Kent · England
Cotman's Ash External Mastic
Sealing brickwork movement joints, render, cladding and façade joints in Cotman's Ash, with a one-year guarantee on every job. Call for a quick quote.
- Water getting into walls through failed joints
- Failed seals between different materials
- Plants rooting in failed movement joints
About our external mastic in Cotman's Ash
Getting the depth right is half the job. Backing rod controls how deep the sealant goes and keeps it off the back of the joint, leaving it bonded to two faces so it can move with the wall. We work on brickwork movement joints, render & cladding joints and copings & trims, and people most often call us about failed sealant between panels on a façade and sealant pulling away from one side of the joint.
Around Cotman's Ash, older buildings can be stone, brick or timber-framed, many with extensions added later. The joints where those materials meet are the weak points, and they need the right sealant at the right depth.
Every job comes with our 12-month guarantee, wherever you are in Kent.
- Where
- Cotman's Ash (TN15)
- Region
- Kent
- Guarantee
- 12 months on all our work
- Quote
- A clear price before we start
- Phone
- 0345 464 0079
- Updated
- 26 October 2026
What happens on the day
Our applicators work methodically: protect, prepare, seal, tidy. Typically it takes a few hours to a few days, depending on the length of joint and the access and we leave things clean and tidy. In a small place like Cotman's Ash, access is normally the main thing to plan. For outside work, also let us know about exposed walls and any outbuildings involved.
- We inspect the joints and agree which need resealing and how they’ll be reached.
- The old mastic and anything lodged in the joint is removed.
- We clean both faces of the joint and prime them where the product calls for it.
- Backing rod goes in next, setting the depth and keeping the sealant off the back of the joint.
- The new sealant, chosen to suit the brick or render, is applied and tooled to a neat finish.
How to prepare
- Mention any sign-in or site rules at work premises
- Tell us about access, such as stairs, a lift or high-level joints
- Move anything stored near the joints
Getting a quote
For external mastic in Cotman's Ash, ring 0345 464 0079 or send us an email. Tell us what the problem is and where, and we’ll agree the price before any work begins.
Related advice
Also near Cotman's Ash
Also in Cotman's Ash
For landlords and businesses
Housing providers, facilities teams and property managers book us too in Cotman's Ash and across Kent. Several sites can go on one quote, and we are fully insured.
Landlords and letting agents in Cotman's Ash can book us as well as homeowners. Sealant work between tenants is a simple way to keep a property in good order.
DIY versus a professional finish
Not every job suits DIY: high-level joints, fire-rated gaps, external movement joints and big jobs call for the right materials, safe access and experience.
Sealing over old silicone is the commonest DIY error. New silicone won’t bond to old, so it lifts and traps water and mould underneath. All the old material has to come out first.
What sealant work cannot fix
New sealant cannot fix everything, and we’d rather say so up front. Sealant won’t put right:
- Structural movement, which needs a surveyor or engineer
- Damp that isn’t coming from the joint
- Cracks in the bricks or render themselves, away from the joints
If you’re not sure, just ring 0345 464 0079 or send us an email and we will give you a straight answer.
Surfaces we seal
- Brickwork movement joints
- Concrete & block
- Copings & trims
- Render & cladding joints
- Façade panels
- Joints between brick and frames
Surface by surface
Render joints
Cracks along render joints let water in behind the coat. A sound joint keeps the render dry behind.
Brickwork movement joints
Vertical joints in long brick walls let the brickwork expand without cracking. They’re resealed over backing rod with a low-modulus sealant in a colour to suit the brick.
Signs you need external mastic in Cotman's Ash
Poor preparation causes many early failures: joint faces that were dusty or damp, unprimed where they needed it, or still carrying old sealant. The new sealant then lets go long before it should.
The most common problems we see are:
- Brick movement joints where the sealant has split
- Hard, crazed mastic that has stopped moving
- Moss and dirt in joints with no sealant left
- Failed seals between different materials
If you live in an older home near Church of Saint Mary the Virgin, an extension built onto an older house moves differently, and the joint between them takes the strain.
Questions to ask before booking
- Whether VAT is included
- Who does the work, and how experienced they are
- Whether all the old sealant comes out first
- How the surfaces are prepared before sealing
Cotman's Ash buildings and the weather
Rainfall in the South East is lower than in much of the UK, though outdoor sealant still has to go onto a dry joint, so the forecast decides the day. With historic houses such as Lullingstone Castle (about 3.4 miles north-west) nearby, there’s older building stock in the area around Cotman's Ash as well as newer homes. In older buildings, older brick and stone need a sealant that suits them, at the right joint depth.
Rented homes near Kemsing station change hands often, and split movement joints are easy to miss on a rental until damp shows inside. Schools such as Kemsing Primary School are buildings too, and its movement joints, gutters and trims need looking after like any other building’s.
Cotman's Ash is about 3 miles north-east of Sevenoaks, in Kent. Our applicators cover external mastic for homes and businesses in Cotman's Ash, as part of our work across Kent. Our area takes in 922 places across Kent, from the larger towns to small villages. You can also see our page for London, about 19 miles away.
Postcode districts we cover here for external mastic: TN15. Close by, we work in Woodlands (1 mile north-east), Heaverham (1 mile south-east), Knatts Valley (1 mile north), Romney Street (1 mile north-west) and Kemsing (1 mile south-west). Within a short drive, we also cover Maidstone (13 miles east), Dartford (9 miles north), Sevenoaks (3 miles south-west), Royal Tunbridge Wells (13 miles south), Gravesend (10 miles north-east) and Tonbridge (8 miles south).
Landmarks near Cotman's Ash
In Cotman's Ash, that means homes and buildings near The Rising Sun pub and Kemsing Down, among other places. Cotman's Ash’s nearest station is Kemsing station, about 1.4 miles south of the centre. Nearby you will also find Kemsing Castle Bank (0.9 miles south-west) and Sevenoaks Hospital (2.8 miles south-west). Open spaces near Cotman's Ash include Dryhill Nature Reserve.
Cotman's Ash questions
Do you cover smaller places like Cotman's Ash?
Yes, Cotman's Ash is covered. We work across London and the South East, and smaller places are part of that. The journey is planned ahead, so it helps to know about access.
Is Cotman's Ash in your area for external mastic?
Yes. Our work covers London and the South East, and Cotman's Ash is part of that. Just phone 0345 464 0079 or drop us an email with a few details of the job, and we will send you a clear quote.
When will the joints need doing again?
It depends on the exposure, the movement and the product. Treat it as a maintenance item and look at it yearly and reseal when it splits.
Do I need to be at home?
It depends on the job. Inside work needs someone to give us access, while outside work can sometimes be arranged differently.
Do you have insurance?
Yes. We are fully insured.
How much does external mastic cost in Cotman's Ash?
Every job is different, so each one gets its own quote. For a quick quote, call 0345 464 0079 or drop us an email with a short description of the job.
Can you match the colour of my brickwork?
We aim for a joint that suits the wall rather than one that jumps out. We’ll talk through colour options before we start from the range available.
Why is there a gap in my brick wall?
Walls move with heat, cold and moisture, and planned joints take up that movement. The gap is sealed with a flexible sealant over backing rod.
What affects the cost of external mastic
Some jobs are bigger than they look, and some smaller. The main factors:
- How many areas need sealing
- When we can work, for business premises
- Any mould that needs treating
- Access and height
The cost reflects the work involved, not a rough estimate. That is why we ask a few questions first.
Helping us quote
You do not need to know the technical terms. It helps if you can tell us:
- What the problem is, such as mould, gaps, leaks or cracking
- Pictures of the joints, sent by email
- The address or postcode of the job
- The rough size of the job
Call for a quick quote, or email us if that’s easier. Describe what needs sealing and we will explain what’s involved and give you a clear price.