Hertfordshire · England
External Mastic in Boxmoor
Sealing brickwork movement joints, render, cladding and façade joints for Boxmoor, backed by a 12-month guarantee. Call for a quick quote.
- Sealant pulling away from one side of the joint
- Movement joints filled with mortar instead of sealant
- Water getting into walls through failed joints
How to look after the new joints
So the new joints stay in good condition:
- Deal with leaking gutters that soak the joints below
- Keep soil, plants and ivy away from the joints
- Check external joints each spring
- Tell anyone working on the walls about the movement joints
Look over the joints once a year, ideally after winter. Watch for splits, edges coming away or growth in the joint.
If you can see gaps, plants or bare sections in a joint, have it checked. Earlier resealing means a smaller job and a better result.
External mastic in Boxmoor
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. If you have joints with sealant missing in places and panel joints letting water in, we can help, on brickwork movement joints, façade panels and copings & trims alike.
In a smaller place like Boxmoor, some homes face open ground, so exposed walls and rooflines take more wind-driven rain. Joints on those sides are generally the first to go.
All our work is covered by a one-year guarantee, wherever you are in Hertfordshire.
- Place
- Boxmoor (HP1, HP3, HP2)
- Wider area
- Hertfordshire
- Cover
- 12 months on all our work
- Quotes
- A clear quote up front
- Telephone
- 0345 464 0079
- Last updated
- 26 October 2026
When to call us in Boxmoor
Sometimes a movement joint was filled with mortar or a rigid filler by mistake. The joint can’t move, so the wall cracks somewhere else instead.
People usually contact us when they notice one of these:
- Failed seals between different materials
- Joints where the bead has come unstuck
- Moss and dirt in joints with no sealant left
- Panel joints letting water in
If you live in an older home near Church of St John the Evangelist and Attached Church Hall, the joints between older walls, newer extensions and the roofline need a sealant that can move.
Questions to ask before you book
- What guarantee comes with the work
- Which sealant they’ll use, and why
- Whether they’re fully insured
- How the joint is cleaned and prepared
Questions from Boxmoor
Is Boxmoor within the area you cover?
Yes, we do. We work across 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 older homes in Boxmoor 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.
What is backing rod for?
Backing rod goes into deeper joints as a matter of course. It controls the depth and stops the sealant bonding to the back so the bead can stretch.
Is it OK to seal over old sealant?
No, because it fails. We remove every bit of old sealant first.
How long should I leave it?
It depends on the product and the temperature. Before we leave, we will tell you the cure time.
Where do you work from?
Our base is in Crawley, and we cover South East England, London and all of Scotland.
Can a movement joint be filled with mortar?
No, not where the gap is a movement joint. Pointing it stops it working, and the wall may crack nearby. We will reseal it with a flexible sealant.
Are you ARBOMaster approved?
Yes. We’re an ARBOMaster approved applicator.
How it works
You don’t need to clear the whole room or building, only the area right around the joints. Everything nearby is protected, and the job takes a few hours to a few days, depending on the length of joint and the access for a typical job. For a job in Boxmoor, we agree the time, the access and parking before the day. Outdoor jobs depend on a dry day, since sealant needs a dry surface.
- Each joint is checked and the colour of the new sealant agreed.
- We take out the old sealant until the faces are sound.
- Closed-cell backing rod is pushed in so the sealant bonds to two sides only.
- Primer is applied wherever the sealant needs it.
- A low-modulus exterior sealant is gunned in and tooled to a neat finish.
How to prepare
- Let us know about parking restrictions
- Clear the area around the work
- Plan for the work area to be out of bounds to pets and children
Get a quote
Asking for a quote is easy: tell us what needs doing and where, and roughly how big it is. A few photos by email make the job easier to understand, and we will take it from there.
Related advice
Quotes for external mastic in Boxmoor
For a quick quote, just ask. What matters most is:
- Which sealant suits the joint
- When we can work, for business premises
- The number and length of the joints
- How many rooms, windows or areas are involved
Homes and businesses are quoted the same way: the amount of work, the access and the products needed. Ask us for a quote and we’ll explain what it covers.
What we need to know
Before you ask for a quote, have a think about:
- Any previous sealing or DIY work
- The rough size of the job
- What the problem is, such as mould, gaps, leaks or cracking
- The address or postcode of the job
Want a quote for external mastic? Please ring 0345 464 0079 or email us and tell us about the job. You will know what we plan to do, and what it will cost, before any work begins.
Why act early in Boxmoor
Mortar or ordinary filler might look like a quick way to close an open joint, but it locks the joint solid. The wall then cracks somewhere else. A flexible sealant over backing rod is what the joint needs. In an older home around Boxmoor, damp from a failed joint can get into timber and plaster, and that’s a much bigger job than renewing the sealant.
Combining jobs into one visit normally makes better use of the time than several visits, so it’s worth mentioning everything you’d like done. You’ll get one clear quote for the whole job.
Why choose Mr Mastic in Boxmoor
- Homes, businesses and hotels
- Neat joints and a tidy finish
- We’re fully insured
- Trusted Arbo and Everbuild sealants
Read how sealant jobs are priced and customer reviews.
Places near Boxmoor
What else we do in Boxmoor
Walls and rooflines in Boxmoor
Boxmoor is part of Hemel Hempstead, one of the post-war new towns. Homes here were built in phases, many of them in the post-war decades, so whole streets can have gutters, trims and wall joints reaching the end of their life together. Compared with the north and west, the South East gets less rain, but outside sealant still needs a dry, clean surface, so outdoor work is planned around the forecast.
Letting a property close to Hemel Hempstead station? Then split movement joints are easy to miss on a rental until damp shows inside. Managing a site like Boxmoor Primary School? Then movement joints, cladding joints and gutters on larger buildings need the same care as a house’s.
Boxmoor is about 1 mile south-west of Hemel Hempstead, in Hertfordshire. Homes, rented property, offices and hotels in Boxmoor can book us for external mastic, old or new, large or small. Every job comes with our one-year guarantee. 381 places in Hertfordshire are on our list, from the larger towns to small villages. London is on our list too, around 24 miles away.
Postcode districts we cover here for external mastic: HP1, HP3 and HP2. If you need external mastic at a property on Cardy Road, Heath Lane and London Road or anywhere close by, our applicators can take on the job. Being close to the A4251, Boxmoor is easy for our applicators to reach for external mastic. We also cover the places around Boxmoor: Warner's End (1 mile north), Grovehill (1 mile north-east), Woodhall Farm (1 mile north-east), Apsley (1 mile south-east) and Hemel Hempstead (1 mile north-east). Within a short drive, we also cover Watford (7 miles south-east), St Albans (7 miles east), Welwyn Garden City (13 miles east), Harpenden (8 miles north-east), Hatfield (11 miles east) and Borehamwood (11 miles south-east).
Local landmarks in Boxmoor
Locally, jobs take us to homes and businesses close to Gadebridge Park, The Hemel Hempstead School and Fishery Inn. There’s a railway station in Boxmoor itself: Hemel Hempstead station. A little further out are Hemel Hempstead Hospital (0.7 miles north-east). The countryside around Boxmoor includes Long Deans.
Different surfaces, different methods
Render joints
Render has movement joints and stop beads that need sealing. They’re resealed in a sealant that suits the render.
Copings and trims
A failed coping joint lets water into the top of the wall. Resealing them is a small job that protects a lot.
Work for landlords, hotels and businesses
Hotels need rooms back in use, so we plan the work room by room. We’ve worked in hotels as well as homes and businesses.
We also work for property managers and facilities teams in Boxmoor and across Hertfordshire. Several sites can go on one quote, and we’re fully insured.