Tim S wrote:

The grout on the new shower is already showing signs of black mould
spores. Since we have a chance to nip this in the bud, what would be the
best way of doing so?

Bleach first - get it killed - it's not permanant - if mould likes your
shower, the spores are always going to be floating around - but I've found
bleach keeps it knocked back.

Is it the grout or silicone or something else that's sprouting the mould?

You're right to ask - in fact it's the flexible seal between the tiles
and the base of the shower, not the hard stuff between the tiles that
has sprouted the mould.

Daniele
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Wanted: TEAC A-2300SX, Akai GX-4000D