Portsmouth · England
Window & door mastic in Cosham, Portsmouth
Window mastic in Cosham from a team with over 20 years’ experience. 180+ five-star Google reviews and a 4.9 rating.
- Gaps between the frame and the inside reveal
- Leaking joints at the ends of sills
- Cold air getting in at the frame edge
About our window mastic in Cosham
Every window and door frame has a gap around it, and mastic is what closes it. When it cracks, hardens or pulls away, draughts and rain get in. Our applicators cut it out and replace it with a flexible, weatherproof sealant. If you have gaps where the sill meets the wall and rain getting in at the frame or under the sill, we can help, on timber windows & doors, composite doors and patio & French doors alike.
In a smaller place like Cosham, some walls face open ground and catch the full force of the weather, so exposed windows and doors face the weather head on. The mastic around frames on those walls tends to age faster.
Each job carries a 12-month guarantee, large or small.
- Where
- Cosham (PO6, PO3, PO2)
- Region
- Portsmouth
- Guarantee
- A year, on every job
- Quotes
- A clear quote up front
- Telephone
- 0345 464 0079
- Last updated
- 26 October 2026
Do you need window mastic in Cosham?
Older frames were often sealed with products that set hard. Once it has hardened, the frame’s movement tears it from the wall, leaving a hairline gap down one side.
People generally contact us when they notice one of these:
- Draughts coming in around windows and doors
- Damp patches on the reveal after heavy rain
- Hard, cracked sealant around windows
- Sealant in the wrong colour for the frame
If you let a flat or house near Cosham station, sound mastic around windows and doors keeps out the draughts and damp that tenants notice first.
Before you book anyone
- How the joint is cleaned and prepared
- Is VAT in the price?
- Whether all the old sealant comes out first
- What product goes in the joint
Places near Cosham
More services for Cosham
How it works
Before we leave, we go over the finished joints with you. The visit itself usually takes anything from an hour or two to a full day, depending on how many frames there are, depending on the amount of work. A visit to Cosham is planned like any other: the time, the access and where to park are agreed in advance. If the work is outside, the weather plays a part, as sealant needs a dry surface.
- We check how each frame can be reached safely.
- All the failed sealant is cut away.
- The surfaces are cleaned and left dry, and primed where the sealant calls for it.
- Backing rod fills deep voids and the sealant goes in on top.
- The joint is shaped to shed water and the area tidied.
Before we arrive
- Tell us about any previous sealing or DIY attempts
- Clear the area around the work
- Mention any sign-in or site rules at work premises
How to get a quote
We quote each job on its own, so the first step is telling us about yours. Just call 0345 464 0079 or email us with the details, and pictures are welcome.
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DIY sealant or a professional job?
Not every job suits DIY: work at height, external movement joints, fire-rated sealant and large areas need the right product, the right access and the right method.
Sealing over old silicone is the commonest DIY error. Silicone does not stick to old silicone, so it lifts and traps water and mould underneath. All the old material has to come out first.
Windows and doors in Cosham
Cosham is within about 1 mile of the coast, where wind-driven rain is a fact of life and, nearer the shore, so is salt air. Both are hard on the mastic around window and door frames, which can dry out and crack sooner where a building faces the weather. Historic houses like Warblington Castle (about 4.4 miles east) are a reminder that the area around Cosham has older buildings as well as new. Where a home is older, older frames set in brick or stone need a sealant that suits them, and sometimes that’s traditional sand mastic.
For site and facilities teams at buildings such as Court Lane Junior Academy, the mastic around its windows and doors needs looking after like any other building’s. For an older house near a landmark such as Church of St Philip, replacement windows fitted into old openings often leave uneven gaps that need backing and a flexible joint.
Cosham is about 2 miles south-west of Purbrook, in Portsmouth. We provide window mastic to homes and businesses in Cosham and nearby, as part of our work across Portsmouth. Our Portsmouth coverage runs to 19 places, and Cosham is one of them.
Postcode districts we cover here for window mastic: PO6, PO3 and PO2. Whether your property is on Dean Road, Park Lane and Elgin Road or a nearby road, our applicators can take on the job. Cosham is on the A397, so it’s easy for us to get to with everything needed for window mastic. We also cover Wymering (1 mile north-west), Hilsea (1 mile south), Drayton (1 mile east), Widley (1 mile north-east) and Paulsgrove (1 mile west). Larger places within reach include Southsea (4 miles south), Milton (3 miles south), Landport (3 miles south), Portsea (3 miles south-west), Portsmouth Point (4 miles south-west) and Fratton (3 miles south).
Near you in Cosham
Locally, jobs take us to homes and businesses close to The First Post pub, Alexandra Park and Springfield School. Cosham has its own railway station: Cosham station. Nearby you will also find Tricorn Centre (2.9 miles south) and World War I Remembrance Centre (1 mile south-east). For a walk, there’s Southmoor Nature Reserve and Portsdown Hill.
Common questions in Cosham
I let a flat near Cosham station. Can you help?
Yes. We work for landlords and letting agents as well as householders, and several properties can go on one quote. You can call 0345 464 0079 or send us an email with the details for a clear quote.
Does the coastal weather in Cosham affect outside sealant?
Coastal weather is harder on outside sealant: there’s more wind-driven rain and, closer to the shore, salt in the air. The right product, a clean joint and the right depth all help it cope.
Do you hold any approvals?
Yes. Mr Mastic is an ARBOMaster approved applicator.
Can you reach windows above the ground floor?
Yes, in most cases. We plan safe access before the job.
What does window mastic cost?
We do not publish prices, because the cost depends on the job: how much there is, what’s there now, how we reach it and what it needs. We agree the price before any work begins.
What do you put in the joint?
We choose the sealant for the joint, not the other way round. Movement, water and weather all affect the choice, and we will tell you what we’re using.
How long will my window job take?
A few frames take a few hours, while a whole house takes longer. You’ll get a timescale with the quote.
Are you fully insured?
Yes. Full insurance covers our work, and we can confirm the details when we quote.
Quotes for window mastic in Cosham
The quote reflects the job in front of us. We take into account:
- Working hours on commercial sites
- The old material and how stubborn it is
- How many areas need sealing
- Any mould that needs treating
Combining jobs into one visit generally 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 to tell us for a quote
When you call or email, these details help:
- Whether it has been sealed before
- The address or postcode of the job
- The type of property
- How many joints, rooms or windows are involved
To get a quote, phone 0345 464 0079 or drop us an email with the location and a short description of the problem. We will give you a clear quote before any work starts.
What sealant work can’t fix
A few problems are outside what sealant work can do:
- Faulty window hardware
- Soft or decayed wood in the frame
- A failed sealed unit that has misted up
If in doubt, call 0345 464 0079 or drop us an email and we’ll say what we think.
Joints and surfaces we work on
- Patio & French doors
- Window sills
- uPVC windows
- Aluminium frames
- Timber windows & doors
- Composite doors
How the job changes by surface
Patio & French doors
Patio and French doors have the longest joints on most houses. Most leaks start at the bottom corners, so we pay close attention there.
Window sills
Masonry sills can have joints where water gets in, including the one between the sill and the frame above. We seal those with a sealant suited to masonry.
How to look after the new joints
Joint life depends on how it’s used and looked after. Here’s what we suggest:
- Clear any debris from frame drain holes
- Check the mastic once a year
- Wipe condensation off the frames
- Clean frames with a soft cloth and soapy water
Silicone cannot normally be painted, so mention any painting plans before any work starts. There are paintable sealants for joints that need it.
A small gap around a frame only grows. As the old mastic shrinks further, more air gets through, and a cold room gets colder. Resealing closes it.