Is it necessary to use a bonding agent with stucco?

Products that increase the adhesion of plaster to substrate or plaster to plaster are called bonding agents, and are either surface applied to a substrate or integrally mixed into the stucco.

A distinction should be made between framed construction and solid backing (such as masonry or concrete). Framed construction requires the installation of moisture-resistant paper behind the lath. There is no need to have stucco bond to the paper, so bonding agents are not used with framed construction, only solid surface substrates.

It is generally good practice to prepare the solid substrate so a bonding agent is not necessary. The prepared surface should be clean (all surface materials removed), sound (hard surface), and mechanically roughened. High-pressure water blasting is the usual process in the preparation step. If this type of preparation does not result in a clean, sound, and roughened substrate, bonding agents offer another solution.