External sealant replacement for windows, doors and expansion joints
External sealant is the material that fills and seals the joint between a frame and the surrounding masonry - or between two different building materials. It is designed to flex with movement, repel water and stay bonded to both surfaces.
When it fails, rainwater and cold air find the smallest gaps and track inside. Left unaddressed, water that enters around a frame will eventually reach timbers, plasterwork or structural elements beneath.
We remove failed sealant properly and replace it with the right external-grade materials, applied to last.
When external resealing is needed
External sealant replacement is usually required when you notice:
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Sealant that is cracking, splitting or turning brittle
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Gaps opening between the frame and the brickwork
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Sealant that has pulled away from one side of the joint
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Water marks or damp patches appearing after rainfall
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Draughts around the frame perimeter even when the window is closed
If you are actively getting water in around a frame, the related problem page is: Water leaking around windows and doors.
Which sealant is used and why it matters
Not all external sealants are the same. The right material depends on the joint type, the substrates being sealed and the exposure conditions.
Polysulphide sealant
Polysulphide is a durable, paint-over-able sealant commonly used around concrete and masonry, particularly on commercial buildings, curtain walling and older construction. It handles significant movement and tolerates wet conditions during application. On the right substrate, it is extremely long-lived.
Silicone sealant
Silicone is flexible, UV-stable and moisture-resistant, making it well-suited to sealing between frames and masonry on domestic properties. It does not accept paint, so it is supplied in colours matched to the surrounding material. Applied correctly to clean, prepared surfaces, a silicone perimeter joint on a well-sheltered domestic property should last 15 to 20 years.
Polyurethane sealant
Polyurethane offers a middle ground - it is paintable, flexible, and bonds well to most construction materials. It is commonly used where a coloured finish is important or where the joint will see regular light foot or vehicle traffic (expansion joints in paved areas, for example).
Choosing the wrong sealant for the substrate or conditions shortens the lifespan significantly. We always select the material appropriate to the job.
Why perimeter joints fail over time
External joints fail for three main reasons:
Weather exposure. UV radiation, temperature extremes and wind-driven rain gradually break down sealant. Joints on exposed elevations - particularly west and south-facing walls across the Bradford and Harrogate areas - typically deteriorate faster than sheltered ones.
Differential movement. Frames and masonry are made from different materials and expand and contract at different rates. Over years of thermal cycling, stress builds at the joint boundary and adhesion breaks down.
Poor original application. If the old sealant was applied over contamination, applied without a backer rod in an oversized joint, wasn't tooled correctly, or used the wrong product for the substrate, it often fails well before it should. This is common on new-build properties where the original sealant was applied quickly at completion, and on 1960s–1980s properties where aged mastic has hardened and shrunk over decades.
Why resealing over old sealant fails
It is tempting to run a bead of sealant over the top of a failing one. It almost always fails early.
The reason is adhesion. New sealant bonds to what it touches. If it is applied over contamination, old sealant residue, or a surface that cannot accept a bond, it will pull away or split - often within a season. The joint underneath may also have a poor profile, meaning the new bead is too thick, too thin, or insufficiently supported.
Correct removal and surface preparation are what make resealing last.
Our external sealing process
A typical job follows this sequence:
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Remove all failed sealant - mechanical removal of existing material back to clean substrate on both sides of the joint
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Prepare surfaces - remove residue, clean and if required prime to ensure adhesion
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Check joint geometry - assess depth and width; install backer rod where necessary to achieve a correct joint profile
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Apply sealant - the correct external-grade product for the substrate and conditions, applied at the correct temperature
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Tool to profile - tooling to a consistent concave or weathered profile that encourages water to shed rather than sit
Most domestic jobs - a full perimeter of windows on a semi-detached, for example - are completed within a day. Commercial buildings with multiple frames or curtain walling joints will take longer.
Where we find that the draught or leak is coming from a failed gasket inside the frame rather than the external perimeter joint, we will advise on window and door gasket replacement instead.
Where we carry out external resealing work
We regularly work across Bradford, Leeds, Harrogate, Ilkley, Skipton, Wetherby and Otley - particularly on exposed elevations where wind-driven rain makes sealant performance critical. We work on domestic properties, commercial buildings and apartment blocks.
If you are not sure whether external sealant is the right fix, a Building Leak & Damp Inspection can identify the cause before any work begins.
Frequently asked questions
Q1. Will resealing stop the leak permanently? If the perimeter sealant joint is the cause, correct removal and replacement is a reliable long-term fix. On silicone-sealed domestic joints, you should expect 15–20 years of service in normal conditions. Q2. Can you reseal over existing sealant? We do not. Old sealant residue prevents proper adhesion and leads to early failure. All old material is removed first. Q3. Is external resealing disruptive? Most domestic jobs are completed with no internal access required and minimal disruption. We work from the outside. Q4. How long will the job take? A typical domestic property - window perimeters on front and rear elevations - is usually completed in a single visit. Larger buildings or extensive joint runs will take longer, and we will advise at inspection. Q5. What type of sealant do you use for external joints? We use external-grade polyurethane or hybrid sealants selected for the joint type, substrate and exposure. Silicone is not always the right product for external masonry joints - it can be difficult to paint over and does not adhere reliably to all substrates. We use professional-supply products rather than retail equivalents, which makes a material difference to longevity. Q6. How long does external sealant typically last? Good quality external-grade sealant, correctly applied to a properly prepared joint, typically lasts 15–25 years. The main factors are UV exposure, thermal movement and whether the joint was correctly prepared before application. Exposed Yorkshire elevations facing prevailing south-westerly rain will weather faster than sheltered sides.
Not sure if this is the right repair?
If you are dealing with leaks, damp or draughts around windows and doors but are unsure what is causing them, a Building Leak & Damp Inspection will identify the real cause before any repair work is recommended.