Hertfordshire · England
Chells External Mastic
Professional external mastic in and around Chells, with every bit of old sealant taken out first and a 12-month guarantee.
- Plants rooting in failed movement joints
- Movement joints with cracked, split or missing sealant
- Damp patches traced to an open external joint
How we handle external mastic in Chells
Joints between dissimilar materials, like brick against render or concrete against a steel frame, see movement from both sides. A flexible sealant bridges the two. If you’re dealing with leaking joints around cladding and façade panels and joints pointed up with cement by mistake, we can help.
In a smaller place like Chells, some homes face open ground, and walls and rooflines facing the weather take the worst of it. That’s where gutter joints and wall joints tend to fail first.
We guarantee the work for a year. If there’s a problem with our work within the year, let us know and we’ll sort it.
- Place
- Chells (SG2, SG1)
- Region
- Hertfordshire
- Guarantee
- A year, on every job
- Quotes
- A clear quote up front
- Phone
- 0345 464 0079
- Updated
- 26 October 2026
Looking after it afterwards
To keep the joints looking good and working properly:
- Point out the joints to other trades
- Act on the first splits you see
- Leave the joints unpainted unless we have said otherwise
- Wash walls gently around the sealant
If you have more work done on the wall, such as new render, cladding or an opening, show the contractor the movement joints. They should be kept open and resealed, not filled.
A joint that has stopped moving pushes the movement elsewhere, usually as cracking in the brickwork or render nearby. Resealing it early helps prevent that.
Outside joints around Chells
Chells is part of Stevenage, one of the post-war new towns. Many homes date from the post-war decades and were built in phases, so neighbouring houses often have rooflines and wall joints of the same age, wearing out at the same time. London and the South East are among the drier parts of the UK, but outside sealant still needs a dry, clean surface, so outdoor work is planned around the forecast.
If you let a flat or house near Stevenage station, failed wall and movement joints let damp in, so they’re worth checking between tenancies. In the older streets around St Hugh & St John, an extension built onto an older house moves differently, and the joint between them takes the strain.
Chells is about 1 mile east of Stevenage, in Hertfordshire. If you need external mastic in Chells, it’s easy to get a quote: please ring 0345 464 0079 or email us. We cover Hertfordshire from our Crawley base, Chells included. Our Hertfordshire coverage runs to 381 places, Chells among them. We also work in London, around 29 miles away.
Postcode districts we cover here for external mastic: SG2 and SG1. That includes homes and businesses on Scott Road, Eliot Road and Newton Road. If you’re just outside Chells, we cover Stevenage (1 mile west), St Nicholas (1 mile north-west), Pin Green (1 mile west), Aston End (1 mile south-east) and Bedwell (1 mile south-west). Within a short drive, we also cover St Albans (13 miles south-west), Bishop's Stortford (14 miles east), Welwyn Garden City (8 miles south), Harpenden (10 miles south-west), Hitchin (5 miles north-west) and Hoddesdon (13 miles south-east).
Local landmarks in Chells
Typical jobs here are in homes near Lodge Farm Primary School. Chells’s nearest station is Stevenage station, about 1.8 miles south-west of the centre. Well-known places in the area include Lister Hospital (2.1 miles north-west) and Benington Castle (2.4 miles south-east). The countryside around Chells includes Pryor's Wood.
How it works
When we get to you, we compare the joints with what we discussed. If we find something unexpected, we talk it through with you first. Most jobs then take a few hours for a handful of joints, longer for a whole elevation. A visit to Chells is planned like any other: the time, the access and where to park are agreed in advance. If the work is outside, the weather plays a part, as sealant needs a dry surface.
- 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.
- The faces are brushed clean and primed where the product requires it.
- We fit closed-cell backing rod to control the depth.
- We apply the sealant, tool it and check the whole run.
Getting ready for the visit
- Tell us about any water getting in
- Mention any parking rules near the property
- Try not to wet indoor joints just before the visit
How to get a quote
The more we know about the job, the more useful the quote. Let us know the location, the problem and roughly how many joints, and add photos by email if you can.
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Work for landlords, hotels and businesses
Landlords and letting agents in Chells can book us as well as householders. Resealing between tenancies keeps a property looking cared for before the next move-in.
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.
Places near Chells
Also in Chells
When to call us in Chells
Buildings move more than people expect. Brickwork grows a little over the years, blockwork and concrete shrink, and all of it moves with heat and moisture. All of that ends up in the joint sealant.
People generally contact us when they notice something like this:
- Sealant pulling away from one side of the joint
- Gaps where render, brick and frames meet
- Movement joints with cracked, split or missing sealant
- Panel joints letting water in
Managing a site like The Nobel School? Then movement joints, cladding joints and gutters on larger buildings need the same care as a house’s.
What to look for in a quote
- Which sealant they’ll use, and why
- When the joint can take water or movement
- The length of the guarantee
- Is the old sealant removed completely?
Why act early in Chells
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 damage spreads beyond the joint. Around Chells, water from a failed joint in an older home can soak into timber and plaster, which is far harder to put right than the sealant itself.
Combining jobs into one visit is usually more efficient than separate visits, so it’s worth mentioning everything you’d like done. You will get one clear quote for the whole job.
What you get with us
- A 12-month guarantee on all work
- Sanitary silicone with an anti-fungal additive in wet areas
- 20+ years of sealant experience
- White, clear, grey or another colour, product permitting
Take a look at what affects the cost or customer reviews.
Should I try it myself first?
What a professional job adds is preparation and the right product. Joints are cleaned back to sound surfaces and dried, and the sealant is matched to the joint and its conditions, and the work is guaranteed for a year.
Some sealant jobs are within reach of a careful DIYer, such as a straightforward joint indoors. The common mistakes are sealing over old sealant, sealing a damp joint and using far too much.
Chells questions
I let a flat near Stevenage station. Can you help?
Yes, rental work is part of what we do. Just ring 0345 464 0079 or send us an email and tell us about the property, and we’ll send you a clear quote.
Do you cover smaller places like Chells?
Yes, smaller places are covered as well as towns. We work across London and the South East. Just mention lanes, gates or anything else about the route when you book.
What’s an expansion joint in brickwork?
A vertical gap in a long brick wall is normally a movement joint. It gives the wall room to move and needs a flexible seal, not mortar.
Where do you work from?
We are based in Crawley, West Sussex, and we cover South East England, London and all of Scotland.
Can new sealant go over the old?
No, it will not last. It may look fine at first, but the new layer lifts away from the old one. The old sealant has to come out completely.
Are you fully insured?
Yes. We are fully insured, with over 20 years’ experience in sealant work.
Why do you put foam in the joint first?
That is backing rod, a closed-cell foam. It keeps the sealant at the right depth and bonded to the sides only, which would stop it stretching.
Will the new joint stand out?
We aim for a joint that suits the wall rather than one that jumps out. We will talk through colour options before work begins, matched as closely as the range allows.
What the job involves on each surface
Copings and trims
A failed coping joint lets water into the top of the wall. Sealing them early saves the wall below.
Render joints
The face of render can be soft, so a low-modulus sealant is kinder to the joint edges. We prime where the product needs it.