West Sussex · England
External Mastic in Crosspost
Specialist external mastic for Crosspost: careful preparation, the right product and tidy work. Call for a quick quote.
- Plants rooting in failed movement joints
- Hard, crazed mastic that has stopped moving
- Leaking joints around cladding and façade panels
Looking after it afterwards
After the cure time, these simple habits help:
- Walk round the building once a year and look at the joints
- Keep movement joints as flexible joints, not mortar
- Avoid pressure-washing directly into sealant joints
- Fix overflowing gutters above sealed joints
Don’t let soil, plants or ivy build up against the new joints. Damp material against the sealant shortens its life.
An open movement joint lets rain into the wall every time it pours. That can lead to damp patches, staining and frost damage which cost more to put right than the joint.
External mastic in Crosspost, done properly
We are ARBOMaster approved applicators, and each external joint gets a sealant suited to it. Porous or awkward surfaces are primed where the sealant needs it and we use one wherever it does. If you have damp patches traced to an open external joint and joints with sealant missing in places, we can help, on render & cladding joints, façade panels and copings & trims alike.
External sealant needs dry, clean surfaces, so work around Crosspost is planned for dry weather. Tell us about access to all sides of the building, including outbuildings and garages.
Our work is backed for twelve months, in Crosspost and everywhere else we cover.
- Where
- Crosspost (RH17)
- Wider area
- West Sussex
- Guarantee
- One year on every job
- Quotes
- A clear quote up front
- Phone
- 0345 464 0079
- Last updated
- 26 October 2026
Your questions about external mastic in Crosspost
Do you cover Crosspost for external mastic?
Yes, Crosspost is within the area we cover. Our work covers London and the South East. Just phone 0345 464 0079 or email us with a few details of the job, and we will send you a clear quote.
I let a flat near Wivelsfield station. Can you help?
Yes, landlords and agents are among the people we work for. Just phone 0345 464 0079 or send us an email with the address and what needs doing, and we will send you a clear quote.
How long will you be here?
As a guide, most jobs take a few hours for a handful of joints, longer for a whole elevation. Bigger jobs take longer, and we’ll say how long yours will take.
What is a movement joint?
A movement joint is a planned break in the wall that absorbs expansion and shrinkage. It’s sealed with a flexible sealant, not mortar.
What do you put in the joint?
We choose the sealant for the joint, not the other way round. Movement, water and weather all affect the choice, and we’ll tell you what we’re using.
Is it worth trying it myself?
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.
Should I point up the gap in my brickwork?
No. Rigid materials can’t move with the wall and the joint fails. If it has already been filled, we can generally cut it out and reseal it.
Are you ARBOMaster approved?
Yes. We hold ARBOMaster approved applicator status, and we are fully insured.
Different surfaces, different methods
Concrete and blockwork
Concrete faces can be dusty and porous, so cleaning and priming matter. We prime where the sealant needs it.
Copings and trims
A failed coping joint lets water into the top of the wall. Resealing them is a small job that protects a lot.
The process
We keep the work tidy and contained to the area we are working on, so you can get on with your day. The job generally takes anything from a few hours to several days, depending on the building, and we explain the cure time before we leave. Somewhere as small as Crosspost, access is often the only tricky part. For outside work, also let us know about exposed walls and any outbuildings involved.
- We look at every joint and agree a colour to suit the wall.
- We take out the old sealant until the faces are sound.
- Backing rod goes in so the sealant can stretch between the two faces.
- Primer is applied wherever the sealant needs it.
- A low-modulus exterior sealant is gunned in and tooled to a neat finish.
Preparing for the visit
- Plan for the work area to be out of bounds to pets and children
- Clear the area around the work
- Let us know about parking restrictions
Get a quote
If you are in Crosspost and need external mastic, phone 0345 464 0079 or send us an email. Tell us what the problem is and where, and we’ll agree the price before any work begins.
Advice
Why deal with it now?
A low-modulus sealant is chosen because it moves without pulling hard at the edges. That matters on brick, render and concrete, which can be weaker at the face. Too stiff a sealant can pull at the edges and break them. Older cottages and farmhouses around Crosspost can have timber floors and frames, where water from a failed joint can cause rot if it’s left.
Every job is a little different, so each one gets its own quote. The number of joints, how easy they are to reach and the sealant needed all make a difference, and we will explain the quote if you ask.
What you get with us
- Rated 4.9 stars on Google
- Homes, businesses and hotels
- White, clear, grey or another colour, product permitting
- Anti-fungal sanitary silicone in wet areas
Read our cost guide and what customers say.
What external mastic looks like in Crosspost
Historic houses like Ockenden Manor (about 3.1 miles north-east) are a reminder that the area around Crosspost has older buildings as well as new. In older buildings, older brick and stone need a sealant that suits them, at the right joint depth. 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.
For landlords with property near Wivelsfield station, outside joints that have cracked can let damp into a rental, so check them between lets. For site and facilities teams at buildings such as Bolney CofE Primary School, larger buildings have long runs of movement joint that eventually need resealing.
Crosspost is about 4 miles north-west of Burgess Hill, in West Sussex. Homes, rented property, offices and hotels in Crosspost can book us for external mastic. The work is guaranteed for a year. Across West Sussex, we cover 371 places, Crosspost among them. We also work in Crawley, around 9 miles away.
Our applicators cover all of RH17 for external mastic and the streets around it. We cover properties on Cowfold Road and Chapel Road and the roads around them. We also cover the places around Crosspost: Bolney (1 mile north-east), Twineham Green (1 mile south), Twineham (2 miles south), Wineham (2 miles south-west) and Kent Street (2 miles west). Further out, we also cover Crawley (9 miles north), Horsham (7 miles north-west), Worthing (14 miles south-west), Haywards Heath (5 miles east), Burgess Hill (4 miles south-east) and East Grinstead (13 miles north-east).
Landmarks near Crosspost
The nearest railway station is Wivelsfield station, about 4.2 miles east. Well-known places in the area include The Dene Hospital (2.5 miles south-east) and Cuckfield Museum (3.2 miles north-east). For a walk, there’s Blunts Wood and Paiges Meadow.
DIY sealant or a professional job?
If you’ve already had a go yourself, that is fine. We remove it and do the joint properly.
If you are set on DIY, put the effort into preparation: remove every trace of old sealant, clean and dry the joint, and follow the product’s cure time. If it fails, we can still redo it.
Signs you need external mastic in Crosspost
If plants are growing out of a joint, the sealant has generally failed or was never there. Roots and dirt hold water against the wall and speed up the damage.
The problems people usually mention when they call are:
- Panel joints letting water in
- Old sealant gone brittle and cracked
- Plants rooting in failed movement joints
- Joints with sealant missing in places
For an older house near a landmark such as St Mary Magdalene's Church, an extension built onto an older house moves differently, and the joint between them takes the strain.
Comparing quotes
- Which colour the sealant will be
- What happens if they find a problem under the old sealant
- When the joint can take water or movement
- Whether VAT is included
What we cannot put right
Before booking, it’s worth knowing the limits too:
- Adding movement joints to masonry that has none
- Cracked brickwork or render that needs a builder or plasterer
- Damp that is not coming from the joint
Not sure which it is? You can ring 0345 464 0079 or send us an email and we will tell you honestly before booking.
Surfaces we seal
- Joints between brick and frames
- Render & cladding joints
- Brickwork movement joints
- Façade panels
- Concrete & block
- Copings & trims