Greater London · England
Dulwich External Mastic
External mastic across Dulwich and nearby, with every bit of old sealant taken out first.
- Brick movement joints where the sealant has split
- Water getting into walls through failed joints
- Joints where the bead has come unstuck
Why deal with it now?
A failed movement joint lets water into the wall. Dealing with it early keeps the repair to the joint, instead of the wall and finishes around it. In older London homes, water behind a failed joint soaks into brick and timber without much sign, and once it shows in Dulwich, the repair is bigger than a sealant job.
A failed joint rarely gets cheaper to fix by waiting. If you are not sure whether it needs doing, ring 0345 464 0079 or send us an email for an honest opinion and a quote.
Why choose Mr Mastic in Dulwich
- You choose the colour before work begins
- Rated 4.9 stars on Google
- Full insurance on every job
- Arbo and Everbuild products
How we handle external mastic in Dulwich
We’re ARBOMaster approved applicators, and each external joint gets a sealant suited to it. Porous or awkward surfaces are primed where the sealant needs it, and we don’t skip that step. If you’re dealing with rain getting behind render or cladding at a joint and movement joints filled with mortar instead of sealant, we can put it right.
London’s terraces and conversions often share walls, gutters and downpipes with their neighbours, so one failed joint can cause damp for more than one household. For a flat in Dulwich, check the lease for who looks after the outside.
You’re covered for a year from the day we finish. If there’s a problem with it, please phone 0345 464 0079 or send us an email.
- Place
- Dulwich (SE22, SE21, SE23)
- Region
- Greater London
- Cover
- One year on every job
- Quote
- Quoted before any work starts
- Call
- 0345 464 0079
- Updated
- 26 October 2026
Different surfaces, different methods
Joints between dissimilar materials
Different materials may need different primers. We prepare both faces so the sealant bonds properly.
Cladding and façade panels
If the façade has a specified sealant, that is what we use, or one the system allows. Tell us what the building has when you get in touch.
What we do, step by step
Good joint work is mostly preparation, so that is where we spend the time. 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. In a London area like Dulwich, 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.
- We inspect the joints and agree which need resealing and how they’ll be reached.
- Old sealant and any debris are cut and raked out.
- The joint faces are cleaned and primed where the sealant needs it.
- Closed-cell backing rod is fitted to set the depth and stop three-sided bonding.
- We gun in a flexible exterior sealant in a colour that suits the wall and tool it neatly.
Getting ready for the visit
- Clear the area around the work
- Plan for the work area to be out of bounds to pets and children
- Let us know about earlier repairs to the joints
Getting a quote
We quote each job on its own, so the first step is telling us about yours. Simply phone 0345 464 0079 or send us an email and describe the job.
Related advice
Landlord and commercial work in Dulwich
For anyone letting property in or around Dulwich, jobs at different addresses can be quoted together. Send us the addresses and the work at each, and photos by email help.
We also work for property managers and facilities teams in Dulwich and across Greater London. Several sites can go on one quote, and we’re fully insured.
FAQs for Dulwich
Can parking be tricky for a visit in Dulwich?
Parking in Dulwich, as in most of London, takes a little planning: a visitor permit or a nearby bay makes the day run more smoothly, so mention what’s available when you book.
Can you help a landlord with a rental near West Dulwich station?
Yes, landlords and agents are among the people we work for, and several properties can go on one quote. You can phone 0345 464 0079 or send us an email with the details for a clear quote.
When is the sealant fully cured?
Most sealants are touch-dry well before they’re fully cured. We’ll tell you how long to leave the joint before we leave.
Do you guarantee your work?
Yes. Every job comes with a one-year guarantee.
Do you come to Dulwich?
Yes. We’re based in Crawley and work across South East England, London and Scotland.
What do you put in the joint?
Each joint gets the product that suits it. Where it moves, gets wet or faces the weather makes a difference, and we will tell you what we are using.
Can I do it myself?
For a simple, easy-to-reach joint, a careful DIYer can do a reasonable job. Most DIY failures come from sealing over old material, wet joints or too much sealant.
Do you have insurance?
Yes. We’re fully insured for every job we do.
Do you need external mastic in Dulwich?
A lot of failed joints come down to preparation: dusty or wet faces, no primer where one was needed, or old sealant left in. The new sealant then lets go long before it should.
Keep an eye out for any of the following:
- Rigid filler in a joint that should flex
- Sealant pulling away from one side of the joint
- Cracked joints where brick meets render or frames
- Hard, crazed mastic that has stopped moving
For landlords with property near West Dulwich station, failed wall and movement joints let damp in, so they’re worth checking between tenancies.
Comparing quotes
- Whether VAT is included
- How much experience the applicator has
- How the colour is chosen
- The length of the guarantee
Aftercare tips
How long the joints last depends on use and care. We suggest:
- Keep soil, plants and ivy away from the joints
- Point out the joints to other trades
- Avoid pressure-washing directly into sealant joints
- Act on the first splits you see
Have a quick look at the joints each spring. Splits, gaps at the edges or plants in the joint are early warning signs.
Leaks behind façade panels and render often go unseen. When it finally shows inside, the joint may have been open for years so early resealing is worth it.
Walls and rooflines in Dulwich
Historic houses like Kingswood House (about 1.1 miles south) are a reminder that the area around Dulwich has older buildings as well as new. In older buildings, older walls and rooflines need a sealant that moves with them and suits the material. London and the South East are among the drier parts of the UK, though outdoor sealant still has to go onto a dry joint, so the forecast decides the day.
Managing a site like St Anthony's Catholic Primary School? Then larger buildings have long runs of movement joint that eventually need resealing. If you live in an older home near Christ's Chapel of God's Gift, an extension built onto an older house moves differently, and the joint between them takes the strain.
Dulwich is about 1 mile south-east of Herne Hill, in Greater London. Homes, rented property, offices and hotels in Dulwich can book us for external mastic, old or new, large or small. The work is guaranteed for a year. Our area takes in 764 places across Greater London, large and small.
Here we cover the SE22, SE21 and SE23 postcode area for external mastic. If you need external mastic at a property on Court Lane, Druce Road and Boxall Road or a nearby road, our applicators can take on the job. With the A2216 close by, Dulwich is simple for us to get to for external mastic. Other places close to Dulwich include Dulwich Village (1 mile north-west), West Dulwich (1 mile south), Herne Hill (1 mile north-west), Sydenham Hill (1 mile south-east) and Forest Hill (1 mile east). Within a short drive, we also cover London (4 miles north), City of Westminster (6 miles north-west), Marylebone (6 miles north-west), Kensington (7 miles north-west), St Pancras (6 miles north) and Shoreditch (6 miles north).
Around Dulwich
Typical jobs here are in homes near The Crown and Greyhound pub, Dulwich Park and Alleyn's School, among other places. Dulwich’s nearest station is West Dulwich station, roughly 0.7 miles south-west. Well-known places in the area include Dulwich Community Hospital (0.9 miles north) and Greenwich Castle (4 miles north-east). The countryside around Dulwich includes Knight's Hill and Centre for Wildlife Gardening.
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.
Overfilling a joint is a classic DIY mistake. A thick, smeared bead looks untidy and does not move well, and the joint depth matters as much as the finish.