Greater London · England
Sand mastic for sash & case windows in Westminster, Greater London
Sand mastic across Westminster and nearby, with every bit of old sealant taken out first and a 12-month guarantee.
- Failed mastic on an exposed elevation
- Mastic round period door frames that has failed
- Mastic dropping out of the joint
Sand mastic in Westminster
Sand mastic has long been used to fill the joint between timber frames and masonry. It’s made from sand and a linseed-oil-based binder and built up by hand. On older homes, it suits the building far better than silicone. If you have modern sealant on a period surround and draughty sash windows at the surround, we can put it right, on period & listed homes, tenement windows and timber door frames alike.
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 Westminster 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 will sort it.
- Location
- Westminster (SW1P, W1J, SW1V)
- Region
- Greater London
- Cover
- 12 months on all our work
- Quote
- A clear quote up front
- Phone
- 0345 464 0079
- Last updated
- 26 October 2026
How we quote for sand mastic
The price is agreed before any work begins. It takes into account:
- Working hours on commercial sites
- The type of sealant required
- How many areas need sealing
- The number and length of the joints
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 the work is at height. Your quote takes all of that into account.
Asking for a quote
The more you tell us, the more accurate the quote. When you get in contact, it helps to mention:
- How many joints, rooms or windows are involved
- What the problem is, such as mould, gaps, leaks or cracking
- If someone has resealed it before
- The address or postcode of the job
To get a quote, call 0345 464 0079 or send us an email with the location and a short description of the problem. We’ll send you a clear quote before any work starts.
Signs you need sand mastic in Westminster
Timber swells and shrinks with the weather. The movement cracks the mastic over time.
Most people get in touch when they notice something like this:
- Open joints round the window box
- Old cement repairs round a window that have failed
- Mastic dropping out of the joint
- Mastic round period door frames that has failed
For site and facilities teams at buildings such as Harris Westminster Sixth Form, the mastic around its windows and doors needs looking after like any other building’s.
What to look for in a quote
- Is VAT in the price?
- How long the guarantee is
- How the surfaces are prepared before sealing
- How hidden problems are handled
What we do, step by step
A visit follows a simple pattern: we look at the joints together, mask and protect the surrounding surfaces, do the work and tidy away. Most jobs take a few hours per window, depending on the condition of the joints. Parking in much of London is by permit or pay-and-display, so it helps to know what’s near you in Westminster. It helps if you can point us to a visitor permit or a bay close to the door.
- We check the window surrounds and agree which joints need renewing.
- The loose and crumbling mastic is raked out and the joint cleaned.
- Deep voids are packed so the mastic is the right thickness.
- Sand mastic is mixed and applied by hand, then shaped to the joint.
- We dress the surface so it sits neatly against the masonry.
How to prepare
- Mention any leaks or damp you’ve noticed
- Let us know about earlier repairs to the joints
- Mention any sign-in or site rules at work premises
Ask for a quote
We quote each job on its own. Simply call 0345 464 0079 or send us an email and describe the job.
Read more
Leave it or put it right?
New sash windows are a major, costly change and on a listed home, consent may be needed. Where the frames are in good order, new mastic seals the surround. In a flat in Westminster, failed sealant seldom stays inside your own four walls: water from a shower or window joint can reach the flat below, and gaps in fire-stopping matter to everyone in the building.
Every job is a little different, so each one gets its own quote. The number of joints, how easy they are to reach and the sealant needed all play a part, and we will explain the quote if you ask.
Why choose Mr Mastic in Westminster
- ARBOMaster approved applicator
- Full insurance on every job
- Anti-fungal sanitary silicone in wet areas
- Homes, businesses and hotels
Common questions in Westminster
Is Westminster in your area for sand mastic?
Yes, Westminster is within the area we cover. We work across London and the South East. You can call 0345 464 0079 or drop us an email and let us know what needs doing, and we’ll give you a clear price.
Is parking an issue for sand mastic in Westminster?
Parking in Westminster, as in most of London, takes a little planning: a visitor permit or a nearby bay makes the day run more smoothly.
Where do you work from?
We’re a Crawley-based firm. We work across South East England, London and Scotland.
Can I choose the sealant colour?
Generally, yes. White, clear and grey are common, and other colours are available for many products, and we agree the colour with you before any work starts.
Are you an approved applicator?
Yes. We hold ARBOMaster approved applicator status.
Should I use sand mastic or silicone?
We’ll talk it through with you. Period homes often look best with sand mastic and newer frames suit modern sealant.
What exactly is sand mastic?
It’s the traditional filler for the joint round timber windows and doors. It combines sand with a linseed-oil-based binder.
How long does sand mastic take to harden?
It forms a skin fairly soon and it hardens fully over a longer time. Timing depends on the weather and the joint.
Looking after it afterwards
Once the sealant has cured, a few habits help it last:
- Inspect the joints round the windows every year or so
- Renew mastic before redecorating the windows
- Make sure water runs off the sill
- Find out about consent before window work on a listed home
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.
How the job changes by surface
Timber door frames
Round a period front door, sand mastic gives the right look.
Sash and case windows
Most of our sand mastic work is on sash windows. We renew the mastic round each box.
What sand mastic looks like in Westminster
In a converted house or block, who looks after the windows depends on the lease, so check that before booking. Historic houses like Clarence House (about 0.4 miles north-west) are a reminder that the area around Westminster has older buildings as well as new. In older buildings, older frames set in brick or stone need a sealant that suits them, and sometimes that’s traditional sand mastic.
As a London address, Westminster can be tricky for parking: let us know about parking bays, permits or a driveway. Homes close to Christ Church include some older properties, and frames set in older brick or stone need a sealant that suits the wall as well as the frame.
Westminster is about 1 mile south-east of City of Westminster, in Greater London. Anywhere in SW1P, we cover sand mastic for homes and businesses. Westminster is one of 764 towns and villages in Greater London we cover for sand mastic.
Work in SW1P, W1J and SW1V is quoted and booked the same way as anywhere else. Whether your property is on Eaton Lane, Wilton Road and Castle Lane or anywhere close by, we can help. Westminster is on the A4 and A202, which makes it straightforward to reach with everything needed for sand mastic. Neighbouring places we cover for sand mastic include Millbank (1 mile north), Victoria (1 mile south-west), Pimlico (1 mile south), Vauxhall (1 mile south-east) and Lambeth (1 mile south-east). Within a short drive, we also cover Kensington (3 miles west), Shoreditch (3 miles north-east), Walthamstow (8 miles north-east), Hoxton (3 miles north-east), Whitechapel (3 miles north-east) and Hampstead (4 miles north-west).
Local landmarks in Westminster
Locally, jobs take us to homes and businesses close to St Matthew's School, St James's Park and Blewcoat School and the streets around them. Nearby too are London Library (0.6 miles north) and Grafton Arms (within half a mile south). For rail, the closest station is London Victoria station, about 0.6 miles south-west. Other landmarks nearby include Westminster Hospital (less than half a mile east) and The Crime Museum (less than half a mile south). Green spaces nearby include Barnsbury Wood and St. James's Park Lake.
What sealant work cannot fix
To be straight with you, there are a few things sealant will not fix:
- Timber that has rotted
- Broken panes
- Crumbling stone or brickwork round the window
If in doubt, ring 0345 464 0079 or drop us an email and we’ll say what we think before you book.
Joints and surfaces we work on
- Stone surrounds
- Timber door frames
- Sash and case windows
- Brick reveals
- Period & listed homes
- Tenement windows