Greater London · England
North Harrow External Mastic
Problem with your movement joints in North Harrow? We cut out the old, prepare the joints and apply the right sealant, with a one-year guarantee.
- Cracked joints where brick meets render or frames
- Rigid filler in a joint that should flex
- Sealant that has lost its bond to the brick or render
About our external mastic in North Harrow
Low-level joints can usually be done from the ground. For joints higher up, give us some details of the building and we’ll confirm what access is needed. We work on concrete & block, copings & trims and façade panels, and the jobs we see most are rain getting behind render or cladding at a joint and sealant pulling away from one side of the joint.
London’s terraces and conversions often share walls, gutters and downpipes with their neighbours, so a leaking gutter joint or failed wall joint can affect more than one home. In a converted house in North Harrow, it’s worth checking who is responsible for the outside before booking.
There’s a 12-month guarantee on every job, large or small.
- Where
- North Harrow (HA2, HA1, HA5)
- Region
- Greater London
- Cover
- 12 months on all our work
- Quotes
- A clear price before we start
- Call
- 0345 464 0079
- Page updated
- 26 October 2026
What affects the quote in North Harrow
We quote each job individually. These are the things that affect it:
- How many areas need sealing
- The product the joint needs
- Whether old sealant or filler has to be cut out
- The size of the job
No two jobs are quite the same, so each one gets its own quote. The number of joints, how easy they are to reach and the sealant needed all play a part, and we will explain the quote if you ask.
What to tell us for a quote
To make quoting easier, please include:
- A few pictures by email, if you can
- What the problem is, such as mould, gaps, leaks or cracking
- Whether it has been sealed before
- The address or postcode of the job
For a quote, ring 0345 464 0079 or send us an email and tell us where the job is and what the problem looks like. We will give you a clear quote before any work starts.
Why act early in North Harrow
Running new sealant over the old bead rarely lasts. 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 North Harrow, the repair is bigger than a sealant job.
Homes and businesses are quoted the same way: the amount of work, how we reach it and what it needs, along with when we can work on site. Ask us for a quote and we’ll explain what it covers.
Why choose Mr Mastic in North Harrow
- Homes, businesses and hotels
- Anti-fungal silicone where joints get wet
- You choose the colour before work begins
- More than 20 years in sealant work
Read our cost guide and our reviews.
What we can’t put right
We won’t take on work that won’t last, so here’s what sealant can’t put right:
- Adding movement joints to masonry that has none
- Subsidence or other structural problems
- Damp that is not coming from the joint
If you are not sure, just phone 0345 464 0079 or email us and we will give you a straight answer before you book.
Where we work in North Harrow
- Brickwork movement joints
- Joints between brick and frames
- Copings & trims
- Façade panels
- Render & cladding joints
- Concrete & block
North Harrow buildings and the weather
Compared with the north and west, the South East gets less rain, though outdoor sealant still has to go onto a dry joint, so the forecast decides the day. London terraces and converted houses often share gutters, downpipes and walls, so it’s worth agreeing who is responsible before work starts.
Homes close to Church of St Alban include some older properties, and the joints between older walls, newer extensions and the roofline need a sealant that can move. Managing a site like Longfield Primary School? Then its movement joints, gutters and trims need looking after like any other building’s. North Harrow is in London, so parking needs planning: let us know about parking bays, permits or a driveway.
North Harrow is about 1 mile north-west of Harrow, in Greater London. Across the HA2 area, our applicators can take on external mastic. North Harrow is one of 764 towns and villages in Greater London where we work for external mastic. London is on our list too, around 13 miles away.
We cover every part of the HA2, HA1 and HA5 postcode area for external mastic. Local streets include The Avenue, Pinner Road and Durham Road. We also cover the places around North Harrow: Rayners Lane (1 mile south-west), Harrow (1 mile south-east), Roxbourne (1 mile south-west), Eastcote (1 mile west) and Greenhill (1 mile east). Further out, we also cover London (13 miles south-east), City of Westminster (10 miles south-east), Marylebone (10 miles south-east), Kensington (9 miles south-east), St Pancras (11 miles east) and Shoreditch (13 miles east).
Local landmarks in North Harrow
Around North Harrow, our work takes us to homes and buildings near Nower Hill High School, Heathfield School and Headstone Manor Recreation Ground. North Harrow’s nearest station is Harrow-on-the-Hill station, roughly 1.2 miles east of the centre. A little further out are St. George's Shopping Centre (1 mile east) and Hilfield Castle (5 miles north). Not far away are Northala Fields and Islip Manor Meadows.
North Harrow questions
Do you work for landlords with property near Harrow-on-the-Hill station?
Yes. We work for letting agents and landlords as well as householders. You can ring 0345 464 0079 or drop us an email with the details for a clear quote.
Can parking be tricky for a visit in North Harrow?
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.
Do you work in North Harrow?
Yes. We work in North Harrow and the rest of Greater London. To book, phone 0345 464 0079 or email us.
How do I get a quote for external mastic in North Harrow?
It depends on the job, so we quote each one individually. To get one, call 0345 464 0079 or send us an email with a short description of the job.
How long will you be here?
It depends on the size of the job, but as a guide it takes anything from a few hours to several days, depending on the building. We’ll give you a better idea when we quote.
What information do you need?
A short description and the location, plus photos if you have them. If we need more, we’ll ask.
Why do you put foam in the joint first?
That is backing rod, a closed-cell foam. It keeps the sealant at the right depth and bonded to the sides only, which would stop it stretching.
Should I point up the gap in my brickwork?
No, not where the gap is a movement joint. Pointing it stops it working, and the wall may crack nearby. We will reseal it with a flexible sealant.
Looking after it afterwards
Aftercare is simple, and it makes a real difference:
- Make sure movement joints aren’t pointed over
- Tell anyone working on the walls about the movement joints
- Get split or bare joints resealed while the damage is small
- Walk round the building once a year and look at the joints
Only paint over the joint if we’ve confirmed the sealant can take paint. Many exterior sealants are not designed to be painted.
Small splits are the time to act. At that stage it’s a simple cut out and reseal.
What the job involves on each surface
Joints between dissimilar materials
Each side of the joint may need its own preparation. Both surfaces are cleaned and primed as the product requires.
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.
How the visit works
There is not much for you to do on the day. Show us the job and we will take it from there. The job generally takes anything from a few hours to several days, depending on the building from start to finish. In a London area like North Harrow, 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 inspect the joints and agree which need resealing and how they’ll be reached.
- The old mastic and anything lodged in the joint is removed.
- The joint faces are cleaned and primed where the sealant needs it.
- We push in closed-cell backing rod so the sealant is the right depth and bonds to the sides only.
- The new sealant, chosen to suit the brick or render, is applied and tooled to a neat finish.
Getting ready for the visit
- For indoor joints, keep the area dry beforehand if you can
- Move anything stored near the joints
- Mention any tricky access
Get a quote
We don’t publish a price list, as no two jobs are quite the same. Instead, we give you a clear quote for your job. To arrange one, phone 0345 464 0079 or drop us an email.
Read more
DIY sealant or a professional job?
Overfilling a joint is a classic DIY mistake. A heavy bead looks messy and copes badly with movement, and the joint depth matters as much as the finish.
Some jobs are best left to a professional: work at height, external movement joints, fire-rated sealant and large areas call for the right materials, safe access and experience.