Greater London · England
External Mastic in Harrow on the Hill
We cover Harrow on the Hill for sealing brickwork movement joints, render, cladding and façade joints. Old sealant removed completely, joints prepared properly.
- Movement joints with cracked, split or missing sealant
- Water getting into walls through failed joints
- Sealant that has lost its bond to the brick or render
About our external mastic in Harrow on the Hill
Short cuts in external joints show up within a season or two. New sealant over old, joints packed with mortar and beads with no backing rarely last long. We take the old material out and do it properly. If you have panel joints letting water in and old sealant gone brittle and cracked, we can help, on copings & trims, façade panels and concrete & block alike.
Working on the outside of a London home means planning access: shared paths, upper floors and parking. In Harrow on the Hill, joints up high may need ladders or other access, which is worth talking through when you book.
Every job comes with a one-year guarantee.
- Where
- Harrow on the Hill (HA1, HA0, HA2)
- Region
- Greater London
- Guarantee
- One year on every job
- Price
- A clear price before any work starts
- Phone
- 0345 464 0079
- Last updated
- 26 October 2026
Harrow on the Hill questions
Is parking an issue for external mastic in Harrow on the Hill?
It can be, so it helps to tell us about permits, visitor bays or off-street space when you book. The visit is then planned around what’s available.
Do you cover Harrow on the Hill for external mastic?
Yes, Harrow on the Hill is within the area we cover. We work across London and the South East. Just ring 0345 464 0079 or email us with a few details of the job.
Will you leave a mess?
No. The area is protected while we work and cleaned up afterwards.
How long will you be here?
A typical job takes anything from a few hours to several days, depending on the building, including the preparation. Your quote will say how long we expect yours to take.
What sealant do you use?
Products from Arbo and Everbuild, among others, picked for each joint. We explain the product when we quote.
Can you quote for more than one area?
Yes, we can. Several rooms, windows or areas can go on one quote.
Can a movement joint be filled with mortar?
No. Mortar locks the joint solid, so the wall cracks somewhere else instead. Use a flexible sealant with backing rod.
Are you an approved applicator?
Yes. ARBOMaster is the approved applicator scheme for Arbo sealants, and we are part of it.
Looking after it afterwards
So the new joints stay in good condition:
- Act on the first splits you see
- Keep soil, plants and ivy away from the joints
- Walk round the building once a year and look at the joints
- Keep movement joints as flexible joints, not mortar
Have a quick look at the joints each spring. Watch for splits, edges coming away or growth in the joint.
A joint that has stopped moving pushes the movement elsewhere, often as cracks near the joint. Resealing it early helps prevent that.
What happens on the day
The work is kept neat and contained to the area we are working on. The job usually takes anything from a few hours to several days, depending on the building, and we tell you how long to leave it before we go. For a job in Harrow on the Hill, 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.
- First, the joints are inspected and the access agreed.
- Every bit of old sealant and any mortar or debris is cut out.
- Joint faces are cleaned back and primed if the sealant needs it.
- We fit closed-cell backing rod to control the depth.
- We apply the sealant, tool it and check the whole run.
Before we arrive
- Keep pets and children clear of the area while we work
- Clear the area around the work
- Tell us if parking is tricky
Get a quote
If you are in Harrow on the Hill and need external mastic, ring 0345 464 0079 or drop us an email. Tell us what the problem is and where, and you’ll get a clear quote before we start.
Related advice
What we cannot put right
We will not take on work that won’t last, so these are the limits:
- Adding movement joints to masonry that has none
- Rising or penetrating damp from elsewhere in the wall
- Structural movement, which needs a surveyor or engineer
Not sure which it is? You can ring 0345 464 0079 or drop us an email and we’ll tell you honestly.
Surfaces we seal
- Joints between brick and frames
- Brickwork movement joints
- Render & cladding joints
- Façade panels
- Copings & trims
- Concrete & block
What affects the cost of external mastic
The quote reflects the job in front of us. We take into account:
- Whether the work is at height
- The type of sealant required
- How many areas need sealing
- Whether old sealant or filler has to be cut out
The cost reflects the work involved, not a rough estimate. That is why we ask about the job first and give you a clear quote before any work starts.
What to tell us for a quote
You do not need to know the technical terms. It helps if you can tell us:
- The rough size of the job
- The type of property
- The problem you’ve noticed
- A few pictures by email, if you can
Getting a quote is simple: tell us 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.
Nearby places to Harrow on the Hill
Other services in Harrow on the Hill
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.
Some jobs are best left to a professional: work at height, external movement joints, fire-rated sealant and large areas call for the right materials, safe access and experience.
Outside joints around Harrow on the Hill
Historic houses like Northolt Manor (about 2.1 miles south-west) are a reminder that the area around Harrow on the Hill 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. 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.
Managing a site like St George’s Primary Catholic Voluntary Academy? Then movement joints, cladding joints and gutters on larger buildings need the same care as a house’s. For an older house near a landmark such as Christ Church, older walls, gutters and the joints where extensions meet them need a flexible sealant. As a London address, Harrow on the Hill can be tricky for parking: tell us about permits, visitor bays or off-street space when you book.
Harrow on the Hill is about 1 mile south-east of Harrow, in Greater London. Harrow on the Hill gets the same service as everywhere we cover: the old material taken out, joints prepared properly and a 12-month guarantee. Harrow on the Hill is one of 764 towns and villages in Greater London we cover for external mastic. London is on our list too, around 11 miles away.
Work in HA1, HA0 and HA2 works the same way as everywhere else we cover. Local streets include New Road, Amery Road and London Road, and we cover them all. Neighbouring places we cover for external mastic include Roxeth (1 mile west), Northwick Park (1 mile north-east), South Harrow (1 mile west), Harrow (1 mile north-west) and Sudbury (1 mile south-east). We also work in nearby towns such as London (11 miles south-east), City of Westminster (9 miles south-east), Marylebone (9 miles east), Kensington (7 miles south-east), St Pancras (10 miles east) and Shoreditch (11 miles east).
Local landmarks in Harrow on the Hill
We work in homes and buildings around Northwick Park, St Dominic's Sixth Form College and Orley Farm School, among other places. For rail, the closest station is Sudbury Hill Harrow station, roughly 0.5 miles south of the centre. A little further out are Kodak Museum (2 miles north) and Clementine Churchill Hospital (less than half a mile south-east). Not far away are Middle Lake and Northala Fields.
Surface by surface
Cladding and façade panels
Panels heat up and cool down quickly, so the joint sealant has to cope with frequent movement. The sealant is chosen with that in mind.
Brickwork movement joints
Brick movement joints are often mistaken for a missing mortar line. If that’s happened, we rake it out and reseal it properly.
Landlord and commercial work in Harrow on the Hill
For anyone letting property in or around Harrow on the Hill, several properties can be quoted together. Send us the addresses and the work at each.
Businesses can book us for washrooms, kitchens, offices and more. For commercial premises, we can talk through working times when we quote.