Portsmouth · England
External Mastic in Cosham
Specialist external mastic for Cosham: the right sealant, proper preparation and a neat finish. Ask us for a quick quote.
- Leaking joints around cladding and façade panels
- Damp patches traced to an open external joint
- Failed seals between different materials
External mastic for homes and businesses in Cosham
Ground-floor and low-level joints are straightforward to reach. For joints higher up, give us some details of the building and we will confirm what’s needed to reach them safely. Common call-outs are for joints where the bead has come unstuck and joints with sealant missing in places, across render & cladding joints, brickwork movement joints and copings & trims.
Houses in smaller places like Cosham can stand more in the open than those in a built-up town, and walls and rooflines facing the weather take the worst of it. Joints on those sides are normally the first to go.
We guarantee the work for a year. If there’s a problem with our work within the year, let us know and we will sort it.
- Place
- Cosham (PO6, PO3, PO2)
- Wider area
- Portsmouth
- Guarantee
- One year on every job
- Price
- Quoted before any work starts
- Phone
- 0345 464 0079
- Last updated
- 26 October 2026
Work for landlords, hotels and businesses
If you manage several properties in or around Cosham, jobs at different addresses can go on one quote. Send us the addresses and the work at each, and pictures by email help.
We regularly work with letting and managing agents. Tell us the address, the job and how access works.
External mastic in Cosham: local notes
Cosham is close to the coast, and homes near the sea take more wind-driven rain, with salt in the air closer to the shore. Both are hard on movement joints and outside wall joints, which can dry out and crack sooner where a building faces the weather. Compared with the north and west, the South East gets less rain, though outdoor sealant still has to go onto a dry joint, so the forecast decides the day.
If you let a flat or house near Cosham station, outside joints that have cracked can let damp into a rental, so check them between lets. If you look after a building such as Court Lane Junior Academy, movement joints, cladding joints and gutters on larger buildings need the same care as a house’s.
Cosham is about 2 miles south-west of Purbrook, in Portsmouth. Jobs in Cosham get the same care as everywhere else we work: the old material taken out, joints prepared properly and a 12-month guarantee. Our Portsmouth coverage runs to 19 places, and Cosham is one of them.
Every address in PO6, PO3 and PO2 is covered for external mastic. Whether your property is on Dean Road, Park Lane and Elgin Road or a nearby road, we can help. With the A397 close by, Cosham is easy for our applicators to reach. Nearby, we also carry out external mastic in Wymering (1 mile north-west), Hilsea (1 mile south), Drayton (1 mile east), Widley (1 mile north-east) and Paulsgrove (1 mile west). Further out, we also cover 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).
Local landmarks in Cosham
Typical jobs here are in homes near The First Post pub, Alexandra Park and Springfield School and the streets around them. There’s a railway station in Cosham itself: Cosham station. Well-known places in the area include Tricorn Centre (2.9 miles south) and World War I Remembrance Centre (1 mile south-east). Not far away are Southmoor Nature Reserve and Portsdown Hill.
What sealant work can’t fix
New sealant can’t fix everything, and we’ll tell you before work begins. It won’t solve:
- Rising or penetrating damp from elsewhere in the wall
- Cracking across the wall rather than at a joint
- Render that is blown, hollow or coming away
If you’re not sure, just phone 0345 464 0079 or send us an email and we will give you a straight answer before booking.
Surfaces we seal
- Render & cladding joints
- Copings & trims
- Façade panels
- Brickwork movement joints
- Concrete & block
- Joints between brick and frames
What happens if it’s left?
Water gets in through a failed movement joint and can run behind render or cladding. Resealing early keeps the job to the joint itself, instead of the wall and finishes around it. In a smaller place like Cosham, wherever a wall is exposed, a failed outside joint is a real source of damp. Indoors, a failed seal lets water into floors and panels as it would anywhere.
Homes and businesses are quoted the same way: the amount of work, how we reach it and what it needs, plus any working-time requirements on site. Ask us for a quote and we’ll go through it with you.
What you get with us
- Homes, businesses and hotels
- Colour agreed with you before work begins
- A 12-month guarantee on all work
- More than 20 years in sealant work
See our cost guide and customer reviews.
Aftercare tips
Joint life depends on how it’s used and looked after. We suggest:
- Tell anyone working on the walls about the movement joints
- Check the sealant is paintable before painting near it
- Avoid pressure-washing directly into sealant joints
- Clear growth from the base of walls and joints
Keep the joints clear of soil, plants and climbing growth. Anything that holds water against the joint wears it out sooner.
If you can see gaps, plants or bare sections in a joint, have it checked. Earlier resealing means a smaller job and a better result.
Signs you need external mastic in Cosham
Weeds, moss and debris in a joint are a sign the sealant has gone. Dirt and roots then trap moisture in the joint.
If you can see any of these, it’s time to have the joints looked at:
- Movement joints with cracked, split or missing sealant
- Hard, crazed mastic that has stopped moving
- Joints where the bead has come unstuck
- Joints pointed up with cement by mistake
For an older house near a landmark such as Church of St Philip, old and new materials meet at the roofline and walls, which is where sealant earns its keep.
What your quote should include
- Whether you can choose the colour
- What happens if they find a problem under the old sealant
- Whether all the old sealant comes out first
- The length of the guarantee
What we do, step by step
Most of a good job is in the preparation, and we don’t rush it. Every joint is cleaned and dried before new material goes in. All told, the work takes a few hours for a handful of joints, longer for a whole elevation. For a job in Cosham, we agree the time, the access and parking before the day. Outdoor jobs depend on a dry day, since sealant needs a dry surface.
- We start by walking round the building and agreeing the joints and the access.
- We cut out the old mastic and rake out anything in the joint.
- The faces are brushed clean and primed where the product requires it.
- We fit closed-cell backing rod to control the depth.
- The exterior sealant is applied, tooled and checked along its length.
Preparing for the visit
- Move anything stored near the joints
- Tell us about access, such as stairs, a lift or high-level joints
- On commercial sites, let us know about site rules
How to get a quote
Want a quote for external mastic? Please call 0345 464 0079 or email us with a few details. We’ll explain what we’d do and send you a clear quote before any work starts.
Advice
Cosham: your questions answered
Is Cosham within the area you cover?
Yes, smaller places are covered as well as towns. We work across London and the South East. Just mention lanes, gates or anything else about the route when you book.
I let a flat near Cosham station. Can you help?
Yes, rental work is part of what we do. Just ring 0345 464 0079 or drop us an email and tell us about the property, and we’ll send you a clear quote.
When is the sealant fully cured?
Most sealants are touch-dry well before they’re fully cured. We will give you the cure time for the product we used.
How long does the job take?
As a guide, most jobs take anything from a few hours to several days, depending on the building. Bigger jobs take longer, and we will tell you how long to expect.
Does someone need to be in?
If the work is inside, we need someone to let us in. Once we’ve agreed the job, you do not need to watch us work.
What does external mastic cost?
We do not publish prices, because the cost depends on the job: its size, the old material, access and the product needed. You’ll get a clear quote before we start.
Do you hold any approvals?
Yes. We are ARBOMaster approved, the scheme for applicators of Arbo sealants.
What information do you need?
Only a few details: the address or postcode, what’s wrong and any access issues. After that, simply call 0345 464 0079 or drop us an email.
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Should I try it myself first?
Overfilling a joint is a classic DIY mistake. A heavy bead looks messy and copes badly with movement, and the joint depth matters as much as the 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.