Mould (or mildew) are a form of fungi that will thrive where the following are present:

- Food source (in a bathroom this is commonly soap scum)

- Moisture

- Low light

Given your bathroom hasn't been used for a year it is likely the mould is dormant, which means that it has stopped spreading. This doesn't mean the mould is dead. If mould has been visible then mould spores will be present. Once the above conditions are present it will reactivate and start spreading. Therefore in undertaking your renovation, make sure all traces of mould and its spores are destroyed/removed. Domestic bleach will chemically kill mould and destroy its spores, however the best practice is to remove it physically. If the mould is dry then I would suggest wearing protective face mask to prevent ingestion of any spores; depending on the type of mould (and there are many different types) the spores can lead to ill health. Better still call in a professional, particularly if you have traces of mould noticeable within the substrate of your bathroom.

Going forward for your renovation, consider using surfaces that are not porous and sealants that have mould inhibitors. Grout is porous and mould loves developing deep within this cement mix. So look for wall and floor products that don't use grout, they do exist. All the best.

Thank you for your vicevic

We had an investment property flooded and Mould went through everything. Called in experts. Stripped all Mouldy plaster out. Sanded back all Mouldy timber including subframe. Hepa Air purifier to remove airborne spores, tape up room before above work to avoid spores spreading through house. Under the subfloor was musty so Mould was in The soil. They took out the top couple of inches of soil.

Dry thoroughly with a good heater before rebuilding.
Bleach tends to bleach rather than kill Mould. Vinegar is supposed to be better than bleach, but Mould spores bury into porous surfaces so hard to kill. Any Mouldy silicon has to be removed, area dried for a couple of days before redoing silicon with a wet area silicon.

Mould has not returned.
Hope this helps. Ours was extreme, with ironically only the bathroom not affected.