Mortar mix is a combination of cement and sand that is used to hold together construction type blocks. When water is added, it becomes a workable paste that sets hard. It is used with materials like bricks and stones to make walkways and walls.
Mortar was originally made of mud or clay. There is evidence of the use of mortar in cultures around the world. Iranian and Babylonian structures used mortar from about 2900 BC on. The earliest Egyptian pyramids used the mud or clay combination, while later buildings used gypsum or lime.
This continued on with the ancient Greeks and Romans who perfected the use of concrete and mortar in building their elaborate city schemes. In later cultures, the water soluble ingredient lime became the primary active ingredient, which was ultimately damaging to the stability of many structures.
There are many grades of mortar mixes found at home improvement stores. It is important to recognize that each has its place in construction. Consumers should always purchase the mortar mix that is intended for their project. The most common types are N, S, M, Glass Block, and Refractory.
Type N is the most widely used type of mortar mix. It is a medium-strength mortar, which means it is intended for use with projects that do not hold a great deal of weight. It is best suited to projects like garden walls and barbecues. It is easy to work with and can be handled by most weekend warrior homeowners.
Type S is a stronger mortar mix and is best for heavyweight projects like retaining walls and foundations. Outdoor projects do well with this mortar mix. It is only slightly more difficult to work with than Type N.
Type M is a heavy duty mortar mix. It is intended for use with stone and can hold heavy loads. This type works well when building stone retaining walls and similarly heavy structures.
Glass Block Mortar is simply Type S mortar that has been colored white so it can be tinted. This color change helps it to blend better with glass blocks, but otherwise has no significant difference in makeup or workability. If the consumer chooses, they could substitute the cheaper Type S when working with glass blocks.
Refractory Mortar is made with a calcium aluminate base, which makes it more resistant to heat. It is used for projects where the finished structure will be exposed to heat. It is most often used for barbecues and chimneys.
Lime is an optional ingredient in mortar mix. Some construction specialists recommend adding it to a mix when it is not included. Hydrated lime is lime that already has been mixed with a very small amount of water. This water activates the lime, without making it into paste. Lime that has not been hydrated can create popping and pitting, so hydrated lime is recommended.