Cross Joints in Paving
The term ‘cross joint’ or straight joints is applied to those paving patterns that include ‘crossroads’ where four corners of four slabs meet at one point. Whilst cross joints invariably occur in chequerboard designs, where all slabs are laid in a grid pattern, these are usually laid to smaller sized square slabs all of one equal dimension (45cm x 45cm, 60cm x 60cm) which tend to be relatively flat across their surfaces.
Where problems can occur using cross joints are in random rectangular patterns, where a cross becomes visually aesthetically jarring, or when using larger sized slabs, as these tend to be less than level across the plane, gently curving up at the corners by a millimetre or two. This curvature can become a problem, causing a ‘lip’ to form.
Another reason for avoiding cross joints is not so obvious; when grouting takes place, the objective is to fill the 20mm or so deep gap between slabs. Even those slabs that have been properly and fully slurried to their backs may have a few square centimetres at the very corner, and when four corners meet, there is a possibility/likelihood that the grout will settle under the slabs at that point, creating a ‘slump’ in the depth of the grout during the early stages of grouting operations. Where the pointing gap is only 5 – 6mm, this problem rarely arises, but if the gap is 10mm, slumping becomes more likely.
In some instances, four corners, where slumping has taken place, especially on porcelain, the sharp corners have caused cuts to children’s feet when playing barefoot (swimming pools etc) and care taken when planning such projects.
Sandstone patio with several poor details, with cross joints and long straight lines spoiling the effect of random rectangular pattern. (Other ‘design defects’ include a number of places where two slabs of the same size have been laid together, which also detracts from the random pattern.)
