There are three main types of cement adhesive that are used to bond things to concrete or to bond concrete together. They are epoxy, resin, and traditional mortar. The three different types of cement adhesive each have different strengths and weaknesses, and each is appropriate for different situations.
Epoxy is a particularly hard and weather-resistant type of cement adhesive. Epoxy is by far the most durable long-term cement adhesive, able to withstand extremes of weather, temperature, UV light exposure, and even certain types of chemical exposure that cement is likely to encounter. Epoxy is often used to bond concrete or cement in basements or in exterior applications, and certain epoxy-modified mortars may be used to bond block or other concrete building materials together. Epoxy can be expensive, however, and its strength is not always needed in every application.
Resin is another type of cement or concrete bonding adhesive. Resin-based adhesives are able to dry and cure quickly, meaning they can be ready for use more rapidly than epoxy-based adhesives. Resins have the additional advantage of being resistant to shrinkage and wear after they have dried.
Common uses of resin-based adhesives are airport runways, bridges, and other high traffic areas. They are used where the cement or concrete and the bonded materials must maintain their present size and shape under situations of high stress and repeated use. Again, as with epoxy, resins are not often used in normal everyday concrete applications because of the cost and skill level required to properly use the resin-based cement or concrete adhesives.
Mortar is the most commonly used, most readily available and most easily applied bonding agent available for cement or concrete. Mortar is made from a combination of lime, sand, and water, as well as from other types of cementitious products, depending on the use. Mortar holds up well to outdoor temperatures, but dries hard and may be prone to cracking or expansion if not applied properly or if subjected to temperature extremes or ground heave. Mortar is an economical and easy-to-use solution for average concrete or cement bonding projects, and has the added plus of being readily available at most home centers.