Greater London · England
Window Mastic in Harrow
Specialist window mastic for Harrow: the right sealant, proper preparation and a neat finish. Ask us for a quick quote.
- A bead that doesn’t match the frame
- Cracked internal joints between frame and plaster
- Mastic that has split away from the wall
How we handle window mastic in Harrow
Mr Mastic’s applicators have more than 20 years’ experience with window and door sealants. We’re fully insured ARBOMaster approved applicators, and we give a one-year guarantee on the work. We work on window sills, uPVC windows and patio & French doors, and common reasons people get in touch are rushed sealant from a window installation and rain getting in at the frame or under the sill.
London has a lot of flats and conversions, where windows are often on upper floors. In a converted house or block, the lease generally says who is responsible for the windows, so it’s worth checking before booking.
All of our work is guaranteed for twelve months, in Harrow and everywhere else we cover.
- Place
- Harrow (HA2, HA1, UB5, HA3)
- Wider area
- Greater London
- Cover
- 12 months on all our work
- Quotes
- Quoted before any work starts
- Phone
- 0345 464 0079
- Last updated
- 26 October 2026
Signs you need window mastic in Harrow
On timber frames, paint and putty build up around the joint. Mastic painted over many times cracks with the paint, and timber moves with moisture as well as temperature.
Common reasons people contact us are:
- A bead that doesn’t match the frame
- Cold air getting in at the frame edge
- Black, perished sealant on frames
- Gaps left after new windows were fitted
Harrow is in London, so parking needs planning: let us know about parking bays, permits or a driveway.
Before you book anyone
- How the surfaces are prepared before sealing
- Whether you can choose the colour
- Is the old sealant removed completely?
- Is VAT in the price?
What affects the cost of window mastic
Your quote is based on your job. We look at:
- Working hours on commercial sites
- How many rooms, windows or areas are involved
- Which sealant suits the joint
- The size of the job
We do not show prices on the website, because each job is priced on what it involves. Call for a quick quote.
Helping us quote
To help us quote quickly, please include:
- What the problem is, such as mould, gaps, leaks or cracking
- Roughly how big the job is
- Any access issues, like height or stairs
- If someone has resealed it before
For a quote, call 0345 464 0079 or email us with the location and a short description of the problem. You will have a clear quote before work begins.
What window mastic looks like in Harrow
In London conversions and blocks, the lease decides who is responsible for the frames, so check that before you book. With historic houses such as Headstone Manor (about 1.4 miles north) nearby, there’s older building stock in the area around Harrow as well as newer homes. Where a home is older, older timber frames in brick or stone need a different approach from a modern uPVC window.
If you live in an older home near Church of St Peter, replacement windows fitted into old openings often leave uneven gaps that need backing and a flexible joint. Schools such as Whitmore High School are buildings too, and the mastic around its windows and doors needs looking after like any other building’s.
Harrow is about 7 miles south of Watford, in Greater London. From the centre of Harrow to the outskirts, we cover window mastic for every kind of property, from flats and houses to offices and hotels. We cover 764 towns and villages across Greater London, large and small. You can also see our page for London, roughly 12 miles from Harrow.
Postcode districts we cover here for window mastic: HA2, HA1, UB5 and HA3. You will find streets such as High Street, London Road and Perceval Square, and we cover them all. You will find Harrow on the B457 and B458, which makes it straightforward to reach with everything needed for window mastic. We also cover Roxeth (1 mile south), South Harrow (1 mile south), North Harrow (1 mile north-west), Harrow on the Hill (1 mile south-east) and Rayners Lane (1 mile west). Further out, we also cover London (12 miles south-east), City of Westminster (9 miles south-east), Marylebone (10 miles south-east), Kensington (8 miles south-east), St Pancras (11 miles east) and Shoreditch (12 miles east).
What’s near Harrow
Around Harrow, our work takes us to homes and buildings near Kingsfield Arms, Grange Primary School and Northwick Park, among other places. The nearest railway station is Harrow-on-the-Hill station, roughly 0.7 miles north-east. Nearby you will also find St. George's Shopping Centre (0.7 miles north-east) and Clementine Churchill Hospital (1 mile south-east). For a walk, there’s Islip Manor Meadows and Northala Fields.
How it works
On the day, there’s very little for you to do. Show us the job and we’ll take it from there. The job generally takes a few hours for a handful of frames, longer for a whole house. For a job in Harrow, 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 window and door with you.
- The old mastic is cut out and the surfaces cleaned back.
- Deep gaps are filled with backing rod to set the depth.
- We apply a weatherproof sealant to match the frame and tool it neatly.
- Every joint is checked before we leave.
How to prepare
- Mention any tricky access
- Keep pets and children clear of the area while we work
- On commercial sites, let us know about site rules
Ask for a quote
Asking for a quote is easy: let us know the job and the location, and roughly how big it is. A few photos by email make the job easier to understand, and we’ll come back to you with a quote.
Read more
When it isn’t the sealant
We won’t take on work that will not last, so these are the limits:
- Worn gaskets, brush seals or a door that has dropped
- Damp problems in the wall away from the window
- A failed sealed unit that has misted up
Not sure which it is? You can call 0345 464 0079 or email us and we will tell you honestly.
Where we work in Harrow
- uPVC windows
- Aluminium frames
- Composite doors
- Patio & French doors
- Window sills
- Timber windows & doors
Common questions in Harrow
Can you help a landlord with a rental near Harrow-on-the-Hill station?
Yes, we work for letting agents and landlords. You can ring 0345 464 0079 or drop us an email with the address and a few details, and we’ll give you a fixed price before any work starts.
Can you do window mastic in Harrow?
Yes. We work across London and the South East, and Harrow is part of that. You can ring 0345 464 0079 or email us and let us know what needs doing.
Can I do it myself?
For a simple, easy-to-reach joint, a careful DIYer can do a reasonable job. The usual mistakes are sealing over old sealant, sealing a damp joint and using too much.
What does window mastic cost?
The cost depends on the size of the job, access and how much old sealant has to come out. Ask us for a quote.
Can resealing stop a draught around my window?
It will if the frame joint is the problem. We check where the draught is before we start.
Do you do commercial work?
Yes, regularly. We can plan bigger jobs in stages to suit the site.
Do you have sealant for grey or black windows?
Yes, in most cases. Tell us the frame colour when you get in touch and we will use the nearest match.
Do you guarantee window mastic?
Yes. Our 12-month guarantee covers every job, inside or out.
Surface by surface
Composite doors
If the door itself is draughty, the issue may be the door seals or hinges rather than the frame mastic. We seal the frame and let you know about anything else.
Patio & French doors
Door frames take knocks and movement every time the doors are used. The sealant must cope with it.
Nearby places to Harrow
What else we do in Harrow
Why act early in Harrow
Running fresh sealant over the old joint is tempting, but new sealant can’t bond to old, crumbling mastic. It peels before long, and water still gets in behind. The old mastic has to come out. Damp from a failed joint spreads quietly in older London brickwork and timber, and once it shows in Harrow, the repair is bigger than a sealant job.
The cost reflects the work involved, not guesswork. That is why we ask a few questions first and send you a clear quote before work begins.
Why choose Mr Mastic in Harrow
- We leave the area clean and tidy
- A choice of colours where the product allows
- Fully insured
- 20+ years of sealant experience
See our cost guide and our reviews.
DIY versus a professional finish
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.
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, then guaranteed for a year.