Greater London · England
Sand mastic for sash & case windows in Underhill, Greater London
Specialist sand mastic for Underhill: careful preparation, the right product and tidy work. Call for a quick quote.
- Cement or filler used on old window joints that has cracked
- Weathered mastic on the most exposed windows
- Window mastic to renew ahead of painting
Your questions about sand mastic in Underhill
Is parking a problem for a job in Underhill?
It can be, so it helps to tell us about permits, visitor bays or off-street space when you book. That way the visit can be planned around it.
I let a flat near New Barnet station. Can you help?
Yes. We work for landlords and letting agents as well as householders, and several properties can be quoted together. Just call 0345 464 0079 or drop us an email with the address and what needs doing, and we will give you a clear quote.
What exactly is sand mastic?
It’s the traditional filler for the joint round timber windows and doors. It’s made with sand and a linseed-oil-based binder.
Which is right for my windows, sand mastic or modern sealant?
For period timber windows in stone or brick, sand mastic is often the better fit. Modern frames normally suit a flexible sealant, and we’ll explain why.
Which products do you use?
Each joint gets the product that suits it. Where it moves, gets wet or faces the weather makes a difference, and we’ll tell you what we’re using.
Do you do commercial work?
Yes, regularly. We can plan bigger jobs in stages to suit the site.
Do I have to be there?
If the work is inside, we need someone to let us in. After that, you can carry on with your day.
Is there any odour?
It depends on the product. Some products have a noticeable smell, others very little.
How we handle sand mastic in Underhill
If your home is listed or in a conservation area, check with your local planning authority whether consent is needed for work to windows. Sand mastic is often favoured as a like-for-like material. If you’re dealing with crumbling sand mastic round a window and draughts and rain around sash boxes, we can put it right, whatever the surface.
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.
The work is guaranteed for twelve months. If something isn’t right with it in that time, tell us and we will put it right.
- Place
- Underhill (EN5, N20)
- Wider area
- Greater London
- Cover
- One year on every job
- Quote
- A clear price before we start
- Telephone
- 0345 464 0079
- Page updated
- 26 October 2026
Landlord and commercial work in Underhill
Mouldy or split sealant often shows up at the end of a tenancy, and it’s quick to put right between tenancies. Several properties can be quoted together.
Letting agents often deal with us directly. Send the address, what’s needed and the access arrangements.
Common problems we fix in Underhill
Age is the main cause. Sand mastic is a maintenance item like any pointing and how long it lasts depends on the weather it faces.
Signs it’s time to call us include:
- Tired mastic found when preparing windows for paint
- Old sand mastic that has cracked, crumbled or fallen out
- Patchy fillers round a sash window
- Cracked mastic round a front door frame
Rented homes near New Barnet station change hands often, and cracked sand mastic around sash windows lets in the draughts tenants complain about.
Before you book anyone
- Whether all the old sealant comes out first
- How the colour is chosen
- Whether they’re fully insured
- Which sealant they’ll use, and why
DIY versus a professional finish
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.
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.
What we can’t put right
Sealant is not the answer to every problem, and we’d rather say so up front. It won’t solve:
- Sashes that need overhauling
- Cracked or broken glass
- Timber that has rotted
Not sure which it is? You can phone 0345 464 0079 or email us and we will tell you honestly.
Joints and surfaces we work on
- Tenement windows
- Stone surrounds
- Timber door frames
- Brick reveals
- Sash and case windows
- Period & listed homes
What we do, step by step
The work is kept neat and contained to the area we are working on, so you can get on with your day. The job usually takes a few hours for a single window, longer for several, and we tell you how long to leave it before we go. Parking in much of London is by permit or pay-and-display, so it helps to know what’s near you in Underhill. A visitor permit or a nearby bay makes the visit run more smoothly.
- We look at the surrounds with you and agree the joints to renew.
- We remove the old, loose mastic.
- Deep gaps are packed so the mastic sits at the right depth.
- The sand mastic is mixed and pressed into the joint by hand.
- We dress the finish so it sits neatly against the masonry.
Before we arrive
- Clear the area around the work
- Try not to wet indoor joints just before the visit
- Let us know about parking restrictions
Get a quote
A good description makes for an accurate quote. Tell us where the job is, what’s wrong and how much there is, and email pictures if that is easy.
Advice
Why it’s worth doing now in Underhill
A silicone bead can be quicker, but on period stone or brick it often looks out of place. Sand mastic suits the building and blends with the stone or brick. 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 Underhill, the repair is bigger than the sealant job would have been.
The cost depends on the amount of work, how much old material has to come out and how easy the joints are to reach. You’ll have a clear quote before any work starts.
What you get with us
- Rated 4.9 stars on Google
- Anti-fungal sanitary silicone in wet areas
- Over 20 years’ experience
- An ARBOMaster approved applicator
Read what affects the cost and customer reviews.
What the job involves on each surface
Period and listed homes
Materials matter on listed and conservation-area homes. Like-for-like sand mastic is normally favoured.
Sash and case windows
On a sash window, the mastic joint shows on the outside so we finish it carefully.
Underhill homes and the weather
In a converted house or block, who looks after the windows depends on the lease, so check that before you book. Rainfall in the South East is lower than in much of the UK, but outside sealant still needs a dry, clean surface, so outdoor work is planned around the forecast.
Managing a site like St Catherine's RC School? Then its window and door frames need their mastic kept sound, just like a home’s. In the older streets around St John the Baptist Church, frames set in older brick or stone need a sealant that suits the wall as well as the frame.
Underhill is about 1 mile west of Barnet, in Greater London. Homes, rented property, offices and hotels in Underhill can book us for sand mastic. The work is guaranteed for a year. Our area takes in 764 places across Greater London, large and small. For nearby work, see our London page, about 11 miles away.
We work across EN5 and N20 for sand mastic. Streets in the area include Park Road, May's Lane and Manor Road. We also cover the places around Underhill: Barnet (1 mile east), New Barnet (1 mile east), Monken Hadley (1 mile north), Hadley Wood (1 mile north-east) and Cockfosters (2 miles east). Within a short drive, we also cover London (11 miles south-east), City of Westminster (9 miles south), Marylebone (9 miles south), Kensington (10 miles south), St Pancras (9 miles south) and Shoreditch (10 miles south-east).
Local landmarks in Underhill
Locally, jobs take us to homes and businesses close to Susi Earnshaw Theatre School, Highlands Gardens and The Red Lion pub, among other places. The nearest railway station is New Barnet station, roughly 1 mile east of the centre. Other landmarks nearby include Francis Skaryna Belarusian Library and Museum (2.2 miles south) and Barnet General Hospital (0.9 miles west). Open spaces near Underhill include Greenhill Gardens and Darland's Lake.