Mortar 101

Typically when using the term mortar in our trade we are discussing a paste used to bind building blocks such as stones, bricks, and concrete masonry units together, fill and seal the irregular gaps between them, and rarely add decorative colors or patterns in masonry walls. In its broadest sense mortar includes pitch, asphalt, and soft mud or clay, such as used between mud bricks. Mortar comes from Latin mortarium meaning crushed. Alternating letters in the words MASON WORK, have been used to give mortar types, their names. “MaSoN wOrK” That’s 5 types of mortar. The difference? Different Ratios of the 3 ingredients.

1. Sand serves as an aggregate. The aggregate is used to give the other ingredients something in which to bind. Also used as a filler, increasing or decreasing amounts can weaken to strengthen a mix. Sand of course can be found in dozens of shapes, sizes, consistencies, and colors.

2. Portland cement is the most common type of cement in general use around the world, used as a basic ingredient of concrete, mortar, stucco, and most non-speciality grout. It was developed from other types of hydraulic lime in England in the mid 19th century and usually originates from limestone.

3. Mason’s Lime or Calcium hydroxide, traditionally called slaked lime, is an inorganic compound with the chemical formula Ca(OH)2. It is a colorless crystal or white powder and is obtained when calcium oxide (called lime or quicklime) is mixed, or “slaked” with water. It has many names including hydrated lime, caustic lime, builders’ lime, slack lime, cal, or pickling lime. Calcium hydroxide is used in many applications, including food preparation. Limewater is the common name for a saturated solution of calcium hydroxide.


Type M — The strongest (Highest PSI @ 2500) of the group, this type is most commonly used for load bearing walls and below grade applications, such as foundations or retaining walls.  The low concentration of lime helps to achieve this high strength, but takes away from bonding ability. (A poor choice for tuckpointing anything.)

Type S — Also strong, @ 1800 PSI, Type S is most commonly used for laying.  Because of it’s increased amount of lime, it offers the most flexibility in use and resistance to movement and weather.

Type N — A common mix for tuckpointing, and laying softer materials, Type N is the most flexible and resilient @ 750 PSI.  Furthering the concentration of lime in the mix does take away from the structural strength aspects, but in turn offers more resilience and flexibility. Perfect for tuckpointing most exterior walls and chimneys.

Type O — At 350 PSI, this is the lowest strength mortar available in pre-mix. Not often used outdoors, Type O’s uses are limited to non load bearing walls and is generally an interior only used mix.

Type K — Type K is the least seen or used. Type K mortar is generally used only for interior or historical pointing of soft, hand-made brick. Type K mortar has the lowest compressive strength @ 75 PSI.

Lime Mortar/Type L — Not really a type or mortar or a mortar alone by means of the definition of the word (mortar). Type L is a mix, of only, lime and sand, NO CEMENT. It’s not commonly worked with and is generally only used for Historical tuckpointing purposes.



We are tested on International Building Code 2015 edition for seismic retrofitting (earthquake) and The American Masonry Institute standards of proper masonry water proofing repair, and we are also a EPA trained Lead based paint renovation certified firm, for those bad lead based painted chimneys out there. To our knowledge, no other company in the Portland Metro area carries and maintains all 4 of these credentials. The owner Louis is also the youngest vice president ever motioned into position in the history of the Oregon Chimney Sweep Association. Every May he proctors an exam test for the association for new companies who want to become certified to increase the quality and integrity of work provided in the trade. Please visit the Oregon Chimney Sweep Association page. 

Call Portland Fireplace and Chimney today (503) 758-4710!

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