Spray Mounting, which involves the use of spray adhesives, is not considered a professional form of mounting, nor is it considered archival. However, it can be effective if used, with caution, on a small scale for mock-ups, models, small photographs, and collages where the convenience outweighs the disadvantages. The problem is that when a spray is used, the adhesive tends to collect on the topmost fibers of the surface. Even when the artwork is pressed out by hand during the mounting procedure, the adhesive still does not penetrate as fully as it will with other mounting methods. Consequently, the mounting is taking place between the top fibers of one surface and the top fibers of the other. As the temperature and humidity change and the artwork and the backing expand and contract at different rates, the artwork may pull away and bubble. Beyond a certain size of artwork, the expansion and contraction would be so strong that, even if the spray were used correctly, lifting and bubbling would inevitably occur. For this reason, many sprays cannot be used with artwork above a certain size. Technical information such as this is usually printed on the spray can. Read the instructions for the brand you are using and follow them completely.
(Excerpt from ART HARDWARE: The Definitive Guide to Artists’ Materials, by Steven Saitzyk © 1987)