. TIMING OF JOINTING-UP
The right time to joint-up new brickwork is a key consideration. The mortar should still be soft enough to allow a jointing tool to compress it easily into full contact with the arrises of the bricks. Attempting to joint up when the mortar is too soft or wet has the effect of drawing cement paste to the surface in a watery, rivened pattern. When it is dry, this leaves the mortar joint with a porous surface and reduced weather resistance. Jointing-up too soon also causes the mortar to spread on to the brick face, leading to staining. It will also be uneven, as the overly soft mortar offers little resistance to the jointing tool, making it difficult to maintain a consistent line or depth. Jointing-up when the mortar is too dry or hard means excessive force is required to compress the joint and this may result in the surface of the joint becoming blackened by over-rubbing, and create a crumbly and porous texture.
The precise timing of jointing is affected by various factors, including the suction rate of the bricks, the existing water content of the bricks, the mortar mix design, and the temperature, humidity and prevailing wind. For example, bricks with low water absorbency or suction rate, such as
Staffordshire Blue engineering bricks, can be laid first thing in the morning and will not be ready to be jointed until the late afternoon. Cold and/or wet weather will cause mortar to remain soft for longer, thus lengthening the period between laying and jointing-up. Conversely, very dry bricks with a high suction rate might need to be jointed up after laying just a few bricks. This is made worse in warm, dry weather, when the mortar can ‘go off’ so quickly that it prevents an adequate bond between brick and mortar before jointing-up has even been considered. To try to mitigate the effects of these extremes, bricks of low water absorbency should be kept dry, while bricks of high absorbency may be sprayed with water to make them practical to use.
The timing of jointing-up is clearly not an exact science due to the number of variable factors that affect it. The best course of action is to test areas of brickwork periodically to see if they are ready to receive a joint finish. If so, jointing-up can be carried out; if not, it is wise to wait a little longer.