Hertfordshire · England
London Colney External Mastic
Movement joints in London Colney need attention? We cut out the old, prepare the joints and apply the right sealant.
- Failed sealant between panels on a façade
- Old sealant gone brittle and cracked
- Movement joints filled with mortar instead of sealant
Why deal with it now?
Pointing a movement joint with mortar might seem a neat fix, but it locks the joint solid. The wall then cracks somewhere else. The correct repair is a flexible sealant with the right backing. Homes in smaller places like London Colney can face more weather, and failed outside joints let damp into walls. Inside, a split seal lets water into floors and panels just as it would anywhere.
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 make a difference, and we will explain the quote if you ask.
Why choose Mr Mastic in London Colney
- ARBOMaster approved applicator
- Colour agreed with you before work begins
- Every job guaranteed for a year
- We leave the area clean and tidy
See our cost guide or our reviews.
External mastic in London Colney, done properly
As ARBOMaster approved applicators, we choose exterior sealants to suit the joint and the surfaces. Some surfaces need a primer before sealing and we use one wherever it does. If you have brick movement joints where the sealant has split and moss and dirt in joints with no sealant left, we can help.
In and around London Colney, older properties sit alongside newer ones, each with its own outside joints. Older homes need their gutter and trim joints kept tight, newer ones their movement joints.
The work is covered for a year after we finish. If anything isn’t right with it, phone 0345 464 0079 or email us.
- Where
- London Colney (AL2, AL1)
- Region
- Hertfordshire
- Cover
- A year, on every job
- Quote
- A clear price before work begins
- Telephone
- 0345 464 0079
- Updated
- 26 October 2026
Walls and rooflines in London Colney
Compared with the north and west, the South East gets less rain, but outside sealant still needs a dry, clean surface, so outdoor work is planned around the forecast. Historic houses like Batchwood Hall (about 3.9 miles north-west) are a reminder that the area around London Colney has older buildings as well as new. Where a home is older, older walls and rooflines need a sealant that moves with them and suits the material.
Schools such as Bowmansgreen Primary School are buildings too, and larger buildings have long runs of movement joint that eventually need resealing. For an older house near a landmark such as Church of St Peter, old and new materials meet at the roofline and walls, which is where sealant earns its keep.
London Colney is about 2 miles south-east of St Albans, in Hertfordshire. We carry out external mastic for homeowners, landlords and businesses in London Colney and the surrounding area, as part of our work across Hertfordshire. London Colney is one of 381 towns and villages in Hertfordshire where we work. London is on our list too, around 18 miles away.
All of AL2 and AL1 is within our area for external mastic. We cover properties on High Street, London Road and Haseldine Road and the roads around them. Other places close to London Colney include Broad Colney (1 mile south), Tyttenhanger (1 mile north), Shenleybury (1 mile south), Sleapshyde (2 miles north-east) and Colney Heath (2 miles north-east). Further out, we also cover Watford (6 miles south-west), Hemel Hempstead (7 miles west), Stevenage (14 miles north), Welwyn Garden City (7 miles north-east), Harpenden (7 miles north) and Hoddesdon (12 miles east).
Local landmarks in London Colney
Typical jobs here are in homes near White Horse pub, Highfield Park and Samuel Ryder Academy, among other places. The nearest railway station is Park Street station, about 1.9 miles west. A little further out are Napsbury Hospital (0.5 miles west) and St Albans Musical Museum (2.6 miles north-west). Open spaces near London Colney include Verulamium Lake and Broad Colney Lakes.
Landlords, agents and businesses in London Colney
Letting agents often deal with us directly. Send the address, what’s needed and the access arrangements.
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 that we can handle for you.
Places near London Colney
Other services in London Colney
Common problems we fix in London Colney
Many joints fail because they were sealed too deep or with nothing behind them. 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 most common problems we see are:
- Brick movement joints where the sealant has split
- Old sealant gone brittle and cracked
- Damp patches traced to an open external joint
- Leaking joints around cladding and façade panels
For landlords with property near Park Street station, split movement joints are easy to miss on a rental until damp shows inside.
Before booking anyone
- Whether all the old sealant comes out first
- How much experience the applicator has
- Which sealant they’ll use, and why
- How hidden problems are handled
How it works
All our tools and materials come with us in the van. After a quick look at the joints together, the area is protected and the work begins. Most jobs take a few hours to a few days, depending on the length of joint and the access. A visit to London Colney is planned like any other: the time, the access and where to park are agreed in advance. If the work is outside, the weather plays a part, as sealant needs a dry surface.
- 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.
- Both sides are cleaned back to sound material and primed if needed.
- We push in closed-cell backing rod so the sealant is the right depth and bonds to the sides only.
- A flexible exterior sealant is applied and tooled in a colour to suit the wall.
How to prepare
- Mention any leaks or damp you’ve noticed
- Clear items away from the joints we’re working on
- On commercial sites, let us know about site rules
How to get a quote
A good description makes for an accurate quote. Let us know the location, the problem and roughly how many joints.
Read more
London Colney questions
Do you cover London Colney for external mastic?
Yes. We work across London and the South East, and London Colney is part of that. You can phone 0345 464 0079 or send us an email and let us know what needs doing, and we’ll send you a clear quote.
Do you work for landlords with property near Park Street station?
Yes, landlords and agents are among the people we work for, and several properties can go on one quote. Just phone 0345 464 0079 or drop us an email with the address and what needs doing, and we will send you a clear quote.
How long should I leave it?
It depends on the product. We tell you how long to leave it before we go.
Do you work for hotels and businesses?
Yes, regularly. We can plan bigger jobs in stages.
Do you guarantee your work?
Yes. There’s a 12-month guarantee on every job, large or small.
Do you work at height?
It depends on the building. We work on joints that can be reached safely. Tell us about the building and we will confirm what access is needed.
Are you an approved applicator?
Yes. Mr Mastic is an ARBOMaster approved applicator and we’re fully insured too.
Can a movement joint be filled with mortar?
No. Mortar locks the joint solid, so the movement cracks the wall elsewhere. It needs a flexible sealant over backing rod.
What the job involves on each surface
Brickwork movement joints
People sometimes point up a brick movement joint by mistake. Where one has been mortared, we cut it out and reseal it with sealant.
Joints between dissimilar materials
Where a frame or panel meets masonry, water often finds a way in. We cut out the old sealant and reseal with a product suited to both surfaces.
DIY versus a professional finish
What a professional job adds is preparation and the right product. Joints are cleaned back to sound surfaces and dried, and the sealant is chosen for how the joint moves and where it is.
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.
Aftercare tips
Looking after new joints is easy, and it makes a real difference:
- Have failed joints looked at early
- Look over the joints every year, ideally after winter
- Clear growth from the base of walls and joints
- Leave the joints unpainted unless we have said otherwise
Don’t paint over the new sealant unless we’ve said the product is paintable. Many exterior sealants aren’t designed to be painted.
Leave a failed movement joint and water keeps getting into the wall. That can lead to damp patches, staining and frost damage.