Inspiration and advice for your building project
When a wall is built from brick or stone, the visible joints on its face are filled with the same mortar that was used to join the building material. These face joints give a neat finish and help protect the wall from the elements.
Mortar, being softer than the building material around it, wears away over time. For outer-skin brick walls, raking out the joints and ‘repointing’ damaged face joints with fresh mortar is quite straightforward. An angle grinder is often used to remove the old joint, then fresh sand and cement mortar is pressed into the joint and neatened up with a trowel.
With solid walls, the job isn’t so simple. For starters, you can’t just attack the wall with an angle grinder, because you’ll damage the stone. Then there’s the mortar. On the cottage featured here we found three different types of mortar had been used to patch in the face joints. None of them were correct for the property and at least one risked damaging it.
Solid walls (without a cavity) need to breathe. For that, the mortar needs a high lime content. Once water gets behind cracked concrete it can’t get out again and damp sets in. So, for the repointing of solid walls – in this case stone – it’s a good idea to call in an expert. You’ll pay £40-70/m² for this work.
In this feature we’ll be following stonemasons AEP Developments as they repoint the stonework on an 18th century cottage.
1. Just a taste of the patched-in mess of face joints before the work starts. Not only is there a mixture of materials, but the profile of the pointing ranges from semi-recessed to plastered-on-top — not good. Inevitably with an older house, plants have been growing up against the walls and these have to be pinned back and then restrained before any work can start on the building. Repointing is a messy job so plastic sheets are laid over flower beds and areas of grass.
2. The old pointing is removed with a hammer and chisel, with particular care taken near the areas shown in the following four steps. Disturbing old mortar around windows can affect the way they fit (and open). The chisel is used on its own to chip out only the loose material.
3. If mortar gets pushed into this gap it can move the door frame and make the door hard to open and close. Loose mortar is raked out gently with a narrow chisel. Metal gutter brackets are prone to falling out if they are disturbed during the chopping-out phase. A lot of stone had already weathered away beneath this one, so the team were very careful. The power cable for outside lamps is often run inside the pointing. It was easy to spot on this job because the joint was a different colour in the course leading up to the lamp.
4. This is what is left after the old mortar has been removed. The edge of the stone is revealed all round and there is now a gap wide enough to take (and hold) the fresh mortar which will soon be applied to the wall.
5. Plenty of dust is left in the gaps between stones afterwards. This is brushed out before pointing begins.
6. To keep the colour of the mortar consistent for the whole job, the mix is carefully measured out. In this case, three buckets of yellow building sand, one bucket of lime and a quarter bucket of white cement. Each full bucket is levelled off at the top while the quarter-full bucket of white cement is measured off to a line drawn inside the bucket.
7. Repointing is generally done from the top of the wall downwards. However, the first half metre of a solid wall without a damp-proof course (as here) holds a lot of moisture so this section is done first — giving it more time to dry. The mortar is pushed in firmly, working from right to left.
8. Once two or three courses have been filled, the vertical joins between are filled too. Notice that the mortar is allowed to overlap all the joints and no attempt is made at this point to neaten it up. With the bottom half metre of the wall complete, the top section is started. Within five hours, a team of two complete this stage on this 24m2 wall. The mortar is left until nearly dry. How long the drying process takes depends on the weather and the position of the house in relation to the sun. In this case, the mortar is ready in just a couple of hours.
9. A wire brush is used to take off the excess mortar and leave a face joint that is just lower than the face of the wall. In other areas of the country, a deeper joint or one that is flush with the wall may be more appropriate. The wire brush also cleans up the stonework as it moves over the surface. You can see the finished pointing, and the cleaner stone, emerging in this picture.
10. A close-up of the finished job. With the face joints now clearly defining the stones, the wall not only looks great, it is now ready to shrug off the weather for years to come.