Our house has stone mullions (reconstituted bath stone) & they're almost constantly mouldy. We had to replace a lot of single glazing which had caused a lot of condensation issues so we've sorted that. I use a dehumidifier but as the stone is porous & so cold we still get mould growing.
I have issues cleaning it as I can't use strong chemicals due to health & don't want to damage the stone. Is there a long term option? I'll get someone to clean properly with chemicals if there's then something I can do to prevent it recurring. Some local people have suggested painting (with gloss I think) but is that the best solution? I didn't want to ruin the look of the stone before but I now hate the mullions so much I'lol pint them if that'll solve my issue.