Hertfordshire · England
External Mastic in Gosmore
External mastic for Gosmore, by sealant specialists with 20+ years’ experience. 180+ five-star Google reviews and a 4.9 rating.
- Cracked joints where brick meets render or frames
- Weathered mastic that no longer stretches
- Movement joints with cracked, split or missing sealant
External mastic in Gosmore, done properly
Many failed façade joints only get noticed once there’s a stain or a damp patch inside. We inspect them, agree which need doing and reseal with a weatherproof, flexible sealant in a matching colour. We work on concrete & block, copings & trims and façade panels, and people most often call us about leaking joints around cladding and façade panels and cracked joints where brick meets render or frames.
External sealant needs dry, clean surfaces, so work around Gosmore is planned for dry weather. Let us know about access to every wall, plus any garages or outbuildings.
Whatever the size of the job, it’s backed by our one-year guarantee in Gosmore and across Hertfordshire.
- Location
- Gosmore (SG4)
- Region
- Hertfordshire
- Cover
- A year, on every job
- Quote
- A clear price before any work starts
- Call
- 0345 464 0079
- Last updated
- 26 October 2026
Common problems we fix in Gosmore
Many joints fail because they were sealed too deep or with nothing behind them. If the sealant sticks to the back as well as the sides, it cannot stretch and tears as soon as the joint widens.
The most common problems we see are:
- Movement joints filled with mortar instead of sealant
- Old sealant gone brittle and cracked
- Rain getting behind render or cladding at a joint
- Cracked joints where brick meets render or frames
Managing a site like St Ippolyts Church of England Aided Primary School? Then larger buildings have long runs of movement joint that eventually need resealing.
Comparing quotes
- Who does the work, and how experienced they are
- Is the old sealant removed completely?
- Is VAT in the price?
- Which colour the sealant will be
Nearby places to Gosmore
Also in Gosmore
When it is not the sealant
We will not take on work that won’t last, so these are the limits:
- Adding movement joints to masonry that has none
- Cracks in the bricks or render themselves, away from the joints
- Render that’s blown, hollow or coming away
Not sure which it is? You can call 0345 464 0079 or drop us an email and we will tell you honestly before booking.
What we seal
- Render & cladding joints
- Concrete & block
- Copings & trims
- Façade panels
- Brickwork movement joints
- Joints between brick and frames
Different surfaces, different methods
Joints between dissimilar materials
Different materials may need different primers. Both surfaces are cleaned and primed as the product requires.
Render joints
Cracks along render joints let water in behind the coat. Resealing the joints early keeps water out and helps it last.
What we do, step by step
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. After that, the work takes a few hours for a handful of joints, longer for a whole elevation. Somewhere like Gosmore needs a little journey planning: tell us about narrow lanes, gates, long drives and where we can park. Everything for the job comes with us, so a second trip is avoided where possible.
- 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.
- The exterior sealant is applied, tooled and checked along its length.
Preparing for the visit
- Clear items away from the joints we’re working on
- Mention any sign-in or site rules at work premises
- Tell us if parking is tricky
Ask for a quote
Call for a quick quote, or send an email if you’d rather. Describe what needs sealing and we will explain what’s involved before giving you a price.
Advice
Gosmore buildings and the weather
Historic houses like Knebworth House (about 4.7 miles south-east) are a reminder that the area around Gosmore 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. Compared with the north and west, the South East gets less rain, though outdoor sealant still has to go onto a dry joint, so the forecast decides the day.
In the older streets around Church of St Ippolyts (church of England), older walls, gutters and the joints where extensions meet them need a flexible sealant. For landlords with property near Hitchin station, outside joints that have cracked can let damp into a rental, so check them between lets.
Gosmore is about 1 mile south of Hitchin, in Hertfordshire. Every kind of property in Gosmore can book us for external mastic, old or new, large or small. Every job comes with our 12-month guarantee. Across Hertfordshire, we cover 381 places, Gosmore among them. Our London page covers work nearby.
Our applicators cover all of SG4 for external mastic. We cover properties on London Road, Mill Lane and Orchard Close. We also cover the places around Gosmore: St Ippolyts (1 mile east), St Ibbs (1 mile south-east), Sperberry Hill (1 mile south-east), Charlton (1 mile north-west) and Little Almshoe (1 mile south-east). We also work in nearby towns such as Hemel Hempstead (15 miles south-west), Stevenage (4 miles south-east), St Albans (13 miles south), Welwyn Garden City (10 miles south), Harpenden (9 miles south-west) and Hatfield (12 miles south).
Around Gosmore
We work in homes and buildings around St Mary's Church, Butts Close and The Bird in Hand pub. Other local landmarks include Hitchin Girls' School (1.1 miles north) and Kingshott School (0.8 miles north-east). The closest station to Gosmore is Hitchin station, roughly 1.5 miles north of the centre. Nearby you’ll also find North Hertfordshire Museum (1.3 miles north) and Wymondley Castle (1.7 miles east). The countryside around Gosmore includes Markham's Hill and Purwell Ninesprings.
For landlords and businesses
We also work for businesses, from offices to washrooms and kitchens. For commercial premises, we can talk through working times when we quote.
We work for letting agents and landlords as well as householders. Sealant work between tenants keeps a property looking cared for.
Can I do it myself?
Not every job suits DIY: work at height, external movement joints, fire-rated sealant and large areas call for the right materials, safe access and experience.
Sealing over old silicone is the commonest DIY error. New silicone won’t bond to old, so it lifts and traps water and mould underneath. Everything old must be removed first.
Common questions in Gosmore
Can you do external mastic in Gosmore?
Yes. Our work covers London and the South East, and Gosmore is part of that. You can ring 0345 464 0079 or drop us an email and let us know what needs doing, and we will send you a clear quote.
Can you help a landlord with a rental near Hitchin station?
Yes. We work for letting agents and landlords as well as householders. Just phone 0345 464 0079 or drop us an email with the address and what needs doing, and we will send you a clear quote.
What is a movement joint?
A movement joint is a planned break in the wall that absorbs expansion and shrinkage. It should be filled with flexible sealant, never mortar.
What information do you need?
The location, the problem and the rough size of the job. Photos by email help too.
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. Larger jobs naturally take longer, and we’ll tell you how long to expect.
Can you work on commercial sites?
Yes. Commercial and hotel work is a large part of what we do. We can talk about working times when we quote.
What do you put in the joint?
We choose the sealant for the joint, not the other way round. Where it moves, gets wet or faces the weather makes a difference.
Should I point up the gap in my brickwork?
No. A mortar-filled joint cannot move, so the wall cracks somewhere else instead. It needs a flexible sealant over backing rod.
Leave it or put it right?
Resealing a run of joints in one go is generally better than patching one at a time. Joints of the same age tend to fail together. Around Gosmore, older homes often have timber in their floors and frames, where water from a failed joint can cause rot if it’s left.
There are no prices on our website, because each job is priced on what it involves. For a quick quote, please phone 0345 464 0079 or email us and we’ll talk you through it.
Why book with us
- Rated 4.9 stars on Google
- We leave the area clean and tidy
- 12-month guarantee on every job
- Full insurance on every job
See our cost guide or our reviews.