Why does my sealant go black?

Mould grows in trapped moisture behind or within the bead, usually where ventilation is poor or the bead was applied to a damp joint.

How long before I can use the shower?

Follow the product cure time — usually 12 to 24 hours.

Small works

Silicone and sealant renewal

The cheapest job that prevents the most expensive damage

The short answer

Blackened or lifting silicone around a bath, shower tray or worktop is letting water past. Renewal is a one to two hour job: strip the old sealant completely, dry and sterilise the joint, then apply a single continuous bead of sanitary-grade silicone. Left alone, it ends as a damaged ceiling in the flat below.

What the work involves

Cutting out old sealant, removing mould residue, drying the joint fully, filling the bath before sealing where relevant, then applying and tooling one clean bead.

Rules and responsibilities in Scotland

No certification applies, but in a flat, water escaping into the property below becomes a liability and insurance question.

What commonly goes wrong

Applying new silicone over old, and sealing a damp joint so mould grows straight back through the new bead.

What it usually costs

Indicative ranges only, to help you judge a quote. They are not an estimate for your property — only the business doing the work can give you that.

Materials cost very little; the labour is in stripping and drying.
Doing a bathroom and kitchen in one visit is efficient.
A ceiling repair in the flat below costs vastly more than the seal did.

What to do, in order

1Strip the old sealant back to clean surfaces.
2Treat and dry the joint properly.
3Fill the bath with water before sealing around it.
4Apply one continuous sanitary-grade bead.
5Leave it to cure fully before using the bath or shower.

Local detail for the Lothians

In Edinburgh tenements a failed bath seal is one of the most common causes of a complaint from the flat below.
Poorly ventilated internal bathrooms in converted flats blacken sealant faster.
Keep the dates — evidence of prompt repair matters in a shared-building claim.

When you need a professional

If water has already reached a ceiling or an electrical fitting below, get the leak traced properly before resealing.

Common questions

Why does my sealant go black?: Mould grows in trapped moisture behind or within the bead, usually where ventilation is poor or the bead was applied to a damp joint.
How long before I can use the shower?: Follow the product cure time — usually 12 to 24 hours.

Lothian Property is a property information and professional-introduction service operated by Maybury Scotland Limited. Lothian Property is not an estate agency. Where requested, we may connect homeowners with independent estate agents and other property professionals. How we work.

Tile and grout repairs
Replacing cracked tiles and regrouting so a tired bathroom looks maintained again.
Bathroom and kitchen extractor fans
Replacing or upgrading extraction so condensation and mould stop coming back.
Leaking taps and running toilets
A drip or a running cistern is a small job that quietly adds to a metered water bill and stains the fittings.

Last reviewed 5 September 2026.