Hertfordshire · England
Colney Heath External Mastic
Our applicators work in Colney Heath on sealing brickwork movement joints, render, cladding and façade joints. Old material cut out, joints cleaned and sealed neatly and a 12-month guarantee.
- Leaking joints around cladding and façade panels
- Rain getting behind render or cladding at a joint
- Brick movement joints where the sealant has split
External mastic in Colney Heath, done properly
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. Common call-outs are for gaps where render, brick and frames meet and joints where the bead has come unstuck, across render & cladding joints, copings & trims and façade panels.
Somewhere as small as Colney Heath, 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.
A 12-month guarantee comes with the work, just as it does everywhere we cover.
- Place
- Colney Heath (AL4)
- Region
- Hertfordshire
- Cover
- One year on every job
- Quotes
- A clear price before any work starts
- Telephone
- 0345 464 0079
- Last updated
- 26 October 2026
FAQs for Colney Heath
I let a flat near Welham Green station. Can you help?
Yes, we work for letting agents and landlords. You can call 0345 464 0079 or drop us an email with the address and a few details, and we will give you a fixed price before any work starts.
Do older homes in Colney Heath need their sealant replacing?
In most cases, yes, if it hasn’t been done for a while. Sealant does not last for ever, and its life depends on use, cleaning and weather, and many homes in Colney Heath may already be on their second or third set.
Can you work on commercial sites?
Yes. We’ve worked for hotels, offices and other businesses and we are fully insured.
Is there any odour?
Some sealants have a smell while they cure, which fades as it sets. Ventilation helps.
Can I do it myself?
Some simple jobs can be done by a careful DIYer. Most DIY failures come from sealing over old material, wet joints or too much sealant.
Will it make a mess?
Very little: the area around the joints is protected first, and we clear up the old sealant and our materials before we leave.
Do you seal joints where cladding meets other materials?
Yes. Where different materials meet is one of the most common joints we seal. We use a flexible sealant suited to both surfaces with primer where required.
Where do you work from?
Our base is Crawley, with over 20 years’ experience. Our area covers South East England, London and Scotland.
What the job involves on each surface
Joints between dissimilar materials
Wherever two materials meet, they move differently. We seal the joint with a flexible exterior sealant so neither cracks the other.
Render joints
Rendered walls have joints at beads, openings and changes of material. We reseal them with a flexible exterior sealant that suits the render colour.
When to call us in Colney Heath
Poor preparation causes many early failures: joint faces that were dusty or damp, unprimed where they needed it, or still carrying old sealant. The sealant never bonds properly.
These are the problems we’re asked about most:
- Rain getting behind render or cladding at a joint
- Moss and dirt in joints with no sealant left
- Sealant that has lost its bond to the brick or render
- Weathered mastic that no longer stretches
In the older streets around Church of St Mark, older walls, gutters and the joints where extensions meet them need a flexible sealant.
What your quote should include
- Is VAT in the price?
- Whether they’re fully insured
- Which colour the sealant will be
- Whether all the old sealant comes out first
What sealant work cannot fix
Sealant isn’t the answer to every problem, and we’d rather say so up front. Sealant won’t put right:
- Damp that is not coming from the joint
- Render that is blown, hollow or coming away
- Subsidence or other structural problems
If in doubt, phone 0345 464 0079 or email us and we’ll say what we think before you book.
What we seal
- Façade panels
- Copings & trims
- Brickwork movement joints
- Joints between brick and frames
- Render & cladding joints
- Concrete & block
How the visit works
Before we leave, we go over the finished joints with you and tell you how long to leave it. The visit itself normally takes anything from a few hours to several days, depending on the building, depending on the size of the job. Somewhere like Colney Heath 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.
- Backing rod sized to the joint goes in to set the depth.
- We apply the sealant, tool it and check the whole run.
Getting ready for the visit
- Clear items away from the joints we are working on
- Mention if the joints have been sealed before
- For indoor joints, keep the area dry beforehand if you can
Getting a quote
If you’re in Colney Heath and need external mastic, phone 0345 464 0079 or send us an email. A short description of the job and where it is helps us quote, and we’ll agree the price before any work begins.
Advice
Walls and rooflines in Colney Heath
With historic houses such as Hatfield House (about 2.3 miles north-east) nearby, there’s older building stock in the area around Colney Heath as well as newer homes. In older buildings, older walls and rooflines need a sealant that moves with them and suits the material. 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.
Letting a property close to Welham Green station? Then split movement joints are easy to miss on a rental until damp shows inside. Managing a site like Colney Heath Junior Mixed Infant and Nursery School? Then movement joints, cladding joints and gutters on larger buildings need the same care as a house’s.
Colney Heath is about 2 miles south-west of Hatfield, in Hertfordshire. We carry out external mastic for homeowners, landlords and businesses in Colney Heath and nearby. Colney Heath is one of 381 towns and villages in Hertfordshire where we work. There’s also a page for London, about 18 miles away.
We cover every part of AL4 for external mastic. You will find streets such as High Street, Fair View and Roestock Lane, all of which we cover. We also cover the places around Colney Heath: Sleapshyde (1 mile north-west), Welham Green (1 mile east), Smallford (1 mile north-west), Hatfield (2 miles north-east) and Tyttenhanger (2 miles west). Further out, we also cover Watford (8 miles south-west), Hemel Hempstead (9 miles west), Stevenage (12 miles north), St Albans (3 miles west), Welwyn Garden City (5 miles north-east) and Harpenden (7 miles north-west).
What’s near Colney Heath
Locally, jobs take us to homes and businesses close to Chalkdrawers Arms, Bishop's Hatfield Girls' School and North Mimms Park. The closest station to Colney Heath is Welham Green station, roughly 1.7 miles east. Well-known places in the area include Hill End Hospital (2.3 miles west) and The Bunker at Hatfield Police Station (1.9 miles north). For a walk, there’s Verulamium Lake and Colney Heath Local Nature Reserve.
How to look after the new joints
A little care helps the new joints last. We recommend:
- Look over the joints every year, ideally after winter
- Wash walls gently around the sealant
- Act on the first splits you see
- Keep soil, plants and ivy away from the joints
Keep the joints clear of soil, plants and climbing growth. Anything that holds water against the joint wears it out sooner.
A joint that has stopped moving pushes the movement elsewhere, generally as cracking in the brickwork or render nearby. Catch it early and you reduce the risk.
Quotes for external mastic in Colney Heath
The quote reflects the job in front of us. We take into account:
- Access and height
- When we can work, for business premises
- The type of sealant required
- The old material and how stubborn it is
Rather than a set price list, we look at what your job involves: the amount of work, the old material and the access. You will know the price before we begin.
What we need to know
Before you ask for a quote, have a think about:
- Where the property is
- The type of property
- Roughly how big the job is
- If someone has resealed it before
For a quick quote, get us on the phone, or email us if that’s easier. Describe what needs sealing and we will talk you through the work and give you a clear price.
Can I do it myself?
The biggest DIY mistake is sealing over old sealant. Silicone doesn’t stick to old silicone, so it peels away and traps moisture behind it. All the old material has to come out first.
Overfilling a joint is a classic DIY mistake. A heavy bead looks messy and copes badly with movement, and getting the depth right matters as much as the look.