Greater London · England
Sand mastic for sash & case windows in St John's Wood, Greater London
Sand mastic across St John's Wood and nearby, with old sealant always removed completely and a 12-month guarantee.
- Open joints round the window box
- Cement or filler used on old window joints that has cracked
- Mastic that needs renewing before redecorating
Sand mastic in St John's Wood
Sand mastic skins over fairly quickly, but it takes longer to harden fully. Traditional guidance is not to paint over it and we’ll advise if you are redecorating. If you have cracked mastic round a front door frame and old cement repairs round a window that have failed, we can put it right.
London has a lot of flats and conversions, where windows are often on upper floors. Who looks after the outside of the frames can depend on the lease, so check that first.
A 12-month guarantee comes as standard, so you’re covered after we have gone.
- Location
- St John's Wood (NW8, NW6, NW3)
- Wider area
- Greater London
- Cover
- One year on every job
- Quote
- Quoted before any work starts
- Telephone
- 0345 464 0079
- Last updated
- 26 October 2026
Aftercare tips
No joint lasts for ever, but care makes a real difference. Our tips:
- Do not paint over the new mastic
- Sort the mastic before the decorators arrive
- Get any rot dealt with first
- Take care around the mastic when scraping paint
Leave the new mastic alone while it firms up. It skins over quickly but needs longer to fully harden.
Once mastic starts to crumble, rain gets in. It can soak into the frame and the surrounding masonry, so renewing it early is worth it.
Work for landlords, hotels and businesses
Whether it’s one flat or a portfolio, the work is the same standard: old sealant fully removed, joints prepared properly and a 12-month guarantee.
We also work for property managers and facilities teams. Several sites can be quoted together, and we’re fully insured.
St John's Wood: your questions answered
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, so mention what’s available when you book.
I let a flat near South Hampstead station. Can you help?
Yes. We work for landlords and letting agents as well as householders, and several properties can go on one quote. You can phone 0345 464 0079 or send us an email with the details for a clear quote.
Will you leave a mess?
We keep the work tidy. Nearby surfaces are protected, and the area is left clean when we finish.
Which products do you use?
We choose the sealant for the joint, not the other way round. Where it moves, gets wet or faces the weather makes a difference.
Will the old sealant be removed?
Yes, always, and completely. New sealant won’t bond properly to old, so the joint is cleaned back first.
Is consent needed for window work on a listed home?
Speak to your local planning authority before work starts. Like-for-like sand mastic is often the preferred finish but the decision is theirs.
How long does sand mastic take to harden?
It forms a skin fairly soon, then hardens over a longer period. The weather and joint depth both affect it.
Should I try DIY first?
That depends on the joint. High-level, external movement and fire-rated joints are professional jobs.
What the job involves on each surface
Brick reveals
Loose mastic comes out and deep gaps are packed before the new mastic goes in.
Period and listed homes
A traditional finish suits a period property.
DIY sealant or a professional job?
If you do try it yourself, take your time over the preparation: take out all the old sealant, make sure the joint is clean and dry, and give it the full cure time. If it fails, we can still redo it.
Some sealant jobs are within reach of a careful DIYer, like a short, easy-to-reach joint indoors. The common mistakes are sealing over old sealant, sealing a damp joint and using far too much.
How the visit works
We keep the work tidy and contained to the area we’re working on, so you can get on with your day. The job normally takes anything from a few hours to a full day, depending on how many windows, and we tell you how long to leave it before we go. In St John's Wood, as in most of London, parking needs a little planning. A visitor permit or a nearby bay makes the visit run more smoothly.
- First we agree which joints need doing.
- Old mastic and any loose material are raked out.
- We pack any deep voids first.
- The sand mastic is mixed and pressed into the joint by hand.
- We dress the finish so it sits neatly against the masonry.
How to prepare
- Let us know about stairs, lifts or work at height
- For business premises, tell us about site rules or sign-in
- Keep children and pets away from the work area
Getting a quote
It all starts with a short chat. Tell us what’s wrong, where it is and how much there is. When it suits you, phone 0345 464 0079 or email us.
Advice
Windows and doors in St John's Wood
In a converted house or block, who looks after the windows depends on the lease, so it’s worth checking before booking. Historic houses like Winfield House (about 0.6 miles south-east) are a reminder that the area around St John's Wood has older buildings as well as new. Where a home is older, older timber frames in brick or stone need a different approach from a modern uPVC window.
If you let a flat or house near South Hampstead station, any sash windows need sound mastic to keep draughts and rain out. Homes close to Church of All Souls include some older properties, and the windows may be timber, sash or later replacements, and each needs the right sealant against the wall.
St John's Wood is about 1 mile south of Hampstead, in Greater London. Anywhere in NW8, we cover sand mastic for homes and businesses. Our Greater London coverage runs to 764 places, St John's Wood among them.
We work across NW8, NW6 and NW3 for sand mastic and the streets around it. Streets in the area include The Lane, Hall Road and Hill Road, all of which we cover. You’ll find St John's Wood on the A5205, so it’s easy for us to get to with everything needed for sand mastic. If you are just outside St John's Wood, we cover 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). We also work in nearby towns such as 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).
Near you in St John's Wood
We work in homes and buildings around Cecil Sharp House, Primrose Hill and Arnold House School, among other places. Nearby too are Quintin Kynaston Community Academy (under half a mile north-west) and Cafe Med pub (within half a mile north-west). There’s a railway station in St John's Wood itself: 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). Not far away are The Long Water and Primrose Hill.
When something else is needed
It helps to know what we cannot do too:
- Whether work needs listed building consent
- Putty and glazing repairs
- Masonry that needs repairing
If in doubt, ring 0345 464 0079 or send us an email and we’ll say what we think.
Surfaces we seal
- Sash and case windows
- Timber door frames
- Tenement windows
- Stone surrounds
- Period & listed homes
- Brick reveals
Do you need sand mastic in St John's Wood?
Shallow joints are a common cause. A thin layer does not hold well, which is why we pack deep voids first and get the depth right.
Signs it’s time to call us include:
- Cement or filler used on old window joints that has cracked
- Gaps between timber frames and stone or brick
- Mastic round period door frames that has failed
- Window mastic to renew ahead of painting
If you look after a building such as George Eliot Primary School, larger buildings have plenty of frames, and the mastic around each one ages.
Questions to ask before you book
- What preparation is included
- What happens if the job turns out different
- How long the guarantee is
- Whether all the old sealant comes out first