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Finding the Right Type of Mortar

By September 28, 2012April 16th, 2021No Comments

When you walk into a home improvement store, do you know what type of mortar you need for your latest project?

Purchasing mortar for your household projects can confusing to the novice home builder, with such a variety of types of mortar available to choose from. Are you building a walkway, or a brick oven? Your project specs will determine the type of mortar that you buy. Knowledge of the types of mortar will save you time and money.

The following article from FineHomeBuilding.com gives you tips on finding the right type of mortar for your needs.

Mortar: What Type Do You Need?

Understanding the types of mortar will help you choose the one with the right properties for your project

by David Ericson

Mortars are often ordered based on compressive strength; but even more important properties are bond strength and flexibility. Bond strength and flexibility work together, holding masonry units in place yet flexing in response to lateral loads or expanding and contracting in response to temperature swings.

Premix or self-mix? Mixing cement and lime on-site provides flexibility to a skilled mason but requires careful measuring. Pre-mixed masonry cement ensures consistency but rules out on-site fine-tuning of the recipe.

What is mortar made of?

To achieve the balance of properties for a particular application, you mix different proportions of portland cement, hydrated lime, sand and water. Portland cement yields greater compressive strength but lower water retention during the cure, thus risking shrinkage cracks. Lime yields lower compressive strength but greater bond strength and flexibility. Sand, the aggregate, adds volume and minimizes shrinkage as the cement dries. Water makes the mix workable and activates hydration, the chemical reaction that hardens the cement.

Type M: high compression strength

Type M has the highest proportion of portland cement, with 3 parts portland cement, 1 part lime and 12 parts sand. Type M has a high compressive strength (at least 2500 psi) and is recommended primarily for walls bearing heavy loads, but also, due to its durability, for masonry below grade or in contact with the earth: foundations, retaining walls, sidewalks and driveways.

Type S: compression and tensile strength

Type S is sometimes specified for masonry at or below grade, but offers another quality. S has high compressive strength (1800 psi) but adds high tensile bond strength. S contains 2 parts portland cement, 1 part hydrated lime and 9 parts sand, and yields maximum flexural strength to fight wind, soil pressure or earthquakes.

Type N: for exterior, above-grade walls

Type N is a medium compressive-strength (750 psi) mortar made of 1 part portland cement, 1 part lime and 6 parts sand. Type N is recommended for most exterior, above-grade walls exposed to severe weather, including chimneys.

Type O: for interior or non-load-bearing use

Type O has a low compressive strength (about 350 psi), containing 1 part portland cement, 2 parts lime and 9 parts sand. O is recommended for interior and limited exterior use in non-load-bearing walls.

This simple list can save you stress and apprehension at the hardware store. Your new intellectual prowess on a mortar choice will astound friends and family. Mortar may seem inconsequential in the scheme of things, but you’ll be glad that you chose the right type of mortar. You could end up with a shattered walkway because the weak mortar was not up to the task of carrying you and those heavy winter clothes.

Would you prefer a second opinion or are you ready to purchase mortar? Contact Camosse Masonry for the right supplies. Make sure you get your money’s worth and do your homework on the right mortar for your mortar project. Always remember, one does not simply walk into mortar.