What Is Unmodified Portland Cement Mortar?

Cement and mortar are often confused by laymen, who also tend to confuse both with concrete. However, each one is a different material. Concrete is a mixture of mortar and a large aggregate material such as gravel or stone. Mortar is a paste that is made out of sand, a binding agent and water. Portland cement, a mixture of powdered minerals that have been fired in a kiln, is often used as a binding agent in making mortar.

Ingredients

There are several different types of mortar, each using different binding agents. Portland cement mortar uses only Portland cement. Portland cement mortar uses one part Portland cement for every three parts sand. Water is added until the mixture is doughy. Light hand pressure should be enough to press a stone into it, without adding too much water that will make it runny.

Modifications

Varying amounts of powdered limestone are sometimes added to Portland cement mortar. This gives it some of the properties of lime mortar while retaining some of the properties of Portland cement mortar. Carbon fibers, methylcellulose, latex and styrene acrylic are sometimes added to increase its strength and workability. Methylcellulose is also sometimes used for special applications to lower the resistance of the concrete to electricity. Other chemicals are sometimes added to make the mortar resistant to chemical corrosion so that it can be used in waste-water treatment.

Uses

Portland cement mortar sets faster than masonry mortars that use lime as a binding agent. It also creates a harder and more inflexible final product than lime masonry mortar does. It is more resistant to water than lime masonry mortars, which is not always desirable. Portland cement mortar is used where a fast setting time, a strong final product and resistance to water are important. It is also a safe mortar to use with drinking water. For some of these reasons, Portland cement mortar is often used to line the insides of water pipes to protect them from corrosion and extend their lives.

Mixing

Portland cement is usually sold in 94-pound bags. One of these bags takes up almost exactly 1 cubic foot of space. This makes mixing precise amounts of mortar very easy. Following the standard mixture for Portland cement mortar, you know that you need exactly one bag of cement for every 4 cubic feet of mortar your project requires.

References

• Ask the Builder: Flagstone Patio Set on Sand
• Portland Cement Association: Concrete Technology - Frequently Asked Questions
• MC2: Mortar Mixes
• Masonry: Brickwork Restoration - How to Work with Lime
• Raymond International: Portland Cement Mortar Lining
• Cement and Concrete Research; Carbon Fiber Reinforced Cement Mortar Improved by Using Acrylic Dispersion as an Admixture; Jingyao Cao and D.D.L. Chung

Resources

• Portland Cement Association: Aggregate