What Is Mastic Pointing? A Guide for New Builds

If you’ve been handed a programme with “mastic pointing” on it and wondered exactly what’s included, you’re not alone. It’s one of those trade phrases that gets used loosely on site, and that’s often where gaps, delays and snagging lists start.

We’re Pioneer Sealants Ltd, Bedford-based specialist sealant applicators with over 20 years in construction behind the company. We do mastic pointing for housebuilders, developers and main contractors across Bedfordshire, London, the South East, the Midlands and East Anglia. This guide explains what it means, where it goes, which sealant suits which joint, and what a good finish looks like.

What mastic pointing actually means

Mastic pointing is the sealant work that closes the gaps between different parts of a building, mainly where frames meet the surrounding wall. “Pointing” is borrowed from bricklaying, where you finish the mortar joints. With mastic pointing, instead of mortar you’re running a flexible sealant into the joint so it can move with the building and still keep the weather out.

On most sites it covers:

Window and door perimeters, outside and in, where the frame meets brick, block, render or cladding.
Sills and heads, including under sills and along window head flashings.
Cladding and panel junctions, where one material stops and another starts.
Service penetrations through external walls, such as pipes, vents and flues (weather sealing only).
Movement joints in brickwork and blockwork, if they’re included in the package.

The last point is worth checking on every job. Some contractors include movement joints in “mastic pointing” and some price them separately, so make sure everyone’s reading the same scope. We’ve written a separate guide on brick movement joint sealant if that’s part of your work.

Why it matters on a new build

A frame perimeter is one of the main routes for water to get into a new home. Frames, brick and render all expand and shrink at different rates, so a rigid filler cracks and lets water track in behind. A flexible sealant bead, applied properly, takes up that movement.

It’s also one of the first things a buyer notices. A neat, colour-matched bead around every window makes a plot look finished. Lumpy, smeared or mismatched mastic is a classic snagging item, and it’s far cheaper to get it right first time than to cut it out and redo it after handover.

Choosing the right sealant for the joint

There isn’t one cartridge for everything. What we use depends on the specification, the materials either side of the joint and how much movement is expected. On external pointing that’s usually a low-modulus silicone, a polyurethane or a modified polymer (hybrid) sealant, such as Arbo MP20. Polysulphide still has its place on some commercial and façade specifications.

We use and apply products from brands including Arbo, Sika, Dow (DOWSIL), Tremco CPG, Soudal and Bostik, and we follow the manufacturer’s instructions on primers, joint size and curing. Porous surfaces like brick and render often need a primer, and skipping it is a common reason beads peel away within a year or two.

Colour matters too. Most ranges come in brick tones, greys, anthracite, white and frame colours. We match to the frame or the masonry, agree which with the site manager, and keep it consistent across the whole elevation.

What a good mastic pointing job looks like

Here’s what we check on our own work, and what’s worth checking on anyone’s:

The joint is clean and dry before sealing. No dust, old mortar, release agents or wet render.
There’s a backer rod in deeper gaps. It sets the depth of the bead and stops the sealant sticking to the back of the joint, so it can stretch without tearing.
The bead is the right size. Not a thin skim over a wide gap, and not a fat lump smeared over the brick face.
Edges are crisp. We mask where the surface is textured and tool every bead so it’s smooth and concave.
No gaps at corners, sill ends or behind trims. These are the spots where water gets in first.
One colour per elevation, unless the spec says otherwise.

If we arrive and find frames that aren’t fixed properly, wet plaster or gaps too big for sealant alone, we’ll flag it to the site manager with photos before we seal, rather than hiding it under a tidy-looking bead.

How we work on site

We work plot by plot, block by block or as one package across a whole development, fitting around your build programme. We work to the site’s RAMS, permits and inductions. We hold an NVQ Level 2 Sealant Applicator qualification, are IPAF trained for work at height and SSSTS trained, we hold Constructionline Silver, and we carry £10m employer’s liability and £5m public liability insurance. We’ve worked with housebuilders and contractors including Vistry and Berkeley, and on commercial projects such as Salisbury Square in the City of London.

You can see more on our window and door mastic page, or read about our commercial mastic contractor service. If your site is in the capital, our London mastic and sealant contractor page covers how we work there.

Mastic pointing FAQ

Is mastic pointing the same as repointing brickwork?
No. Repointing replaces the mortar between bricks. Mastic pointing uses a flexible sealant to close the joints around frames, panels and movement joints.

Can you do mastic pointing on an occupied building?
Yes. We reseal frames on finished and occupied buildings too: we cut out the old sealant, clean and prime the joint, fit backer rod where it’s needed and reseal.

Do you do internal mastic as well?
Yes. On new builds we can seal internal frames, skirtings, kitchens and bathrooms in the same visit, so one trade covers the whole plot.

Do you cover London?
Yes, regularly, along with Bedfordshire, the South East, the Midlands and East Anglia.

Need mastic pointing on your site?

Send us the drawings or plot list, a few photos and the site location, and we’ll come back with a clear quote. Call 01234 607 252, WhatsApp 07757 772 880, email office@pioneersealants.co.uk or use our contact page. We’re open Monday to Friday 8:00 to 18:30 and Saturday 9:00 to 16:00.