Repointing a wall involves replacing areas of the mortar holding the individual bricks together. Deteriorating mortar can let water into the joints between the bricks, leading to a risk of frost damage during periods of cold weather. Never repoint your walls if there is a likelihood of frost, as the water within the mortar can freeze and open up cracks in the mortar itself. Repointed walls usually look better than those which have mortar missing and this could be an important factor if you’re considering selling your house in the near future.
Ensure you can access the area safely. You might be able to reach lower-down areas on foot or on a small stepladder but for higher areas, such as a chimney stack, you may need scaffolding and a specialised roof ladder.
Find out what kind of mortar is in your wall already and buy an appropriate mortar to match it. Although many modern houses use a cement-based mortar, older buildings constructed from stone often use a lime-based mix.
Pick out any loose mortar with an electric drill or chisel. You should aim to open up a space between the bricks or stones that is about twice as deep as it is wide. Once you’ve reached this depth, use a small brush to remove any remaining loose pieces or powdery debris. You need a firm surface for the new layer of mortar to bind onto.
Make up the mortar mix according to the instructions on the packet. Cement-based mortars can only be used within a limited time frame, so only make up as much as you will use within about 30 minutes. Lime mortar, on the other hand, gets better the more it is worked, so you can make it up in much larger quantities.
Dampen the wall using a sprayer – the kind available in garden centres for spraying plants is ideal for smaller areas.
Load some mortar onto your trowel. It is best to start with smaller quantities until you get used to the technique required.
Push the mortar into the gap between the bricks or stones with the trowel. Make sure it is pushed in right to the back of the gap; you can use your fingers if necessary. Try to avoid smearing mortar across the adjacent bricks.
Tidy up the job by dragging the end of a short section of pipe along the joint when the mortar has started to set. This will create a neat, indented finish. Do the vertical joints first and then the horizontal. Brush any mortar on the adjacent bricks away with a stiff brush once the mortar is completely dry.
Cover the repointed area with a Hessian or plastic sheet to allow it to dry. This is particularly important for lime-based mortars, which are most effective if allowed to dry slowly.