Greater London · England
Sand mastic for sash & case windows in Northwood, Greater London
Sand mastic across Northwood and nearby, with every bit of old sealant taken out first and a 12-month guarantee.
- A silicone bead on a sash window that spoils the look
- Cracked mastic round a front door frame
- Failed mastic on an exposed elevation
What affects the quote in Northwood
For a quick quote, just ask. The main things that affect it are:
- Working hours on commercial sites
- Whether the work is at height
- Any mould that needs treating
- How much old sealant there is and how hard it is to remove
Doing several joints on one visit generally makes better use of the time than several visits, so tell us about everything that needs sealing. You will get one clear quote for the whole job.
Helping us quote
Photos help, but a description is a good start. Please mention:
- What the problem is, such as mould, gaps, leaks or cracking
- A few pictures by email, if you can
- The address or postcode of the job
- Any previous sealing or DIY work
Call for a quick quote, or email us if that is easier. Describe what needs sealing and we will explain what’s involved.
Sand mastic in Northwood
Sand mastic suits most period window surrounds. On modern frames we’d normally use a flexible sealant and we’ll explain which is best for yours. If you have a silicone bead on a sash window that spoils the look and wind and rain getting in round a sash window, we can put it right, whatever the surface.
Many London homes are flats, with windows high above the street. Who looks after the outside of the frames can depend on the lease, so check that first.
Whatever the size of the job, it’s backed by our 12-month guarantee.
- Where
- Northwood (HA6)
- Region
- Greater London
- Guarantee
- One year on every job
- Price
- Quoted before any work starts
- Call
- 0345 464 0079
- Page updated
- 26 October 2026
Places near Northwood
What else we do in Northwood
Work for landlords, hotels and businesses
Water getting past a failed joint can damage the building, which matters even more when someone else lives there. Keeping joints in good order is simple maintenance.
Whether it’s one flat or a portfolio, you get the same standard of work: the old material taken out, careful preparation and a 12-month guarantee.
Northwood questions
Is parking an issue for sand mastic in Northwood?
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.
Can you do sand mastic in Northwood?
Yes. Our work covers London and the South East, and Northwood is part of that. Just call 0345 464 0079 or send us an email with a few details of the job, and we will give you a clear price.
Can I paint the new mastic?
Sand mastic is normally left unpainted, as guidance on traditional windows advises. Ask us before decorating.
How long does sand mastic take to go off?
It forms a skin fairly soon, then hardens over a longer period. Timing depends on the weather and the joint.
Is it worth trying it myself?
It depends on the job. High-level, external movement and fire-rated joints are professional jobs.
Where do you work from?
Our base is Crawley, with over 20 years’ experience. Our area covers South East England, London and Scotland.
Do you work for hotels and businesses?
Yes. Hotels, offices and other businesses use us.
Do you work for landlords and businesses?
Yes, often. Several properties can be quoted together, and between tenancies is a good time for the work.
When to call us in Northwood
Rain on the window surround works into any crack and pushes it out. Windows facing the weather tend to go first.
It’s worth asking for a quote if you see:
- Window mastic to renew ahead of painting
- Gaps where the frame meets the masonry
- Cracked mastic round a front door frame
- Mastic dropping out of the joint
Managing a site like Frithwood Primary School? Then the mastic around its windows and doors needs looking after like any other building’s.
What to look for in a quote
- How much experience the applicator has
- What preparation is included
- What happens if they find a problem under the old sealant
- What guarantee comes with the work
What sealant work can’t fix
We will always be straight with you, so here’s what sealant can’t fix:
- Planning or listed building consent (your local planning authority decides)
- Sashes that need overhauling
- Broken panes
Not sure which it is? You can phone 0345 464 0079 or drop us an email and we’ll tell you honestly.
Joints and surfaces we work on
- Sash and case windows
- Period & listed homes
- Stone surrounds
- Brick reveals
- Timber door frames
- Tenement windows
DIY versus a professional finish
What a professional job adds is preparation and the right product. We take joints back to clean, dry surfaces, and the sealant is chosen for how the joint moves and where it is, and the work is guaranteed for a year.
The biggest DIY mistake is sealing over old sealant. New silicone will not bond to old, so it lifts and traps water and mould underneath. Everything old must be removed first.
Frames and glazing around Northwood
Rainfall in the South East is lower than in much of the UK, yet outdoor joints still have to be sealed dry, so jobs are booked with the weather in mind. Historic houses like Headstone Manor (about 3.3 miles south-east) are a reminder that the area around Northwood has older buildings as well as new. In older buildings, older timber frames in brick or stone need a different approach from a modern uPVC window.
In the older streets around Emmanuel Church, frames set in older brick or stone need a sealant that suits the wall as well as the frame. If you let a flat or house near Carpenders Park station, any sash windows need sound mastic to keep draughts and rain out.
Northwood is about 3 miles south-east of Rickmansworth, in Greater London. For sand mastic in and around Northwood, please call 0345 464 0079 or email us for a quick quote. We are based in Crawley and cover Greater London. Our Greater London coverage runs to 764 places, Northwood among them. London is on our list too, around 16 miles away.
Work in HA6 works the same way as everywhere else we cover. Streets in the area include Little Stream Close and Sandy Lodge Way, and we cover them all. Other places close to Northwood include Eastbury (1 mile north-east), Moor Park (1 mile north-west), Batchworth Heath (1 mile west), Batchworth (2 miles north-west) and Holywell (2 miles north). Larger places within reach include City of Westminster (14 miles south-east), Marylebone (14 miles south-east), Kensington (12 miles south-east), St Pancras (14 miles south-east), Hampstead (11 miles south-east) and Ruislip (3 miles south).
Landmarks near Northwood
In Northwood, that means homes and buildings near King George V Playing Fields, The Gate Public House and London School of Theology, among other places. The closest station to Northwood is Carpenders Park station, about 1.7 miles north-east of the centre. Nearby you’ll also find Harlequin Centre (2.9 miles north-east) and Heath Robinson Museum (2.2 miles south-east). The countryside around Northwood includes Dews Farm Sand Pits and Tumbling Bay.
What happens on the day
You don’t need to clear the whole room or building before we come, only the area right around the joints. We protect the rest, and the work takes a few hours per window, depending on the condition of the joints in most cases. Many London jobs are in flats, so we come ready for stairs, narrow hallways and shared entrances. If the building has a concierge, managing agent or access rules, tell us when you book.
- Each surround is checked first.
- We rake out the old mastic and clean the joint.
- Large voids are packed out.
- We point the joint with sand mastic by hand.
- The finish is dressed neatly.
Getting ready for the visit
- Mention any tricky access
- Tell us about any water getting in
- For indoor joints, keep the area dry beforehand if you can
Getting a quote
For sand mastic in Northwood, phone 0345 464 0079 or email us. Tell us what the problem is and where, and we’ll agree the price before any work begins.
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Keeping the joints in good condition
Once the sealant has cured, a few habits help it last:
- Avoid patching sand mastic with silicone
- Sort the mastic before the decorators arrive
- Keep sills and gutters clear so water drains away
- Ask a joiner to look at soft timber first
Avoid painting over the new mastic, which is the traditional advice. If you’re redecorating, ask us first.
An open joint round the box lets weather through. The longer it’s left, the more the joint opens as more mastic falls out.