Hertfordshire · England
External & façade joints in North Mymms, Hertfordshire
Movement joints in North Mymms need attention? We cut out the old, prepare the joints and apply the right sealant.
- Joints where the bead has come unstuck
- Plants rooting in failed movement joints
- Movement joints with cracked, split or missing sealant
External mastic in North Mymms
External mastic is a job where short cuts show quickly. New sealant over old, joints packed with mortar and beads with no backing rarely last long. We take the old material out and do it properly. If you have failed seals between different materials and joints where the bead has come unstuck, we can help, whatever the surface.
External sealant needs dry, clean surfaces, so work around North Mymms is planned for dry weather. Tell us about access to all sides of the building, including outbuildings and garages.
A 12-month guarantee comes with the work, just as it does everywhere we cover.
- Where
- North Mymms (AL9)
- Region
- Hertfordshire
- Guarantee
- One year on every job
- Price
- Quoted before any work starts
- Telephone
- 0345 464 0079
- Page updated
- 26 October 2026
Aftercare tips
Simple care keeps the joints in good condition. We recommend:
- Fix overflowing gutters above sealed joints
- Wash walls gently around the sealant
- Keep movement joints as flexible joints, not mortar
- Look over the joints every year, ideally after winter
Follow the cure time we give you before the joint is knocked or disturbed. Most exterior sealants skin fast but take longer to cure right through.
Leave a failed movement joint and water keeps getting into the wall. Over time it can mean damp inside, stained render or frost-damaged brick.
Nearby places to North Mymms
What else we do in North Mymms
What external mastic looks like in North Mymms
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. With historic houses such as Wyllyotts Manor (about 2 miles south-east) nearby, there’s older building stock in the area around North Mymms as well as newer homes. In older buildings, older walls and rooflines need a sealant that moves with them and suits the material.
If you let a flat or house near Brookmans Park station, failed wall and movement joints let damp in, so they’re worth checking between tenancies. For site and facilities teams at buildings such as Brookmans Park Primary School, movement joints, cladding joints and gutters on larger buildings need the same care as a house’s.
North Mymms is about 2 miles north-west of Potters Bar, in Hertfordshire. Wherever you are in the AL9 postcode area, our applicators can take on external mastic. We cover 381 towns and villages across Hertfordshire. We also work in London, around 16 miles away.
Every address in AL9 is covered for external mastic. We cover properties on St Mary's Church Road, Abdale Lane and Warrengate Road and the roads around them. We also cover the places around North Mymms: Welham Green (1 mile north), Colney Heath (2 miles north-west), Sleapshyde (3 miles north-west), Hatfield (3 miles north) and Shenleybury (3 miles west). Further out, we also cover Watford (9 miles south-west), Hemel Hempstead (11 miles west), Stevenage (13 miles north), St Albans (5 miles north-west), Welwyn Garden City (6 miles north) and Harpenden (9 miles north-west).
Local landmarks in North Mymms
We work in homes and buildings around Chancellor's School, North Mimms Park and The Old Maypole Public House and the streets around them. The closest station to North Mymms is Brookmans Park station, roughly 0.7 miles east. Other landmarks nearby include Shenley Hospital (3.5 miles south-west) and Potters Bar Museum (2 miles south-east). For a walk, there’s Furzefield Wood and Lower Halfpenny.
Common problems we fix in North Mymms
Sometimes a movement joint was filled with mortar or a rigid filler. With the joint locked solid, the movement turns into cracks elsewhere in the wall.
Keep an eye out for any of the following:
- Moss and dirt in joints with no sealant left
- Old sealant gone brittle and cracked
- Movement joints with cracked, split or missing sealant
- Sealant pulling away from one side of the joint
Homes close to Church of St Mary the Virgin include some older properties, and an extension built onto an older house moves differently, and the joint between them takes the strain.
What to look for in a quote
- What the cure time is
- Is VAT in the price?
- What happens if they find a problem under the old sealant
- The length of the guarantee
Why deal with it now?
Done well, a resealed joint is a neat, straight line that suits the wall. A hurried job with smeared edges and no backing looks worse and fails sooner. Where a wall is exposed, as many are in small places like North Mymms, wind-driven rain gets into any failed joint, and older walls, once damp, take a long time to dry.
What you pay reflects the work, not a rough estimate. That’s why we ask a few questions first and give you a clear quote before any work starts.
What you get with us
- Anti-fungal silicone where joints get wet
- A choice of colours where the product allows
- Sealant colour chosen to suit
- Rated 4.9 stars on Google
Should I try it myself first?
What a professional job adds is preparation and the right product. We take joints back to clean, dry surfaces, and the sealant is chosen for how the joint moves and where it is, and the work is guaranteed for a year.
If you’ve already had a go yourself, that’s fine. We cut it out and start again.
The process
Once we are on site, we check the joints match what you told us. If we find something unexpected, we talk it through with you first. After that, the work takes anything from a few hours to several days, depending on the building. In a small place like North Mymms, access is usually the main thing to plan. For outside work, also let us know about exposed walls and any outbuildings involved.
- Each joint is checked and the colour of the new sealant agreed.
- Failed sealant is removed back to clean, sound faces.
- Closed-cell backing rod is pushed in so the sealant bonds to two sides only.
- We prime the faces where required.
- We gun in low-modulus sealant and tool it neatly.
How to prepare
- Plan for the work area to be out of bounds to pets and children
- Where the joints are inside, avoid wetting them before we arrive
- Let us know about stairs, lifts or work at height
Ask for a quote
A good description makes for an accurate quote. Let us know the location, the problem and roughly how many joints, and add pictures by email if you can.
Read more
Your questions about external mastic in North Mymms
Is North Mymms within the area you cover?
Yes, smaller places are covered as well as towns. Our work covers London and the South East. Let us know about access, parking and anything unusual about getting there when you book.
Do you work for landlords with property near Brookmans Park station?
Yes, we work for landlords and agents. Just call 0345 464 0079 or email us and tell us about the property, and we will give you a clear quote.
Can I do it myself?
For a simple, easy-to-reach joint, a careful DIYer can do a reasonable job. Most DIY failures come from sealing over old material, wet joints or too much sealant.
Can you seal over the old sealant?
No. Fresh sealant does not stick to old sealant, and anything trapped underneath, including mould and water, stays there. It all has to come out first.
How long does external mastic last?
That depends on the wall, the weather and the movement. Signs to watch for are cracking, hardening and gaps at the edges.
Why is there a gap in my brick wall?
A vertical gap in a long brick wall is generally a movement joint. It gives the wall room to move, and it should be sealed with a flexible sealant.
Can I add another job to the visit?
Yes. Just list everything you need.
How do I get a quote for external mastic in North Mymms?
Size, access and the old material all affect the cost. Call for a quick quote and we will talk you through it.
Work for landlords, hotels and businesses
Letting agents often deal with us directly. Send the address, what’s needed and the access arrangements and we’ll give you a quote.
From a single let to a portfolio, the work is the same standard: the old material taken out, careful preparation and a 12-month guarantee.
What sealant work cannot fix
In fairness, some problems need a different trade:
- Subsidence or other structural problems
- Render that is blown, hollow or coming away
- Damp that is not coming from the joint
If in doubt, ring 0345 464 0079 or email us and we’ll say what we think before you book.
Surfaces we seal
- Joints between brick and frames
- Concrete & block
- Render & cladding joints
- Façade panels
- Brickwork movement joints
- Copings & trims