How to fix missing and damaged grout?

Bill1990

Hi Bunnings workshop community,

I'm looking to see if there is anyone who can advise on this grout situation. In an attempt to clean grout, a metal brush was used which caused the (already old and worn) grout to deteriorate. These left these weird holes (pictures below).

Undamaged grout:

Some samples of damaged grout:

I did a bit of research on grout replacement, but still left with some questions:

1. These holes are very much deeper than those around them, will the general advice of removing a thin layer of grout all around and pushing the grout in fill these holes adequately?
2. As I understand it grout is porous and not part of waterproofing, however due to the severity of the deterioration should I be concerned at all about water damage due to these deep holes (and if so, what should I be looking for)?
3. I want to restore as close to original as possible. How can I identify the grout type I should use? It has a slightly rough texture to it.
4. Following restoring it as closely as possible, the grout seems to be recessed a small amount below the tile surface, what's the best way to replicate that evenly?

Any other advice about rectifying this situation would be much appreciated

Appreciate the help as always!
Bill

MitchellMc

Hi @Bill1990 ,

It looks like the wire brush has removed some of the softer, weathered grout rather than just the surface, which is why you're seeing those deeper voids. Fortunately, this is something that can usually be repaired without having to completely regrout the tiled area.

To answer your questions:

Will new grout fill the deeper holes?
Yes, provided you remove any loose or weakened grout first. I wouldn't just fill the holes, as the new grout won't bond well to deteriorated material. Instead, use a grout saw or grout removal tool to remove the grout to a consistent depth along the affected joints. Ideally, you want to remove at least 2-3mm of grout (or around half the depth of the joint if it's already quite shallow) before applying new grout. This will allow the new grout to bond properly and fill the deeper voids at the same time.

Should you be concerned about waterproofing?
You're correct that grout itself isn't the waterproofing layer. In a properly constructed shower, the waterproof membrane sits behind the tiles. While these holes are unlikely to immediately cause water damage, deteriorated grout can allow more moisture to sit behind the tiles, so it's worth repairing sooner rather than later. If the shower is older, keep an eye out for signs such as loose tiles, persistent dampness on adjoining walls or skirting boards, or cracking, which could indicate a more significant issue.

How do you identify the grout?
From your photos, it appears to be a fairly standard sanded cement-based grout, which has the slightly rough texture you've described. You may not get a perfect colour match, especially if the grout has aged over a number of years, but taking a close-up photo or, if possible, a small sample into your local Bunnings should help the team recommend the closest match. Something like https://www.bunnings.com.au/dunlop-800g-ready-to-go-coloured-grout-slate-grey_p6650124 might be close, but it's best to do a test section.

How do you recreate the recessed finish?
Once the grout has started to firm up, wipe it with a damp grout sponge using light, even strokes. This naturally leaves the grout fractionally below the tile surface, similar to the existing joints. The key is to avoid over-washing, which can pull too much grout from the joints.

Overall, I think you've caught it at a good stage, and a localised regrout should restore the appearance nicely without needing to remove all of the existing grout.

Here are a couple of helpful guides: How to remove grout and How to grout tiles.

Let me also tag @giggles6701, @emmab1986, @kimbaday and @mills28 to see if they have any advice. Check out our Best Advice article too on How to repair tile grout.

Please let me know if you have further questions.

Mitchell