How to install cement board over tiles?

Sean12

Hi there, I'm currently redoing my bathroom shower area due to an existing leak causing the timber frames to rot. Initially I was planning to remove the existing tiles, keeping the cement board underneath intact, then placing another cement board sheet on top which should cover the gap in the corner. However, it turns out removing the tiles (especially closer to the top) is a real pain without destroying the cement board as well. It takes me around 1 hour to remove a single tile with a hammer and chisel (and hammer drill). 

Given its going to take way too long to remove all the tiles in the shower, is it possible to somehow just stick a piece of cement board on top of the existing tiles, and then stick new tiles on top of that? What kind of adhesive would I use to bind the tile surface with the cement board? I don't mind the reduced shower space. 

EricL

Hello @Sean12 

That’s a great question and a really common situation when dealing with older bathrooms where tile removal damages the backing board. Unfortunately, fixing cement sheeting over existing tiles is not a good long-term solution for a shower or wet area, and here’s why.

When you stick cement board on top of existing tiles, you’re relying on the old tile surface for adhesion and structural support. Even if you use a high-bond adhesive, the tile glaze is a non-porous surface, and it’s extremely difficult to get a mechanical bond strong enough to handle constant moisture and thermal expansion. Over time, the layers can separate due to steam and water infiltration. The slightest flex in the wall, grout crack, or adhesive failure allows moisture to seep between the layers. 

Because there’s no proper waterproofing membrane between the old tiles and the new board, water will eventually migrate down to the timber studs again, restarting the rot issue you’re trying to solve. This can happen within months, and it’s difficult to detect until the damage becomes extensive. The result is mould growth, structural weakening, and the need for a complete rebuild later.

A better approach is to remove the entire affected wall section, including the old cement board and tiles, and replace it with fresh cement sheeting. It sounds like a lot of work, but it’s actually quicker and far more reliable in the long run. You can use a small sledgehammer or demolition hammer to break through the tiles and sheeting together in manageable pieces, rather than trying to chip off each tile individually. Once you have the wall stripped to the studs, check for any moisture damage, replace any rotted timber, install a proper waterproof membrane, and then fix new cement sheets. After that, you can tile over a clean, stable, and properly sealed surface.

So, while the idea of layering new materials on top may save some time initially, it almost always leads to hidden water issues later. Replacing the entire sheet ensures you start with a dry, sound, and code-compliant wall structure that will last for decades without recurring leaks.

If you need further assistance, please let us know.

Eric