industrial floor is needed.

What to ask your contractor or applicator

• What substrate preparation, primer and mesh does the system require here?
• How will joints and substrate cracks be treated?
• What is the waterproofing build-up in wet areas?
• Which sealer, what slip resistance, and how often is it renewed?
• Can we see a sample panel on the actual substrate before the full area?

Standards referenced

Screed material properties and classification under EN 13813, where a product is declared against it. System selection, substrate suitability, joint layout, wet-area waterproofing and slip resistance must be confirmed by the designer, the microcement manufacturer's technical data and the project's engineer.