A microcement quote usually names a colour, a finish and a price per square metre. It rarely says what is going on the wall or the floor, layer by layer. That is the part that decides whether the surface is still right in ten years. Here is what is in ours, why each layer is there and the figures from the manufacturer's data sheets that we work to.
The whole thing is about three millimetres
Primer, two base coats with mesh, two top coats and the sealers add up to about three millimetres on a floor or a wall. That is the number that makes everything else possible: it is why a microcement floor can go over a sound existing floor without rebuilding thresholds, why it suits underfloor heating so well and why it has no capacity to bridge movement in whatever is underneath it. Three millimetres of material cannot hold a cracked screed together. It can only follow it. Every rule in the rest of this article comes from that.
Primer
There is no single primer. A porous substrate such as gypsum plaster or a new screed takes a water-based primer that controls suction so the base coat does not dry too fast. A dense or painted one, cement board or an existing sealed surface, takes a grip primer that gives the base coat something to key into. Tile, old screed and anything non-porous take a two-part epoxy primer, blinded with sand while wet so that the next coat has a texture to bite on. Choosing the wrong primer is the most common cause of a microcement floor that lifts in sheets a year later. It is invisible once the floor is finished, which is why we photograph every stage.
Base coats and mesh
The base coats build the thickness and the strength. On a floor and on any wall that will get wet or take knocks, a fibreglass mesh is bedded into the first base coat while it is wet and covered by the second. The mesh does not stop a substrate moving; it spreads slight movements across the surface so they do not concentrate at a board joint and come through as a hairline. On a wet-room wall we do not consider it optional. The base coat for a floor is a harder mix than the one for a wall and there is a universal grade for both; each has its own data sheet and its own coverage. For crack-prone floors the mesh can be doubled.
Top coats
The top coats are the colour and the texture. Ours is a two-part epoxy resin and cement hybrid rather than a cement powder with a liquid polymer stirred in, which is what gives it its figures: compressive strength up to 50 N/mm² at 28 days, adhesion to concrete above 2 N/mm², abrasion resistance tested to EN 13892 and a waterproof rating on the sheet. Each coat goes on at 0.4 to 0.5 mm, about 400 to 500 grams per square metre, with an hour of working time once it is mixed and an application window between 5 and 25°C. It comes in three grain sizes: Rustic, with the largest grain and the most stone-like movement, which can be left with tooth for grip or sanded smooth; Natural, with a smaller visible grain and calmer tone; and Refined, with no visible grain, which reads as a polished plaster. The grain is chosen first and the sheen is chosen separately, with the sealer.
Two things that a waterproof top coat does not change. It still needs a tanking membrane under it in a wet room, because the waterproofing of the room is the membrane and the taped corners, not the finish. And it is still sealed, because the sealer is what takes the wear and sets how the surface cleans.
Sealers
Two coats of a polyurethane sealer finish the system. A single-part matt sealer is for decorative walls that do not get wet. A two-part sealer is for floors, worktops and wet areas, with a stain-resistant grade for kitchens and anywhere strong colours, dyes or rubber feet will sit on the surface. On a textured top coat a smoothing coat goes on first to take the roughness out before the sealer. The sealers are the part of the system that is renewed: a day's visit every few years on a floor, longer on a wall. There is more on sealers here.
The order on site
- Substrate checked, ground or sanded, vacuumed and wiped. Moisture readings taken by instrument on a screed.
- Membrane and taped detailing in a wet room, tested before anything goes over it.
- Primer for the substrate, dry before the next coat.
- First base coat with mesh bedded in, then the second base coat, each dried and sanded.
- Two top coats, each dried and sanded; the final one left a full day before sanding wherever the programme allows.
- Smoothing coat where the texture calls for it, then two coats of sealer, with protection over a floor until it is hard.
A floor is walked on in soft shoes after the sealer has dried and treated normally after it has fully hardened, which is days rather than hours. A floor that is loaded with furniture on the second day is the second most common failure we are asked to look at.
What a quote should tell you
Which primer. Whether there is mesh and where. How many base and top coats. Which sealer and how many coats. Whether the floor or wall has been checked for moisture and movement before the price was given. If a quote cannot answer those, it is a price for a colour, not for a system. The two are not the same thing.
The microcement page has the build-up in short form and the technical hub has the substrate build-ups for walls, floors and underfloor heating. For a specific job, send us the drawings.