I ran a fresh bead of silicone straight over the old mouldy sealant to save time: when the black spots came back through it a few weeks later, it was too late
Applying fresh silicone sealant over existing mould might seem like a time-saving hack, but it’s actually sealing the problem inside rather than solving it. The mould isn’t living on the sealant surface—it’s thriving behind it, and a new layer just gives it more time to work back through. Here’s the proper way to fix it permanently.