Kent · England
External Mastic in Underriver
Specialist external mastic for Underriver: careful preparation, the right product and tidy work. Call for a quick quote.
- Failed seals between different materials
- Failed sealant between panels on a façade
- Rigid filler in a joint that should flex
About our external mastic in Underriver
A movement joint is only as good as its depth. Backing rod controls how deep the sealant goes and keeps it off the back of the joint, so it bonds to the two sides only and can stretch. Typical jobs include panel joints letting water in and gaps where render, brick and frames meet, across brickwork movement joints, render & cladding joints and joints between brick and frames.
External sealant needs dry, clean surfaces, so work around Underriver is planned for dry weather. Tell us about access to all sides of the building, including outbuildings and garages.
We stand behind the work with a 12-month guarantee, so you are not left on your own once the job is done.
- Place
- Underriver (TN15)
- Wider area
- Kent
- Guarantee
- 12 months on all our work
- Quote
- Quoted before any work starts
- Telephone
- 0345 464 0079
- Page updated
- 26 October 2026
Underriver: your questions answered
Will you come out to Underriver?
Yes. Underriver 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.
I let a flat near Hildenborough station. Can you help?
Yes. We work for landlords and letting agents as well as homeowners. You can phone 0345 464 0079 or drop us an email with the details for a clear quote.
Which products do you use?
We choose the sealant for the joint, not the other way round. Movement, water and weather all affect the choice, and we will tell you what we are using.
Is it OK to seal over old sealant?
No. The old sealant always comes out first.
How long will you be here?
As a guide, most jobs take a few hours to a few days, depending on the length of joint and the access. Bigger jobs take longer, and we will say how long yours will take.
Can you work on commercial sites?
Yes, regularly. Larger jobs can be planned room by room or area by area.
Should I try DIY first?
For a simple, easy-to-reach joint, a careful DIYer can do a reasonable job. The usual mistakes are sealing over old sealant, sealing a damp joint and using too much.
Are you ARBOMaster approved?
Yes. We hold ARBOMaster approved applicator status.
What happens if it’s left?
An open joint keeps letting water into the wall with every downpour. 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 Underriver, homes can be exposed to wind and rain, which finds any gap, and damp in older walls is slow to dry out.
Rather than a set price list, we look at what your job involves: how many joints, what’s in them now and how we reach them. The price is agreed before we begin.
Why choose Mr Mastic in Underriver
- You choose the colour before work begins
- 20+ years of sealant experience
- An ARBOMaster approved applicator
- Fully insured
See what affects the cost and our reviews.
Quotes for external mastic in Underriver
We quote each job individually. This is what makes a difference:
- Whether there’s mould to deal with
- The type of sealant required
- How many areas need sealing
- Whether the work is at height
Some things make a job bigger or smaller: how much old sealant there is and how stubborn it is, whether mould needs treating, and whether the work is at height. We take all of that into account in your quote.
What to tell us for a quote
What to tell us when you ask for a quote:
- If someone has resealed it before
- Roughly how big the job is
- Where the property is
- A few pictures by email, if you can
To get a quote, ring 0345 464 0079 or email us and tell us where the job is and what the problem looks like. You’ll have a clear quote before work begins.
Towns and villages near Underriver
What else we do in Underriver
Different surfaces, different methods
Cladding and façade panels
Cladding and façade panels are usually separated by sealed joints. We reseal them with a sealant suited to the panel material.
Concrete and blockwork
Blockwork and concrete shrink over time and move with the seasons. We reseal their joints with backing rod and a flexible product.
DIY versus a professional finish
If you do try it yourself, take your time over the preparation: take out all the old sealant, make sure the joint is clean and dry, and give it the full cure time. If it doesn’t work out, we can still put it right.
Too much sealant is as bad as too little. A thick, smeared bead looks untidy and doesn’t move well, and the joint depth matters as much as the finish.
How the visit works
All our tools and materials come with us in the van, so there’s nothing for you to buy. After a quick look at the joints together, we protect the area and start. Most jobs take a few hours to a few days, depending on the length of joint and the access. Somewhere as small as Underriver, access is often the only tricky part. For outside work, also let us know about exposed walls and any outbuildings involved.
- Each joint is checked and the colour of the new sealant agreed.
- We take out the old sealant until the faces are sound.
- Closed-cell backing rod is pushed in so the sealant bonds to two sides only.
- Primer is applied wherever the sealant needs it.
- We gun in low-modulus sealant and tool it neatly.
How to prepare
- Mention any parking rules near the property
- Mention if the joints have been sealed before
- Tell us about access, such as stairs, a lift or high-level joints
How to get a quote
Asking for a quote is easy: let us know what needs doing and where, and roughly how big it is. A few pictures by email make the job easier to understand, and we’ll take it from there.
Read more
Walls and rooflines in Underriver
Historic houses like Knole House (about 1.6 miles north-west) are a reminder that the area around Underriver has older buildings as well as new. Where a home is older, older walls and rooflines need a sealant that moves with them and suits the material. 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.
Rented homes near Hildenborough station change hands often, and split movement joints are easy to miss on a rental until damp shows inside. If you live in an older home near Church of St Margaret, an extension built onto an older house moves differently, and the joint between them takes the strain. Managing a site like Sevenoaks Preparatory School? Then larger buildings have long runs of movement joint that eventually need resealing.
Underriver is about 3 miles south-east of Sevenoaks, in Kent. Every kind of property in Underriver can book us for external mastic. The work is guaranteed for a year. Our area takes in 922 places across Kent, from the larger towns to small villages. Crawley is on our list too, around 20 miles away.
Postcode districts we cover here for external mastic: TN15. Other places close to Underriver include Budds (1 mile east), Bitchet Green (1 mile north-east), Watt's Cross (2 miles south), Godden Green (2 miles north) and Stone Street (2 miles north-east). Larger places within reach include Maidstone (13 miles east), Dartford (14 miles north), Sevenoaks (3 miles north-west), Royal Tunbridge Wells (8 miles south), Gravesend (14 miles north-east) and Tonbridge (4 miles south-east).
Around Underriver
In Underriver, that means homes and buildings near Knole Park, among other places. The closest station to Underriver is Hildenborough station, about 2.3 miles south of the centre. Nearby you’ll also find Sevenoaks Museum (2.2 miles north-west) and Tonbridge Castle (4 miles south-east). For a walk, there’s Dryhill Nature Reserve and Barden Lake.
Honest limits
Sealant is not the answer to every problem, and we’d rather say so up front. Sealant will not put right:
- Rising or penetrating damp from elsewhere in the wall
- Subsidence or other structural problems
- Adding movement joints to masonry that has none
If you are not sure, just ring 0345 464 0079 or drop us an email and we’ll give you a straight answer before you book.
Where we work in Underriver
- Joints between brick and frames
- Copings & trims
- Brickwork movement joints
- Façade panels
- Concrete & block
- Render & cladding joints
Aftercare tips
Aftercare is simple:
- Clear growth from the base of walls and joints
- Tell anyone working on the walls about the movement joints
- Check external joints each spring
- Check the sealant is paintable before painting near it
Do not paint over the new sealant unless we have said the product is paintable. Many exterior sealants aren’t designed to be painted, and paint can crack as the joint moves.
Once a joint cannot move, the wall finds another way, often as cracks near the joint. Resealing it early helps prevent that.