Hertfordshire · England
Window Mastic in Lemsford
Our applicators work in Lemsford on mastic around window and door frames, sills and patio doors. Old sealant removed completely, joints prepared properly.
- Hard, cracked sealant around windows
- Sealant in the wrong colour for the frame
- Water coming in at the bottom corners of a door
How we handle window mastic in Lemsford
The mastic around a window or door seals the gap between the frame and the wall. 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. If you’re dealing with white mastic on grey or black frames and cold air getting in at the frame edge, we can put it right, whatever the surface.
Outdoor sealant needs dry, clean surfaces, so work on frames around Lemsford is planned for dry weather. Let us know about access to all the frames, upstairs ones included.
The work is covered for a year after we finish. If there’s a problem with it, please ring 0345 464 0079 or email us.
- Place
- Lemsford (AL8)
- Region
- Hertfordshire
- Cover
- One year on every job
- Quotes
- Quoted before any work starts
- Telephone
- 0345 464 0079
- Page updated
- 26 October 2026
What the job involves on each surface
Aluminium frames
Aluminium moves with heat, and the frames are often slimmer than uPVC. A neat, narrow bead in a colour to match keeps the clean look.
Timber windows & doors
Timber moves with moisture as well as heat, so a flexible sealant is essential. The paint or stain needs to be sound where the sealant meets it.
Lemsford: your questions answered
Will you come out to Lemsford?
Yes, Lemsford is covered. We work across London and the South East, and smaller places are part of that. The journey is planned ahead, so it helps to know about access.
Can you do window mastic in Lemsford?
Yes, Lemsford is within the area we cover. We work across London and the South East. You can phone 0345 464 0079 or email us and let us know what needs doing.
Do you guarantee window mastic?
Yes. All our work carries a 12-month guarantee, and we’re fully insured.
Can you match the sealant to my frames?
Yes, in most cases. Mention the frame colour when you ask for a quote and we’ll use the nearest match.
Will new mastic stop draughts?
It will if the frame joint is the problem. We check where the draught is before any work starts.
When is the sealant fully cured?
That depends on the sealant used, so please follow the time we give you when we finish.
Where is Mr Mastic based?
Our base is in Crawley, and we cover South East England, London and all of Scotland.
What information do you need?
Tell us what needs doing and where. We’ll ask anything else we need to know.
When it isn’t the sealant
We won’t take on work that will not last, so these are the limits:
- Damp problems in the wall away from the window
- A failed sealed unit that has misted up
- Worn gaskets, brush seals or a door that has dropped
If you are not sure, just call 0345 464 0079 or send us an email and we’ll give you a straight answer before you book.
Joints and surfaces we work on
- Aluminium frames
- Window sills
- Patio & French doors
- Composite doors
- uPVC windows
- Timber windows & doors
What affects the cost of window mastic
Every job gets its own quote. These are the things that affect it:
- How many areas need sealing
- The size of the job
- The old material and how stubborn it is
- Working hours on commercial sites
The cost reflects the work involved, not guesswork. That’s why we ask a few questions first and agree the price before starting.
What to tell us for a quote
What to tell us when you ask for a quote:
- Roughly how big the job is
- If someone has resealed it before
- Pictures of the joints, sent by email
- How we’d reach the joints
The more we know about the job, the more useful the quote. Tell us where the job is, what’s wrong and how much there is, and email photos if that’s easy.
Windows and doors in Lemsford
Historic houses like Digswell House (about 1.9 miles north-east) are a reminder that the area around Lemsford 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. Rainfall in the South East is lower than in much of the UK, though outdoor sealant still has to go onto a dry joint, so the forecast decides the day.
Letting a property close to Welwyn Garden City station? Then cracked frame mastic tends to show up as a draught or damp complaint, so it’s worth checking between lets. If you look after a building such as Applecroft School, larger buildings have plenty of frames, and the mastic around each one ages. In the older streets around Church of St John the Evangelist, the windows may be timber, sash or later replacements, and each needs the right sealant against the wall.
Lemsford is about 2 miles west of Welwyn Garden City, in Hertfordshire. Whether you are in the middle of Lemsford or further out, window mastic is available for homes and businesses alike. 381 places in Hertfordshire are on our list, large and small. There’s also a page for London, about 21 miles away.
Jobs for window mastic in AL8 works the same way as everywhere else we cover. Local streets include Mill Close, Lemsford Village and Great North Road, all of which we cover. We also cover Stanborough (1 mile south), Coleman Green (2 miles west), Cooper's Green (2 miles south-west), Hatfield (2 miles south) and Smallford (3 miles south-west). Within a short drive, we also cover Watford (12 miles south-west), Hemel Hempstead (10 miles west), Stevenage (8 miles north), St Albans (5 miles south-west), Harpenden (5 miles west) and Hitchin (11 miles north).
What’s near Lemsford
Around Lemsford, our work takes us to homes and buildings near Stanborough Park, Stanborough School and The Sun Inn, among other places. The nearest railway station is Welwyn Garden City station, roughly 1.2 miles east. Other landmarks nearby include Queen Elizabeth II Hospital (2.1 miles south-east) and The Bunker at Hatfield Police Station (2.1 miles south). Not far away are Lemsford Springs.
Nearby places to Lemsford
More services for Lemsford
Why it’s worth doing now in Lemsford
A quick bead over the top of old mastic looks like an easy fix, but new sealant cannot bond to old, crumbling mastic. It soon lifts and the leak carries on behind it. The old mastic has to come out. Around Lemsford, older homes often have timber in their floors and frames, and water through a failed joint can rot timber if it’s left.
Homes and businesses are quoted the same way: the amount of work, how we reach it and what it needs, plus any working-time requirements on site. Call for a quick quote and we’ll explain what it covers.
Why book with us
- Old sealant always removed completely
- Anti-fungal silicone where joints get wet
- We’re fully insured
- 180+ five-star Google reviews
Take a look at how sealant jobs are priced and customer reviews.
What we do, step by step
Before we leave, we go over the finished joints with you and explain the cure time. The visit itself generally takes most of a day for a typical house, less for a few frames, depending on the size of the job. In a small place like Lemsford, access is normally the main thing to plan. For outside work, also let us know about exposed walls and any outbuildings involved.
- Each frame is looked over and we agree which ones need resealing.
- The old mastic is cut out and scraped back to clean surfaces.
- Deep gaps get closed-cell backing rod to set the depth.
- The new sealant goes on in white, brown, anthracite grey, black or clear to suit.
- Every joint is tooled smooth and checked before we leave.
Before we arrive
- Mention if the joints have been sealed before
- Let us know about parking restrictions
- For indoor joints, keep the area dry beforehand if you can
Get a quote
Need a quote? Please call 0345 464 0079 or send us an email and tell us about the job. We will explain what we’d do and give you a clear price before any work starts.
Related advice
Keeping the joints in good condition
After the cure time, these simple habits help:
- Clear any debris from frame drain holes
- Avoid blasting the frames with a pressure washer
- Check the mastic once a year
- Don’t use solvent cleaners on the joint
Have a look at the joints once a year, ideally after winter. Cracks and lifting edges are easy to spot early, and if anything looks wrong, just phone 0345 464 0079 or email us.
A small gap around a frame only grows. As old mastic keeps shrinking, the gap widens, and heat escapes around the frame. A new joint closes it up.
DIY versus a professional finish
A DIY attempt doesn’t rule out a professional job. We remove it and do the joint properly.
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.