Greater London · England
External Mastic in Harmondsworth
Sealing brickwork movement joints, render, cladding and façade joints for homeowners, landlords and businesses in Harmondsworth. Fully insured, ARBOMaster approved and guaranteed for a year.
- Movement joints with cracked, split or missing sealant
- Sealant that has lost its bond to the brick or render
- Plants rooting in failed movement joints
What affects the cost of external mastic
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
- How easy the joints are to reach
- How many areas need sealing
- The size of the job
Combining jobs into one visit is normally more efficient than separate visits, so tell us about everything that needs sealing. We’ll give you a clear price for the lot.
What we need to know
To help us quote quickly, let us know:
- Pictures of the joints, sent by email
- The type of property
- What the problem is, such as mould, gaps, leaks or cracking
- Access, such as stairs, a lift or height
For external mastic in Harmondsworth, call 0345 464 0079 or send us an email. A short description of the job and where it is helps us quote, and you will get a clear quote before work begins.
External mastic in Harmondsworth
Short cuts in external joints show up within a season or two. Overfilled joints, missing backing rod and sealant laid over old sealant all tend to fail early. We strip the joint back and start again. We work on façade panels, render & cladding joints and brickwork movement joints, and people most often call us about damp patches traced to an open external joint and leaking joints around cladding and façade panels.
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.
All our work is covered by a one-year guarantee, wherever you are in Greater London.
- Place
- Harmondsworth (UB7, TW6)
- Wider area
- Greater London
- Guarantee
- One year on every job
- Quote
- A clear quote up front
- Phone
- 0345 464 0079
- Last updated
- 26 October 2026
Can I do it myself?
Too much sealant is as bad as too little. A heavy bead looks messy and copes badly with movement, and the joint depth matters as much as the finish.
A careful DIYer can reseal a simple joint, such as a straightforward joint indoors. Where it goes wrong is sealing over the old bead, working on a wet joint or overloading the gap.
Your questions about external mastic in Harmondsworth
Do you work for landlords with property near Heathrow Terminal 5 Rail station?
Yes, rental work is part of what we do. Just phone 0345 464 0079 or drop us an email and tell us about the property, and we will send you a clear quote.
Can parking be tricky for a visit in Harmondsworth?
It can be, so it helps to tell us about permits, visitor bays or off-street space when you book. That way the visit can be planned around it.
Do I need to be at home?
It depends on the job. For work indoors, someone needs to let us in, while outside work can sometimes be arranged differently.
How do I get a quote for external mastic in Harmondsworth?
Every job is different, so each one gets its own quote. To get one, ring 0345 464 0079 or drop us an email with a short description of the job.
What do you put in the joint?
The product depends on the job: anti-fungal sanitary silicone in wet areas, and other sealants where joints move or face the weather. We use products from Arbo and Everbuild.
How long does external mastic take?
It depends on the size of the job, but as a guide it takes a few hours for a handful of joints, longer for a whole elevation. We will tell you when we quote.
Should I try DIY first?
Sometimes. The key is preparation: remove all the old material and work on a clean, dry joint. We can always put it right if it fails.
Can a movement joint be filled with mortar?
No. Cement or mortar cannot stretch and the joint fails. Where a joint has been mortared, it can often be raked out and sealed properly.
Different surfaces, different methods
Concrete and blockwork
Concrete and block walls shrink as they dry and move with temperature. We reseal their joints with backing rod and a flexible product.
Cladding and façade panels
Panels heat up and cool down quickly, so the joint sealant has to cope with frequent movement. We choose the product to suit.
Signs you need external mastic in Harmondsworth
Weeds, moss and debris in a joint are a sign the sealant has gone. Roots and dirt hold water against the wall and speed up the damage.
People normally contact us after spotting something like this:
- Rain getting behind render or cladding at a joint
- Joints with sealant missing in places
- Movement joints filled with mortar instead of sealant
- Sealant that has lost its bond to the brick or render
For site and facilities teams at buildings such as Harmondsworth Primary School, movement joints, cladding joints and gutters on larger buildings need the same care as a house’s.
What to look for in a quote
- Whether all the old sealant comes out first
- What the quote includes, VAT included or not
- Whether you can choose the colour
- What preparation is included
Places near Harmondsworth
More services for Harmondsworth
Keeping the joints in good condition
Looking after new joints is easy, and it makes a real difference:
- Walk round the building once a year and look at the joints
- Deal with leaking gutters that soak the joints below
- Clear growth from the base of walls and joints
- Act on the first splits you see
Make sure anyone working on the wall later knows where the movement joints are. They must stay as flexible joints, never rendered or pointed over.
Gaps, plants or missing sealant in a joint are worth getting looked at. Early work is quicker and leaves a better finish.
What we do, step by step
We bring everything the job needs with us. Once we have agreed what’s being done, we protect the area and start. Most jobs take 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 Harmondsworth. 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.
- A flexible exterior sealant is applied and tooled in a colour to suit the wall.
Before we arrive
- Clear the area around the work
- Let us know about parking restrictions
- Keep children and pets away from the work area
Getting a quote
Quotes start with a quick conversation. Describe the problem, the location and the size of the job. Whenever you’re ready, phone 0345 464 0079 or email us.
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What happens if it’s left?
Mortar or ordinary filler might look like a quick way to close an open joint, but it stops the joint moving. The wall then cracks somewhere else. The correct repair is a flexible sealant with the right backing. In a flat in Harmondsworth, failed sealant seldom stays inside your own four walls: water can reach the neighbours below, and gaps in fire-rated joints affect the whole building.
What it costs depends on the size of the job, how much old material has to come out and access to the work. We give a clear quote before any work starts, so you know where you stand.
Why book with us
- Quality sealants from Arbo and Everbuild
- An ARBOMaster approved applicator
- 4.9 on Google from 180+ five-star reviews
- Colour agreed with you before work begins
Read our cost guide and our reviews.
Outside joints around Harmondsworth
London terraces and converted houses often share gutters, downpipes and walls, so it’s worth agreeing who is responsible before work starts. The South East is one of the drier parts of the UK, yet outdoor joints still have to be sealed dry, so jobs are booked with the weather in mind.
In the older streets around Church of St Mary, older walls, gutters and the joints where extensions meet them need a flexible sealant. Harmondsworth is in London, so parking needs planning: let us know about parking bays, permits or a driveway.
Harmondsworth is about 1 mile south-west of West Drayton, in Greater London. Anywhere in UB7, we can carry out external mastic at your property. Across Greater London, we cover 764 places, and Harmondsworth is one of them. For nearby work, see our London page, about 17 miles away.
Jobs for external mastic in UB7 and TW6 works the same way as everywhere else we cover. If you need external mastic at a property on Moor Lane, Hatch Lane and High Street or anywhere close by, we can help. We also cover Longford (1 mile south-west), Sipson (1 mile north-east), Heathrow (2 miles south-east), Harlington (2 miles east) and Stanwell (2 miles south). We also work in nearby towns such as City of Westminster (14 miles east), Marylebone (14 miles east), Kensington (12 miles east), Hampstead (14 miles east), Ruislip (7 miles north-east) and Brompton (14 miles east).
Near you in Harmondsworth
Around Harmondsworth, our work takes us to homes and buildings near Harlington Community School and The Five Bells Inn. The closest station to Harmondsworth is Heathrow Terminal 5 Rail station, roughly 1 mile south. A little further out are British Airways Heritage Collection (3.5 miles north) and Harlington (1.4 miles east). Open spaces near Harmondsworth include Crane Meadows and Staines Reservoirs.