Kent · England
Knockholt External Mastic
Specialist external mastic for Knockholt: careful preparation, the right product and tidy work. Call for a quick quote.
- Plants rooting in failed movement joints
- Failed sealant between panels on a façade
- Joints where the bead has come unstuck
About our external mastic in Knockholt
On houses, flats and commercial buildings across Knockholt, we reseal joints in brickwork, render, cladding and façade panels. The preparation is the same whatever the wall: clean joint faces and the right depth. If you are dealing with old sealant gone brittle and cracked and joints pointed up with cement by mistake, we can put it right.
Outside joints can only be sealed when they’re dry, so work in Knockholt is booked around the forecast. Tell us about access to all sides of the building, including outbuildings and garages.
We guarantee the work for a year. If something isn’t right with it in that time, tell us and we’ll put it right.
- Place
- Knockholt (TN14)
- Wider area
- Kent
- Cover
- A year, on every job
- Quotes
- A clear quote up front
- Phone
- 0345 464 0079
- Last updated
- 26 October 2026
How the job changes by surface
Concrete and blockwork
Concrete faces can be dusty and porous, so cleaning and priming matter. We prime where the sealant needs it before sealing.
Joints between dissimilar materials
Different materials may need different primers. We prepare both faces so the sealant bonds properly.
FAQs for Knockholt
Is Knockholt in your area for external mastic?
Yes, Knockholt is within the area we cover. We work across London and the South East. Just ring 0345 464 0079 or drop us an email with a few details of the job, and we’ll give you a clear price.
Is Knockholt within the area you cover?
Yes. Knockholt is within the area we cover, which takes in towns, villages and rural addresses. We work across London and the South East. Just mention lanes, gates or anything else about the route when you book.
Do you have insurance?
Yes. Full insurance covers our work.
How long does external mastic take?
That depends on the amount of work, but as a guide it takes a few hours to a few days, depending on the length of joint and the access. We will tell you when we quote.
Is it worth trying it myself?
For a simple, easy-to-reach joint, a careful DIYer can do a reasonable job. Most DIY failures come from sealing over old material, wet joints or too much sealant.
Where do you work from?
Our base is in Crawley, and we work across South East England, London and Scotland.
What sealant do you use?
It depends on the joint: anti-fungal sanitary silicone in wet areas, and other sealants where joints move or face the weather. Brands we use include Arbo and Everbuild.
Can you do several jobs on one visit?
Yes. Several rooms, windows or areas can go on one quote.
Work for landlords, hotels and businesses
From a single let to a portfolio, you get the same standard of work: old sealant fully removed, joints prepared properly and a 12-month guarantee.
We also work for property managers and facilities teams. We can quote a run of properties together.
What sealant work can’t fix
We’d rather tell you now than do work that will not last, so these are the limits:
- Loose or hollow render, which needs re-rendering
- Structural movement, which needs a surveyor or engineer
- Damp from another source, such as a leaking gutter or a bridged damp-proof course
If in doubt, phone 0345 464 0079 or send us an email and we’ll say what we think before you book.
Joints and surfaces we work on
- Concrete & block
- Render & cladding joints
- Brickwork movement joints
- Façade panels
- Copings & trims
- Joints between brick and frames
Walls and rooflines in Knockholt
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. Historic houses like Down House (about 2.7 miles north-west) are a reminder that the area around Knockholt has older buildings as well as new. Where a home is older, older brick and stone need a sealant that suits them, at the right joint depth.
Rented homes near Knockholt station change hands often, and outside joints that have cracked can let damp into a rental, so check them between lets.
Knockholt is about 4 miles north-west of Sevenoaks, in Kent. From the centre of Knockholt to the outskirts, we cover external mastic for every kind of property, from flats and houses to offices and hotels. Our Kent coverage runs to 922 places, and Knockholt is one of them. For nearby work, see our London page (16 miles or so).
We work across the TN14 postcode area for external mastic. Whether your property is on Main Road and Blueberry Lane or a nearby road, our applicators can take on the job. If you’re just outside Knockholt, we cover Knockholt Pound (1 mile north-east), Halstead (2 miles north-east), Sepham Heath (2 miles north-east), Pratt's Bottom (2 miles north) and Twitton (3 miles east). Larger places within reach include Dartford (11 miles north-east), Sevenoaks (4 miles south-east), Royal Tunbridge Wells (14 miles south-east), Gravesend (14 miles north-east), Tonbridge (11 miles south-east) and Northfleet (13 miles north-east).
What’s near Knockholt
Around Knockholt, our work takes us to homes and buildings near The Three Horseshoes pub. For rail, the closest station is Knockholt station, roughly 2.7 miles north-east of the centre. A little further out are Orpington Hospital (3.6 miles north) and Otford Heritage Centre (3.9 miles east). Green spaces nearby include Betsom's Hill and Downe Bank.
Why act early in Knockholt
An open joint keeps letting water into the wall with every downpour. Wet masonry is more easily damaged by frost around the joint, so the damage spreads beyond the joint. In a small place like Knockholt, homes can be exposed to wind and rain, which finds any gap, and older walls, once damp, take a long time to dry.
Rather than a set price list, we price the job in front of us: how many joints, what’s in them now and how we reach them. You will know the price before we begin.
Why book with us
- A choice of colours where the product allows
- 12-month guarantee on every job
- Quality sealants from Arbo and Everbuild
- A sealant colour to suit the surroundings
Read our cost guide and our reviews.
How to look after the new joints
Good habits help new joints last longer. Our tips:
- Fix overflowing gutters above sealed joints
- Make sure movement joints are not pointed over
- Keep soil, plants and ivy away from the joints
- Ask before painting over external sealant
Have a quick look at the joints each spring. Splits, gaps at the edges or plants in the joint are early warning signs.
An open movement joint lets rain into the wall every time it pours. Over time it can mean damp inside, stained render or frost-damaged brick which cost more to put right than the joint.
When to call us in Knockholt
Buildings move more than people expect. Brickwork grows a little over the years, blockwork and concrete shrink, and all of it moves with heat and moisture. The sealant in the movement joints takes that strain.
Look out for these signs:
- Movement joints with cracked, split or missing sealant
- Failed seals between different materials
- Joints where the bead has come unstuck
- Rain getting behind render or cladding at a joint
For an older house near a landmark such as St Katharine's Church, older walls, gutters and the joints where extensions meet them need a flexible sealant.
What to look for in a quote
- The length of the guarantee
- How long to leave it before use
- Is the old sealant removed completely?
- What the quote includes, VAT included or not
How the visit works
There’s no need to move everything out, just the space around the work. We protect the rest, and the job takes anything from a few hours to several days, depending on the building for a typical job. Somewhere as small as Knockholt, access is often the only tricky part. For outside work, also let us know about exposed walls and any outbuildings involved.
- We look at every joint and agree a colour to suit the wall.
- Failed sealant is removed back to clean, sound faces.
- Closed-cell backing rod is pushed in so the sealant bonds to two sides only.
- We prime the faces where required.
- We gun in low-modulus sealant and tool it neatly.
Preparing for the visit
- Let us know about parking restrictions
- Where the joints are inside, avoid wetting them before we arrive
- Tell us about access, such as stairs, a lift or high-level joints
How to get a quote
Asking for a quote is easy: let us know what needs doing and where, and roughly how big it is. Photos by email help us understand the job, and we will take it from there.