Marine adhesives are categorized according to their immediate tackiness and the procedure used to apply them. They are also differentiated by their ability to withstand a wide range of marine conditions. The two main types of marine adhesive are contact and epoxy.
Contact adhesives are a type of marine adhesive that immediately, on contact, stick to the surface being glued. They begin to harden quickly, so these types of adhesives are good for what is referred to as "running repairs;" that is, repairs while the boat is out of its home slip. Contact adhesives do not work well for repairs that require adjustment after the initial repair. For this reason, they shouldn’t be used for temporary bonds.
Like marine adhesives in general, contact adhesives are usually able to withstand harsh environmental conditions. Some, but not all, contact adhesives can be used under the water line, in conditions where the bond will be continuously submerged. Many types of contact adhesives will soften or give at elevated temperatures, making these types of marine adhesive not ideal for use in very warm climates.
Epoxy adhesives are a type of marine adhesive that consists of two substances that are not adhesive separately, but that become sticky when they are mixed together. This type of marine adhesive takes time to harden, which makes it better for use in projects that might require replacing or moving parts to create the correct fit. The time it takes for epoxy adhesives to harden can usually be regulated by changing the temperature. Higher temperatures cause the epoxy to set up more quickly.
Once epoxy adhesives harden, the bond they form is usually much stronger than the bond formed by contact adhesives. The bond is also generally more able to withstand high temperatures without melting. While these resulting bonds are very durable, it can make parts fixed with epoxy adhesives difficult to replace. They are also useful for filling gaps and craters, and many can be used below the water line. When an epoxy-based marine adhesive is used on a flat surface, it is helpful to use either weights or a vice to hold the project together, since it will take a long time to dry.
Both contact adhesives and epoxy adhesives can be used to adhere a number of different surfaces to one another, such as fiberglass, wood, and plastic. Care should be taken, however, to select the appropriate adhesive for the materials being glued. The product labeling should be consulted for this information.