How to regrout with void behind tile?

Question

Hi While removing grout from bathroom wall tiles I discovered there is a void behind the tiles at the bottom of the shower recess.

I concerned when I come regrout the tiles that the void will cause a problem when grouting that area. Are there any hints about groutung that area to prevent too much grout faling in behind. The deepest section of the worst affected tile is about 9mm behind the base of the tile.

MitchellMc · Answer

Sorry @grprojects, it doesn't appear your images have come through. If you continue to have issues, feel free to send them through to workshop@bunnings.com.au.

I’ve created a rendering to illustrate the typical layers of a waterproofed and tiled area. You start with your slab or floor, and the walls are lined with cement board. The cement board should extend all the way down to meet the slab. The joins are then taped, and a waterproofing membrane is applied across the floor and up the wall in one continuous layer.

If there is a void behind the tiles, it isn’t possible to create a continuous, fully effective waterproof layer, as water could simply escape into the gap.

I understand this may be a long-standing issue, but it doesn’t align with standard building practices. My concern is that if water can enter any recess or void, it could cause significant damage to the timber framing behind the cement sheets and the subfloor over time.

Mitchell

grprojects · Answer

To clarify, this has been like this since the house was built, we are the original owners. Also, I did not penetrate the membrane when removing the old grout as the old grout flaked away which I clearly saw fall into the void.  There is only one join that is really bad, the distance between the back of the tiles and the membrane is 7mm.

The pics are not that clear, it is best that I could achieve.

MitchellMc · Answer

Hi @grprojects,

There should be no gap behind the tile. Does it appear that the wall sheeting falls short of the bottom corner? It would be a requirement for the sheets to meet the floor, as the floor and the walls of the recess need to be waterproofed in one continuous layer. With a void behind the tile, I'm not sure how that could be possible.

I'd be a bit more concerned about whether you have an active membrane preventing water escaping from the recess rather than lost grout in the void. I think this needs a bit more assessment before carrying on and grouting over the area. Is there any way you could capture this void in a photo you could show us? Otherwise, I'd recommend you enlist the services of a waterproofing specialist to take a look at it for you.

Please let me know if you have any questions.

Mitchell