Portsmouth · England
Sand mastic for sash & case windows in Cosham, Portsmouth
Sand mastic in Cosham from a team with over 20 years’ experience. 180+ five-star Google reviews and a 4.9 rating.
- Silicone on a period window that looks wrong
- Wind and rain getting in round a sash window
- Mastic that needs renewing before redecorating
About our sand mastic in Cosham
Across Cosham, we renew sand mastic around sash and case windows. Every joint is cleaned out and filled by hand for a neat, traditional finish. We work on tenement windows, period & listed homes and stone surrounds, and people most often call us about crumbling sand mastic round a window and weathered mastic on the most exposed windows.
Homes around Cosham range from older properties to newer houses, and their windows range just as widely. Each frame material needs the right sealant against the right wall.
Every job is covered by a 12-month guarantee.
- Where
- Cosham (PO6, PO3, PO2)
- Wider area
- Portsmouth
- Cover
- A year, on every job
- Quotes
- A clear price before work begins
- Phone
- 0345 464 0079
- Page updated
- 26 October 2026
Keeping the joints in good condition
Once the sealant has cured, a few habits help it last:
- Ask a joiner to look at soft timber first
- Find out about consent before window work on a listed home
- Make sure water runs off the sill
- Keep modern sealant off the mastic
Don’t run silicone over the new mastic. If you see a crack, ask us to take a look before trying a quick fix.
An open joint round the box lets weather through. The longer it’s left, the more the joint opens.
What affects the cost of sand mastic
Every job gets its own quote. These are the things that affect it:
- Mould in or behind the old joints
- The old material and how stubborn it is
- How many rooms, windows or areas are involved
- The type of sealant required
Doing several joints on one visit is usually more efficient than separate visits, so tell us about everything that needs sealing. We will give you a clear quote for the lot.
Asking for a quote
To help us quote quickly, please include:
- How we’d reach the joints
- Photos by email, if that’s easy
- Where the job is, and your postcode
- If it’s domestic, commercial or a hotel
There’s no standard price list, as no two jobs are quite the same. Instead, we give you a clear price for your job. To arrange one, call 0345 464 0079 or drop us an email.
DIY sealant or a professional job?
What a professional job adds is preparation and the right product. We take joints back to clean, dry surfaces, and the sealant is matched to the joint and its conditions.
If you do try it yourself, take your time over the preparation: remove every trace of old sealant, clean and dry the joint, and follow the product’s cure time. If it does not work out, we can still put it right.
When something else is needed
We will always be straight with you, so here’s what new sealant will not do:
- Decisions on consent for listed homes
- Rotten sashes, sills or window boxes (a joiner’s job)
- Masonry that needs repairing
If in doubt, call 0345 464 0079 or send us an email and we will say what we think before booking.
Surfaces we seal
- Sash and case windows
- Period & listed homes
- Tenement windows
- Brick reveals
- Timber door frames
- Stone surrounds
What happens on the day
There isn’t much for you to do on the day. Show us the job and we will take it from there. The work itself takes anything from a few hours to a full day, depending on how many windows, including the tidy-up. In a smaller place like Cosham, parking is seldom the issue; lanes, gates and long drives are worth mentioning. For outside work, side access and the height of the joints help us plan.
- 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.
- We apply the mastic by hand and shape it.
- The surface is finished to suit the stone or brick.
Before we arrive
- Tell us if parking is tricky
- For business premises, tell us about site rules or sign-in
- Mention any tricky access
Ask for a quote
Want a quote for sand mastic? Please phone 0345 464 0079 or send us an email with a few details. We’ll explain what we’d do and give you a clear quote before work begins.
Advice
Do you need sand mastic in Cosham?
Previous repairs in cement or silicone often trap water or crack away. They do not suit the joint, and they usually need raking out.
Keep an eye out for any of the following:
- Mastic worn away on windows facing the weather
- Draughty sash windows at the surround
- Old cement repairs round a window that have failed
- Gaps round a timber door in stone or brick
Homes close to Church of St Philip include some older properties, and frames set in older brick or stone need a sealant that suits the wall as well as the frame.
Comparing quotes
- Whether the sealant suits the joint
- How hidden problems are handled
- Which colour the sealant will be
- Is VAT in the price?
What happens if it’s left?
New mastic over crumbling mastic won’t hold. We remove the loose material first so the new mastic stays put. In an older home around Cosham, damp from a failed joint can get into timber and plaster, which is far harder to put right than the sealant itself.
What it costs depends on how much there is to do, how hard the old material is to remove and how easy the joints are to reach. You’ll have a clear quote before any work starts.
What you get with us
- 180+ five-star Google reviews
- Quality sealants from Arbo and Everbuild
- Any old sealant cut out fully, not covered over
- Full insurance on every job
Take a look at what affects the cost and customer reviews.
Sand mastic in Cosham: local notes
Cosham is close to 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 older windows and doors, which can dry out and crack sooner where a building faces the weather. With historic houses such as Warblington Castle (about 4.4 miles east) nearby, there’s older building stock in the area around Cosham 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.
For landlords with property near Cosham station, cracked sand mastic around sash windows lets in the draughts tenants complain about. If you look after a building such as Court Lane Junior Academy, larger buildings have plenty of frames, and the mastic around each one ages.
Cosham is about 2 miles south-west of Purbrook, in Portsmouth. For sand mastic in and around Cosham, it’s easy to get a quote: please call 0345 464 0079 or send us an email. We cover Portsmouth from our Crawley base. Our Portsmouth coverage runs to 19 places, and Cosham is one of them.
Jobs for sand mastic in PO6, PO3 and PO2 works the same way as everywhere else we cover. You’ll find streets such as Dean Road, Park Lane and Elgin Road. Cosham sits on or near the A397. Other places close to Cosham include Wymering (1 mile north-west), Hilsea (1 mile south), Drayton (1 mile east), Widley (1 mile north-east) and Paulsgrove (1 mile west). We also work in nearby towns such as 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).
What’s near Cosham
Around Cosham, our work takes us to homes and buildings near The First Post pub, Alexandra Park and Springfield School and the streets around them. Cosham has its own railway station: Cosham station. Other landmarks nearby include Tricorn Centre (2.9 miles south) and World War I Remembrance Centre (1 mile south-east). Green spaces nearby include Southmoor Nature Reserve and Portsdown Hill.
Also near Cosham
Other services in Cosham
Common questions in Cosham
Does the coastal weather in Cosham affect outside sealant?
Near the sea, outside joints face more wind, rain and salt than they would inland, so the choice of sealant and the preparation matter even more. Walls facing the sea are usually the first to need attention.
Do you work for landlords with property near Cosham station?
Yes, landlords and agents are among the people we work for, and several properties can go on one quote. Just ring 0345 464 0079 or drop us an email with the address and what needs doing, and we’ll give you a clear quote.
Is it OK to seal over old sealant?
No, it will not last. It can look neat for a few weeks, but the new layer lifts away from the old one. The old sealant has to come out completely.
Will you leave a mess?
No. We work neatly, protect the area around the joints and tidy up afterwards.
Do you take out the old sealant first?
Yes. Sealing over the old bead is the commonest cause of early failure, and it’s something we never do.
Do you do commercial work?
Yes. Hotels, offices and other businesses use us.
What’s sand mastic made of?
Sand plus a binder based on linseed oil. It’s applied by hand and finished to sit neatly against the masonry.
Where is Mr Mastic based?
We are based in Crawley, and we cover South East England, London and all of Scotland.