Hertfordshire · England
Sand Mastic in Old Knebworth
Specialist sand mastic for Old Knebworth: the right sealant, proper preparation and a neat finish. Call for a quick quote.
- Failed mastic on an exposed elevation
- Open joints round the window box
- A silicone bead on a sash window that spoils the look
How we handle sand mastic in Old Knebworth
We work across Old Knebworth renewing sand mastic on sash windows and doors. Every joint is cleaned out and filled by hand, finished to suit the masonry. We are often asked to deal with mastic round period door frames that has failed and failed mastic on an exposed elevation, across timber door frames, period & listed homes and brick reveals.
Around Old Knebworth, many homes face open ground, so their windows and doors take the full weather. That exposure dries out and cracks the mastic around frames and sills faster.
A one-year guarantee comes as standard, so you are not left on your own once the job is done.
- Location
- Old Knebworth (SG3)
- Wider area
- Hertfordshire
- Guarantee
- One year on every job
- Quotes
- A clear price before any work starts
- Call
- 0345 464 0079
- Updated
- 26 October 2026
Aftercare tips
Joint life depends on how it’s used and looked after. Here’s what we suggest:
- Do not paint over the new mastic
- Find out about consent before window work on a listed home
- Keep sills and gutters clear so water drains away
- Take care around the mastic when scraping paint
When preparing windows for paint, take care around the mastic. It can be damaged by heavy scraping.
Crumbling mastic lets rain into the joint. That water can reach the timber frame and the wall, so renewing it early is worth it.
Different surfaces, different methods
Timber door frames
Round a period front door, sand mastic gives the right look.
Brick reveals
Sand mastic is also used where timber frames meet brick. It suits older brickwork.
Why it’s worth doing now in Old Knebworth
New sash windows are a major, costly change and on a listed home, consent may be needed. Where the frames are in good order, new mastic seals the surround. In a small place like Old Knebworth, homes can be exposed to wind and rain, which finds any gap, and older walls, once damp, take a long time to dry.
What it costs depends on the amount of work, how much old material has to come out and access to the work. We give a clear quote before work begins.
Why choose Mr Mastic in Old Knebworth
- Fully insured
- Any old sealant cut out fully, not covered over
- Rated 4.9 stars on Google
- We leave the area clean and tidy
Take a look at how sealant jobs are priced and what customers say.
Old Knebworth questions
Is Old Knebworth in your area for sand mastic?
Yes, Old Knebworth is within the area we cover. We work across London and the South East. You can call 0345 464 0079 or send us an email and let us know what needs doing.
I let a flat near Knebworth station. Can you help?
Yes, we work for letting agents and landlords. You can call 0345 464 0079 or send us an email with the address and a few details, and we will give you a fixed price before we start.
Is it possible to take out silicone and use sand mastic instead?
Yes, it’s a common request. All the old silicone is removed first so the mastic can sit properly.
Is it possible to paint over sand mastic?
Sand mastic is normally left unpainted, as guidance on traditional windows advises. Talk to us before any painting near it.
How long will you be here?
As a guide, most jobs take a few hours per window, depending on the condition of the joints. Larger jobs naturally take longer, and we’ll say how long yours will take.
Can you match the sealant colour?
We help you choose a colour that suits. The product needed can limit the range.
Where is Mr Mastic based?
We work from Crawley. Our applicators cover Old Knebworth.
Can you work on commercial sites?
Yes. Hotels, offices and other businesses use us, and we’re fully insured.
What affects the cost of sand mastic
You’ll get a clear quote before work begins. It takes into account:
- The amount of work
- Whether there’s mould to deal with
- How easy the joints are to reach
- Working hours on commercial sites
There are no prices on our website, because the cost depends so much on the job itself. For a quick quote, please phone 0345 464 0079 or drop us an email and we will talk you through it.
What to tell us for a quote
When you call or email, it’s useful to know:
- Roughly how big the job is
- A few pictures by email, if you can
- Access, such as stairs, a lift or height
- Any previous sealing or DIY work
We quote each job on its own, so start by telling us what you need. Just call 0345 464 0079 or send us an email with the details, and photos are welcome.
Landlord and commercial work in Old Knebworth
For anyone letting property in or around Old Knebworth, several properties can be quoted together. Just tell us the addresses and what each one needs, and photos by email help.
Letting agents often deal with us directly. Tell us the address, the job and how access works and we’ll quote.
Frames and glazing around Old Knebworth
With historic houses such as Knebworth House (about 0.2 miles north-west) nearby, there’s older building stock in the area around Old Knebworth as well as newer homes. Where a home is older, older frames set in brick or stone need a sealant that suits them, and sometimes that is traditional sand mastic. 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.
Schools such as Barnwell School are buildings too, and its window and door frames need their mastic kept sound, just like a home’s. If you live in an older home near Church of St Mary and St Thomas, the joint between an old wall and a newer frame is normally the first place rain gets in. For landlords with property near Knebworth station, cracked sand mastic around sash windows lets in the draughts tenants complain about.
Old Knebworth is about 3 miles south-west of Stevenage, in Hertfordshire. Across the SG3 area, our applicators can take on sand mastic. Our Hertfordshire coverage runs to 381 places, and Old Knebworth is one of them. You can also see our page for London, about 26 miles away.
Postcode districts we cover here for sand mastic: SG3. Streets in the area include Old Knebworth Lane and Park Lane. Other places close to Old Knebworth include 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). Further out, 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. The closest station to Old Knebworth is Knebworth station, roughly 1 mile east. Other landmarks nearby include Lister Hospital (3.7 miles north) and Stevenage Museum (2.2 miles north). For a walk, there’s Mardley Heath.
Nearby places to Old Knebworth
What else we do in Old Knebworth
What happens on the day
Once we are on site, we compare the joints with what we discussed. If anything is different, we explain it before carrying on. Most jobs then take a few hours for a single window, longer for several. Somewhere like Old Knebworth needs a little journey planning: tell us about narrow lanes, gates, long drives and where we can park. We bring what the job needs, so it can be finished in one trip where possible.
- We check the window surrounds and agree which joints need renewing.
- We rake out the old mastic and clean the joint.
- We pack any deep gaps so the mastic sits at the right depth.
- We mix the sand mastic and apply it by hand, shaping it to the joint.
- The mastic is finished to sit tidily against the stone or brick.
Preparing for the visit
- Mention any parking rules near the property
- Plan for the work area to be out of bounds to pets and children
- Tell us about any water getting in
Getting a quote
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 add photos by email if you can.
Advice
Honest limits
Honest advice matters more to us than a booking, so here’s what sealant cannot fix:
- Sashes that rattle, stick or won’t open
- Timber that has rotted
- Decisions on consent for listed homes
If you’re not sure, just phone 0345 464 0079 or email us and we’ll give you a straight answer before booking.
What we seal
- Stone surrounds
- Sash and case windows
- Brick reveals
- Tenement windows
- Period & listed homes
- Timber door frames