Greater London · England
External Mastic in South Hampstead
Our applicators work in South Hampstead on sealing brickwork movement joints, render, cladding and façade joints. Old material cut out, joints cleaned and sealed neatly.
- Cracked joints where brick meets render or frames
- Failed sealant between panels on a façade
- Joints with sealant missing in places
About our external mastic in South Hampstead
As ARBOMaster approved applicators, we choose exterior sealants to suit the joint and the surfaces. Some surfaces need a primer before sealing and we use one wherever it does. Common call-outs are for rigid filler in a joint that should flex and water getting into walls through failed joints, on brickwork movement joints, façade panels and copings & trims.
Modern London flats rely on sealed movement joints and cladding joints. Period houses have different weak points, such as gutter joints, trims and the line where an extension meets the old wall.
Our work is backed for twelve months, in South Hampstead and everywhere else we cover.
- Location
- South Hampstead (NW3, NW8, NW6)
- Wider area
- Greater London
- Cover
- One year on every job
- Quote
- A clear price before we start
- Phone
- 0345 464 0079
- Last updated
- 26 October 2026
Common problems we fix in South Hampstead
Sometimes a movement joint was filled with mortar or a rigid filler. With the joint locked solid, the movement turns into cracks elsewhere in the wall.
Any of these means the joints need attention:
- Rain getting behind render or cladding at a joint
- Cracked joints where brick meets render or frames
- Weeds or debris growing in open joints
- Failed sealant between panels on a façade
Letting a property close to South Hampstead station? Then outside joints that have cracked can let damp into a rental, so check them between lets.
What to look for in a quote
- How the surfaces are prepared before sealing
- Are they insured?
- What happens if the job turns out different
- Whether you can choose the colour
How the visit works
There isn’t much for you to do on the day. Show us the job and we will take it from there. The work itself takes a few hours to a few days, depending on the length of joint and the access. For a job in South Hampstead, parking and access are the things to plan: tell us about permits, visitor bays or off-street space, which floor we’re working on and whether there’s a lift.
- We start by checking each joint, agreeing the ones to redo and how we will reach them.
- Old sealant and any debris are cut and raked out.
- The joint faces are cleaned and primed where the sealant needs it.
- Closed-cell backing rod is fitted to set the depth and stop three-sided bonding.
- A flexible exterior sealant is applied and tooled in a colour to suit the wall.
Before we arrive
- Move anything stored near the joints
- Let us know about parking restrictions
- Mention any sign-in or site rules at work premises
Getting a quote
Need a quote? Please ring 0345 464 0079 or drop us an email and tell us about the job. We will explain what we’d do and give you a clear quote before we start.
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Outside joints around South Hampstead
Compared with the north and west, the South East gets less rain, though outdoor sealant still has to go onto a dry joint, so the forecast decides the day. London terraces and converted houses often share gutters, downpipes and walls, so check who is responsible for the outside before booking.
For site and facilities teams at buildings such as The UCL Academy, larger buildings have long runs of movement joint that eventually need resealing. In the older streets around Church of All Souls, the joints between older walls, newer extensions and the roofline need a sealant that can move.
South Hampstead is about 1 mile south of Hampstead, in Greater London. From the centre of South Hampstead to the outskirts, we cover external mastic for every kind of property. Our area takes in 764 places across Greater London, from the larger towns to small villages.
Jobs for external mastic in NW3, NW8 and NW6 works the same way as everywhere else we cover. Local streets include Avenue Road, Acacia Road and Harben Road, all of which we cover. We also cover the places around South Hampstead: Swiss Cottage (1 mile north), St John's Wood (1 mile south), Haverstock (1 mile east), Belsize Park (1 mile east) and Primrose Hill (1 mile east). Further out, we also cover London (4 miles south-east), Kensington (3 miles south-west), St Pancras (3 miles south-east), Shoreditch (4 miles east), Walthamstow (7 miles north-east) and Hoxton (4 miles east).
Local landmarks in South Hampstead
We work in homes and buildings around Cafe Med pub, St. Mary's Town and Country School and Holy Trinity CofE Primary School, among other places. Nearby too are Cecil Sharp House (1.1 miles east) and Primrose Hill (0.6 miles east). There’s a railway station in South Hampstead itself: South Hampstead station. Other landmarks nearby include Isokon Gallery (0.8 miles north-east) and O2 Centre (0.5 miles north-west). The countryside around South Hampstead includes Adelaide Nature Reserve and The Long Water.
Leave it or put it right?
A low-modulus sealant is chosen because it moves without pulling hard at the edges. That matters on brick, render and concrete, which can be weaker at the face. Too stiff a sealant can pull at the edges and break them. In a London flat, a failed joint rarely stays your problem alone: water can reach the neighbours below, and gaps in fire-rated joints affect the whole building.
A failed joint rarely gets cheaper to fix by waiting. If you’re unsure, call 0345 464 0079 or email us for an honest opinion and a quote.
Why book with us
- Any old sealant cut out fully, not covered over
- Tidy, careful work
- Every job guaranteed for a year
- Approved under the ARBOMaster scheme
Keeping the joints in good condition
Joint life depends on how it’s used and looked after. We suggest:
- Get split or bare joints resealed while the damage is small
- Never let anyone fill a movement joint with mortar
- Tell anyone working on the walls about the movement joints
- Ask before painting over external sealant
Give the sealant the cure time we tell you before anything rubs against it. Most exterior sealants skin fast but take longer to cure right through.
Leave a failed movement joint and water keeps getting into the wall. Over time it can mean damp inside, stained render or frost-damaged brick.
When something else is needed
Some problems need a builder, plumber or other trade rather than us:
- Cutting new joints into brickwork, which is building work rather than sealant work
- Loose or hollow render, which needs re-rendering
- Damp that is not coming from the joint
If you’re not sure, just call 0345 464 0079 or email us and we will give you a straight answer.
What we seal
- Brickwork movement joints
- Joints between brick and frames
- Concrete & block
- Copings & trims
- Façade panels
- Render & cladding joints
South Hampstead: your questions answered
Can you do external mastic in South Hampstead?
Yes, South Hampstead is within the area we cover. Our work covers London and the South East. Just ring 0345 464 0079 or email us with a few details of the job.
Is parking an issue for external mastic in South Hampstead?
In much of London, parking needs planning: a visitor permit or a bay close to the door helps a lot, so mention what’s available when you book.
I’m a tenant. Can you help?
Of course. Check with your landlord; we can send the quote to them too.
Will the old sealant be removed?
Yes. All of the old material is cut out and the joint cleaned.
Can new sealant go over the old?
No, it won’t last. It may look fine at first, but the new bead soon lifts. The old sealant has to come out completely.
Where are you based?
Mr Mastic is based in Crawley. We cover South Hampstead and the rest of Greater London, along with the rest of our area.
Can you reach joints on upper floors?
It depends on the height and the site. Low-level joints are straightforward; for higher ones, send details and we will confirm the access.
Is there a guarantee?
Yes. All our work carries a one-year guarantee.
Can I do it myself?
The difference is mostly in the preparation and the product. Joints are cleaned back to sound surfaces and dried, and the sealant is chosen for how the joint moves and where it is.
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 does not work out, we can still put it right.
Quotes for external mastic in South Hampstead
Every job gets its own quote. These are the things that affect it:
- How many rooms, windows or areas are involved
- Working hours on commercial sites
- The amount of work
- Which sealant suits the joint
A few things move the cost up or down: how much old sealant there is and how stubborn it is, whether mould needs treating, and whether we need extra access for height. We take all of that into account in your quote.
Asking for a quote
Photos help, but a description is a good start. Try to tell us:
- If it’s domestic, commercial or a hotel
- Photos by email, if that’s easy
- The problem you’ve noticed
- How many joints, rooms or windows are involved
Getting a quote is simple: let us know what needs doing and where, and roughly how big it is. Photos by email help us understand the job, and we will come back to you with a quote.