Is microcement waterproof? The honest answer (and what the sealer does)

Yes. After 7 days of curing, microcement is waterproof: water neither stains it nor penetrates it. That is the material doing it, not the sealer. What the sealer adds is something else, and it is just as necessary: the everyday chemical resistance —soapy water, a spilled glass of wine, cleaning—, protection against wear and the level of sheen you choose. Two layers of the system, two different jobs. And because honesty comes first, the answer comes with its limits: microcement is not designed for water containers.

What the microcement does and what the sealer does

The system has two halves and they are worth keeping apart. The microcement coats —preparation and finish— give the continuous mineral texture and, once cured after 7 days, they are waterproof in themselves: the water stays on top.

The Smart Varnish adds what microcement alone does not have: chemical resistance to soap, food and cleaning products, protection against the abrasion of daily use, and the matte or satin finish. In showers, basins and other wet areas it is mixed with Smart Booster, which reinforces the sealer —not the microcement— and raises its resistance to abrasion and to aggressive cleaners.

No hidden steps: primer, thin coats of microcement and sealer. The sealer is not optional, but its job is to protect and to give the finish, not to waterproof.

Waterproof, surface by surface

Showers

Yes: walls and built shower trays. Our microcement shower kits include the sealer reinforced with Booster, which is what takes the shower gel, the shampoo and the weekly clean. One rule matters: the tray needs the right fall towards the drain, so the water runs instead of pooling.

Bathroom walls and floors

Yes. A microcement bathroom has no joints, so mould has nowhere to settle: a damp cloth does almost all the maintenance.

Kitchen splashbacks

Yes. Steam, splashes and grease are exactly what the sealer is there for, reinforced here with Booster too.

Worktops

Water is not the problem: heat is. Hot pans do not agree with microcement, and we say it plainly: a beautiful worktop, yes; trivets, too. Here are our microcement countertop kits with their limits stated.

Outdoors

Yes: terrace floors, facades and outdoor stairs take sun, rain and frost with the same kits. You have the detail in our outdoor microcement kit.

Where it does not belong: water containers

Waterproof does not mean suitable for everything. Microcement is not designed to hold water permanently, so bathtubs and swimming pools are out. It is not a matter of sealing or of extra coats: it simply is not the use it is formulated for.

On floors, the other side of the same coin: check that the fall drains the water properly. Standing water for hours in the same spot, day after day, is the one thing it will not forgive.

Stains, cracks and repair

Stains. With the sealer applied and reinforced with Booster, the surface takes water, soap, food residue, oil, vinegar, coffee or wine with no visible mark for up to 8 hours. Wipe the spill promptly and the finish stays flawless. An honest warning: do not leave a puddle of bleach on it for long, because it can mark.

Cracks. Microcement does not crack on its own. When cracks appear, the cause is almost always underneath: a surface that moves, coats that are too thick, or drying times that were not respected. Our system needs no mesh: it is flexible by formulation, and mesh would only add thickness. Two limits we always repeat: treat any rising damp before coating, and avoid underfloor heating, which we do not recommend.

Repair. A worn or damaged area is recovered by sanding lightly and reapplying on that spot. And the sealer is renewed: in bathrooms, kitchens and other wet or heavily used areas, refresh the Smart Varnish every 2 years (every 3-4 elsewhere) and the protection is back where it started.

Microcement against tiles, Venetian plaster and polished concrete

Tiles are waterproof; their joints are the weak point where mould settles. Microcement goes straight over the existing tiles, with the joints filled, leaving a continuous surface with no corner to colonise. That is exactly what our bathroom microcement kits do.

Venetian plaster protects walls from ambient humidity and breathes beautifully, but its wax sealing is decorative: no showers and no splash zones. The full comparison is in our guide to Venetian plaster.

Polished concrete is a structural floor: thick, poured and laid with machinery. Microcement gives the same mineral look, with no building work: here you have everything about polished concrete.

Frequently asked questions

Is microcement waterproof without sealer?

Yes, after 7 days of curing water neither stains it nor penetrates it. But the sealer is not optional: without it you have no chemical resistance to soap, food or cleaning, no protection against wear, and no matte or satin finish.

Can microcement be used in the shower?

Yes: walls and built trays, with the sealer mixed with Booster. Choose the kit by size and surface, mind the fall towards the drain, and the shower becomes a weekend project.

And in a bathtub or a swimming pool?

No. Microcement is not meant for water containers. Those cases need specific systems, different from a DIY kit.

What are the drawbacks of microcement?

It asks for patience between coats and a well prepared surface, and it has its honest noes: hot pans on the worktop, underfloor heating and water containers.