Greater London · England
External Mastic in Harlesden
Movement joints in Harlesden need attention? We remove the old material, prepare the joints and seal them properly.
- Gaps where render, brick and frames meet
- Movement joints with cracked, split or missing sealant
- Joints pointed up with cement by mistake
External mastic in Harlesden, done properly
As ARBOMaster approved applicators, we choose exterior sealants to suit the joint and the surfaces. Some surfaces need a primer before sealing. If you have panel joints letting water in and sealant pulling away from one side of the joint, we can help.
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, and both kinds of building are found across London.
Each job carries a 12-month guarantee.
- Where
- Harlesden (NW10, W3, NW26)
- Wider area
- Greater London
- Guarantee
- A year, on every job
- Quote
- A clear price before work begins
- Call
- 0345 464 0079
- Page updated
- 26 October 2026
When it is not the sealant
We will always be straight with you, so here’s what new sealant won’t do:
- Damp that is not coming from the joint
- Render that’s blown, hollow or coming away
- Walls that need new movement joints cut into them
Not sure which it is? You can phone 0345 464 0079 or send us an email and we will tell you honestly before you book.
Surfaces we seal
- Render & cladding joints
- Concrete & block
- Copings & trims
- Brickwork movement joints
- Façade panels
- Joints between brick and frames
Also near Harlesden
Other services in Harlesden
What happens on the day
Good joint work is mostly preparation, and we do not rush it. Every joint is cleaned and dried before new material goes in. All told, the work takes a few hours for a handful of joints, longer for a whole elevation. Parking in much of London is by permit or pay-and-display, so it helps to know what’s near you in Harlesden. It helps if you can point us to a visitor permit or a bay close to the door.
- First we look over the joints with you, agree which to renew and talk through access.
- Old sealant and any debris are cut and raked out.
- We clean both faces of the joint and prime them where the product calls for it.
- We push in closed-cell backing rod so the sealant is the right depth and bonds to the sides only.
- We gun in a flexible exterior sealant in a colour that suits the wall and tool it neatly.
Getting ready for the visit
- Let us know if you’ve seen damp or leaks
- Let us know about stairs, lifts or work at height
- Clear items away from the joints we’re working on
Ask for a quote
Every job is quoted individually, so start by telling us what you need. Simply ring 0345 464 0079 or send us an email and describe the job.
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Do you need external mastic in Harlesden?
Weeds, moss and debris in a joint are a sign the sealant has gone. Roots and dirt hold water against the wall and make things worse.
The most common problems we see are:
- Joints where the bead has come unstuck
- Hard, crazed mastic that has stopped moving
- Gaps where render, brick and frames meet
- Moss and dirt in joints with no sealant left
In the older streets around Church of All Souls, older walls, gutters and the joints where extensions meet them need a flexible sealant.
Questions to ask before you book
- How the surfaces are prepared before sealing
- Whether VAT is included
- Which colour the sealant will be
- What guarantee comes with the work
Surface by surface
Brickwork movement joints
Brick movement joints are often mistaken for a missing mortar line. Where one has been mortared, we cut it out and reseal it with sealant.
Cladding and façade panels
If the façade has a specified sealant, that’s what we use. Tell us what the building has when you get in touch.
Common questions in Harlesden
Do you cover Harlesden for external mastic?
Yes. Our work covers London and the South East, and Harlesden is part of that. You can ring 0345 464 0079 or drop us an email and tell us what needs doing, and we will give you a clear price.
Do you work for landlords with property near Willesden Junction station?
Yes, rental work is part of what we do. Just ring 0345 464 0079 or send us an email and tell us about the property, and we will give you a clear price.
Where do you work from?
We are based in Crawley, and we work across South East England, London and Scotland.
What colours does the sealant come in?
There’s a good range of exterior colours, including greys, browns, whites and stone tones. We choose the closest to your brick or render so it does not stand out.
How do I get a quote for external mastic in Harlesden?
Size, access and the old material all affect the cost. Call for a quick quote.
Can you seal joints between render and window frames?
Yes. Where different materials meet is one of the most common joints we seal. We use a flexible sealant suited to both surfaces with primer where required.
Can you seal over the old sealant?
No, it won’t last. It can look neat for a few weeks, but the new layer lifts away from the old one. Removing the old sealant completely is the only lasting way.
Is it OK to fill a movement joint with cement?
No, not where the gap is a movement joint. Pointing it stops it working, and the wall may crack nearby. We’ll reseal it with a flexible sealant.
Should I try it myself first?
If you do try it yourself, take your time over the preparation: remove every trace of old sealant, clean and dry the joint, and follow the product’s cure time. If it does not work out, we can still put it right.
Too much sealant is as bad as too little. A heavy bead looks messy and copes badly with movement, and getting the depth right matters as much as the look.
Looking after it afterwards
Once the sealant has cured, a few habits help it last:
- Make sure movement joints are not pointed over
- Act on the first splits you see
- Check the sealant is paintable before painting near it
- Point out the joints to other trades
Make sure anyone working on the wall later knows where the movement joints are. They should be kept open and resealed, not filled.
Water getting behind cladding or render can go unnoticed for a long time. By the time there’s a damp patch, the damage can be well established.
What external mastic looks like in Harlesden
In terraces and conversions, gutters and walls are often shared with the neighbours, so it’s worth agreeing who is responsible before work starts. Historic houses like Pitzhanger Manor (about 3.1 miles south-west) are a reminder that the area around Harlesden has older buildings as well as new. In older buildings, older walls and rooflines need a sealant that moves with them and suits the material.
For site and facilities teams at buildings such as John Keble CofE Primary School, its movement joints, gutters and trims need looking after like any other building’s. Rented homes near Willesden Junction station change hands often, and failed wall and movement joints let damp in, so they’re worth checking between tenancies.
Harlesden is about 4 miles west of City of Westminster, in Greater London. Jobs in Harlesden get the same care as everywhere else we work: old sealant removed completely, careful preparation and a one-year guarantee. Our area takes in 764 places across Greater London, from the larger towns to small villages. For nearby work, see our London page.
We cover every part of NW10, W3 and NW26 for external mastic. If you need external mastic at a property on Fry Road, Wood Road and Park Road or anywhere close by, our applicators can take on the job. Close by, we work in College Park (1 mile south-east), Old Oak Common (1 mile south), Church End (1 mile north), Stonebridge (1 mile north-west) and Willesden Green (1 mile north-east). Larger places within reach include London (7 miles east), City of Westminster (4 miles east), Marylebone (5 miles east), Kensington (3 miles south-east), St Pancras (6 miles east) and Shoreditch (7 miles east).
Local landmarks in Harlesden
Locally, jobs take us to homes and businesses close to St Claudine's Catholic School for Girls, Royal Oak Inn and Roundwood Park, among other places. Harlesden has its own railway station: Willesden Junction station. Well-known places in the area include Central Middlesex Hospital (1 mile west) and Brent Museum and Archives (1.1 miles north-east). Green spaces nearby include Castlebar Hill and The Long Water.
What affects the quote in Harlesden
Some jobs are bigger than they look, and some smaller. What affects the quote:
- How much old sealant there is and how hard it is to remove
- The size of the job
- Whether the work is at height
- How many rooms, windows or areas are involved
Every job is a little different, so we quote each one individually. The number of joints, how easy they are to reach and the sealant needed all play a part.
Asking for a quote
A few details help us give you an accurate quote. When you get in contact, it helps to mention:
- The type of property
- Roughly how big the job is
- What’s wrong with the joints now
- Pictures of the joints, sent by email
If you are in Harlesden and need external mastic, ring 0345 464 0079 or drop us an email. Tell us what the problem is and where, and you will get a clear quote before we start.