Waterproof Glue

There is a difference between waterproof glue and water-resistent glue. How well each type holds up to exposure to moisture determines it categorization. Waterproof glue is also called yellow glue. Technically speaking, it is known as polyurethane glue, and it actually requires a slight amount of moisture to cure properly. When working with waterproof glue for outdoor use, dampen the surface of the materials being joined before applying the glue. In a 24-hour period, polyurethane glues are at full strength. 

Water-Resistent vs. Waterproof Glue

Water-resistent glues work well when used with patio furniture, birdhouses, fenceposts, etc. Occasional rain or moisture will cause them no harm, but constant exposure to water or moisture will ruin their bond. Waterproof glue, on the other hand, keeps its bond even under constant exposure to moisture. Bonded materials can't be submerged in water, but short of that the bond will hold. You also have a longer setup time when working with waterproof glues. 

Application

Make sure you choose a waterproof glue that passes Type I water resistance which tests the glue in a number of high-temp and high-humidity situations. Waterproof yellow glue tends to foam up around the edge of the bond, but it may be wiped away when still tacky. Otherwise it needs to be sanded once fully cured.