Greater London · England
Sand mastic for sash & case windows in Dulwich, Greater London
Our applicators work in Dulwich on traditional burnt sand mastic around sash and case windows and doors in stone and brick. Old material cut out, joints cleaned and sealed neatly.
- Gaps where the frame meets the masonry
- Wind and rain getting in round a sash window
- Window mastic to renew ahead of painting
Can I do it myself?
Overfilling a joint is a classic DIY mistake. A heavy bead looks messy and copes badly with movement, and getting the depth right matters as much as the look.
The difference is mostly in the preparation and the product. Joints are cleaned back to sound surfaces and dried, and the sealant is matched to the joint and its conditions.
About our sand mastic in Dulwich
We work across Dulwich renewing sand mastic on sash windows and doors. Every joint is cleaned out and filled by hand, finished to suit the masonry. If you’re dealing with draughts and rain around sash boxes and window mastic to renew ahead of painting, we can put it right.
Many London homes are flats, with windows high above the street. In a converted house or block, the lease normally says who is responsible for the windows, so it’s worth checking before booking.
The work is guaranteed for twelve months. If something is not right with it in that time, tell us and we’ll put it right.
- Location
- Dulwich (SE22, SE21, SE23)
- Wider area
- Greater London
- Guarantee
- 12 months on all our work
- Quotes
- A clear price before work begins
- Telephone
- 0345 464 0079
- Page updated
- 26 October 2026
Dulwich questions
Do you cover Dulwich for sand mastic?
Yes. Our work covers London and the South East, and Dulwich is part of that. Just call 0345 464 0079 or email us with a few details of the job.
Do you work for landlords with property near West Dulwich station?
Yes. We work for letting agents and landlords as well as homeowners. You can ring 0345 464 0079 or drop us an email with the details for a clear quote.
Where are you based?
We are based in Crawley, and we work across South East England, London and Scotland.
What’s sand mastic made of?
Sand plus a binder based on linseed oil. It’s built up in the joint by hand and shaped to suit the surround.
Do you remove the old sealant?
Yes, always, and completely. New sealant will not bond properly to old, so the joint is cleaned back first.
Can I do it myself?
You can, for simple jobs. The key is preparation: remove all the old material and work on a clean, dry joint. We can always put it right if it fails.
Is it possible to paint over sand mastic?
Sand mastic is normally left unpainted, as guidance on traditional windows advises. Talk to us before any painting near it.
Do you hold any approvals?
Yes. ARBOMaster is the approved applicator scheme for Arbo sealants, and we’re part of it.
How to look after the new joints
How long the joints last depends on use and care. Here’s what we suggest:
- Check with your local planning authority if your home is listed
- Keep modern sealant off the mastic
- Do not paint over the new mastic
- Ask a joiner to look at soft timber first
Avoid sealing over the mastic with silicone. If anything cracks, get it looked at before trying a quick fix.
Sound mastic protects the frame. Once it fails, water can sit against the timber, which can lead to rot.
What sand mastic looks like in Dulwich
Rainfall in the South East is lower than in much of the UK, though outdoor sealant still has to go onto a dry joint, so the forecast decides the day. With historic houses such as Kingswood House (about 1.1 miles south) nearby, there’s older building stock in the area around Dulwich as well as newer homes. In older buildings, older frames set in brick or stone need a sealant that suits them, and sometimes that is traditional sand mastic.
As a London address, Dulwich can be tricky for parking: let us know about parking bays, permits or a driveway. For landlords with property near West Dulwich station, cracked sand mastic around sash windows lets in the draughts tenants complain about.
Dulwich is about 1 mile south-east of Herne Hill, in Greater London. We carry out sand mastic for householders, landlords and businesses in Dulwich and nearby. Dulwich is one of 764 places in Greater London where we work for sand mastic.
Our applicators cover all of the SE22, SE21 and SE23 postcode area for sand mastic. We cover properties on Court Lane, Druce Road and Boxall Road and the roads around them. Dulwich sits on or near the A2216, which makes travel easy. Nearby, we also carry out sand mastic in Dulwich Village (1 mile north-west), West Dulwich (1 mile south), Herne Hill (1 mile north-west), Sydenham Hill (1 mile south-east) and Forest Hill (1 mile east). We also work in nearby towns such as London (4 miles north), City of Westminster (6 miles north-west), Marylebone (6 miles north-west), Kensington (7 miles north-west), St Pancras (6 miles north) and Shoreditch (6 miles north).
Local landmarks in Dulwich
In Dulwich, that means homes and buildings near The Crown and Greyhound pub, Dulwich Park and Alleyn's School and the streets around them. Dulwich’s nearest station is West Dulwich station, about 0.7 miles south-west of the centre. Well-known places in the area include Dulwich Community Hospital (0.9 miles north) and Greenwich Castle (4 miles north-east). The countryside around Dulwich includes Knight's Hill and Centre for Wildlife Gardening.
How the job changes by surface
Period and listed homes
A traditional finish suits a period property.
Tenement and terrace windows
Rows of sash windows on tenements and terraces often need renewing together. We can do one window or several.
Nearby places to Dulwich
Other services in Dulwich
When to call us in Dulwich
Timber swells and shrinks with the weather. That movement opens up the mastic joint little by little.
These are the problems we are asked about most:
- Draughty sash windows at the surround
- Mastic round period door frames that has failed
- Mastic worn away on windows facing the weather
- Open joints round the window box
If you live in an older home near Christ's Chapel of God's Gift, the joint between an old wall and a newer frame is generally the first place rain gets in.
Before you book anyone
- Who turns up on the day
- What product goes in the joint
- Is VAT in the price?
- The length of the guarantee
What we can’t put right
Honest advice matters more to us than a booking, so here’s what sealant cannot fix:
- Damaged stone surrounds
- Cracked or broken glass
- Sash cords, weights and draught-proofing of the sashes
Not sure which it is? You can ring 0345 464 0079 or send us an email and we will tell you honestly.
What we seal
- Period & listed homes
- Tenement windows
- Stone surrounds
- Brick reveals
- Sash and case windows
- Timber door frames
Why deal with it now?
Not every draught comes from the sashes themselves. Open mastic joints round the box can let air in and new mastic seals them. Converted houses in London often have a bathroom above someone else’s living room, and a slow leak from a failed seal can end up in the flat below. Putting it right early is much less trouble for homes in Dulwich.
A failed joint rarely gets cheaper to fix by waiting. If you are unsure, ring 0345 464 0079 or drop us an email and we’ll give you an honest view and a quote.
Why book with us
- An ARBOMaster approved applicator
- Experience in homes, commercial sites and hotels
- We’re fully insured
- Tidy, careful work
Take a look at what affects the cost and what customers say.
How it works
Before we leave, we go over the finished joints with you. The visit itself generally takes anything from a few hours to a full day, depending on how many windows, depending on the size of the job. Parking in much of London is by permit or pay-and-display, so it helps to know what’s near you in Dulwich. A visitor permit or a nearby bay makes the visit run more smoothly.
- First, we look at the surrounds with you and agree what needs doing.
- Old, loose mastic is raked out and the joint cleaned.
- We pack any deep gaps so the mastic sits at the right depth.
- The mastic is mixed, pressed into the joint by hand and shaped.
- We dress the surface so it sits neatly against the masonry.
How to prepare
- Let us know about parking restrictions
- Where the joints are inside, avoid wetting them before we arrive
- Keep children and pets away from the work area
How to get a quote
Quotes start with a quick conversation. Tell us what’s wrong, where it is and how much there is, and we will explain how we’d tackle it. Whenever you’re ready, ring 0345 464 0079 or email us.