Hertfordshire · England
External Mastic in Welwyn
External mastic across Welwyn and nearby, with every bit of old sealant taken out first.
- Water getting into walls through failed joints
- Joints pointed up with cement by mistake
- Moss and dirt in joints with no sealant left
Quotes for external mastic in Welwyn
Some jobs are bigger than they look, and some smaller. What affects the quote:
- The product the joint needs
- Any mould that needs treating
- The amount of work
- Whether the work is at height
Leaving a failed joint generally makes the job bigger, not smaller, as water and mould keep getting in. If you’re not sure whether it needs doing, ring 0345 464 0079 or drop us an email and we will give you an honest view and a quote.
Asking for a quote
You don’t need to know the technical terms. Just tell us:
- What the problem is, such as mould, gaps, leaks or cracking
- Whether it’s a home or a business
- How we’d reach the joints
- How many joints, rooms or windows are involved
Quotes start with a quick conversation. Describe the problem, the location and the size of the job, and we will explain how we’d tackle it. When it suits you, ring 0345 464 0079 or drop us an email.
External mastic in Welwyn, done properly
Joints in render and cladding are easy to overlook until a damp patch appears. We look over the joints, agree the ones to renew and reseal with a flexible, weatherproof product. We work on brickwork movement joints, joints between brick and frames and façade panels, and people most often call us about failed seals between different materials and water getting into walls through failed joints.
In and around Welwyn, older properties sit alongside newer ones, each with its own outside joints. Older gutters and trims need their joints resealed; newer brick and render need their movement joints kept sound.
Big or small, it’s backed by our one-year guarantee.
- Place
- Welwyn (AL6)
- Wider area
- Hertfordshire
- Cover
- 12 months on all our work
- Price
- A clear price before work begins
- Telephone
- 0345 464 0079
- Page updated
- 26 October 2026
Other services in Welwyn
Different surfaces, different methods
Cladding and façade panels
Cladding and façade panels are generally separated by sealed joints. Each joint gets a sealant that suits the panel and its movement.
Copings and trims
Joints in copings, parapets and trims are exposed to the worst of the weather. We reseal them with an exterior sealant suited to the material.
External mastic in Welwyn: local notes
Rainfall in the South East is lower than in much of the UK, yet outdoor joints still have to be sealed dry, so jobs are booked with the weather in mind. With historic houses such as Digswell House (about 0.9 miles south-east) nearby, there’s older building stock in the area around Welwyn as well as newer homes. In older buildings, older walls and rooflines need a sealant that moves with them and suits the material.
Schools such as Monk's Walk School are buildings too, and larger buildings have long runs of movement joint that eventually need resealing. In the older streets around Parish Church of St Mary, old and new materials meet at the roofline and walls, which is where sealant earns its keep. If you let a flat or house near Welwyn North station, split movement joints are easy to miss on a rental until damp shows inside.
Welwyn is about 2 miles north-west of Welwyn Garden City, in Hertfordshire. Anywhere in AL6, we can carry out external mastic at your property. We cover 381 towns and villages across Hertfordshire, large and small. Our London page covers work nearby.
We cover every part of the AL6 postcode area for external mastic. Whether your property is on High Street, London Road and Mimram Place or anywhere close by, we can help. If you’re just outside Welwyn, we cover Monkswood (1 mile south-east), Ayot St Peter (1 mile south-west), Ayot Green (1 mile south-west), Pottersheath (2 miles north) and Codicote (2 miles north-west). Further out, we also cover Watford (14 miles south-west), Hemel Hempstead (12 miles south-west), Stevenage (6 miles north), St Albans (7 miles south-west), Harpenden (6 miles west) and Hitchin (9 miles north).
Local landmarks in Welwyn
Typical jobs here are in homes near Stable Door pub, Danesbury Park and Homerswood Primary and Nursery School. For rail, the closest station is Welwyn North station, roughly 1.1 miles south-east of the centre. Other landmarks nearby include Queen Elizabeth II Hospital (3.5 miles south) and Datchworth Museum (2.7 miles north-east). The countryside around Welwyn includes Mardley Heath.
Should I try it myself first?
Too much sealant is as bad as too little. A heavy bead looks messy and copes badly with movement, and the joint depth matters as much as the finish.
The difference is mostly in the preparation and the product. Joints are cleaned back to sound surfaces and dried, and the sealant is matched to the joint and its conditions, then guaranteed for a year.
Welwyn: your questions answered
Do you cover smaller places like Welwyn?
Yes, Welwyn is covered. Our work covers London and the South East, and smaller places are part of that. The journey is planned ahead, so it helps to know about access.
Do you work for landlords with property near Welwyn North station?
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 will give you a clear price.
Can you quote for more than one area?
Yes. More than one area can be quoted together.
Is the work guaranteed?
Yes, for a year. If there’s a problem with our work in that time, tell us and we will put it right.
Do you do commercial work?
Yes. Hotels, offices and other businesses use us, and we are fully insured.
Do the sealants smell?
There can be a smell while the sealant cures, which fades as it sets. Ventilation helps.
Are you fully insured?
Yes. We are fully insured.
Will you leave a mess?
We keep the work tidy. Nearby surfaces are protected, and the area is left clean when we finish.
The process
There’s no need to move everything out, just the space around the work. Everything nearby is protected, and the work takes anything from a few hours to several days, depending on the building in most cases. Parking around Welwyn is usually easier than in a town centre, but mention any lanes, gates or long drives. For outside work, side access and the height of the joints help us plan.
- We look at every joint and agree a colour to suit the wall.
- Failed sealant is removed back to clean, sound faces.
- Backing rod goes in so the sealant can stretch between the two faces.
- We prime the faces where required.
- A low-modulus exterior sealant is gunned in and tooled to a neat finish.
Before we arrive
- Where the joints are inside, avoid wetting them before we arrive
- Move anything stored near the joints
- On commercial sites, let us know about site rules
Get a quote
Every job is quoted individually, so start by telling us what you need. Just ring 0345 464 0079 or send us an email with the details and send photos if you have them.
Advice
Keeping the joints in good condition
Simple care keeps the joints in good condition. We recommend:
- Check external joints each spring
- Get split or bare joints resealed while the damage is small
- Show decorators and builders where the movement joints are
- Leave the joints unpainted unless we have said otherwise
Keep pressure washers away from the sealant. High-pressure water can lift the edges and let water in behind.
Leaks behind façade panels and render often go unseen. By the time there’s a damp patch, the damage can be well established, so it’s worth resealing at the first signs.
Landlord and commercial work in Welwyn
Hotels need rooms back in use, so the work can be planned room by room around your bookings where we can. We’ve worked in hotels as well as homes and businesses.
We work for letting agents and landlords as well as homeowners. Sealant work between tenants is a simple way to keep a property in good order.
Honest limits
In fairness, there are a few things sealant will not fix:
- Damp that is not coming from the joint
- Cracks in the bricks or render themselves, away from the joints
- Cutting new joints into brickwork, which is building work rather than sealant work
If in doubt, call 0345 464 0079 or send us an email and we’ll say what we think before you book.
What we seal
- Copings & trims
- Joints between brick and frames
- Façade panels
- Render & cladding joints
- Brickwork movement joints
- Concrete & block