Hertfordshire · England
External & façade joints in Lea Valley, Hertfordshire
Sealing brickwork movement joints, render, cladding and façade joints for homes and businesses in Lea Valley and across Hertfordshire. Fully insured, ARBOMaster approved and guaranteed for a year.
- Plants rooting in failed movement joints
- Failed sealant between panels on a façade
- Movement joints filled with mortar instead of sealant
External mastic in Lea Valley
As ARBOMaster approved applicators, we choose exterior sealants to suit the joint and the surfaces. Some surfaces need a primer before sealing. If you’re dealing with movement joints with cracked, split or missing sealant and failed seals between different materials, we can put it right.
Somewhere as small as Lea Valley, homes and farm buildings often face open ground, so walls and rooflines take the full force of wind and rain. Joints on those walls need a sealant that moves with the building and stays in place.
Whatever the size of the job, it’s backed by our one-year guarantee in Lea Valley and across Hertfordshire.
- Where
- Lea Valley (AL4)
- Wider area
- Hertfordshire
- Guarantee
- 12 months on all our work
- Quote
- A clear price before any work starts
- Telephone
- 0345 464 0079
- Last updated
- 26 October 2026
Keeping the joints in good condition
Joint life depends on how it’s used and looked after. We suggest:
- Get split or bare joints resealed while the damage is small
- Walk round the building once a year and look at the joints
- Wash walls gently around the sealant
- Leave the joints unpainted unless we have said otherwise
Look over the joints once a year, ideally after winter. Watch for splits, edges coming away or growth in the joint.
Leaks behind façade panels and render often go unseen. When it finally shows inside, the joint may have been open for years.
What external mastic looks like in Lea Valley
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. With historic houses such as Shaw's Corner (about 2.5 miles north-east) nearby, there’s older building stock in the area around Lea Valley as well as newer homes. In older buildings, older walls and rooflines need a sealant that moves with them and suits the material.
For landlords with property near Harpenden station, outside joints that have cracked can let damp into a rental, so check them between lets. If you look after a building such as High Beeches Primary School, movement joints, cladding joints and gutters on larger buildings need the same care as a house’s.
Lea Valley is about 1 mile east of Harpenden, in Hertfordshire. If you need external mastic in Lea Valley, please phone 0345 464 0079 or send us an email for a quick quote. We’re based in Crawley and cover Hertfordshire, Lea Valley included. Lea Valley is one of 381 places in Hertfordshire where we work for external mastic. For nearby work, see our London page.
Every address in AL4 is covered for external mastic, from the main roads to the quietest streets. That includes homes and businesses on Castle Rise, Lower Luton Road and Marshalls Way. Lea Valley sits on or near the B653, so getting to you is simple. We also cover Mackerye End (1 mile north), The Folly (1 mile east), Batford (1 mile west), Amwell (1 mile south-east) and Harpenden (1 mile west). Further out, we also cover Watford (11 miles south), Hemel Hempstead (8 miles south-west), Stevenage (9 miles north-east), St Albans (5 miles south), Welwyn Garden City (6 miles east) and Hitchin (9 miles north).
Landmarks near Lea Valley
Typical jobs here are in homes near Lydekker Park, The Cherry Trees pub and Sir John Lawes School, among other places. For rail, the closest station is Harpenden station, about 1.4 miles west of the centre. Nearby you’ll also find St Albans City Hospital (4.2 miles south) and Harpenden Museum (1.6 miles west). Open spaces near Lea Valley include Wheathampstead Local Nature Reserve.
When something else is needed
We will always be straight with you, so here’s what sealant cannot fix:
- Rising or penetrating damp from elsewhere in the wall
- Walls that need new movement joints cut into them
- Loose or hollow render, which needs re-rendering
If in doubt, call 0345 464 0079 or email us and we will say what we think.
What we seal
- Brickwork movement joints
- Concrete & block
- Render & cladding joints
- Joints between brick and frames
- Copings & trims
- Façade panels
Nearby places to Lea Valley
Also in Lea Valley
FAQs for Lea Valley
Can you help a landlord with a rental near Harpenden station?
Yes, we work for landlords and agents. Just phone 0345 464 0079 or email us and tell us about the property, and we will send you a clear quote.
Do you cover smaller places like Lea Valley?
Yes, Lea Valley is covered. We work across London and the South East, and smaller places are part of that. The journey is planned ahead, so it helps to know about access.
How do you reach high-level joints?
It depends on the building. Send us pictures and a rough idea of the height.
Can new sealant go over the old?
No. New silicone won’t bond to old silicone, and anything trapped underneath, including mould and water, stays there. We remove it all first.
What do you put in the joint?
Quality sealants from brands including Arbo and Everbuild, chosen to suit the joint. We explain the product when we quote.
Can you work on commercial sites?
Yes. Commercial and hotel work is a large part of what we do. Working times can be discussed when we quote.
How long does external mastic last?
That depends on the wall, the weather and the movement. Signs to watch for are cracking, hardening and gaps at the edges.
Are you ARBOMaster approved?
Yes. We’re approved under the ARBOMaster scheme.
For landlords and businesses
From a single let to a portfolio, you get the same standard of work: the old material taken out, careful preparation and a 12-month guarantee.
Letting agents often deal with us directly. Tell us the address, the job and how access works and we’ll give you a quote.
Common problems we fix in Lea Valley
Every building moves. Clay bricks expand slightly over their life, concrete and block shrink, and everything moves with temperature and wet. All of that ends up in the joint sealant.
Most people get in touch after spotting something like this:
- Sealant that has lost its bond to the brick or render
- Brick movement joints where the sealant has split
- Damp patches traced to an open external joint
- Joints pointed up with cement by mistake
In the older streets around All Saints, the joints between older walls, newer extensions and the roofline need a sealant that can move.
What your quote should include
- When the joint can take water or movement
- What preparation is included
- Is VAT in the price?
- The length of the guarantee
How it works
Good joint work is mostly preparation, and we do not rush it. Joints are cleaned back and dried before anything new goes in. All told, the work takes a few hours to a few days, depending on the length of joint and the access. Somewhere as small as Lea Valley, access is often the only tricky part. For outside work, also let us know about exposed walls and any outbuildings involved.
- We start by checking each joint, agreeing the ones to redo and how we will reach them.
- The old mastic and anything lodged in the joint is removed.
- Both sides are cleaned back to sound material and primed if needed.
- Closed-cell backing rod is fitted to set the depth and stop three-sided bonding.
- We gun in a flexible exterior sealant in a colour that suits the wall and tool it neatly.
Getting ready for the visit
- Let us know about stairs, lifts or work at height
- Let us know about parking restrictions
- Keep children and pets away from the work area
How to get a quote
To get a quote, phone 0345 464 0079 or email us and tell us where the job is and what the problem looks like. You will have a clear quote before we start.
Advice
How we quote for external mastic
You will get a clear quote before any work starts. It’s based on:
- How much there is to do
- The product the joint needs
- Whether the work is at height
- When we can work, for business premises
What you pay reflects the work, not a rough estimate. That is why we ask about the job first and give you a clear price before any work starts.
Helping us quote
A few details help us give you an accurate quote. When you get in contact, it helps to mention:
- The problem you’ve noticed
- The type of property
- Whether it has been sealed before
- Where the job is, and your postcode
Call for a quick quote, or send an email if you’d rather. Describe what needs sealing and we will explain what’s involved.
Can I do it myself?
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.
Sealing over old silicone is the commonest DIY error. New silicone won’t bond to old, so it peels away and traps moisture behind it. All the old material has to come out first.