Greater London · England
External & façade joints in Harefield, Greater London
External mastic in Harefield from a team with over 20 years’ experience. 180+ five-star Google reviews and a 4.9 rating.
- Sealant that has lost its bond to the brick or render
- Damp patches traced to an open external joint
- Movement joints filled with mortar instead of sealant
Your questions about external mastic in Harefield
Do you work for landlords with property near Denham station?
Yes, landlords and agents are among the people we work for. You can call 07833 053749 or email us with the details for a clear quote.
Is parking a problem for a job in Harefield?
London parking needs a little planning, so let us know about permits, bays or a driveway when you book. That way the visit can be planned around it.
Where is Mr Mastic based?
We work from Crawley. Our applicators cover Harefield.
What is a movement joint?
Walls move with heat, cold and moisture, so long walls have planned gaps to take that movement. It’s closed with backing rod and a flexible sealant.
Can I do it myself?
Some simple jobs can be done by a careful DIYer. The usual mistakes are sealing over old sealant, sealing a damp joint and using too much.
How much does external mastic cost in Harefield?
We don’t publish prices, because the cost depends on the job: its size, the old material, access and the product needed. We agree the price before any work begins.
How long does external mastic last?
There’s no fixed answer: sunny, exposed elevations and busy joints wear faster. Check them each year and reseal when they split or harden. Every job carries our 12-month guarantee.
Do you do commercial work?
Yes. Larger jobs can be planned room by room or area by area.
About our external mastic in Harefield
Failed sealant is cut out, the depth set with closed-cell backing rod, and the joint resealed with a low-modulus sealant made for outside. We pick a colour that sits well with the wall. We work on joints between brick and frames, concrete & block and render & cladding joints, and the jobs we see most are sealant pulling away from one side of the joint and hard, crazed mastic that has stopped moving. Need a sealant company near Harefield? That is us.
In London terraces and converted houses, gutters and walls are often shared with the house next door, so a leaking gutter joint or failed wall joint can affect more than one home. For a flat in Harefield, check the lease for who looks after the outside.
The work is guaranteed for twelve months. If there’s a problem with our work within the year, let us know and we will sort it.
- Location
- Harefield (UB9)
- Wider area
- Greater London
- Guarantee
- 12 months on all our work
- Price
- A clear quote up front
- Call
- 07833 053749
- Last updated
- 26 October 2026
Towns and villages near Harefield
What else we do in Harefield
Why deal with it now?
A low-modulus sealant is chosen because it moves without pulling hard at the edges. That protects surfaces like brick, render and concrete. A stiffer product can damage the joint edge as it fails. 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 Harefield.
Some things make a job bigger or smaller: the old material and how easily it comes out, any mould to treat, and whether the work is at height. We take all of that into account in your quote.
What you get with us
- Old sealant always removed completely
- More than 20 years in sealant work
- You choose the colour before work begins
- We leave the area clean and tidy
How the visit works
You don’t need to clear the whole room or building before we come, just the space around the work. We protect the rest, and the work takes a few hours for a handful of joints, longer for a whole elevation in most cases. In a London area like Harefield, the main things to plan are parking and access: let us know about parking, the floor we’ll be working on and any lift or shared entrance.
- 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.
- Both sides are cleaned back to sound material and primed if needed.
- 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.
Preparing for the visit
- Let us know if you’ve seen damp or leaks
- Keep children and pets away from the work area
- For indoor joints, keep the area dry beforehand if you can
Get a quote
A good description makes for an accurate quote. Let us know the location, the problem and roughly how many joints, and email photos if that is easy.
Related advice
Harefield buildings and the weather
London terraces and converted houses often share gutters, downpipes and walls, so check who is responsible for the outside before booking. With historic houses such as Ickenham Hall (about 3.4 miles south-east) nearby, there’s older building stock in the area around Harefield as well as newer homes. Where a home is older, older walls and rooflines need a sealant that moves with them and suits the material.
If you live in an older home near Harefield Baptist Church, old and new materials meet at the roofline and walls, which is where sealant earns its keep. For landlords with property near Denham station, failed wall and movement joints let damp in, so they’re worth checking between tenancies.
Harefield is about 3 miles south of Rickmansworth, in Greater London. We provide external mastic to homeowners, landlords and businesses in Harefield and the surrounding area, as part of our work across Greater London. 786 places in Greater London are on our list, large and small.
Our applicators cover all of the UB9 postcode area for external mastic. Streets in the area include High Street, Vernon Drive and New Park Road, and we cover them all. If you’re just outside Harefield, we cover Hill End (1 mile north), Woodcock Hill (1 mile north-east), Batchworth Heath (2 miles north-east), Batchworth (2 miles north-east) and Mill End (2 miles north). Larger places within reach include City of Westminster (15 miles south-east), Kensington (14 miles south-east), Hampstead (13 miles east), Ruislip (4 miles south-east), Ealing (10 miles south-east) and Hayes (7 miles south-east).
Near you in Harefield
Locally, jobs take us to homes and businesses close to The King's Arms Public House, The Green and The Harefield Academy. Harefield’s nearest station is Denham station, roughly 2 miles south of the centre. Other landmarks nearby include Chiltern Open Air Museum (3.4 miles north-west) and Harefield Hospital (less than half a mile north-west). Not far away are Dews Farm Sand Pits and Horse Shoe Bay.
Work for landlords, hotels and businesses
Landlords and agents in Harefield can book us as well as householders. Resealing between tenancies keeps a property looking cared for.
Housing providers, facilities teams and property managers book us too in Harefield and across Greater London. We can quote a run of properties together.
Quotes for external mastic in Harefield
The price is agreed before any work begins. It’s based on:
- How many rooms, windows or areas are involved
- Whether the work is at height
- Which sealant suits the joint
- Mould in or behind the old joints
Doing several joints on one visit is normally more efficient than separate visits, so tell us about everything that needs sealing. You’ll get one clear quote for the whole job.
What to tell us for a quote
What to tell us when you ask for a quote:
- The address or postcode of the job
- Photos by email, if that’s easy
- Any access issues, like height or stairs
- The problem you’ve noticed
Need a quote? Please call 07833 053749 or send us an email and tell us about the job. We’ll explain what we’d do and give you a clear price before we start.
Surface by surface
Brickwork movement joints
Vertical joints in long brick walls let the brickwork expand without cracking. We reseal them with a low-modulus sealant over backing rod.
Concrete and blockwork
Wide joints in concrete need the depth controlling carefully. We size the backing rod to the gap so the sealant isn’t too deep.
What sealant work cannot fix
It helps to know what we can’t do too:
- Cutting new joints into brickwork, which is building work rather than sealant work
- Cracking across the wall rather than at a joint
- Rising or penetrating damp from elsewhere in the wall
If you’re not sure, just ring 07833 053749 or drop us an email and we will give you a straight answer.
Where we work in Harefield
- Brickwork movement joints
- Joints between brick and frames
- Copings & trims
- Concrete & block
- Render & cladding joints
- Façade panels
Common problems we fix in Harefield
Weeds, moss and debris in a joint are a sign the sealant has gone. Roots and dirt hold water against the wall and speed up the damage.
Keep an eye out for any of the following:
- Failed sealant between panels on a façade
- Cracked joints where brick meets render or frames
- Joints with sealant missing in places
- Rain getting behind render or cladding at a joint
For site and facilities teams at buildings such as Harefield Infant School, larger buildings have long runs of movement joint that eventually need resealing.
Comparing quotes
- How much experience the applicator has
- How hidden problems are handled
- What the cure time is
- Which colour the sealant will be