Primers & Bonding Agents

What each product actually does

Substrate primers seal porous surfaces, control absorption, bind residual dust and improve adhesion of the system above. On concrete and masonry they also reduce the risk of pinholing and outgassing in the applied coating or sealant.

Bonding agents create adhesion between new cementitious material and an existing substrate, which matters for repair mortars, screeds and toppings. Acrylic and SBR bonding agents can be used as a bonding coat or as a gauging liquid depending on the product; epoxy bonding agents give the highest bond strength and are used where the duty is structural.

Reinforcement primers are applied to cleaned steel in a concrete repair to give additional protection in aggressive or chloride-contaminated conditions. Zinc-rich versions provide sacrificial protection.

Getting the timing right

Most bonding agents and primers have an overcoat window: a minimum time before the next layer can go on, and a maximum after which adhesion falls away and the primer must be reapplied. Applying a repair mortar over a bonding coat that has fully dried out is one of the most common site errors, and it produces exactly the debonding the bonding agent was meant to prevent.

Plan the sequence so the applicator can work within the window. On hot or windy days the window shortens considerably, which is a practical reason to prime in smaller sections rather than the whole area at once.

• •Use the primer named on the technical data sheet for that product and substrate
• •Respect both the minimum and maximum overcoat times
• •Prime in workable sections, especially in hot or windy conditions
• •Reapply if the window is exceeded rather than proceeding
• •Confirm whether the bonding agent is a bond coat or a gauging liquid