Hertfordshire · England
Old Knebworth External Mastic
Specialist external mastic for Old Knebworth: the right sealant, proper preparation and a neat finish. Call for a quick quote.
- Water getting into walls through failed joints
- Sealant pulling away from one side of the joint
- Failed seals between different materials
What external mastic looks like in Old Knebworth
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. Historic houses like Knebworth House (about 0.2 miles north-west) are a reminder that the area around Old Knebworth has older buildings as well as new. In older buildings, older brick and stone need a sealant that suits them, at the right joint depth.
In the older streets around Church of St Mary and St Thomas, older walls, gutters and the joints where extensions meet them need a flexible sealant. If you look after a building such as Barnwell School, larger buildings have long runs of movement joint that eventually need resealing. Rented homes near Knebworth station change hands often, and split movement joints are easy to miss on a rental until damp shows inside.
Old Knebworth is about 3 miles south-west of Stevenage, in Hertfordshire. Every kind of property in Old Knebworth can book us for external mastic, old or new, large or small. Every job comes with our one-year guarantee. Across Hertfordshire, we cover 381 places, and Old Knebworth is one of them. For nearby work, see our London page (26 miles or so).
Postcode districts we cover here for external mastic: SG3. Whether your property is on Old Knebworth Lane and Park Lane or anywhere close by, our applicators can take on the job. If you’re just outside Old Knebworth, we cover Nup End Green (1 mile south-west), Driver's End (1 mile south-west), Rableyheath (1 mile south), Pottersheath (1 mile south) and Langley (2 miles north-west). Within a short drive, we also cover Hemel Hempstead (13 miles south-west), Stevenage (3 miles north-east), St Albans (10 miles south-west), Welwyn Garden City (5 miles south), Harpenden (7 miles south-west) and Hitchin (6 miles north-west).
Local landmarks in Old Knebworth
We work in homes and buildings around Knebworth Park and Robin Hood And Little John Public House, among other places. Old Knebworth’s nearest station is Knebworth station, about 1 mile east of the centre. Other landmarks nearby include Lister Hospital (3.7 miles north) and Stevenage Museum (2.2 miles north). Green spaces nearby include Mardley Heath.
External mastic in Old Knebworth
For buildings in Old Knebworth, we reseal external joints of all kinds, from brick movement joints to cladding panels. The preparation is the same whatever the wall: clean, sound faces and a controlled depth. Typical jobs include joints with sealant missing in places and joints where the bead has come unstuck, on concrete & block, joints between brick and frames and copings & trims.
Somewhere as small as Old Knebworth, homes and farm buildings often face open ground, where walls and rooflines take the weather head on. Gutter joints and wall joints there need a sealant that can flex and stay put.
All of our work is guaranteed for twelve months, and the guarantee is the same wherever you are.
- Where
- Old Knebworth (SG3)
- Region
- Hertfordshire
- Guarantee
- 12 months on all our work
- Quotes
- Quoted before any work starts
- Telephone
- 0345 464 0079
- Last updated
- 26 October 2026
FAQs for Old Knebworth
Is Old Knebworth within the area you cover?
Yes, smaller places are covered as well as towns. We work across London and the South East. Let us know about access, parking and anything unusual about getting there when you book.
Can you do external mastic in Old Knebworth?
Yes, Old Knebworth is within the area we cover. Our work covers London and the South East. Just call 0345 464 0079 or email us with a few details of the job.
Do you work at height?
It depends on the height and the site. Low-level joints are straightforward; for higher ones, send details and we will confirm the access.
Do you use backing rod?
Backing rod controls the sealant depth and keeps it off the back of the joint. That way it bonds to the two sides only and can stretch.
How long before the joint can be used?
Most sealants are touch-dry well before they’re fully cured. We will tell you how long to leave the joint.
Is it messy?
No. The area is protected while we work and cleaned up afterwards.
What does external mastic cost?
There’s no set price, as it depends on the job: how much there is, what’s there now, how we reach it and what it needs. We agree the price before any work begins.
Why is there a gap in my brick wall?
It’s a deliberate gap that lets the wall expand and contract without cracking. It should be filled with flexible sealant, never mortar.
Towns and villages near Old Knebworth
Other services in Old Knebworth
What we cannot put right
Honest advice matters more to us than a booking, so here’s what sealant cannot fix:
- Walls that need new movement joints cut into them
- Failed render or damaged cladding panels
- Rising or penetrating damp from elsewhere in the wall
Not sure which it is? You can call 0345 464 0079 or email us and we’ll tell you honestly before you book.
Where we work in Old Knebworth
- Joints between brick and frames
- Façade panels
- Concrete & block
- Copings & trims
- Render & cladding joints
- Brickwork movement joints
What happens on the day
We bring everything the job needs with us. Once we’ve agreed what’s being done, we protect the area and start. It normally takes a few hours for a handful of joints, longer for a whole elevation. Somewhere as small as Old Knebworth, access is often the only tricky part. If the job is outside, mention outbuildings, exposed walls and how to reach them.
- We start by walking round the building and agreeing the joints and the access.
- We cut out the old mastic and rake out anything in the joint.
- The faces are brushed clean and primed where the product requires it.
- Backing rod sized to the joint goes in to set the depth.
- We apply the sealant, tool it and check the whole run.
How to prepare
- Tell us if parking is tricky
- Mention any sign-in or site rules at work premises
- Mention any tricky access
Get a quote
Every job is quoted individually. Just ring 0345 464 0079 or send us an email with the details.
Advice
Different surfaces, different methods
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.
Concrete and blockwork
The face of concrete or block is often dusty, so preparation is key. A primer goes on where the product requires one before the bead.
Landlords, agents and businesses in Old Knebworth
We work for letting agents and landlords as well as householders. Sealant work between tenants keeps a property looking cared for.
From a single let to a portfolio, you get the same standard of work: old sealant fully removed, joints prepared properly and a one-year guarantee.
Why it’s worth doing now in Old Knebworth
A properly done movement joint is an even line in a colour that suits the wall. A rushed bead with no backing looks untidy and doesn’t last so it’s worth doing right. In a small place like Old Knebworth, homes can be exposed to wind and rain, which finds any gap, and damp in older walls is slow to dry out.
Rather than a set price list, we look at what your job involves: 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
- White, clear, grey or coloured to suit, where the product allows
- Experience in homes, commercial sites and hotels
- 12-month guarantee on every job
- Anti-fungal sanitary silicone in wet areas
Looking after it afterwards
Joint life depends on how it’s used and looked after. We suggest:
- Fix overflowing gutters above sealed joints
- Act on the first splits you see
- Clear growth from the base of walls and joints
- Look over the joints every year, ideally after winter
Keep pressure washers away from the sealant. A strong jet can damage the edges of the bead over time.
Leave a failed movement joint and water keeps getting into the wall. That can lead to damp patches, staining and frost damage which cost more to put right than the joint.
What affects the cost of external mastic
The quote reflects the job in front of us. We take into account:
- The type of sealant required
- The number and length of the joints
- When we can work, for business premises
- The old material and how stubborn it is
Commercial jobs are quoted on the same basis as homes: the amount of work, how we reach it and what it needs. Call for a quick quote and we’ll explain what it covers.
What to tell us for a quote
The more you tell us, the more accurate the quote. When you get in contact, it helps to mention:
- The type of property
- If someone has resealed it before
- Access, such as stairs, a lift or height
- Where the job is, and your postcode
We do not publish a price list, because every job is different. Instead, we give you a clear price for your job. To get started, phone 0345 464 0079 or send us an email.