Bonding Mortar Primer

Bonding Mortar Primer

Bonding mortar, or slurry primer, is a general term used for the adhesive material that is spread on the back side of paving slabs (See Adhesives) to ensure a strong bond between the bedding mortar and the paving slab.

On most paving products and materials laid on bedding mortar, this is an essential part of the laying process – especially when working with hard materials such as porcelain, or softer paving including sandstone, which is more porous and requires a water-resistant bridge to enable a bond between the materials.

Always ensure the back of the slabs are brushed or washed to remove any dust before applying the bonding mortar, otherwise adhesion may be compromised.

Take care to cover the whole of the back of the slab, not simply the central region, to prevent voids towards the outer edges. It should be painted on with a brush, or spread on using the flat edge of a comb trowel to a depth of between 2 and 3mm – sufficient to fill the voids in the pattern on the back of the slab.

Place the slab in position and lightly tap down, adjusting the joint as required.

For a ‘belt and braces’ method, apply the bonding mortar to the mortar bed as well as the back of the paving slab.