5.2.1.9 Surface Porosity
Surface porosity is important because it can affect not only the surface energy and roughness causing changes in the adhesive placement and adhesion, but also the long-term reliability and performance of an adhesive joint. By definition, porous solids allow liquids or gases to permeate throughout. Therefore, if a porous material is bonded, it may absorb substances that can potentially harm the integrity of the bond. For example, plywood laminated with an adhesive may absorb moisture after being exposed to environmental conditions, which may lead to delamination. Therefore, it would be prudent to select an adhesive that resists moisture, seals porous material and prevents the absorption of moisture; or alternatively, change the design. Another reason to be cautious is that some porous materials may come with additives that leach out of the surface over time. This is of particular concern with certain plastics and rubbers that leach oil as they age.