Sealant is one of the last trades through a building, and one of the first things a client notices. A smeared bead around a basin, a gap at a skirting or a missing joint at a window can turn a clean walk-round into a long snag list. For main contractors and developers, the fix is to treat mastic as part of the finishing plan, not an afterthought. This guide lists the usual snags and how to clear them early.
The snags that come up most
- beads that are uneven, smeared or not tooled, especially on show joints
- missing sealant at window boards, door frames, skirting and worktop upstands
- sealant on the wrong colour, or a colour that doesn’t match the finish next to it
- gaps or splits where joints were sealed before other trades finished
- caulk or sealant damaged by later trades or decorators
- movement joints filled with the wrong product, or with no backing rod
- missing or untidy seals at service penetrations through fire-resisting walls
Get the sequence right
Many snags are caused by order of works. Sealing before the decorator finishes means the bead gets painted or knocked. Sealing before the flooring goes down means a perimeter joint that no longer meets the floor. Plan the mastic package around the programme, floor by floor or plot by plot, so each area is sealed when the surrounding finishes are complete. Our construction mastic page explains how we work to the programme and the specification.
Do a sealant-only walk-round
A general snagging walk often misses sealant because it is low down or out of sight. Before the client visit, do a separate round that looks only at joints. Take a torch. Check behind doors, under worktops, around WCs and at the base of window frames. Mark each item with a photo and a location, and group them by type so they can be closed in one visit rather than several.
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Washrooms and kitchens
Wet areas get extra scrutiny. Clients look closely at sanitary joints around trays, baths, basins, IPS panels and urinals. A sanitary silicone with anti-mould additives is the norm. Make sure the bead is continuous, there are no pinholes, and it is not stained by grout haze or cleaning products. Our washroom sealing service covers these areas.
Fire-resisting walls and floors
Late service runs often leave gaps in fire-resisting walls and floors. These should be sealed with the specified product to the manufacturer’s tested detail, not just filled with whatever is to hand. Check that each penetration matches what the designer specified and that the records the client needs are in hand. Design and sign-off sit with the designer, principal designer, fire engineer and building control. Our guide to fire stopping after fit-out has a checklist.
Protecting joints and keeping records
Once a joint is sealed, protect it until handover where you can. Brief later trades and cleaners that fresh sealant needs time to cure and should not be scraped, painted or wiped with solvents. A short note in the site induction or on the daily briefing sheet helps. Where joints are damaged by others, record who and where, so the cost of putting them right can be dealt with fairly.
Gather product data sheets, colours used and any guarantee documents for the O&M manual. These help the client’s facilities team plan future maintenance. Tell us what records you need and we’ll confirm with the quote.
Quick answers
Can snagging be done as a separate visit?
Yes. Some contractors book a mastic snagging visit near handover once all trades are finished. Send the snag list with photos and locations and we can price it as a fixed quote.
Why do beads go wrong when other trades follow?
Fresh sealant can be marked, painted over or knocked before it cures. Sealing after finishes are complete, and protecting new joints where possible, avoids most of this.
Who should check fire-rated seals before handover?
The person responsible for compliance on the project, usually with the designer or fire engineer and building control. The installer seals to the specified tested detail; sign-off sits with the designer and building control.
Related services
- Construction and new-build mastic
- Commercial washroom and wet-area sealing
- Fire-rated sealing and fire stopping
More advice
- CDM and RAMS Basics for Sealant Work
- Fire Stopping After M&E and Fit-Out Works
- Colour-Matched Sealant on Commercial Jobs
- BS EN 15651 Sealant Classes in Plain English
- 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.