Microcement over tiles: what to know before you start

Can microcement go over tiles?

Usually, yes. In most bathrooms microcement goes straight over the old tiles, as long as they're firmly stuck down.

A tile that moves can crack the thin coat on top of it, so a loose tile can't just be coated over. It comes out first, and a new tile the same size and shape goes in.

How the tiles are checked

At the site visit we check each tile. A tile that sounds hollow when you tap it, often called drummy, has come loose from the wall or floor behind it.

A drummy tile comes out, and we put in another tile the same size and shape so the surface stays flat. It doesn't have to match, because it gets covered. If a whole wall or floor is loose, it's usually better to strip that part back.

How the tiles are prepared

Before any microcement goes on, the tiles are prepared so the surface is clean, flat and solid:

• The tiles are cleaned so there's no grease, soap scum or dust on them.
• The grout lines are filled, so the surface is flat and stable.
• A primer goes on. It's a coat that helps the microcement grip the tiles.
• Two base coats go on, with fibreglass mesh to help stop cracks coming through. On walls the mesh goes between the two base coats, and on floors it goes down first.
• Two top coats go on. On walls, each coat goes on while the last is still a little damp, so the layers bond together.
• The surface is sealed to protect it from water and stains.

Laying microcement on a hot Perth day

Heat makes microcement go off, meaning set, faster. On a hot day we put an additive or ice in the mix to slow it down. We also lay less each day, so the job can take a bit longer when it's hot.

Going over tiles in a shower

Under the tiles in a shower there should be a waterproof layer, called a membrane. Going over the tiles leaves that membrane exactly as it was put in.

That only helps if the membrane is doing its job. If the shower leaks, has water damage nearby or has gaps in the grout or silicone, it has to be repaired first, because microcement won't fix a leak.

In the corners, where the walls meet the floor and where two walls meet, we wrap the mesh around the corner and tape the joins before the coats go on.

Will the floor be higher?

A little. The finished coat is usually 2 to 3 mm thick, so over old floor tiles the floor goes up by a few millimetres.

That's normally fine, but it's worth checking doors that sit close to the floor and the step into a shower. We look at both when we see the room.

When going over tiles isn't the right call

Going over tiles isn't the right call in every room. These are the times we'd tell you to sort something out first, or strip the tiles off:

• Lots of the tiles are loose or cracked.
• The shower leaks or there's water damage around it.
• The slab or wall under the tiles is cracked or moving.

Questions