Child Item

Are black spots in new grout mould?

Hi,

We are removing the grout from

our shower, which was installed as part of renovations about 8 years ago. The reason for this work is that thw original grout wasn’t drying out after showers (12 hours in between, sometimes days whent we went away) and in areas the grout was reducing to well below the height off the tiles. Our cleaning process has been to use a scrubbing brush on the tiles with a mixture of vinegar, dishwashing detergent and water which we spray on the glass and tiles.

To remove the grout, I have been using a grout saw and the multipurpose Ryobi tool from Bunnings - game changer.

I am now even more worried as there are black specs showing in the grout, sometimes with pinkish looking sections and of course, the grout which still hasn’t dried after two days of continuous industrial fan going in the bathroom. Last night, when i removed a section of grout, some water seeped into the grout from below. There isn’t any water damage under the floor - we checked under the house (Queenslander).

I would love any advice that can be provided on:

a) are the black specs mould (some of it has been below a layer if white grout) - we have since sprayed with mould killer

b) is the pink discolouration mould?

c) how do we dry out the grout so we can regrout?

d) how do I know when I am at the level of the waterproofing? - worried I will break it.

d) is this a bigger job than we imagined and do we need to be lifting all the tiles and then retiling.

e) what would have caused this?

Thanks in advance for any advice/help.

Find more posts tagged with

Tools and Materials

Repairing

Tiling

Cleaning

Accepted answers

All comments

BEALE

These are the black specks coming out of the grout

MitchellMc

Welcome to the Bunnings Workshop community @BEALE. It's a pleasure to have you join us, and many thanks for your question about grout.

From what you’ve described, it sounds like the situation isn’t as serious as it seems. The black specks in your old grout are most likely just part of the original grout mix and are tiny aggregates, and the pinkish areas aren’t necessarily mould either. Grout is naturally porous, so it absorbs water, and it never truly dries out underneath tiles, which explains why it can feel damp even after a fan has been running. That said, removing any soft or crumbling grout and re-grouting is the right approach. You don’t need to completely dry out the area first, and there’s no need to lift tiles as long as the adhesive and waterproofing membrane underneath are intact.

When re-grouting, make sure to cut back the old grout a few millimetres below the tile surface, fill in properly, let it cure, and then apply a grout sealer. That will prevent water from penetrating and should resolve the issues you were noticing. Do not remove any more grout than what you have already, as you will hit the membrane, and the consequences of that are potentially having to remove all the tiles in your bathroom and reapplying the membrane, as membranes can not have patch repairs on damage.

If you want extra protection, epoxy grout is an option, but standard cement-based grout with a good sealer is usually sufficient. In short, this is a fairly standard repair job, and once re-grouted and sealed, your shower should be good to go.

Here's a helpful guide: How to grout tiles.

Please let me know if you have any questions.

Mitchell

BEALE

Thank you MitchellMc! Truely appreciate your advice and pleased to know we are not up for more major repairs.

I’ll keep going and will update with new photos.

BEALE

Grouting completed. Polishing tiles next up and then sealing. Quite pleased with our efforts. Thanks again for the advice.

MitchellMc

Looks great @BEALE! Well done and many thanks for sharing your results.

Mitchell

BEALE

We ended up having to regrout the shower wall tiles as well. Finished that yesterday using Dunlop Ready to Go Magellan Grey - matched the existing grout well.

Learnings are to not wipe the grout too many times so that the colour doesn’t fade - this happened to the floor times - newbie error.

Not to leave the grout too long (went to the other extreme to stop colour fade) so that it sets like rock - if it does though, can gently use a scraping tool to remove excess grout and then clean up once the grout has set.

I found the Ready to Go products set more quickly (good thing when on a tight timeframe) and is not as thick as I prefer - I found it hard to wipe at the 45 degree angle into the gaps with a sponge - padded trowel wasn’t effective either.

About to start the silicone stage. Advice from a traddie years ago was to clean up the gaps with Shellite and not be stingy with the application as it helps with applying the silicone.

Side projects in between the bathroom project have been to remove the concrete at the base of our back steps and then top with sandstone crazy pave; and to clean up and reseal the older crazy pave under our arbour. Still some mould on the older sandstone and have mortar staining on the newer tiles - used the sweep in dry mortar and dampen with spray method as large area - not sure we would use this method again due to the staining.

Child Item