Greater London · England
External & façade joints in Coldharbour, Greater London
External mastic for Coldharbour, by sealant specialists with 20+ years’ experience. Rated 4.9 on Google from 180+ five-star reviews.
- Sealant pulling away from one side of the joint
- Brick movement joints where the sealant has split
- Weathered mastic that no longer stretches
External mastic for homes and businesses in Coldharbour
Failed sealant is cut out, the depth set with closed-cell backing rod, and the joint resealed with a low-modulus sealant made for outside. We pick a colour that sits well with the wall so the line blends in. Common call-outs are for sealant pulling away from one side of the joint and brick movement joints where the sealant has split, across brickwork movement joints, render & cladding joints and concrete & block.
Newer London blocks are built with movement joints in brick and render, and with cladding joints sealed with mastic. Period houses have different weak points, such as gutter joints, trims and the line where an extension meets the old wall.
We stand behind the work with a 12-month guarantee.
- Location
- Coldharbour (SE9, BR7)
- Wider area
- Greater London
- Guarantee
- 12 months on all our work
- Quotes
- Quoted before any work starts
- Call
- 0345 464 0079
- Page updated
- 26 October 2026
Why act early in Coldharbour
It often makes sense to reseal all the failing joints on an elevation together. They’ve weathered the same way. Converted houses in London often have a bathroom above someone else’s living room, and a slow leak from a failed seal can end up in the flat below. Dealing with it early is far simpler.
The cost reflects the work involved, not guesswork. That is why we ask about the job first and give you a clear price before work begins.
Why Coldharbour customers choose us
- White, clear, grey or another colour, product permitting
- Anti-fungal sanitary silicone in wet areas
- Neat joints and a tidy finish
- We agree the colour with you first
Take a look at our cost guide or our reviews.
DIY versus a professional finish
If you do try it yourself, take your time over the preparation: take out all the old sealant, make sure the joint is clean and dry, and give it the full cure time. If it fails, we can still redo it.
The difference is mostly in the preparation and the product. We take joints back to clean, dry surfaces, and the sealant is chosen for how the joint moves and where it is, then guaranteed for a year.
Quotes for external mastic in Coldharbour
There’s no set price list, because jobs vary so much. What we look at:
- How many areas need sealing
- Any working-time requirements on site
- The number and length of the joints
- Whether there’s mould to deal with
There are no prices on our website, because the cost depends so much on the job itself. For a quick quote, please call 0345 464 0079 or email us.
Helping us quote
You don’t need to know the technical terms. Just tell us:
- Where the property is
- A few pictures by email, if you can
- The type of property
- If someone has resealed it before
Want a quote for external mastic? Please ring 0345 464 0079 or email us and tell us about the job. We will explain what we’d do and give you a clear price before we start.
Surface by surface
Brickwork movement joints
Brick walls have vertical movement joints to absorb expansion. We reseal them with a low-modulus sealant over backing rod coloured to suit the wall.
Copings and trims
Joints in copings, parapets and trims are exposed to the worst of the weather. We reseal them with an exterior sealant suited to the material.
Common problems we fix in Coldharbour
A lot of failed joints come down to preparation: 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.
People normally contact us when they notice one of these:
- Movement joints filled with mortar instead of sealant
- Panel joints letting water in
- Old sealant gone brittle and cracked
- Brick movement joints where the sealant has split
If you live in an older home near St Alban, an extension built onto an older house moves differently, and the joint between them takes the strain.
What to look for in a quote
- Whether VAT is included
- How hidden problems are handled
- The length of the guarantee
- How long to leave it before use
Nearby places to Coldharbour
Other services in Coldharbour
When something else is needed
A few problems are outside what sealant work can do:
- Structural movement, which needs a surveyor or engineer
- Cracked brickwork or render that needs a builder or plasterer
- Walls that need new movement joints cut into them
If in doubt, ring 0345 464 0079 or drop us an email and we will say what we think before booking.
Joints and surfaces we work on
- Render & cladding joints
- Joints between brick and frames
- Façade panels
- Brickwork movement joints
- Concrete & block
- Copings & trims
What we do, step by step
There’s no need to move everything out, just the space around the work. Everything nearby is protected, and the job takes anything from a few hours to several days, depending on the building for a typical job. For a job in Coldharbour, parking and access are the things to plan: tell us about permits, visitor bays or off-street space, which floor we are working on and whether there’s a lift.
- We look at every joint and agree a colour to suit the wall.
- Failed sealant is removed back to clean, sound faces.
- Closed-cell backing rod is pushed in so the sealant bonds to two sides only.
- Primer is applied wherever the sealant needs it.
- We gun in low-modulus sealant and tool it neatly.
How to prepare
- Let us know about stairs, lifts or work at height
- Mention any sign-in or site rules at work premises
- Clear items away from the joints we’re working on
Ask for a quote
We do not publish a price list. Instead, we give you a clear quote for your job. To arrange one, call 0345 464 0079 or drop us an email.
Read more
FAQs for Coldharbour
Can you help a landlord with a rental near Mottingham station?
Yes, landlords and agents are among the people we work for. Just call 0345 464 0079 or drop us an email with the address and what needs doing, and we’ll give you a clear price.
Do you cover Coldharbour for external mastic?
Yes, Coldharbour is within the area we cover. Our work covers London and the South East. Just call 0345 464 0079 or drop us an email with a few details of the job, and we will give you a clear quote.
Do you remove the old sealant?
Always. Sealing over old sealant is the main reason resealing fails early, so we never do it.
Does someone need to be in?
It depends on the job. For work indoors, someone needs to let us in, and for outside work we will agree access with you when we book.
Is it OK to fill a movement joint with cement?
No. A mortar-filled joint cannot move, so the movement cracks the wall elsewhere. It needs a flexible sealant over backing rod.
Is there any odour?
That depends on the sealant. Some smell for a while, some hardly at all.
When is the sealant fully cured?
It depends on the product and the conditions. We tell you how long to leave it before we go.
Where do you work from?
We’re a Crawley-based firm. We work across South East England, London and Scotland.
What external mastic looks like in Coldharbour
With historic houses such as Eltham Palace (about 1.1 miles north) nearby, there’s older building stock in the area around Coldharbour as well as newer homes. Where a home is older, older walls and rooflines need a sealant that moves with them and suits the material. London and the South East are among the drier parts of the UK, but outside sealant still needs a dry, clean surface, so outdoor work is planned around the forecast.
For landlords with property near Mottingham station, split movement joints are easy to miss on a rental until damp shows inside. Coldharbour is in London, so parking needs planning: let us know about parking bays, permits or a driveway.
Coldharbour is about 4 miles north-west of Orpington, in Greater London. For external mastic in and around Coldharbour, please call 0345 464 0079 or email us for a quick quote. We cover Greater London from our Crawley base. 764 places in Greater London are on our list. London is on our list too, around 8 miles away.
Every address in SE9 and BR7 is covered for external mastic. If you need external mastic at a property on Green Lane, Horley Road and Dorset Road or a nearby road, our applicators can take on the job. We also cover the places around Coldharbour: Mottingham (1 mile west), Chinbrook (1 mile west), New Eltham (1 mile north-east), Eltham (1 mile north) and Middle Park (1 mile north-west). Within a short drive, we also cover London (8 miles north-west), City of Westminster (11 miles north-west), Marylebone (10 miles north-west), Kensington (12 miles north-west), St Pancras (10 miles north-west) and Shoreditch (9 miles north-west).
Around Coldharbour
We work in homes and buildings around Elmstead Wood and St Thomas More Catholic Comprehensive School and the streets around them. For rail, the closest station is Mottingham station, roughly 0.6 miles north. A little further out are The Glades (2.4 miles south-west) and Metropolitan Police Museum (2.2 miles east). For a walk, there’s The Tarn and Summer Hill.