Greater London · England
External & façade joints in Greenhill, Greater London
Sealing brickwork movement joints, render, cladding and façade joints for Greenhill, backed by a one-year guarantee. Ask us for a quote.
- Brick movement joints where the sealant has split
- Moss and dirt in joints with no sealant left
- Movement joints filled with mortar instead of sealant
External mastic in Greenhill, done properly
A movement joint is a deliberate break that lets a wall expand and contract. The sealant in it has to stretch and squeeze for years, so once it splits or hardens, the joint stops working and water gets in. We’re often asked to deal with movement joints with cracked, split or missing sealant and old sealant gone brittle and cracked, across render & cladding joints, joints between brick and frames and façade panels.
Outside work in London starts with access: side passages, upper floors and where to park. For a home in Greenhill, tell us how high the joints are and how to reach the back of the building.
All our work is covered by our one-year guarantee, wherever you are in Greater London.
- Location
- Greenhill (HA1, HA3, HA2)
- Wider area
- Greater London
- Guarantee
- 12 months on all our work
- Price
- A clear quote up front
- Phone
- 0345 464 0079
- Page updated
- 26 October 2026
Questions from Greenhill
Do you work for landlords with property near Harrow-on-the-Hill station?
Yes. We work for landlords and letting agents as well as homeowners, and several properties can go on one quote. You can phone 0345 464 0079 or drop us an email with the details for a clear quote.
Is Greenhill in your area for external mastic?
Yes. We work across London and the South East, and Greenhill is part of that. You can ring 0345 464 0079 or send us an email and let us know what needs doing.
Do you use backing rod?
We fit closed-cell backing rod wherever the joint depth needs controlling. It controls the depth and stops the sealant bonding to the back, so the joint can move.
Where is Mr Mastic based?
We’re a Crawley-based firm. We work across South East England, London and Scotland.
Do you work at height?
Each building is different. Send us photos and a rough idea of the height and we’ll confirm how they can be reached safely.
What is a movement joint?
Most straight vertical gaps in brickwork are movement joints. It gives the wall room to move, and it should be sealed with a flexible sealant.
Will the old sealant be removed?
Always. Sealing over old sealant is the main reason resealing fails early, and it’s something we never do.
Will you leave a mess?
No. We protect the surfaces around the joints, and we clear up the old sealant and our materials before we leave.
Also near Greenhill
Other services in Greenhill
How the visit works
On the day, there’s very little for you to do. Show us the job and we will take it from there. The work itself takes anything from a few hours to several days, depending on the building. For a job in Greenhill, parking and access are the things to plan: let us know about parking, the floor we will be working on and any lift or shared entrance.
- We start by checking each joint, agreeing the ones to redo and how we will 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.
- Backing rod goes in next, setting the depth and keeping the sealant off the back of the joint.
- We gun in a flexible exterior sealant in a colour that suits the wall and tool it neatly.
Getting ready for the visit
- On commercial sites, let us know about site rules
- Try not to wet indoor joints just before the visit
- Let us know about stairs, lifts or work at height
Get a quote
Asking for a quote is easy: let us know the job and the location. A few photos by email make the job easier to understand, and we’ll take it from there.
Related advice
What external mastic looks like in Greenhill
With historic houses such as Headstone Manor (about 1.1 miles north-west) nearby, there’s older building stock in the area around Greenhill as well as newer homes. In older buildings, older brick and stone need a sealant that suits them, at the right joint depth. London and the South East are among the drier parts of the UK, yet outdoor joints still have to be sealed dry, so jobs are booked with the weather in mind.
Greenhill is in London, so parking needs planning: tell us about permits, visitor bays or off-street space when you book. If you look after a building such as Saint Jerome Church of England Bilingual School, its movement joints, gutters and trims need looking after like any other building’s.
Greenhill is about 1 mile north-east of Harrow, in Greater London. Jobs in Greenhill get the same care as everywhere else we work: old sealant removed completely, careful preparation and a one-year guarantee. Our area takes in 764 places across Greater London, from the larger towns to small villages. London is on our list too, around 12 miles away.
Here we cover the HA1, HA3 and HA2 postcode area for external mastic. That includes homes and businesses on Lyon Road, Hill Road and Byron Road and the roads around them. Neighbouring places we cover for external mastic include Wealdstone (1 mile north), Northwick Park (1 mile south-east), Harrow (1 mile south-west), Kenton (1 mile east) and Roxeth (1 mile south-west). Further out, we also cover London (12 miles south-east), City of Westminster (9 miles south-east), Marylebone (9 miles south-east), Kensington (8 miles south-east), St Pancras (10 miles south-east) and Shoreditch (12 miles east).
Local landmarks in Greenhill
We work in homes and buildings around Royal Oak pub, Northwick Park and Harrow High School and the streets around them. Greenhill has its own railway station: Harrow-on-the-Hill station. Other landmarks nearby include St. Anns (within half a mile south-west) and Hilfield Castle (4.8 miles north). The countryside around Greenhill includes Masons Field and Northala Fields.
Why act early in Greenhill
A low-modulus sealant is chosen because it moves without pulling hard at the edges. That matters on brick, render and concrete, which can be weaker at the face. Too stiff a sealant can pull at the edges and break them. Converted houses in London often have a bathroom above someone else’s living room, so a small leak from tired sealant can mean a neighbour’s ceiling and a lot of disruption. Dealing with it early is far simpler for homes in Greenhill.
A few things move the cost up or down: how much old sealant there is and how stubborn it is, any mould to treat, and whether the work is at height. We take all of that into account in your quote.
Why choose Mr Mastic in Greenhill
- A choice of colours where the product allows
- 180+ five-star Google reviews
- We leave the area clean and tidy
- Experience in homes, commercial sites and hotels
Take a look at our cost guide and our reviews.
Aftercare tips
Looking after new joints is easy, and it makes a real difference:
- Deal with leaking gutters that soak the joints below
- Walk round the building once a year and look at the joints
- Point out the joints to other trades
- Get split or bare joints resealed while the damage is small
Avoid pressure-washing straight into the joints. High-pressure water can lift the edges and let water in behind.
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, all bigger jobs than a reseal.
Landlords, agents and businesses in Greenhill
Businesses can book us for washrooms, kitchens, offices and more. For commercial premises, we can talk through working times when we quote.
Water getting past a failed joint can damage the building, which is a bigger problem in a rented property. Resealing at the right time is simple maintenance.
Should I try it myself first?
Some jobs are best left to a professional: high-level joints, fire-rated gaps, external movement joints and big jobs call for the right materials, safe access and experience.
A DIY attempt does not rule out a professional job. We remove it and do the joint properly.
How we quote for external mastic
Some jobs are bigger than they look, and some smaller. What affects the quote:
- Any mould that needs treating
- The size of the job
- The product the joint needs
- When we can work, for business premises
What it costs depends on the size of the job, how hard the old material is to remove and how easy the joints are to reach. You’ll have a clear quote before any work starts, so you know where you stand.
Helping us quote
The more you tell us, the more accurate the quote. When you get in contact, it helps to mention:
- A few pictures by email, if you can
- Any access issues, like height or stairs
- Any previous sealing or DIY work
- The type of property
Want a quote for external mastic? Please call 0345 464 0079 or drop us an email and tell us about the job. You will know what we plan to do, and what it will cost, before any work begins.
Signs you need external mastic in Greenhill
Every building moves. Clay bricks expand slightly over their life, concrete and block shrink, and everything moves with temperature and wet. All of that ends up in the joint sealant.
Keep an eye out for these signs:
- Moss and dirt in joints with no sealant left
- Sealant pulling away from one side of the joint
- Movement joints with cracked, split or missing sealant
- Cracked joints where brick meets render or frames
Homes close to Church of St John the Baptist include some older properties, and old and new materials meet at the roofline and walls, which is where sealant earns its keep.
What to look for in a quote
- How much experience the applicator has
- Which sealant they’ll use, and why
- How hidden problems are handled
- Which colour the sealant will be