Greater London · England
Window & door mastic in Streatham, Greater London
Window mastic for Streatham, by sealant specialists with 20+ years’ experience. 180+ five-star Google reviews and a 4.9 rating.
- Cracked sealant at the sill ends
- Cracked internal joints between frame and plaster
- Black, perished sealant on frames
How we handle window mastic in Streatham
Over two decades of sealing frames has taught us which products suit which walls. We are fully insured ARBOMaster approved applicators, and every job is covered by a 12-month guarantee. If you’re dealing with mastic that has split away from the wall and gaps where the sill meets the wall, we can put it right, on window sills, uPVC windows and patio & French doors alike.
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, letting in draughts and water.
Big or small, you get the same 12-month guarantee in Streatham and across Greater London.
- Location
- Streatham (SW16, SW2, CR4, SW12)
- Wider area
- Greater London
- Cover
- A year, on every job
- Quote
- A clear price before any work starts
- Telephone
- 0345 464 0079
- Updated
- 26 October 2026
Can I do it myself?
Too much sealant is as bad as too little. A heavy bead looks messy and copes badly with movement, and getting the depth right matters as much as the look.
A DIY attempt doesn’t rule out a professional job. We remove it and do the joint properly, so tell us about it when you ask for a quote.
Common problems we fix in Streatham
Timber windows bring their own problems. Mastic painted over many times cracks with the paint, and timber moves with moisture as well as temperature.
The most common problems we see are:
- Draughts coming in around windows and doors
- Mastic that has split away from the wall
- White mastic on grey or black frames
- Water coming in at the bottom corners of a door
Homes close to St Leonard's Church include some older properties, and the joint between an old wall and a newer frame is generally the first place rain gets in.
What your quote should include
- Are they insured?
- How much experience the applicator has
- How long to leave it before use
- What guarantee comes with the work
Places near Streatham
What else we do in Streatham
Why act early in Streatham
The work is quick compared with the damage it prevents: the visit takes a few hours for a few frames, or a day or more for a whole house. Leave it until water is coming in and you may need plastering and decorating as well. In London conversions, one flat’s bathroom is often above another flat’s ceiling, and a slow leak from a failed seal can end up in the flat below. Putting it right early is much less trouble.
A failed joint rarely gets cheaper to fix by waiting, because water and mould keep working on it. If you are not sure whether it needs doing, phone 0345 464 0079 or email us for an honest opinion and a quote.
Why choose Mr Mastic in Streatham
- Trusted Arbo and Everbuild sealants
- 4.9 on Google from 180+ five-star reviews
- We’re fully insured
- Sanitary silicone with an anti-fungal additive in wet areas
Different surfaces, different methods
Window sills
Sills catch the water running down the glass, so the sill ends and the joint under the frame are vital. Each is cleaned out and resealed.
Composite doors
If the door itself is draughty, the issue may be the door seals or hinges rather than the frame mastic. We will tell you if that’s what we find.
Streatham: your questions answered
Is parking a problem for a job in Streatham?
Parking in Streatham, as in most of London, takes a little planning: a visitor permit or a bay close to the door helps a lot.
Do you cover Streatham for window mastic?
Yes. Our work covers London and the South East, and Streatham is part of that. Just phone 0345 464 0079 or email us with a few details of the job, and we’ll give you a clear price.
Do you work for letting agents?
Yes, often. Several properties can be quoted together, and between tenancies is a good time for the work.
Do you seal inside as well as outside?
Yes. Draughts often come through the inside gap too, so sealing both is often worthwhile.
Do you remove the old sealant?
Yes. We cut out all the old sealant and clean the joint.
How do I get a quote for window mastic in Streatham?
It depends on the job, so we quote each one individually. For a quick quote, ring 0345 464 0079 or drop us an email and tell us what needs doing and where.
Do I have to be there?
That depends on where the joints are. Inside work needs someone to give us access.
Are you fully insured?
Yes. We’re fully insured for every job we do.
What affects the cost of window mastic
The price is agreed before any work begins. It takes into account:
- Whether old sealant or filler has to be cut out
- Any working-time requirements on site
- Mould in or behind the old joints
- Whether the work is at height
Commercial jobs are quoted on the same basis as homes: the amount of work, the access and the products needed, plus any working-time requirements on site. Call for a quick quote and we will explain what it covers.
Asking for a quote
Photos help, but a description is a good start. Please mention:
- If someone has resealed it before
- What the problem is, such as mould, gaps, leaks or cracking
- A few pictures by email, if you can
- Where the job is, and your postcode
We quote each job on its own, so start by telling us what you need. Simply phone 0345 464 0079 or send us an email and describe the job and send pictures if you have them.
Work for landlords, hotels and businesses
A neglected joint can let water reach the structure, which is a bigger problem in a rented property. Keeping joints in good order is simple maintenance that we can handle for you.
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.
What happens on the day
When we get to you, we compare the joints with what we discussed. If anything is different, we explain it before carrying on. Most jobs then take most of a day for a typical house, less for a few frames. In a London area like Streatham, the main things to plan are parking and access: tell us about permits, visitor bays or off-street space, which floor we’re working on and whether there’s a lift.
- First, we go round the frames with you and agree the list.
- We remove the old mastic and clean the frame edge and wall.
- Deep gaps get closed-cell backing rod to set the depth.
- A flexible exterior sealant is applied in a colour to suit the frame.
- Every joint is tooled smooth and checked before we leave.
Before we arrive
- Let us know if you’ve seen damp or leaks
- Move anything stored near the joints
- Tell us about any previous sealing or DIY attempts
Getting a quote
For a quote, phone 0345 464 0079 or drop us an email and tell us where the job is and what the problem looks like. You’ll have a clear quote before any work starts.
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Window mastic in Streatham: local notes
With historic houses such as Kingswood House (about 2 miles east) nearby, there’s older building stock in the area around Streatham as well as newer homes. Where a home is older, older timber frames in brick or stone need a different approach from a modern uPVC window. Compared with the north and west, the South East gets less rain, yet outdoor joints still have to be sealed dry, so jobs are booked with the weather in mind.
For landlords with property near Streatham station, sound mastic around windows and doors keeps out the draughts and damp that tenants notice first. For site and facilities teams at buildings such as St Andrew's Catholic Primary School, the mastic around its windows and doors needs looking after like any other building’s.
Streatham is about 5 miles south of London, in Greater London. We carry out window mastic for homes and businesses in Streatham and nearby, as part of our work across Greater London. Streatham is one of 764 towns and villages in Greater London we cover for window mastic.
All of SW16, SW2, CR4 and SW12 is covered for window mastic, from the main roads to the quietest streets. You will find streets such as Stanthorpe Road, Gleneagle Mews and Madeira Road, and we cover them all. You will find Streatham on the A205 and A216, so it’s easy for us to get to. If you’re just outside Streatham, we cover Streatham Park (1 mile west), Furzedown (1 mile west), Streatham Hill (1 mile north), Hyde farm estate (1 mile north) and Grange Mills (1 mile north-west). Further out, we also cover London (5 miles north), City of Westminster (6 miles north), Marylebone (6 miles north), Kensington (6 miles north-west), St Pancras (7 miles north) and Shoreditch (7 miles north).
Local landmarks in Streatham
Typical jobs here are in homes near Bishop Thomas Grant Catholic Secondary School, Streatham Common and Waldorf School of South West London. There’s a railway station in Streatham itself: Streatham station. Well-known places in the area include Clockworks Museum (1.1 miles east) and Southside Wandsworth (3.3 miles north-west). Open spaces near Streatham include Knight's Hill and Battersea Park Lake.