- 27 Jun 2026
- 4 min read
Sealant fails quietly. It shrinks, cracks, or pulls away from the surface over years — and by the time the damage inside is obvious, water or air has been getting in for a long time. This applies to sealant around windows and external doors, and equally to the silicone joints in bathrooms and kitchens.
External Sealant: Windows and Doors
How External Sealant Fails
External silicone and mastic around window and door frames degrades with UV exposure and repeated thermal movement. The frame expands in summer, contracts in winter — and low-grade sealant cannot sustain that cycling indefinitely. Signs of external sealant failure include:
- Visible cracks or splits running along the bead length
- Sealant pulling away from the frame or the masonry — leaving a gap on one or both edges
- Bubbling or discolouration — indicates UV degradation or moisture trapped beneath
- Draughts around closed windows and doors — even with no visible crack, a failed bead allows significant air infiltration
- Water appearing on the inside of the frame after rainfall
Why Running a New Bead Over the Top Is Wrong
The most common DIY response — and an unfortunately common trade response too — is to run a new bead of silicone over the existing failed sealant. This does not work. The new bead bonds only to the old, degraded sealant, not to the frame or masonry below. The adhesion fails quickly, and you now have two layers of failed sealant and a water trap between them. Perished seals must be fully removed, the substrate cleaned and primed, and fresh sealant applied to bare, prepared surfaces. There are no shortcuts.
Left unaddressed, draughts through failed external sealant add measurably to heating bills. Water ingress behind frame sealant causes timber rot, blown plaster, and in cavity wall construction can saturate insulation — damage that costs far more to fix than a proper reseal.
NSJ provides external sealant replacement across window and door perimeters, using professional-grade, UV-stable silicone specified for UK weather conditions.
Internal Sealant: Bathrooms and Kitchens
Where Internal Sealant Fails First
Inside the property, silicone sealant at bath rims, shower trays, shower enclosures, basin junctions, and kitchen splashbacks carries a high water load daily. Failure is common and often underestimated in its consequences.
- Bath rim silicone — once this cracks or detaches, water tracks behind the bath panel and into the floor void. Timber subfloors rot quickly in this environment.
- Shower tray silicone — the joint between tray and tiles or wall is a high-stress point. Failure here routes water directly into the wall structure.
- Basin junctions — drips and splashes accumulate at the basin-to-wall and basin-to-worktop joint. Failed sealant means this water reaches surfaces and cavities that cannot be ventilated.
- Kitchen splashback — when the bead lifts at the wall-to-worktop junction, water ingress behind tiles causes adhesive failure. Tiles loosen, and the plasterboard or wall board behind deteriorates.
All of these failure points lead to the same result: hidden, persistent moisture that produces black mould, structural decay, and eventually expensive reinstatement work.
The Right Fix for Internal Sealant
As with external sealant, there is no valid shortcut. Running a new bead of retail silicone over failed bathroom sealant produces a bead that looks new for a few weeks and then debonds from the contaminated surface beneath. The full bead must be cut out and removed. The substrate — grout, tile edge, acrylic or enamel — must be cleaned of all residue and any mould-contaminated material. Only then should new, mould-resistant silicone be applied and properly tooled.
NSJ's internal sealant replacement service covers full strip-out and reapplication across baths, showers, basins and kitchen splashbacks. We do not apply over old sealant. If the underlying surface has water damage, we identify it at the time of inspection. Full information on bathroom and kitchen leak and mould problems is on our problems page.
For a building leak and damp inspection or to arrange external or internal reseal across Leeds, Bradford, Harrogate, Ilkley, Wetherby or anywhere across West and North Yorkshire, contact NSJ today.