The sealer is the part of a microcement, stone or textured-plaster surface that you actually touch, clean and wear out. It is also the part that most quotes describe in one word, if at all. The finish underneath is chosen for how it looks; the sealer is chosen for what the surface has to do. Here is how we choose it.
What a sealer does
Three things. It closes the surface, so water and dirt sit on top rather than soaking in. It takes the wear, so that shoes, chairs and cleaning act on a renewable layer rather than on the finish. And it sets the sheen, from dead matt to a polished gloss, independently of the texture underneath. A top coat that is rated waterproof on its data sheet still gets sealed, because none of those three things is about waterproofing.
Single-part matt
A single-component polyurethane, applied by roller at about 60 to 70 grams a square metre, touch dry in a few hours. It is for decorative use: a feature wall, a hallway above dado height, a fireplace, anywhere that is looked at more than it is touched and never gets wet. One coat is sufficient on a feature wall. It is the sealer that keeps a textured finish looking most like itself, because it adds nothing to the surface.
Two-part
A two-component polyurethane, base and hardener mixed on site with about an hour of working time, at the same coverage. It is harder, more stain resistant and it is what goes on floors, worktops, wet rooms and any wall that gets wet or takes traffic. There is a standard grade and a plus grade with added resistance to strong colours, dyes and the plasticisers in rubber feet and mats, which is the one for a kitchen floor or a worktop. It is matt as standard and can be polished to a gloss after it has dried overnight.
Why two coats
One coat seals. Two coats wear. The manufacturer's own guidance is that two coats should always be specified for high-traffic and wet areas and that is the rule we work to, not a thing we add for a price. The second coat is what gives the surface a layer to lose before the first one is reached, which is the difference between a floor that is re-sealed as a day's visit every few years and one that is re-coated.
Smoothing and pore-filling first
A sealer follows the surface it is put on. On a Rustic or Natural grain top coat a smoothing paste goes on first with a plastic trowel to take the roughness out, so the sealer does not hold dirt in the tooth. On a stone finish the surface is open after sanding and a pore-filler goes in before the sealer: a trowelled filler in dry rooms, sanded back so it stays only in the pores, or a thickened wet-area sealer where there is water. Skipping that stage is why some stone floors look plastic and some textured floors never seem clean.
Where water ponds
There is a difference between a surface that gets wet and one that holds water. A shower wall gets wet and dries; a shower tray, a niche and a bath surround hold water. The smoothing paste is not for ponding water and the single-part sealer is not for wet areas at all. In a wet room the floor and the niche get the thickened wet-area route and two coats of the two-part sealer. The walls get the same, which is also why Rock Plaster is a wall finish and not a tray one.
Looking after it
A pH-neutral cleaner, no abrasives, felt under furniture and no rubber-backed mats on a floor sealed with the standard grade. A newly sealed floor is walked on in soft shoes after a day and treated normally after it has fully hardened, which takes days. Re-sealing is a light abrasion and one or two coats, usually in a day. It is the whole of the maintenance. The care guide has the detail.
If a quote says "sealed" and nothing more, ask which sealer, how many coats and whether the surface is smoothed or pore-filled first. The answers tell you what the surface will be like to live with. Ours are in the specification.