One method of application in PICA applications is to apply the silane as a primer on the inorganic substrate before the coating is applied. When used as a primer, the silane is diluted in a solvent and sprayed, dipped or wiped onto the substrate. Various solvents can be used: methanol, ethanol, isopropanol, an ether glycol, or sometimes a mixture of solvents. Water, at levels of 1–5%, is usually added to an alcohol solvent to promote hydrolysis of the silane in the primer. Water can also be used as the solvent if the coupling agent is water soluble, as with an aminosilane.

The concentration of silane in the primer solution during application controls the thickness of the silane coating on the surface. Poor adhesion is obtained if the silane coating is too thick. A thick, cross-linked silane oligomer is a weak layer and the bond would fail in the silane layer. Poor adhesion is also obtained if the silane coating is too thin because not enough silane is present to give improved bond strength and water resistance. A concentration of 0.5–10% silane in the solvent can be used in a primer, but usually levels of 2–5% are used. The solvent can be allowed to evaporate at room temperature or the coated substrate can be heated to drive off solvent; however, heating above 125°C cross-links the adhesion promoter and reduces interpenetration of the coating into the primer matrix to make it less effective. Silane primers are applied as a much thicker coating on a surface than comparable silane treatments on fiberglass or mineral surfaces for reinforcement applications are.

An example of the benefits of silane when used as a primer is shown in Table 25.15 where urethane and epoxy paints were applied to aluminum surfaces using epoxysilane and aminosilane adhesion promoters to improve adhesion. The effects of degreasing and sandblasting the surface were compared to adhesion with the silanes alone.