How to repoint extension brickwork

Video by Skill Builder. This walk-through draws on the video "Repointing Old Brickwork - Best Mix & Tools" from Skill Builder, presented by building expert Roger Bisby. Roger covers mortar ratios, the right tools for raking out, and how to finish joints so they shed water rather than collect it — all practical points that save a lot of grief on the day.

1. Work out what mortar mix the wall needs

Not all mortar is the same, and using the wrong mix is one of the most common mistakes on older properties. A strong cement-heavy mix — say 3:1 or 4:1 — might seem like the sensible choice, but on softer Victorian or Edwardian brick it can actually cause the face of the brick to spall as the hard joint holds moisture against it. The mortar needs to be slightly weaker than the brick, so it gives a little as the building moves.

For most post-war extensions with modern fletton or wire-cut brick, a mix of 5 parts sharp sand to 1 part cement is a reasonable starting point. If the existing mortar looks quite lime-heavy and pale, match it as closely as you can. That said, if you are not sure about the brick type, test a small section first before you commit to the whole wall.

2. Rake out the old mortar to the right depth

You need to remove the old mortar to a depth of around 15 mm to 20 mm — enough to give the new mix something to key into. Any shallower and the new mortar will not bond properly and you will be back doing the same job in a couple of years.

An angle grinder with a pointing disc gets the job done quickly on long runs, but it is easy to damage the brick arris (the sharp edge at the corner of the brick) if your hand wobbles. For smaller areas or more careful work, a plugging chisel and club hammer is slower but gives you more control. Work horizontally first, then do the vertical joints. Always wear goggles and a dust mask — mortar dust is no joke.

3. Prepare the surface before you mix up

Once you have raked out, brush the joints down thoroughly with a stiff-bristled brush to clear loose dust and debris. Then dampen the joints with clean water using a brush or a fine spray. If you apply new mortar to bone-dry brickwork on a warm day, the wall will suck the moisture out of the mix too fast and it will not cure properly — it will just crumble back out.

Do not soak the wall, though. You want the brick damp, not dripping. On a hot summer day in East Kent, damp-down and then wait ten minutes before you start pointing. In cooler weather, a single dampening is usually enough.

4. Mix the mortar consistently

Mix only as much mortar as you can use in roughly 45 minutes. After that the mix starts to go off, becomes harder to work, and the bond is compromised. Most people mix too much on the first go and then end up trying to squeeze in a final dash that has already tightened up.

Add the water gradually — you are looking for a stiff but workable consistency, somewhere between peanut butter and putty. Too sloppy and it will slump out of the joint; too dry and it will not press in cleanly. To be fair, getting the consistency right just takes a bit of practice, but it is worth taking your time on the first batch.

5. Fill and compact the joints

Load a small amount of mortar onto a hawk and use a pointing trowel to press it firmly into the raked joint. Work in short lengths — about 600 mm at a time — pressing the mortar in from the back to avoid leaving voids. Fill horizontal (bed) joints first, then the verticals (perpends).

Compact each pass of mortar as you go. If the joint is deep, you may need two applications rather than trying to pack it all in at once, especially on joints that are 20 mm or more deep. Trying to fill a very deep joint in one hit usually results in the mortar shrinking back and cracking as it dries.

6. Profile and finish the joints

Once the mortar has started to firm up — usually after about 20 to 30 minutes depending on temperature — it is time to profile the joint. A weatherstruck finish (where the joint slopes slightly outward and downward from the top face) is the most effective at shedding rainwater and the most common finish seen on UK housing. Run the edge of the pointing trowel along the joint at a slight angle to get this profile.

Once profiled, leave the mortar to cure for at least 24 hours before brushing off any smears or nibs with a dry stiff brush. Avoid washing the wall down in the first day or two — you want the mortar to cure slowly. Mind you, if heavy rain is forecast, cover the work with a sheet of polythene overnight, especially in cooler months.

When to call a handyman

Call Richard if the repointing runs to more than a couple of square metres, if the extension is on a gable end or upper storey where working at height is involved, or if you notice that the bricks themselves are cracked or spalling rather than just the mortar. Large areas are also hard to keep consistent in colour and profile if you are mixing in small batches — a fresh set of hands and a full day can make a big difference to how the finished job looks.