Most textured wall finishes are for dry rooms. Lime and clay want to breathe; a heavy relief plaster holds water in its own shadows. Rock Plaster is the exception in our range: a hard, textured wall coating that is made for high-traffic walls, is water resistant once sealed and can go in a wet room or outside. It is also the one that carries recycled shell, glass or cork in its surface, which is why it gets asked about.
What it is
A single-component, trowel-applied plaster with a resin binder rather than a lime or cement one. It comes as a white paste, is pigmented to colour and is built up in thin coats, each under a millimetre: a mesh coat first on the full wall system, then one or two body coats, then a finish coat, each dried and sanded before the next. Three grain sizes are made. Rustic has the largest grain and the most movement; Natural sits in the middle; Refined is fine enough to read almost flat. The finish coat can be any of the three, so the same wall can be left with real tooth or taken down to something close to a honed stone.
It is not a lime plaster and it is not a cement one. We say so because the word "mineral" gets used loosely. The resin is what gives it its hardness and its water resistance and it is also why it is sealed rather than left open.
The aggregates
What makes it ours is what goes into the surface. We offer three aggregates, all on sample boards in the studio. Recycled fine shell is trowelled into the body and then sprayed into the surface, for a fine, even sparkle that reads strongest on darker colours and disappears into pale ones. Recycled bottle glass gives a visible, even fleck through the coat and is the most stone-like of the three; on Smoke it reads as a dark granite from across a room. Natural cork gives a salt-and-pepper grain with a warmer, softer surface than the mineral aggregates and suits the pale end of the range. The shell and the glass are recycled material; the cork is a renewable one. None of them changes how the plaster behaves, only how it looks.
Where it goes and where it does not
The maker's own words are "high traffic wall applications including commercial and residential environments", and that is exactly where it earns its keep: hallways, stair enclosures, receptions, bars, the walls of a family bathroom, a cloakroom, a covered outdoor wall. It is suitable for wet and external areas. It is not a floor finish and it should not be used where water can pond, which rules out a shower niche, a shower tray and the inside of a bath. For those, the right system is microcement, or Micro-Stone if you want the stone character to carry through.
The full wall system, with the mesh coat, is what we use on cement board, plasterboard or timber where the wall will take knocks or get wet. The shorter versions without mesh go on sound plasterboard or plaster for decorative walls only. The maker rates them lower for durability. We will tell you which you are being quoted.
Sealing
A decorative wall gets one coat of a single-part matt sealer. A high-traffic or wet wall always gets two coats of a two-part polyurethane, which is what gives it its stain and water resistance. The sealer is matt either way, so the texture is what you see, not a shine over it. On a wet wall the sealed surface is wiped down like any sealed microcement; the texture is shallow enough that it does not hold water.
Why choose it over a plain microcement wall
Texture, mostly. A flat microcement wall shows every scuff and every raking light. Rock Plaster has enough grain to hide the knocks a hallway collects and the aggregate gives it a depth that a flat colour cannot have. It also goes on quickly, four or five days for the full wall system. It dries fast enough to be force-dried between coats. Against that, it is walls only, it is a little harder to wipe than a flat surface and the texture is not for everyone. We would always put a board on the wall in your own light before you decide.
The stone finishes page has it alongside Micro-Stone and Micro-Granite, with the three aggregate boards. Tell us about the project and we will take it from there.