Greater London · England
New-build mastic & snagging in Coldharbour, Greater London
New build mastic for Coldharbour, by sealant specialists with 20+ years’ experience. 180+ five-star Google reviews and a 4.9 rating.
- Shower seals failing in the first year or two
- Sealant applied over dusty or wet surfaces
- Joints pulling apart as timber shrinks
How we handle new build mastic in Coldharbour
We carry out plot mastic and second-fix sealing for builders, and snagging reseals for new-home owners. In both, preparation makes the difference, because that is what rushed new-build sealant generally lacks. We’re often asked to deal with untidy sealant flagged on a snagging list and joints pulling apart as timber shrinks, on plot handovers, show homes and windows & doors.
London homes range from new-build flats to period conversions with new floors laid over old boards. Every joint between floor, skirting and threshold has to cope with some movement, in Coldharbour as anywhere.
There’s a 12-month guarantee on every job, whatever its size.
- Location
- Coldharbour (SE9, BR7)
- Wider area
- Greater London
- Guarantee
- One year on every job
- Price
- A clear quote up front
- Telephone
- 0345 464 0079
- Updated
- 26 October 2026
How to look after the new joints
After the cure time, these simple habits help:
- Resist patching a failed seal with a tube from the DIY shop
- Wipe joints with warm soapy water
- Keep photos and emails about snagging items
- Open a window or run the fan after bathing
Leave the sealant for the cure time we give you before showering or bathing. Most silicones need around a day.
The sooner you deal with untidy or cracking sealant, the less there is to put right. Small faults turn into leaks if left over time.
New homes and floors in Coldharbour
Much of London’s new housing is flats in larger developments, where snags may need reporting through the developer or the managing agent. The South East is one of the drier parts of the UK, yet outdoor joints still have to be sealed dry, so jobs are booked with the weather in mind.
As a London address, Coldharbour can be tricky for parking: tell us about permits, visitor bays or off-street space when you book.
Coldharbour is about 4 miles north-west of Orpington, in Greater London. Across the SE9 area, we cover new build mastic for homes and businesses. Our Greater London coverage runs to 764 places, Coldharbour among them. We also work in London, around 8 miles away.
All of SE9 and BR7 is within our area for new build mastic. If you need new build mastic at a property on Green Lane, Horley Road and Dorset Road or a nearby road, we can help. Other places close to Coldharbour include Mottingham (1 mile west), Chinbrook (1 mile west), New Eltham (1 mile north-east), Eltham (1 mile north) and Middle Park (1 mile north-west). Larger places within reach include London (8 miles north-west), City of Westminster (11 miles north-west), Marylebone (10 miles north-west), Kensington (12 miles north-west), St Pancras (10 miles north-west) and Shoreditch (9 miles north-west).
Local landmarks in Coldharbour
Typical jobs here are in homes near Elmstead Wood and St Thomas More Catholic Comprehensive School. The nearest railway station is Mottingham station, about 0.6 miles north. A little further out are The Glades (2.4 miles south-west) and Metropolitan Police Museum (2.2 miles east). Not far away are The Tarn and Summer Hill.
What sealant work cannot fix
Some problems need a builder, plumber or other trade rather than us:
- Disputes or warranty claims with your builder
- Cracking that points to a structural problem
- A tray or bath that isn’t properly supported, until it’s fixed
If in doubt, phone 0345 464 0079 or email us and we’ll say what we think before booking.
Where we work in Coldharbour
- Windows & doors
- Plot handovers
- Kitchens
- Show homes
- Bathrooms & en suites
- Skirting & floors
DIY versus a professional finish
Some jobs are best left to a professional: high-level joints, fire-rated gaps, external movement joints and big jobs need the right product, the right access and the right method.
A careful DIYer can reseal a simple joint, like a short, easy-to-reach joint indoors. The common mistakes are sealing over old sealant, sealing a damp joint and using far too much.
Quotes for new build mastic in Coldharbour
There’s no set price list, because jobs vary so much. The quote depends on:
- How many areas need sealing
- Whether old sealant or filler has to be cut out
- Any working-time requirements on site
- Access and height
A failed joint rarely gets cheaper to fix by waiting, because water and mould keep working on it. If you’re not sure whether it needs doing, phone 0345 464 0079 or send us an email for an honest opinion and a quote.
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:
- A few photos by email, if you can
- How we’d reach the joints
- The type of property
- The problem you’ve noticed
We don’t publish a price list, because every job is different. Instead, we send you a clear quote for your job. To get started, phone 0345 464 0079 or send us an email.
What we do, step by step
We work through the job in order: protect, prepare, seal, tidy. Typically it takes anything from a few hours to several days, depending on the number of plots, and the area is left clean. Many London jobs are in flats, so we come ready for stairs, narrow hallways and shared entrances. If the building has a concierge, managing agent or access rules, tell us when you book.
- We go through the snagging list or plot schedule and agree the joints to do.
- The old bead comes out in full, with no layer left behind.
- We clean off dust from the build and prime the surfaces where the product needs it.
- New sealant suited to each joint is applied and tooled neatly.
- Finally, each room is checked and you are given the cure time.
Getting ready for the visit
- Mention any sign-in or site rules at work premises
- Mention any tricky access
- Keep children and pets away from the work area
Ask for a quote
Call for a quick quote, or send an email if you’d rather. Tell us about the joints that need doing and we will talk you through the work.
Related advice
Places near Coldharbour
What else we do in Coldharbour
Your questions about new build mastic in Coldharbour
Do you cover Coldharbour for new build mastic?
Yes, Coldharbour is within the area we cover. We work across London and the South East. You can ring 0345 464 0079 or email us and tell us what needs doing.
Do you work for landlords with property near Mottingham station?
Yes, we work for landlords and agents. 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.
Can you reseal over the builder’s sealant?
No. New silicone won’t bond to old silicone, so it soon lifts and traps water. The old sealant always comes out first.
Should I go to my builder first?
If you’re still within the builder’s snagging or warranty period, report it to them first. If they’re slow or the fix does not last, we can help.
What do you put in the joint?
Products from Arbo and Everbuild, among others, picked for each joint. We explain the product when we quote.
Do you hold any approvals?
Yes. We are approved under the ARBOMaster scheme, which is run for the Arbo sealant brand.
Are you insured?
Yes. We are fully insured, and we can confirm the details when we quote.
Where is Mr Mastic based?
We’re based in Crawley, and we cover South East England, London and all of Scotland.
When to call us in Coldharbour
A new house holds a lot of water from the build, and it dries out over the first couple of years. As it does, timber shrinks and joints open and the sealant has to cope with the movement.
Look out for these signs:
- Gaps between new skirting and floors
- Kitchen sealant that has pulled off the wall
- Leaking shower tray seals in a new home
- Sealant that never bonded to the surface
If you’ve bought a new home near Mottingham station, the sealant around baths, showers and frames is worth checking in the first year or two.
What to look for in a quote
- What product goes in the joint
- When the joint can take water or movement
- Who turns up on the day
- What insurance they hold
Different surfaces, different methods
Plot handovers
Plot mastic is carried out to the developer’s schedule. Each joint is cleaned and primed where needed so the sealant lasts.
Show homes
Bathrooms, kitchens and frames in show homes are sealed or resealed to a neat finish ready for viewings. We will plan around viewing times.