West Sussex · England
Blackstone External Mastic
External mastic for Blackstone, by sealant specialists with 20+ years’ experience. 180+ five-star Google reviews and a 4.9 rating.
- Joints pointed up with cement by mistake
- Water getting into walls through failed joints
- Joints where the bead has come unstuck
When it isn’t the sealant
We’ll always be straight with you, so here’s what sealant can’t fix:
- Adding movement joints to masonry that has none
- Render that’s blown, hollow or coming away
- Cracked brickwork or render that needs a builder or plasterer
If in doubt, phone 0345 464 0079 or drop us an email and we’ll say what we think before booking.
What we seal
- Concrete & block
- Joints between brick and frames
- Façade panels
- Render & cladding joints
- Brickwork movement joints
- Copings & trims
About our external mastic in Blackstone
Short cuts in external joints show up within a season or two. New sealant over old, joints packed with mortar and beads with no backing rarely last long. We strip the joint back and start again. Typical jobs include sealant that has lost its bond to the brick or render and brick movement joints where the sealant has split, on joints between brick and frames, render & cladding joints and copings & trims.
Around Blackstone, older buildings can be stone, brick or timber-framed, many with extensions added later. Where one material meets another is where water generally gets in.
We stand behind the work with a 12-month guarantee.
- Location
- Blackstone (BN5)
- Region
- West Sussex
- Cover
- One year on every job
- Quotes
- Quoted before any work starts
- Telephone
- 0345 464 0079
- Page updated
- 26 October 2026
DIY versus a professional finish
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.
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.
How to look after the new joints
Good habits help new joints last longer. A few tips:
- Check external joints each spring
- Have failed joints looked at early
- Never let anyone fill a movement joint with mortar
- Show decorators and builders where the movement joints are
Look over the joints once a year, ideally after winter. Watch for splits, edges coming away or growth in the joint.
Once a joint can’t move, the wall finds another way, generally as cracking in the brickwork or render nearby. Resealing it early helps prevent that.
Blackstone questions
Will you come out to Blackstone?
Yes. Blackstone is within the area we cover, which takes in towns, villages and rural addresses. Our work covers London and the South East. Let us know about access, parking and anything unusual about getting there when you book.
Can you do external mastic in Blackstone?
Yes. We work across London and the South East, and Blackstone is part of that. You can phone 0345 464 0079 or email us and tell us what needs doing, and we’ll give you a clear quote.
Will there be a smell?
Possibly a little. It fades as the sealant cures.
What should I tell you?
Where the job is, what the problem is and roughly how big it is. If you can, email a few photos.
What colours does the sealant come in?
We aim for a joint that suits the wall rather than one that jumps out. Colour is agreed with you before we begin from the range available.
Can you reach joints on upper floors?
That depends on the building and the joints. Where joints can be reached safely, we will do them. Tell us about the building and we’ll confirm what access is needed.
Where do you work from?
We’re based in Crawley, West Sussex, and we cover South East England, London and all of Scotland.
Is the work guaranteed?
Yes. There’s a 12-month guarantee on every job.
What we do, step by step
The work is kept neat and contained to the area we’re working on. The job normally takes a few hours to a few days, depending on the length of joint and the access, and we tell you how long to leave it before we go. Somewhere as small as Blackstone, access is often the only tricky part. If the job is outside, mention outbuildings, exposed walls and how to reach them.
- We start by walking round the building and agreeing the joints and the access.
- We cut out the old mastic and rake out anything in the joint.
- The faces are brushed clean and primed where the product requires it.
- Backing rod sized to the joint goes in to set the depth.
- We apply the sealant, tool it and check the whole run.
How to prepare
- Mention any sign-in or site rules at work premises
- Mention any tricky access
- Where the joints are inside, avoid wetting them before we arrive
How to get a quote
If you are in Blackstone and need external mastic, call 0345 464 0079 or email us. Tell us what the problem is and where, and we will agree the price before any work begins.
Related advice
Blackstone buildings and the weather
London and the South East are among the drier parts of the UK, though outdoor sealant still has to go onto a dry joint, so the forecast decides the day.
In the older streets around The Parish Church of St Bartholomew, an extension built onto an older house moves differently, and the joint between them takes the strain. If you let a flat or house near Hassocks station, split movement joints are easy to miss on a rental until damp shows inside.
Blackstone is about 5 miles west of Burgess Hill, in West Sussex. From the centre of Blackstone to the outskirts, we cover external mastic for every kind of property, from flats and houses to offices and hotels. Blackstone is one of 371 places in West Sussex we cover for external mastic. You can also see our page for Brighton, roughly 8 miles from Blackstone.
Postcode districts we cover here for external mastic: BN5. Streets in the area include Blackstone Lane and Blackstone Street. Neighbouring places we cover for external mastic include Woodmancote (1 mile south-west), High Cross (1 mile north-east), Albourne (1 mile east), Albourne Street (1 mile east) and Albourne Green (1 mile east). Larger places within reach include Crawley (13 miles north), Horsham (10 miles north), Worthing (10 miles south-west), Haywards Heath (8 miles north-east), Burgess Hill (5 miles east) and Littlehampton (15 miles south-west).
Landmarks near Blackstone
Blackstone’s nearest station is Hassocks station, about 3.9 miles east of the centre. Other landmarks nearby include The Dene Hospital (3.8 miles north-east) and The Budding Foundation Museum of Gardening (3.6 miles east). Not far away are Woods Mill and Wolstonbury Hill.
Nearby places to Blackstone
Other services in Blackstone
Different surfaces, different methods
Concrete and blockwork
Blockwork and concrete shrink over time and move with the seasons. Their movement joints are sealed over backing rod with a flexible sealant.
Cladding and façade panels
Cladding and façade panels are normally separated by sealed joints. We reseal them with a sealant suited to the panel material.
Work for landlords, hotels and businesses
We regularly work with letting and managing agents. Send the address, what’s needed and the access arrangements.
We also work for businesses, from offices to washrooms and kitchens. For commercial premises, we can talk through working times when we quote.
Leave it or put it right?
The longer a joint stays open, the more water the wall takes in. In cold weather, frost can damage wet brick and render around the joint, so the problem grows beyond the joint itself. In a small place like Blackstone, homes can be exposed to wind and rain, which finds any gap, and older walls, once damp, take a long time to dry.
Instead of a standard rate, we price the job in front of us: how many joints, what’s in them now and how we reach them. You will know the price before we begin.
What you get with us
- Homes, businesses and hotels
- Any old sealant cut out fully, not covered over
- You choose the colour before work begins
- Rated 4.9 stars on Google
Take a look at what affects the cost or customer reviews.