Hertfordshire · England
Window & door mastic in Nup End Green, Hertfordshire
We cover Nup End Green for mastic around window and door frames, sills and patio doors. Old material cut out, joints cleaned and sealed neatly and a 12-month guarantee.
- Mastic that is falling out in pieces
- Cracked sealant at the sill ends
- Mastic that has split away from the wall
About our window mastic in Nup End Green
Every window and door frame has a gap around it, and mastic is what closes it. When it cracks, hardens or pulls away, draughts and rain get in. The old mastic is removed and the joint resealed with a flexible exterior sealant. We work on uPVC windows, patio & French doors and window sills, and people most often call us about gaps where the sill meets the wall and draughts coming in around windows and doors.
Somewhere as small as Nup End Green, older homes often have timber frames set in stone or brickwork. Older buildings like these do not always suit modern silicone, so the sealant has to be chosen to suit the building.
Our work is backed for twelve months.
- Where
- Nup End Green (SG3)
- Region
- Hertfordshire
- Cover
- One year on every job
- Quotes
- A clear price before work begins
- Telephone
- 0345 464 0079
- Updated
- 26 October 2026
Honest limits
Before booking, it’s worth knowing the limits:
- Draughts through the window seals rather than the frame
- A frame that has rotted at the joint
- Misting between the panes of a double-glazed unit (that needs a new unit)
If in doubt, call 0345 464 0079 or drop us an email and we’ll say what we think.
Surfaces we seal
- Window sills
- Aluminium frames
- Patio & French doors
- uPVC windows
- Composite doors
- Timber windows & doors
Common problems we fix in Nup End Green
Frames are never completely still. Sun on a frame makes it expand, and it contracts again overnight, while the masonry beside it stays put. A sealant that cannot keep up eventually tears.
Most people get in touch when they notice one of these:
- Damp patches on the reveal after heavy rain
- Black, perished sealant on frames
- Leaking joints at the ends of sills
- Gaps left after new windows were fitted
In the older streets around Church of St Mary and St Thomas, the windows may be timber, sash or later replacements, and each needs the right sealant against the wall.
What to look for in a quote
- What the cure time is
- How the joint is cleaned and prepared
- What product goes in the joint
- Whether they seal over old material or remove it
What window mastic looks like in Nup End Green
Compared with the north and west, the South East gets less rain, yet outdoor joints still have to be sealed dry, so jobs are booked with the weather in mind. Historic houses like Knebworth House (about 0.6 miles north-east) are a reminder that the area around Nup End Green has older buildings as well as new. Where a home is older, older timber frames in brick or stone need a different approach from a modern uPVC window.
For landlords with property near Knebworth station, sound mastic around windows and doors keeps out the draughts and damp that tenants notice first.
Nup End Green is about 3 miles south-west of Stevenage, in Hertfordshire. For window mastic in and around Nup End Green, it’s easy to get a quote: please phone 0345 464 0079 or send us an email. We cover Hertfordshire from our Crawley base, Nup End Green included. We cover 381 towns and villages across Hertfordshire, large and small. For nearby work, see our London page.
Every address in SG3 is covered for window mastic. If you’re just outside Nup End Green, we cover Driver's End (1 mile west), Old Knebworth (1 mile north-east), Rableyheath (1 mile south-east), Pottersheath (1 mile south-east) and Codicote (1 mile south-west). Within a short drive, we also cover Hemel Hempstead (13 miles south-west), Stevenage (3 miles north-east), St Albans (9 miles south-west), Welwyn Garden City (5 miles south), Harpenden (6 miles south-west) and Hitchin (6 miles north).
Landmarks near Nup End Green
We work in homes and buildings around Robin Hood And Little John Public House and Knebworth Park. Nup End Green’s nearest station is Knebworth station, roughly 1.4 miles east of the centre. Nearby you will also find Benington Castle (4.9 miles north-east) and Lister Hospital (4.1 miles north). The countryside around Nup End Green includes Mardley Heath.
Your questions about window mastic in Nup End Green
Can you help a landlord with a rental near Knebworth station?
Yes, we work for landlords and agents. You can call 0345 464 0079 or drop us an email with the address and a few details, and we will give you a fixed price before any work starts.
Will you come out to Nup End Green?
Yes, we do. We work across London and the South East, and smaller places are part of that. Longer journeys are simply planned in advance.
Is it OK to seal over old sealant?
No, and we never do. It may look fine at first, but the new layer lifts away from the old one. The old sealant has to come out completely.
Can you do upstairs windows?
Usually, yes. Access is planned before work begins, so mention the height and anything in the way.
Is the work guaranteed?
Yes. Each job is covered for 12 months, inside or out.
Do the sealants smell?
Sometimes, a little. It fades as the sealant cures.
Do you have sealant for grey or black windows?
Normally, yes. Mention the frame colour when you ask for a quote and we’ll use the nearest match.
Do you take out the old sealant first?
Yes. All of the old material is cut out and the joint cleaned before applying anything new.
Work for landlords, hotels and businesses
We also work for property managers and facilities teams in Nup End Green and across Hertfordshire. We can quote a run of properties together.
Hotels need rooms back in use, so the work can be planned room by room. Hotel work is part of what we do, alongside homes and businesses.
Also near Nup End Green
More services for Nup End Green
What happens if it’s left?
Redecorating is a good moment to renew the mastic. Fresh joints finish the job neatly, and it’s easier while the walls are being worked on anyway. Where a wall is exposed, as many are in small places like Nup End Green, wind-driven rain gets into any failed joint, and damp in older walls is slow to dry out.
Commercial jobs are quoted on the same basis as homes: the amount of work, the access and the products needed, along with when we can work on site. Call for a quick quote and we’ll explain what it covers.
What you get with us
- Rated 4.9 stars on Google
- 20+ years of sealant experience
- White, clear, grey or coloured to suit, where the product allows
- Every job guaranteed for a year
Take a look at how sealant jobs are priced or what customers say.
Aftercare tips
Good habits help new joints last longer. A few tips:
- Keep timber frames painted
- Do not paint over the silicone
- Air rooms to keep condensation down around windows
- Keep solvents and bleach off the sealant
Most silicone sealants will not take paint, so if you’re planning to paint the frames or walls, tell us beforehand. We can use a paintable sealant where that matters.
A small gap around a frame only grows. As old mastic keeps shrinking, the gap widens, and a cold room gets colder. A new joint closes it up.
What we do, step by step
Most of a good job is in the preparation, and we do not rush it. Joints are cleaned back and dried before anything new goes in. In total, it generally takes anything from an hour or two to a full day, depending on how many frames there are. Somewhere as small as Nup End Green, access is often the only tricky part. If the job is outside, mention outbuildings, exposed walls and how to reach them.
- We check each frame and agree which ones need doing.
- Next the failed sealant is cut away and the joint cleaned.
- Deep gaps are filled with backing rod to set the depth.
- New exterior sealant goes on in a matching colour and is tooled smooth.
- Finally we tidy up and check each joint.
How to prepare
- Keep pets and children clear of the area while we work
- Try not to wet indoor joints just before the visit
- Tell us if parking is tricky
Getting a quote
The more we know about the job, the more useful the quote. Let us know the location, the problem and roughly how many joints, and email pictures if that is easy.
Read more
Different surfaces, different methods
Window sills
Masonry sills can have joints where water gets in, including the one between the sill and the frame above. We seal those with a sealant suited to masonry.
Aluminium frames
Bi-fold and sliding aluminium doors have long frame joints, and the threshold joint takes a lot of water. Each is cleaned, backed where deep and resealed.