Choosing Mortar For Your Hardcape

When you are at your landscaping supply center loading up on stone for your next outdoor hardscaping project, don’t forget to swing by the accessories and supplies area and pick up the right mortar for the job.  Whether you are installing a new outdoor kitchen, retaining wall, or other hardscape, you will need to choose the right type of mortar for your project.  Mortar is made from Portland cement, lime, sand and water.  The relative amount of each ingredient affects the bonding strength, compressive strength, flexibility, and shrinkage.

Type M mortar has the highest compressive strength and is used primarily for load bearing walls or below grade masonry work such as retaining walls where high compression strength is desirable.  Type S mortar has moderate compression strength, but higher bonding strength than Type M mortar.

Type N mortar has even lower compression strength, but excellent bonding strength and resistance to shrinkage and cracking.  It is commonly used for exterior or interior above grade walls.  You may also encounter type O or type K mortar.  These are low strength mortars typically used for tuckpointing or other masonry repair work.

One other type of mortar is refractory mortar which is specially formulated to be resistant to high temperatures.  It is used to set firebrick that lines the inside of fireplaces.

When choosing a mortar for any outdoor landscaping project, a general rule of thumb is to use the lowest strength mortar that will do the job.  Many landscaping professionals recommend using Type N mortar for most mortar work unless there is some reason that higher compression strength is needed. It’s combination of good compression strength, high bonding strength, flexibility and resistance to shrinkage and weather make Type N mortar a great all round choice.