Greater London · England
External Mastic in Blackfen
We cover Blackfen for sealing brickwork movement joints, render, cladding and façade joints. Old sealant removed completely, joints prepared properly.
- Movement joints filled with mortar instead of sealant
- Movement joints with cracked, split or missing sealant
- Old sealant gone brittle and cracked
How it works
Most of a good job is in the preparation, so that is where we spend the time. Joints are cleaned back and dried before anything new goes in. All told, the work takes a few hours to a few days, depending on the length of joint and the access. In a London area like Blackfen, the main things to plan are parking and access: tell us about permits, visitor bays or off-street space, which floor we are working on and whether there’s a lift.
- First, the joints are inspected and the access agreed.
- Every bit of old sealant and any mortar or debris is cut out.
- The faces are brushed clean and primed where the product requires it.
- We fit closed-cell backing rod to control the depth.
- We apply the sealant, tool it and check the whole run.
Preparing for the visit
- Tell us about access, such as stairs, a lift or high-level joints
- Try not to wet indoor joints just before the visit
- Plan for the work area to be out of bounds to pets and children
How to get a quote
Call for a quick quote, or send an email if you’d rather. Tell us about the joints that need doing and we will talk you through the work before giving you a price.
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External mastic in Blackfen, done properly
Low-level joints can usually be done from the ground. Where joints are higher up, tell us about the building when you get in touch and we will confirm what’s needed to reach them safely. If you have joints with sealant missing in places and joints pointed up with cement by mistake, we can help.
Working on the outside of a London home means planning access: shared paths, upper floors and parking. In Blackfen, joints up high may need ladders or other access, which is worth talking through when you book.
We stand behind the work with a 12-month guarantee, so you’re not left on your own once the job is done.
- Location
- Blackfen (DA15, DA16, SE9)
- Wider area
- Greater London
- Guarantee
- A year, on every job
- Quotes
- A clear price before work begins
- Phone
- 0345 464 0079
- Updated
- 26 October 2026
Leave it or put it right?
Sealing over the top of old mastic doesn’t hold for long. The new layer cannot bond properly to old, weathered material, so we always take the old sealant out. Damp from a failed joint spreads quietly in older London brickwork and timber, and once it shows in Blackfen, the repair is bigger than a sealant job.
The cost depends on how much there is to do, how hard the old material is to remove and access to the work. You will have a clear quote before any work starts, so you know where you stand.
Why book with us
- Arbo and Everbuild products
- Old sealant always removed completely
- 180+ five-star Google reviews
- White, clear, grey or another colour, product permitting
Different surfaces, different methods
Cladding and façade panels
Cladding and façade panels are normally separated by sealed joints. Each joint gets a sealant that suits the panel and its movement.
Copings and trims
Joints in copings, parapets and trims are exposed to the worst of the weather. Each is resealed with a weatherproof, flexible sealant.
Outside joints around Blackfen
Rainfall in the South East is lower than in much of the UK, but outside sealant still needs a dry, clean surface, so outdoor work is planned around the forecast. With historic houses such as Danson House (about 1.2 miles east) nearby, there’s older building stock in the area around Blackfen as well as newer homes. In older buildings, older walls and rooflines need a sealant that moves with them and suits the material.
If you let a flat or house near Falconwood station, split movement joints are easy to miss on a rental until damp shows inside. If you look after a building such as Our Lady of the Rosary Catholic Primary School, its movement joints, gutters and trims need looking after like any other building’s. As a London address, Blackfen can be tricky for parking: tell us about permits, visitor bays or off-street space when you book.
Blackfen is about 2 miles east of Eltham, in Greater London. Our applicators cover external mastic for homeowners, landlords and businesses in Blackfen and nearby, as part of our work across Greater London. We cover 764 towns and villages across Greater London, large and small. London is on our list too, about 9 miles from Blackfen.
Work in DA15, DA16 and SE9 is quoted and booked the same way as anywhere else. Local streets include Days Lane, Gordon Road and Kent Avenue. Nearby, we also carry out external mastic in Falconwood (1 mile north), Avery Hill (1 mile west), East Wickham (1 mile north), New Eltham (1 mile south-west) and Longlands (1 mile south). Within a short drive, we also cover London (9 miles north-west), City of Westminster (11 miles north-west), Marylebone (11 miles north-west), Kensington (13 miles west), St Pancras (10 miles north-west) and Shoreditch (9 miles north-west).
Landmarks near Blackfen
We work in homes and buildings around The George Staples pub, Harris Academy Falconwood and Shoulder of Mutton Green and the streets around them. The nearest railway station is Falconwood station, roughly 0.8 miles north-west. Well-known places in the area include Broadway Shopping Centre (2.3 miles east) and Eltham Community Hospital (1.7 miles west). Open spaces near Blackfen include Summer Hill and The Tarn.
When it isn’t the sealant
We’ll always be straight with you, so here’s what new sealant will not do:
- Cracked brickwork or render that needs a builder or plasterer
- Damp from another source, such as a leaking gutter or a bridged damp-proof course
- Failed render or damaged cladding panels
If you are not sure, just call 0345 464 0079 or drop us an email and we’ll give you a straight answer.
Where we work in Blackfen
- Render & cladding joints
- Brickwork movement joints
- Joints between brick and frames
- Façade panels
- Concrete & block
- Copings & trims
Towns and villages near Blackfen
More services for Blackfen
Should I try it myself first?
The difference is mostly in the preparation and the product. We take joints back to clean, dry surfaces, and the sealant is chosen for how the joint moves and where it is.
The biggest DIY mistake is sealing over old sealant. New silicone will not bond to old, so it lifts and traps water and mould underneath. Everything old must be removed first.
Landlords, agents and businesses in Blackfen
Hotels need rooms back in use, so we plan the work room by room around your bookings where we can. We have worked in hotels as well as homes and businesses.
From a single let to a portfolio, the work is the same standard: old sealant fully removed, joints prepared properly and a 12-month guarantee.
Looking after it afterwards
Joint life depends on how it’s used and looked after. We suggest:
- Get split or bare joints resealed while the damage is small
- Deal with leaking gutters that soak the joints below
- Do not let climbing plants root in the sealant
- Leave the joints unpainted unless we have said otherwise
Avoid pressure-washing straight into the joints. A strong jet can damage the edges of the bead.
A joint that has stopped moving pushes the movement elsewhere, usually as cracking in the brickwork or render nearby. Resealing it early helps prevent that.
Blackfen: your questions answered
Do you cover Blackfen for external mastic?
Yes. We work across London and the South East, and Blackfen is part of that. Just phone 0345 464 0079 or email us with a few details of the job, and we will give you a clear quote.
Can you help a landlord with a rental near Falconwood station?
Yes. We work for landlords and agents as well as householders, and several properties can be quoted together. You can ring 0345 464 0079 or email us with the details for a clear quote.
What do you put in the joint?
It depends on the joint: sanitary silicone where it gets wet, and sealants suited to movement or weather elsewhere. We use products from Arbo and Everbuild.
What is backing rod for?
Backing rod goes into deeper joints as a matter of course. It sets the sealant depth and prevents three-sided bonding.
Do you take out the old sealant first?
Yes, always, and completely. New silicone doesn’t stick to old silicone, so the joint is cleaned back first.
Can you match the colour of my brickwork?
The aim is a neat, even joint in a colour that suits the wall. We’ll talk through colour options before we start from the range available.
How long does external mastic take?
It depends on the size of the job, but as a guide it takes a few hours for a handful of joints, longer for a whole elevation. We’ll tell you when we quote.
What information do you need?
Where the job is, what the problem is and roughly how big it is. Photos by email help too.