Greater London · England
St John's Wood Window Mastic
We cover St John's Wood for mastic around window and door frames, sills and patio doors. Old sealant removed completely, joints prepared properly and a 12-month guarantee.
- Damp patches on the reveal after heavy rain
- Cracked or shrunken mastic around the frame
- Cracked internal joints between frame and plaster
Aftercare tips
Once the sealant has cured, a few habits help it last:
- Wipe condensation off the frames
- Keep paint and stain on wooden frames in good order
- Paint up to the joint, not over it
- Clear any debris from frame drain holes
Check the drainage slots in the frames are not blocked, so rain drains out rather than building up at the sealant.
Look out for the warning signs: split or missing mastic, gaps, damp patches inside or black mould on the reveal. If you notice one, it’s time to get the joint looked at.
Window mastic in St John's Wood, done properly
If you can feel air around a shut window, the gap is often at the frame. A new joint stops the air getting through and quietens the whistle on windy days. Where the air is getting in through the window itself, we’ll say so. If you have leaking joints at the ends of sills and cracked or shrunken mastic around the frame, we can help, whatever the surface.
Much of London’s older housing was built with timber sash windows, some still in place and some long since replaced. Either way, the mastic between frame and brickwork is what stops draughts and rain getting in, in St John's Wood as anywhere.
The work is guaranteed for twelve months. If there’s a problem with our work within the year, let us know and we’ll sort it.
- Place
- St John's Wood (NW8, NW6, NW3)
- Region
- Greater London
- Cover
- 12 months on all our work
- Price
- A clear quote up front
- Phone
- 0345 464 0079
- Last updated
- 26 October 2026
When to call us in St John's Wood
Older frames were often sealed with products that set hard. Once it has hardened, the frame’s movement tears it from the wall, leaving a hairline gap down one side.
People normally contact us when they notice one of these:
- Mastic that’s falling out in pieces
- Gaps left after new windows were fitted
- Water coming in at the bottom corners of a door
- Gaps between the frame and the inside reveal
St John's Wood is in London, so parking needs planning: let us know about parking bays, permits or a driveway.
Before booking anyone
- Who turns up on the day
- Whether you can choose the colour
- Is the old sealant removed completely?
- How the joint is cleaned and prepared
The process
Once we’re on site, we check the joints match what you told us. If we find something unexpected, we talk it through with you first. Most jobs then take a few hours for a few frames, or a day or more for a whole house. In St John's Wood, flats, stairs and shared entrances are part of the routine. Mention any building rules, key holders or managing agents when you book.
- We start by checking each window and door with you.
- We remove the old mastic and clean the frame and the wall.
- We fit backing rod in deep gaps so the sealant is the right depth.
- A flexible, weatherproof sealant is applied in a colour to suit the frame.
- Finally we tidy up and check each joint.
Getting ready for the visit
- Mention any tricky access
- Tell us about any water getting in
- On commercial sites, let us know about site rules
Get a quote
Need a quote? Please ring 0345 464 0079 or drop us an email and tell us about the job. You will know what we plan to do, and what it will cost, before any work begins.
Read more
Windows and doors in St John's Wood
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. With historic houses such as Winfield House (about 0.6 miles south-east) nearby, there’s older building stock in the area around St John's Wood as well as newer homes. In older buildings, older frames set in brick or stone need a sealant that suits them, and sometimes that’s traditional sand mastic.
Schools such as George Eliot Primary School are buildings too, and the mastic around its windows and doors needs looking after like any other building’s. If you let a flat or house near South Hampstead station, renewing tired window mastic between tenants heads off draught and damp complaints.
St John's Wood is about 1 mile south of Hampstead, in Greater London. If you need window mastic in St John's Wood, it’s easy to get a quote: please ring 0345 464 0079 or send us an email. We’re based in Crawley and cover Greater London, St John's Wood included. Our Greater London coverage runs to 764 places, St John's Wood among them.
Every address in NW8, NW6 and NW3 is within our area for window mastic, from the main roads to the quietest streets. We cover properties on The Lane, Hall Road and Hill Road and the roads around them. Main roads around St John's Wood include the A5205, which makes travel easy. Other places close to St John's Wood include South Hampstead (1 mile north), Swiss Cottage (1 mile north), Primrose Hill (1 mile north-east), Lisson Grove (1 mile south) and Haverstock (1 mile north-east). Within a short drive, we also cover London (4 miles south-east), Kensington (3 miles south-west), St Pancras (3 miles east), Shoreditch (4 miles east), Walthamstow (7 miles north-east) and Hoxton (4 miles east).
What’s near St John's Wood
Around St John's Wood, our work takes us to homes and buildings near Cecil Sharp House, Primrose Hill and Arnold House School. You’ll also find Quintin Kynaston Community Academy (within half a mile north-west) and Cafe Med pub (within half a mile north-west). St John's Wood has its own railway station: South Hampstead station. A little further out are Hospital of St John and St Elizabeth (less than half a mile south) and Montfichet's Tower (3.5 miles south-east). Green spaces nearby include The Long Water and Primrose Hill.
What we cannot put right
In fairness, some problems need a different trade:
- Damp coming through the wall itself rather than the frame joint
- Condensation trapped between the panes
- Worn gaskets, brush seals or a door that has dropped
If in doubt, phone 0345 464 0079 or send us an email and we will say what we think before booking.
Joints and surfaces we work on
- Aluminium frames
- Patio & French doors
- Window sills
- Composite doors
- Timber windows & doors
- uPVC windows
Different surfaces, different methods
Composite doors
Draughts round the door leaf usually come from worn seals or adjustment, not the mastic. We seal the frame and let you know about anything else.
Timber windows & doors
Older timber windows in stone or brick can suit sand mastic rather than modern sealant. We can talk through the options.
St John's Wood: your questions answered
Do you work for landlords with property near South Hampstead station?
Yes. We work for landlords and letting agents as well as householders. You can ring 0345 464 0079 or email us with the details for a clear quote.
Can parking be tricky for a visit in St John's Wood?
In much of London, parking needs planning: a visitor permit or a nearby bay makes the day run more smoothly.
What do you put in the joint?
Each joint gets the product that suits it. Where it moves, gets wet or faces the weather makes a difference, and we will explain our choice.
Will new mastic stop draughts?
Often, yes. The gap between frame and wall is a common source of draughts, and sealing the inside and outside joints closes that path.
Do you do commercial work?
Yes. Commercial and hotel work is a large part of what we do, as well as homes. Working times can be discussed when we quote.
Are you ARBOMaster approved?
Yes. Mr Mastic is an ARBOMaster approved applicator and we are fully insured too.
Do you guarantee window mastic?
Yes. Our one-year guarantee covers every job, inside or out.
How long should I leave it?
Many sealants skin over quickly but take longer to cure fully. We will tell you how long to leave the joint.
Leave it or put it right?
Once mastic fails, rain can get between the frame and the wall. Over time that can mean damp patches, damaged plaster and rotting timber. Resealing now is a small job by comparison. Damp from a failed joint spreads quietly in older London brickwork and timber, and by the time it shows on a wall or ceiling in St John's Wood, the repair is bigger than the sealant job would have been.
Some things make a job bigger or smaller: how much old sealant there is and how stubborn it is, any mould to treat, and whether we need extra access for height. We take all of that into account in your quote.
Why book with us
- White, clear, grey or coloured to suit, where the product allows
- Experience in homes, commercial sites and hotels
- An ARBOMaster approved applicator
- More than 20 years in sealant work
Take a look at what affects the cost or what customers say.
DIY sealant or a professional job?
Some sealant jobs are within reach of a careful DIYer, such as a straightforward joint indoors. The common mistakes are sealing over old sealant, sealing a damp joint and using far too much.
If you’re set on DIY, put the effort into preparation: take out all the old sealant, make sure the joint is clean and dry, and give it the full cure time. If it doesn’t work out, we can still put it right.