There are several types of mortar for laying blocks. Each of these mortars is used for different purposes within the block construction industry. For example, type N mortar is used for lighter construction where high strength is not a concern, and type S mortar is used on block projects that require a higher-load mortar. Nonetheless, using specific mortars for your block applications can save you time and money, as well as strengthen your block projects.
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Type N mortar is used for lighter block construction. This includes short garden walls and house walls that are not over 8 feet tall. This mortar meets or exceeds the national standard at 15 to 2,400 psi. This mortar will withstand a large amount of force. However, it does not fare well against side pressure where a large amount of soil is pressing in, nor does it perform well at psi greater than 2,400.
Type S mortar hardens to full hardness in 12 to 15 days and has a psi rating of greater than 2,500. This mortar is best used on block walls that will extend beyond 8 feet or walls that have a greater side force, such as basements or retaining walls that are under 8 feet or more of soil. Type S mortar is used on large commercial construction projects and is well worth using on home projects where strength is needed.
Portland cement is used on block projects where the frost line is shallow. This mortar provides the highest strength rating at greater than 4,000 psi, which exceeds the national standards for lock mortar. Generally, when there is a high probability of frost or ice within 6 to 12 inches from the top of the soil line, the blocks below this level are laid using Portland cement.
Type M mortar ranges somewhere between type S and Portland cement. It has a strength rating of between 3,000 and 4,000 psi and is used in block construction where U-blocks are installed above doors and windows of block walls. This mortar allows for proper curing of the block wall while providing high strength where it is needed.