Greater London · England
Coldblow External Mastic
Sealing brickwork movement joints, render, cladding and façade joints for householders, landlords and businesses in Coldblow. ARBOMaster approved applicators, fully insured, with a 12-month guarantee.
- Failed seals between different materials
- Weathered mastic that no longer stretches
- Panel joints letting water in
The process
There is not much for you to do on the day. Point us to the joints and we’ll get on with it. The work itself takes a few hours for a handful of joints, longer for a whole elevation, including the tidy-up. Many London jobs are in flats, so we come ready for stairs, narrow hallways and shared entrances. Mention any building rules, key holders or managing agents when you book.
- We start by walking round the building and agreeing the joints and the access.
- Every bit of old sealant and any mortar or debris is cut out.
- Joint faces are cleaned back and primed if the sealant needs it.
- Backing rod sized to the joint goes in to set the depth.
- We apply the sealant, tool it and check the whole run.
Getting ready for the visit
- Keep pets and children clear of the area while we work
- Where the joints are inside, avoid wetting them before we arrive
- Let us know if you’ve seen damp or leaks
Get 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’ll explain what’s involved before giving you a price.
Related advice
External mastic in Coldblow
Where two different materials meet, such as brick and render or blockwork and metal, they move at different rates. A flexible exterior sealant takes up that movement. We work on copings & trims, render & cladding joints and façade panels, and people most often call us about sealant pulling away from one side of the joint and damp patches traced to an open external joint.
Outside work in London starts with access: side passages, upper floors and where to park. In Coldblow, joints up high may need ladders or other access, which is worth talking through when you book.
The work is covered for a year after we finish. If anything is not right with it, call 0345 464 0079 or email us.
- Location
- Coldblow (DA5)
- Region
- Greater London
- Guarantee
- A year, on every job
- Price
- Quoted before any work starts
- Telephone
- 0345 464 0079
- Last updated
- 26 October 2026
Can I do it myself?
The biggest DIY mistake is sealing over old sealant. New silicone will not bond to old, so it lifts and traps water and mould underneath. All the old material has to come out first.
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.
What we cannot put right
To be straight with you, some problems need a different trade:
- Movement that’s more than a sealant joint can take
- Rising or penetrating damp from elsewhere in the wall
- Failed render or damaged cladding panels
Not sure which it is? You can ring 0345 464 0079 or email us and we’ll tell you honestly.
Joints and surfaces we work on
- Render & cladding joints
- Brickwork movement joints
- Façade panels
- Copings & trims
- Joints between brick and frames
- Concrete & block
Outside joints around Coldblow
The South East is one of the drier parts of the UK, though outdoor sealant still has to go onto a dry joint, so the forecast decides the day. London terraces and converted houses often share gutters, downpipes and walls, so it’s worth agreeing who is responsible before work starts.
Coldblow is in London, so parking needs planning: let us know about parking bays, permits or a driveway. Letting a property close to Bexley station? Then split movement joints are easy to miss on a rental until damp shows inside.
Coldblow is about 3 miles east of Sidcup, in Greater London. Jobs in Coldblow get the same care as everywhere else we work: the old material taken out, joints prepared properly and a 12-month guarantee. Coldblow is one of 764 places in Greater London we cover for external mastic. London is on our list too, around 12 miles away.
All of DA5 is covered for external mastic, from the main roads to the quietest streets. We cover properties on St Mary's Road, Dartford Road and Wansunt Road and the roads around them. If you’re just outside Coldblow, we cover Joyden's Wood (1 mile south-east), Bowmans (1 mile east), North Cray (1 mile south-west), Crayford (1 mile north-east) and Wilmington (1 mile south-east). Within a short drive, we also cover London (12 miles west), City of Westminster (15 miles west), Marylebone (14 miles north-west), St Pancras (14 miles north-west), Shoreditch (12 miles north-west) and Walthamstow (13 miles north-west).
Local landmarks in Coldblow
Typical jobs here are in homes near The Old Wick pub, St Columba's Catholic Boys' School and Braeburn Park. The nearest railway station is Bexley station, about 0.6 miles west. Other landmarks nearby include Stone Castle (5 miles east) and Bexley Museum (0.7 miles north). The countryside around Coldblow includes Wansunt Pit and Summer Hill.
Nearby places to Coldblow
Other services in Coldblow
Coldblow: your questions answered
Is Coldblow in your area for external mastic?
Yes. Our work covers London and the South East, and Coldblow is part of that. Just ring 0345 464 0079 or send us an email with a few details of the job.
Is parking a problem for a job in Coldblow?
It can be, so it helps to tell us about permits, visitor bays or off-street space when you book. The visit is then planned around what’s available.
Can you quote for more than one area?
Yes. Tell us about everything you’d like done and we will quote it together.
Does someone need to be in?
It depends on the job. Inside work needs someone to give us access, and for outside work we’ll agree access with you when we book.
Do you hold any approvals?
Yes. ARBOMaster is the approved applicator scheme for Arbo sealants, and we’re part of it.
What is backing rod for?
Backing rod goes into deeper joints as a matter of course. It sets the sealant depth and prevents three-sided bonding, so the joint can move.
Do you work for letting agents?
Yes. We work in homes, commercial premises and hotels.
Where is Mr Mastic based?
We are a Crawley-based firm, with over 20 years’ experience. Our area covers South East England, London and Scotland.
How to look after the new joints
To keep the joints looking good and working properly:
- Check external joints each spring
- Don’t let climbing plants root in the sealant
- Deal with leaking gutters that soak the joints below
- Never let anyone fill a movement joint with mortar
Have a quick look at the joints each spring. Splits, gaps at the edges or plants in the joint are early warning signs.
Leave a failed movement joint and water keeps getting into the wall. That can lead to damp patches, staining and frost damage.
What the job involves on each surface
Render joints
Cracks along render joints let water in behind the coat. Resealing the joints early keeps water out and helps it last.
Joints between dissimilar materials
Joints where frames, sills or panels meet the wall are common leak points. We cut out the old sealant and reseal with a product suited to both surfaces.
What we’re called out for in Coldblow
Many joints fail because they were sealed too deep or with nothing behind them. Sealant bonded to three sides has nowhere to go and rips as the joint opens.
If you can see any of these, it’s time to have the joints looked at:
- Failed sealant between panels on a façade
- Failed seals between different materials
- Old sealant gone brittle and cracked
- Water getting into walls through failed joints
If you live in an older home near Church of St Mary the Virgin, an extension built onto an older house moves differently, and the joint between them takes the strain.
Comparing quotes
- Whether you can choose the colour
- Whether VAT is included
- How the joint is cleaned and prepared
- Whether all the old sealant comes out first
How we quote for external mastic
Call for a quick quote. What matters most is:
- The product the joint needs
- Mould in or behind the old joints
- How easy the joints are to reach
- Whether old sealant or filler has to be cut out
Instead of a standard rate, we look at what your job involves: how many joints, what’s in them now and how we reach them. You’ll know the price before we begin.
Asking for a quote
A few details help us give you an accurate quote. When you ask for a quote, tell us:
- Where the property is
- Access, such as stairs, a lift or height
- A few photos by email, if you can
- The type of property
It all starts with a short chat. Tell us what’s wrong, where it is and how much there is, and we will explain how we’d tackle it. Whenever you are ready, call 0345 464 0079 or send us an email.