Oxfordshire · England
Harwell External Mastic
We cover Harwell for sealing brickwork movement joints, render, cladding and façade joints. Old material cut out, joints cleaned and sealed neatly and every job guaranteed for a year.
- Panel joints letting water in
- Rain getting behind render or cladding at a joint
- Plants rooting in failed movement joints
Keeping the joints in good condition
How long the joints last depends on use and care. Here’s what we suggest:
- Wash walls gently around the sealant
- Have failed joints looked at early
- Point out the joints to other trades
- Clear growth from the base of walls and joints
Make sure anyone working on the wall later knows where the movement joints are. They should be kept open and resealed, not filled.
Small splits are the time to act. At that stage it’s a simple cut out and reseal before water has had years to get in.
How we handle external mastic in Harwell
A movement joint is only as good as its depth. Closed-cell backing rod sets the depth and stops the sealant sticking to the back, leaving it bonded to two faces so it can move with the wall. If you have water getting into walls through failed joints and failed seals between different materials, we can help, on brickwork movement joints, concrete & block and copings & trims alike.
Outbuildings, garages and conservatories around homes in places like Harwell add more joints to look after. Leaks usually start at a gutter end, a garage door frame or where an extension meets the house.
Big or small, you get the same one-year guarantee in Harwell and across Oxfordshire.
- Where
- Harwell (OX11)
- Region
- Oxfordshire
- Guarantee
- A year, on every job
- Quotes
- A clear quote up front
- Phone
- 0345 464 0079
- Page updated
- 26 October 2026
Harwell questions
Can you help a landlord with a rental near Didcot Parkway 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’ll give you a clear quote.
Do you cover Harwell for external mastic?
Yes, Harwell is within the area we cover. Our work covers London and the South East. Just call 0345 464 0079 or drop us an email with a few details of the job.
Are you an approved applicator?
Yes. ARBOMaster is the approved applicator scheme for Arbo sealants, and we are part of it.
Is it worth trying it myself?
You can, for simple jobs. Preparation is everything: all the old sealant out, and a clean, dry joint. We can always put it right if it fails.
Do you use backing rod?
That’s backing rod, a closed-cell foam. It stops the sealant going in too deep and bonding to three sides so it can flex with the joint.
Will you leave a mess?
No. The area is protected while we work and cleaned up afterwards.
Can you seal joints between two different materials?
Yes. We cut out the old sealant, prepare both faces and reseal with a flexible exterior product. We pick a colour that works with both materials.
Can I add another job to the visit?
Of course. Doing several areas at once is usually more efficient.
Towns and villages near Harwell
What else we do in Harwell
How the job changes by surface
Brickwork movement joints
Brick moves with heat and moisture, and grows a little over time. That movement goes into the joint, so the sealant in it must stay soft and stretchy.
Cladding and façade panels
Metal and composite panels move a lot with temperature, so the joints work hard every day. We choose the product to suit.
When to call us in Harwell
Weeds, moss and debris in a joint are a sign the sealant has gone. Roots and dirt hold water against the wall and speed up the damage.
If you can see any of these, it’s time to have the joints looked at:
- Joints where the bead has come unstuck
- Old sealant gone brittle and cracked
- Gaps where render, brick and frames meet
- Failed sealant between panels on a façade
If you look after a building such as Harwell Primary School, larger buildings have long runs of movement joint that eventually need resealing.
What your quote should include
- Is VAT in the price?
- How the colour is chosen
- Whether they’re fully insured
- What happens if they find a problem under the old sealant
What happens if it’s left?
Sealing over the top of old mastic doesn’t hold for long. The new layer can’t bond properly to old, weathered material, so we always take the old sealant out. In an older home around Harwell, damp from a failed joint can get into timber and plaster, and that is a much bigger job than renewing the sealant.
The cost reflects the work involved, not guesswork. That is why we ask a few questions first.
Why Harwell customers choose us
- A choice of colours where the product allows
- More than 20 years in sealant work
- Anti-fungal silicone where joints get wet
- Rated 4.9 stars on Google
Read what affects the cost and our reviews.
Landlords, agents and businesses in Harwell
Failed sealant is one of the commonest items on a check-out report, and it’s quick to put right between tenancies. We can quote for more than one property at once.
We regularly work with letting and managing agents. Send the address, what’s needed and the access arrangements and we’ll quote.
What external mastic looks like in Harwell
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.
If you let a flat or house near Didcot Parkway station, failed wall and movement joints let damp in, so they’re worth checking between tenancies. For an older house near a landmark such as Church of St Matthew, an extension built onto an older house moves differently, and the joint between them takes the strain.
Harwell is about 2 miles west of Didcot, in Oxfordshire. Across the OX11 area, we cover external mastic for homes and businesses. Our area takes in 443 places across Oxfordshire, from the larger towns to small villages. We also work in Oxford, around 11 miles away.
Here we cover the OX11 postcode area for external mastic. That includes homes and businesses on High Street, Loder Road and The Styles. Nearby, we also carry out external mastic in West Hagbourne (2 miles south-east), Coscote (2 miles east), Upton (2 miles south-east), Chilton (2 miles south) and East Hagbourne (2 miles east). Further out, we also cover Oxford (11 miles north), Abingdon-on-Thames (5 miles north), Witney (15 miles north-west), Wantage (6 miles west), Grove (6 miles west) and Faringdon (13 miles west).
Landmarks near Harwell
We work in homes and buildings around The Crispin pub, UTC Oxfordshire and UTC Oxfordshire, among other places. For rail, the closest station is Didcot Parkway station, about 2.3 miles east. Well-known places in the area include Atlas Computer Laboratory (2 miles south-west) and Abingdon Community Hospital (4.8 miles north). Open spaces near Harwell include Churn Hill and Mowbray Fields.
DIY sealant or a professional job?
Not every job suits DIY: high-level joints, fire-rated gaps, external movement joints and big jobs call for the right materials, safe access and experience.
A careful DIYer can reseal a simple joint, such as a straightforward joint indoors. The common mistakes are sealing over old sealant, sealing a damp joint and using far too much.
How the visit works
You don’t need to clear the whole room or building, only the area right around the joints. We protect the rest, and the work takes a few hours to a few days, depending on the length of joint and the access for a typical job. In a smaller place like Harwell, parking is seldom the issue; lanes, gates and long drives are worth mentioning. For outside work, side access and the height of the joints help us plan.
- We start by checking each joint, agreeing the ones to redo and how we will reach them.
- We cut out the failed sealant and rake out any dirt or growth.
- We clean both faces of the joint and prime them where the product calls for it.
- Closed-cell backing rod is fitted to set the depth and stop three-sided bonding.
- The new sealant, chosen to suit the brick or render, is applied and tooled to a neat finish.
Before we arrive
- Let us know about parking restrictions
- Let us know about earlier repairs to the joints
- Clear the area around the work
Ask for a quote
Getting a quote is simple: let us know what needs doing and where and its rough size. Photos by email help us understand the job, and we will come back to you with a quote.