In this video, Ask This Old House host Kevin O’Connor explains the differences between three popular masonry materials.
Steps:
1. Portland cement is a fine gray powder that hardens when mixed with water. It’s seldom used by itself but is an important ingredient in many other masonry products.
According to This Old House Magazine, portland cement is “a fine, flourlike powder that gives concrete its color and rock-hard strength.” Natural cement was discovered by the Romans, who mined it from pumice deposits on the slopes of Mount Vesuvius. Mixed with water, the crushed pumice turned to stone. Today, instead of relying on volcanoes, manufacturers bake the necessary minerals — calcium, silicon, aluminum, and iron — in giant rotating kilns heated to 2,800 degrees Fahrenheit.
2. Concrete is a mixture of portland cement, sand, and an aggregate, such as gravel or coarse stone.
3. Concrete is mixed with water, then poured or pumped to create foundation walls, footings, piers, slab floors, driveways, steps, and sidewalks.
4. Once fully cured, concrete can support immense structural loads.
5. Mortar is a mixture of cement, lime, and sand, and is commonly used to hold together bricks, concrete blocks, and stones.
6. Masons use a wide variety of trowels to apply, spread, pack, and tool mortar.
7. When cured, mortar is somewhat softer than concrete, which allows it to accommodate a small amount of movement in a wall without cracking or crumbling.
Pro Tip: Mario Machnicki, a mason featured in This Old House Magazine, warns against using modern cement mortar on old brick walls: “The cement mortar is not helping the wall; it is actually hurting the wall.” The unyielding cement traps moisture inside the brick, causing freeze-and-crack cycles in winter and popping off the brick’s protective fire-skin in summer.
Pro Tip: Mason Lenny Moreira, profiled in This Old House Magazine, follows the mantra “Wetness leads to weakness” when mixing mortar. He blends the dry ingredients — Portland cement, sand, and mason’s lime — first, then adds water slowly and sparingly, aiming for a spreadable consistency similar to cake frosting. He makes a volcano shape in the dry mix and pours only one cup of water into its crater at a time to maintain control of the wet-to-dry ratio.
8. Concrete, cement, and mortar are available in various strengths and mixtures, so be sure to get the right one for your job.
As explained on This Old House, many people confuse these three materials, but they serve very different purposes. Cement is a fine powder that hardens when you add water — the most common type is called Portland cement. It’s rarely used by itself, but it’s the active ingredient in many other building mixes. Concrete is a mixture of Portland cement, sand, and coarse stone called aggregate; when wet, it’s poured into forms to create foundation walls, footings, steps, and sidewalks. Mortar, on the other hand, is designed to bind bricks and stones together rather than stand on its own as a structural element.
