Greater London · England
External Mastic in Sydenham Hill
External mastic for Sydenham Hill and the surrounding area: careful preparation, the right product and tidy work. Call for a quick quote.
- Damp patches traced to an open external joint
- Old sealant gone brittle and cracked
- Joints where the bead has come unstuck
About our external mastic in Sydenham Hill
External mastic is a job where short cuts show quickly. Overfilled joints, missing backing rod and sealant laid over old sealant rarely last long. We strip the joint back and start again. We work on render & cladding joints, copings & trims and brickwork movement joints, and the jobs we see most are joints where the bead has come unstuck and joints pointed up with cement by mistake.
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 Sydenham Hill, check the lease for who looks after the outside.
A 12-month guarantee comes as standard, so you are not left on your own once the job is done.
- Where
- Sydenham Hill (SE26, SE23, SE21)
- Wider area
- Greater London
- Guarantee
- One year on every job
- Quote
- Quoted before any work starts
- Phone
- 0345 464 0079
- Page updated
- 26 October 2026
What happens if it’s left?
Water gets in through a failed movement joint and can run behind render or cladding. Dealing with it early keeps the repair to the joint, instead of the wall and finishes around it. Damp from a failed joint spreads quietly in older London brickwork and timber, and once it shows in Sydenham Hill, the repair is bigger than a sealant job.
What it costs depends on the amount of work, how hard the old material is to remove and how easy the joints are to reach. You will have a clear quote before any work starts.
Why Sydenham Hill customers choose us
- 180+ five-star Google reviews
- Trusted Arbo and Everbuild sealants
- White, clear, grey or coloured to suit, where the product allows
- Anti-fungal silicone where joints get wet
Read our cost guide and our reviews.
Towns and villages near Sydenham Hill
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Quotes for external mastic in Sydenham Hill
Every job gets its own quote. These are the things that affect it:
- Whether old sealant or filler has to be cut out
- The size of the job
- Any working-time requirements on site
- How many areas need sealing
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 explain what it covers.
What to tell us for a quote
What to tell us when you ask for a quote:
- Pictures of the joints, sent by email
- If someone has resealed it before
- What’s wrong with the joints now
- Roughly how big the job is
For a quick quote, get us on the phone, or email us if that is easier. Describe what needs sealing and we’ll explain what’s involved and give you a clear price.
What external mastic looks like in Sydenham Hill
The South East is one of the drier parts of the UK, yet outdoor joints still have to be sealed dry, so jobs are booked with the weather in mind. London terraces and converted houses often share gutters, downpipes and walls, so it’s worth agreeing who is responsible before work starts.
If you look after a building such as Kelvin Grove Primary School, larger buildings have long runs of movement joint that eventually need resealing. If you let a flat or house near Sydenham Hill station, split movement joints are easy to miss on a rental until damp shows inside. If you live in an older home near Church of St Philip the Apostle, an extension built onto an older house moves differently, and the joint between them takes the strain.
Sydenham Hill is about 1 mile east of West Norwood, in Greater London. We provide external mastic to homes and businesses in Sydenham Hill. Our area takes in 764 places across Greater London, large and small.
All of SE26, SE23 and SE21 is within our area for external mastic. That includes homes and businesses on Grange Lane, Dallas Road and Lyall Avenue and the roads around them. If you’re just outside Sydenham Hill, we cover West Dulwich (1 mile west), Sydenham (1 mile south-east), Crystal Palace (1 mile south), Dulwich (1 mile north-west) and Gipsy Hill (1 mile south-west). Larger places within reach include London (5 miles north), City of Westminster (7 miles north-west), Marylebone (7 miles north-west), Kensington (7 miles north-west), St Pancras (7 miles north) and Shoreditch (6 miles north).
Local landmarks in Sydenham Hill
Typical jobs here are in homes near Long Meadow, The Wood House and Sydenham School, among other places. The closest station to Sydenham Hill is Sydenham Hill station, about 0.5 miles west. Other landmarks nearby include Horniman Museum and Gardens (0.6 miles north-east) and Lewisham Shopping Centre (3.2 miles north-east). Not far away are Knight's Hill and Dulwich Upper Wood.
What sealant work cannot fix
Honest advice matters more to us than a booking, so here’s what new sealant will not do:
- Damp that is not coming from the joint
- Failed render or damaged cladding panels
- Cracks in the bricks or render themselves, away from the joints
Not sure which it is? You can ring 0345 464 0079 or email us and we’ll tell you honestly.
Where we work in Sydenham Hill
- Brickwork movement joints
- Render & cladding joints
- Façade panels
- Concrete & block
- Joints between brick and frames
- Copings & trims
How the visit works
Our applicators work methodically: protect, prepare, seal, tidy. For most jobs that takes a few hours to a few days, depending on the length of joint and the access and we leave things clean and tidy. In a London area like Sydenham Hill, 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 start by checking each joint, agreeing the ones to redo and how we’ll reach them.
- The old mastic and anything lodged in the joint is removed.
- We clean both faces of the joint and prime them where the product calls for it.
- We push in closed-cell backing rod so the sealant is the right depth and bonds to the sides only.
- We gun in a flexible exterior sealant in a colour that suits the wall and tool it neatly.
Getting ready for the visit
- Mention any leaks or damp you’ve noticed
- Plan for the work area to be out of bounds to pets and children
- Tell us about access, such as stairs, a lift or high-level joints
How to get a quote
We don’t publish a price list. Instead, we send you a clear quote for your job. To arrange one, phone 0345 464 0079 or drop us an email.
Read more
What the job involves on each surface
Cladding and façade panels
If the façade has a specified sealant, that’s what we use. Tell us what the building has when you get in touch.
Render joints
Water behind render can lead to blown patches. Resealing the joints early keeps water out and helps it last.
Your questions about external mastic in Sydenham Hill
Do you cover Sydenham Hill for external mastic?
Yes. Our work covers London and the South East, and Sydenham Hill is part of that. Just call 0345 464 0079 or send us an email with a few details of the job, and we’ll give you a clear price.
Is parking an issue for external mastic in Sydenham Hill?
It can be, so it helps to tell us about permits, visitor bays or off-street space when you book. That way the visit can be planned around it.
Can I do it myself?
It depends on the job. Work at height, movement joints, fire-rated gaps and large areas are best left to a professional.
How do you reach high-level joints?
That depends on how high the joints are and the ground below. Low-level joints are straightforward; for higher work, tell us about the building and we’ll confirm what’s needed.
How much does external mastic cost in Sydenham Hill?
There’s no set price, as it depends on the job: its size, the old material, access and the product needed. You will get a clear quote before work begins.
Do you seal joints where cladding meets other materials?
Yes. Different materials move at different rates, so the joint between them must be flexible. We choose one that suits both surfaces.
What is backing rod for?
Closed-cell backing rod sets the depth of the sealant and stops it sticking to the back of the joint. That way it bonds to the two sides only and can stretch.
Why is there a gap in my brick wall?
Most straight vertical gaps in brickwork are movement joints. It gives the wall room to move.
Should I try it myself first?
If you are set on DIY, put the effort into preparation: remove every trace of old sealant, clean and dry the joint, and follow the product’s cure time. If it doesn’t work out, we can still put it right.
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, and the work is guaranteed for a year.
Landlord and commercial work in Sydenham Hill
From a single let to a portfolio, you get the same standard of work: old sealant fully removed, joints prepared properly and a 12-month guarantee.
Letting agents often deal with us directly. Tell us the address, the job and how access works and we will give you a quote.