Greater London · England
New Barnet External Mastic
Problem with your movement joints in New Barnet? We remove the old material, prepare the joints and seal them properly, and the work is guaranteed for a year.
- Weeds or debris growing in open joints
- Sealant pulling away from one side of the joint
- Water getting into walls through failed joints
What we are called out for in New Barnet
Joints sealed without backing rod, or far too deep, rarely last. If the sealant sticks to the back as well as the sides, it can’t stretch and tears as soon as the joint widens.
The problems people usually mention when they call are:
- Movement joints filled with mortar instead of sealant
- Brick movement joints where the sealant has split
- Old sealant gone brittle and cracked
- Failed seals between different materials
New Barnet is in London, so parking needs planning: tell us about permits, visitor bays or off-street space when you book.
Questions to ask before you book
- How long to leave it before use
- Whether you can choose the colour
- Whether they’re fully insured
- Whether all the old sealant comes out first
External mastic in New Barnet
Short cuts in external joints show up within a season or two. New sealant over old, joints packed with mortar and beads with no backing rarely last long. We take the old material out and do it properly. If you have joints with sealant missing in places and weathered mastic that no longer stretches, we can help, on copings & trims, concrete & block and façade panels alike.
Newer London blocks are built with movement joints in brick and render, and with cladding joints sealed with mastic. Older terraces have their own weak points: gutter joints, roofline trims and the joint where an extension meets the original wall, and both kinds of building are found across London.
A 12-month guarantee comes as standard, so you’re covered after we have gone.
- Location
- New Barnet (EN5, EN4, N20)
- Region
- Greater London
- Cover
- A year, on every job
- Quote
- A clear price before any work starts
- Call
- 0345 464 0079
- Last updated
- 26 October 2026
What happens if it’s left?
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 London conversions, one flat’s bathroom is often above another flat’s ceiling, so a small leak from tired sealant can mean a neighbour’s ceiling and a lot of disruption. Putting it right early is much less trouble.
What it costs depends on the size of the job, how much old material has to come out and access to the work. You’ll have a clear quote before any work starts, so you know where you stand.
Why choose Mr Mastic in New Barnet
- A choice of colours where the product allows
- Anti-fungal silicone where joints get wet
- An ARBOMaster approved applicator
- Over 20 years’ experience
Take a look at our cost guide and customer reviews.
What affects the cost of external mastic
Some jobs are bigger than they look, and some smaller. What affects the quote:
- Whether there’s mould to deal with
- How much old sealant there is and how hard it is to remove
- Working hours on commercial sites
- How easy the joints are to reach
What you pay reflects the work, not a rough estimate. That is why we ask about the job first and give you a clear quote before work begins.
What to tell us for a quote
A few details help us give you an accurate quote. When you get in contact, it helps to mention:
- How we’d reach the joints
- The type of property
- What the problem is, such as mould, gaps, leaks or cracking
- Roughly how big the job is
A good description makes for an accurate quote. Tell us where the job is, what’s wrong and how much there is, and add photos by email if you can.
Also near New Barnet
What else we do in New Barnet
DIY versus a professional finish
The biggest DIY mistake is sealing over old sealant. Silicone does not stick to old silicone, so it lifts and traps water and mould underneath. All the old material has to come out first.
A DIY attempt doesn’t rule out a professional job. We cut it out and start again, so tell us about it when you ask for a quote.
New Barnet buildings and the weather
In terraces and conversions, gutters and walls are often shared with the neighbours, so it’s worth agreeing who is responsible before work starts. Historic houses like Wyllyotts Manor (about 3.8 miles north) are a reminder that the area around New Barnet has older buildings as well as new. In older buildings, older brick and stone need a sealant that suits them, at the right joint depth.
Homes close to Holy Trinity Lyonsdown include some older properties, and old and new materials meet at the roofline and walls, which is where sealant earns its keep. Rented homes near New Barnet station change hands often, and split movement joints are easy to miss on a rental until damp shows inside.
New Barnet is about 1 mile east of Barnet, in Greater London. From the centre of New Barnet to the outskirts, external mastic is available for homes and businesses alike, from flats and houses to offices and hotels. New Barnet is one of 764 places in Greater London where we work for external mastic. We also work in London, about 11 miles from New Barnet.
Here we cover the EN5, EN4 and N20 postcode area for external mastic. Streets in the area include York Road, Park Road and Henry Road, and we cover them all. If you are just outside New Barnet, we cover Barnet (1 mile west), Cockfosters (1 mile north-east), East Barnet (1 mile south-east), Underhill (1 mile west) and Whetstone (1 mile south). Larger places within reach include London (11 miles south), City of Westminster (9 miles south), Marylebone (9 miles south), Kensington (10 miles south), St Pancras (8 miles south) and Shoreditch (9 miles south-east).
Local landmarks in New Barnet
In New Barnet, that means homes and buildings near Trent School Cockfosters, East Barnet School and The Alexandra pub. There’s a railway station in New Barnet itself: New Barnet station. A little further out are Spires Shopping Centre (1.6 miles north-west) and Francis Skaryna Belarusian Library and Museum (2 miles south). Green spaces nearby include Greenhill Gardens and Darland's Lake.
What sealant work can’t fix
We won’t take on work that won’t last, so these are the limits:
- Adding movement joints to masonry that has none
- Movement that’s more than a sealant joint can take
- Rising or penetrating damp from elsewhere in the wall
Not sure which it is? You can phone 0345 464 0079 or send us an email and we will tell you honestly.
Surfaces we seal
- Render & cladding joints
- Concrete & block
- Façade panels
- Joints between brick and frames
- Brickwork movement joints
- Copings & trims
Aftercare tips
Once the sealant has cured, a few habits help it last:
- Ask before painting over external sealant
- Make sure movement joints aren’t pointed over
- Don’t let climbing plants root in the sealant
- Have failed joints looked at early
Keep pressure washers away from the sealant. High-pressure water can lift the edges.
Leave a failed movement joint and water keeps getting into the wall. Over time it can mean damp inside, stained render or frost-damaged brick which cost more to put right than the joint.
How it works
On the day, there’s very little for you to do. Show us the job and we’ll take it from there. The work itself takes a few hours for a handful of joints, longer for a whole elevation, including the tidy-up. For a job in New Barnet, parking and access are the things to plan: let us know about parking, the floor we’ll be working on and any lift or shared entrance.
- First we look over the joints with you, agree which to renew and talk through access.
- 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.
- Closed-cell backing rod is fitted to set the depth and stop three-sided bonding.
- A flexible exterior sealant is applied and tooled in a colour to suit the wall.
Preparing for the visit
- Mention if the joints have been sealed before
- Keep children and pets away from the work area
- Clear items away from the joints we’re working on
Get a quote
We don’t publish a price list, as no two jobs are quite the same. Instead, we give you a clear price for your job. To arrange one, phone 0345 464 0079 or email us.
Related advice
Common questions in New Barnet
Is parking an issue for external mastic in New Barnet?
Parking in New Barnet, as in most of London, takes a little planning: a visitor permit or a nearby bay makes the day run more smoothly.
Can you do external mastic in New Barnet?
Yes, New Barnet is within the area we cover. Our work covers London and the South East. You can ring 0345 464 0079 or email us and tell us what needs doing, and we will send you a clear quote.
How long does external mastic take?
A typical job takes a few hours to a few days, depending on the length of joint and the access. We’ll confirm how long when we quote.
What do you put in the joint?
Products from Arbo and Everbuild, among others, picked for each joint. We’ll tell you what we are using and why.
Do you work for letting agents?
Yes, often. We can quote for several properties at once.
How long should I leave it?
That depends on the sealant used, so follow the cure time we give you.
Is it OK to fill a movement joint with cement?
No, not if it’s a movement joint. Filling it with mortar defeats its purpose, and the wall may crack nearby. A flexible sealant is the right fill.
Can you quote for more than one area?
Of course. Doing several areas at once is generally more efficient, so mention them when you ask for a quote.