New homes are built quickly, and sealant is one of the last things to go in. That makes it one of the most common snags. Some problems show on the day you move in. Others take months, as the house dries out and settles. This guide covers what to check, how to report it to your builder and what a proper fix looks like.
What to check in the bathroom and kitchen
- Gaps or thin spots along the bath, shower tray and basin, especially in corners.
- Sealant pulling away from the tile or tray as the bath or tray settles.
- A messy bead smeared across tiles, or sealant over grout lines.
- Early mould in a bead that is only months old, which can mean it went on over a damp or dirty joint.
- Kitchen joints along the worktop and around the sink that are patchy or missing.
What to check outside and around frames
- Mastic around window and door frames that is gappy, cracked or missing at the corners.
- Mastic around the sill that doesn’t cover the joint fully.
- Movement joints in brickwork that are open, poorly filled or bridged by mortar.
- Internal gaps between frames and plaster, which can let in draughts.
Take photos with the date. They help if the problem gets worse. Our window mastic guide shows what sound mastic should look like.
Why new-build sealant fails
New houses move. Timber dries out, plaster shrinks and baths and trays settle under use. A bead that was fine at handover can tear when the bath first takes a full load of water. Other failures come from rushed work: sealant laid on dust, on damp plaster or on an unprimed surface, or a bath sealed without being filled first.
A real example: at a new-build in Forge Wood, Crawley, the shower tray seal had failed after 16 months. The builder’s sealant had gone onto a gritty, unprimed surface. We removed it all, primed the surfaces and resealed with sanitary silicone.
Need it done properly? Mr Mastic covers the South East, London and Scotland, with a one-year guarantee on every job. Call or email for a quick quote.
Reporting it to your builder
Many new homes come with a warranty under which the builder is responsible for putting right defects for an initial period, often the first two years. NHBC, for example, advises owners to contact the builder as soon as they reasonably can, within the builder warranty period, and to keep a record of what was reported and when (NHBC: the first two years). Your own warranty documents explain what is covered.
Report sealant problems in writing, with photos, and keep copies. If water is getting through and causing damage, say so clearly.
What a proper snagging reseal involves
A proper fix is not a new bead over the old one. The failed sealant should be cut out completely, the joint cleaned, primed where the surface needs it, and the bath filled before sealing. Then a single, even bead of sanitary silicone goes on.
Our new-build mastic service handles both sides of this: plot mastic and second-fix sealing for developers, and snagging failed sealant for new-home owners. Each job carries our one-year guarantee.
Developers and second fix
For developers and site managers, getting sealant right at second fix saves call-backs later. That means sealing onto dry, clean, primed surfaces, filling baths before they are sealed, and leaving enough time for the sealant to cure before plots are cleaned and handed over.
Quick answers
Should I wait for the builder or fix it myself?
If the home is within the builder’s warranty period, report it to them first. If water is getting through, say so, as it may need dealing with quickly.
Is it normal for new-build sealant to crack?
Some movement is normal as a house dries out. Sealant that tears or lifts in the first year or two is still worth reporting.
Can you seal over the builder’s sealant?
No. New silicone won’t bond to old silicone, so the original sealant has to come out first.
Related services
More advice
- Can You Put New Silicone Over Old Silicone?
- Leaking Shower? How to Tell if It’s the Sealant
- Window Mastic: When to Replace It and How
- All advice
This guide is general information about sealant work. It isn’t legal, fire-safety or structural advice; for those, speak to a qualified professional.