Full Contact Mortar Beds

Full Contact Mortar Beds

To avoid any problems with moisture becoming trapped in voids under paving during laying operations, ensure the slabs are laid over a 100% full bed of mortar. In order to make a laying bed more pliable, it is common practice to create ridges or furrows in the laying mortar, as a means of making laying operations simpler by providing a flexible cushion of mortar, trusting that the ridges will compact, leaving a 100% full bed. In practice, this rarely happens, and a less than full bed is the result. (95% coverage is acceptable.)

Any such voids may become water filled through porous joints or capillary action, drawing moisture from the ground and laying bed, which may become trapped in the voids, creating problems when cold weather turns the water to ice, which expands and lifts the slab clear of the laying bed.

It is advisable to use a screeding board, comprised of two lengths of timber nailed together, one lower than the finished level, set to match the thickness of the slab being laid, with the upper board matching the surface of the paving. As the work progresses, the screeding board will create the correct bed depth at the correct crossfall, ensuring a full mortar laying bed upon which to set the next slab.