Greater London · England
Sand mastic for sash & case windows in Derry Downs, Greater London
Our applicators work in Derry Downs 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 and a one-year guarantee.
- Gaps where the frame meets the masonry
- Patchy fillers round a sash window
- Draughty sash windows at the surround
About our sand mastic in Derry Downs
A silicone bead around a sash window can look out of place and doesn’t suit the building. Sand mastic is the traditional choice, and we can replace one with the other. If you have old cement repairs round a window that have failed and wind and rain getting in round a sash window, we can put it right.
From mansion-block windows to modern glazing in new flats, London has every kind of frame. Over the years, the sealant around them shrinks, cracks and pulls away, which is when draughts and damp patches appear in homes in Derry Downs.
There’s a 12-month guarantee on every job, large or small.
- Location
- Derry Downs (BR5, BR6)
- Region
- Greater London
- Guarantee
- A year, on every job
- Quotes
- A clear quote up front
- Telephone
- 0345 464 0079
- Page updated
- 26 October 2026
What affects the cost of sand mastic
You’ll get a clear quote before work begins. It’s based on:
- Mould in or behind the old joints
- Whether old sealant or filler has to be cut out
- The product the joint needs
- Whether the work is at height
Instead of a standard rate, we look at what your job involves: how many joints, what’s in them now and how we reach them. You’ll know the price before we begin.
What we need to know
There’s no need for technical detail. Just tell us:
- The problem you’ve noticed
- Where the property is
- The type of property
- If someone has resealed it before
Need a quote? Please ring 0345 464 0079 or send us an email with a few details. We’ll explain what we’d do and send you a clear quote before work begins.
FAQs for Derry Downs
Is parking a problem for a job in Derry Downs?
London parking needs a little planning, so let us know about permits, bays or a driveway when you book. The visit is then planned around what’s available.
Do you cover Derry Downs for sand mastic?
Yes, Derry Downs is within the area we cover. Our work covers London and the South East. Just phone 0345 464 0079 or send us an email with a few details of the job, and we will give you a clear price.
Do you offer different sealant colours?
Most of the time, yes. We will tell you which colours the right product comes in.
Where is Mr Mastic based?
Our base is in Crawley, West Sussex, and we cover South East England, London and all of Scotland.
Is it possible to paint over sand mastic?
Sand mastic is normally left unpainted, which is what traditional guidance recommends. Ask us before decorating.
Is it messy?
We keep the work tidy. We protect what’s around the joints, and the area is left clean when we finish.
Is there any odour?
It depends on the product. Some products have a noticeable smell, others very little, and any smell fades as they cure.
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 they decide.
Towns and villages near Derry Downs
Also in Derry Downs
Derry Downs homes and the weather
With historic houses such as Lullingstone Castle (about 3.9 miles south-east) nearby, there’s older building stock in the area around Derry Downs 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. The South East is one of the drier parts of the UK, yet outdoor joints still have to be sealed dry, so jobs are booked with the weather in mind.
Rented homes near St Mary Cray station change hands often, and any sash windows need sound mastic to keep draughts and rain out. Homes close to St Andrew's include some older properties, and the joint between an old wall and a newer frame is generally the first place rain gets in.
Derry Downs is about 1 mile east of Orpington, in Greater London. For sand mastic in and around Derry Downs, it’s easy to get a quote: please call 0345 464 0079 or drop us an email. We cover Greater London from our Crawley base, Derry Downs included. We cover 764 towns and villages across Greater London, large and small. London is on our list too, about 12 miles from Derry Downs.
All of BR5 and BR6 is covered for sand mastic, from the main roads to the quietest streets. Local streets include Kent Road, Park Road and Cross Road, and we cover them all. You will find Derry Downs on the A224, so it’s easy for us to get to with everything needed for sand mastic. We also cover the places around Derry Downs: Orpington (1 mile west), St Mary Cray (1 mile north-west), Poverest (1 mile north-west), Kevington (1 mile east) and St Paul's Cray (1 mile north). We also work in nearby towns such as London (12 miles north-west), City of Westminster (15 miles north-west), Marylebone (15 miles north-west), St Pancras (14 miles north-west), Shoreditch (13 miles north-west) and Walthamstow (15 miles north-west).
Near you in Derry Downs
Around Derry Downs, our work takes us to homes and buildings near Harris Academy Orpington, The Priory School and The Royal Albert pub and the streets around them. For rail, the closest station is St Mary Cray station, about 0.8 miles north-west. Nearby you’ll also find London Borough of Bromley Museum (0.7 miles south-west) and Lullingstone Castle (3.9 miles south-east). Not far away are The Warren and Summer Hill.
Why it’s worth doing now in Derry Downs
Draughts round a sash window are not always the sashes. Open mastic joints round the box can let air in and new mastic seals them. In a London flat, a failed joint rarely stays your problem alone: water can reach the neighbours below, and gaps in fire-rated joints affect the whole building.
Combining jobs into one visit normally makes better use of the time than several visits, so it’s worth mentioning everything you’d like done. You will get one clear quote for the whole job.
What you get with us
- Over 20 years’ experience
- Quality sealants from Arbo and Everbuild
- We are fully insured
- Anti-fungal silicone where joints get wet
Take a look at our cost guide and customer reviews.
How the visit works
On the day, there’s very little for you to do. Point us to the joints and we’ll get on with it. The job generally takes anything from a few hours to a full day, depending on how many windows. Parking in much of London is by permit or pay-and-display, so it helps to know what’s near you in Derry Downs. A visitor permit or a nearby bay makes the visit run more smoothly.
- Each surround is checked first.
- The joint is raked out and cleaned.
- Large voids are packed out.
- We point the joint with sand mastic by hand.
- The finish is dressed neatly.
How to prepare
- Where the joints are inside, avoid wetting them before we arrive
- Plan for the work area to be out of bounds to pets and children
- Let us know about earlier repairs to the joints
Getting a quote
Asking for a quote is easy: let us know the job and the location, and roughly how big it is. A few pictures by email make the job easier to understand, and we’ll come back to you with a quote.
Related advice
Landlords, agents and businesses in Derry Downs
Water getting past a failed joint can damage the building, which matters even more when someone else lives there. Resealing at the right time is simple maintenance that we can handle for you.
Letting agents often deal with us directly. Send the address, what’s needed and the access arrangements and we’ll give you a quote.
Different surfaces, different methods
Brick reveals
We rake out the old mastic and pack deep voids before pointing.
Tenement and terrace windows
In shared buildings, the windows may be part of a wider repair, so check who is responsible first.
Do you need sand mastic in Derry Downs?
Age is the main cause. Sand mastic is a maintenance item like any pointing, depending on exposure and upkeep.
Common reasons people contact us are:
- Silicone on a period window that looks wrong
- Gaps between timber frames and stone or brick
- Mastic round period door frames that has failed
- Mastic that needs renewing before redecorating
Schools such as St Philomena's Primary School are buildings too, and the mastic around its windows and doors needs looking after like any other building’s.
Before you book anyone
- What preparation is included
- Is VAT in the price?
- Are they insured?
- Is the old sealant removed completely?
DIY sealant or a professional job?
A careful DIYer can reseal a simple joint, like a short, easy-to-reach joint indoors. Where it goes wrong is sealing over the old bead, working on a wet joint or overloading the gap.
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, and the work is guaranteed for a year.