Patching & Priming products
Priming products for renders perform the same function as priming for paint. They help the render to adhere to the substrate and they even up the porosity of the substrate. This is even more critical under renders because any differences in the substrate porosity will show through a plaster or render as differences in colour or texture or lines.
Patching products and mesh are used on joins so that any movement is contained within the wall and doesnt show through the render as cracks.
Renders also need to be a certain thickness when applied over cement fibre sheet so that the joins dont show through. This is usually achieved with a thick base coat of render, then the final coat can be a thinner decorative coat.