Mortar for Re-Pointing
The mortar used for re-pointing should generally match the strength of the bricks and be a mix of cement, lime and sand. Suggested mix proportions for most applications would be 1:2:8. Walling that is more exposed to the weather would probably require a stronger mix, such as 1:1:6. Avoid using a harsh sand/cement mix that omits lime, as the mortar will set too quickly and will form a weak bond with the bricks that is easily loosened by frost. As with all mortars, the mix proportions must be accurately and consistently gauged to ensure uniformity of colour and strength.
re-pointed, and the new mortar needs to match the existing, adjacent mortar. This is sometimes referred to a ‘patch pointing’. Choice of sand has a direct influence on colour, with red sand producing a brown mortar and yellow sand producing a grey mortar. However, it may be necessary to introduce colouring additives in order to get the match as close as possible. This kind of detailed work is likely to be within the context of a historic and/or listed building and may even involve building a small temporary wall with raked-out joints (a sample panel), in order to test the colour match of the new mortar. Where listed buildings or buildings in conservation areas are concerned, it is quite common for the relevant Local Authority to specify the building of a sample panel in order to agree the mortar mix and colour to be used.
From a practical point of view, the water content of the mortar needs to be less for re-pointing than for bricklaying, simply because such a level of workability is not required or desired. The mortar for re-pointing must be firm enough to be cut into strips that will adhere to a pointing trowel and maintain their shape for long enough to be inserted into the joint, and then to receive a joint finish within a short period of time. If it is too wet, it will be difficult to push the mortar into the joints without staining the brickwork. The mortar will then have to be left for a period of time to ‘go off’ before a joint finish can be applied. As a test of consistency, the mortar should stand up on the pointing trowel without sagging.
Re-pointing is a slow, time-consuming process so only small amounts of mortar should be mixed at a time, otherwise it will start to go off before it is used. Batches of approximately half a bucketful are usually sufficient.