FREQUENTLY ASKED QUESTIONS

Concrete is a mixture of natural products to include sand, gravel and crushed stone. These materials are mixed with water and Portland cement to act as a bonding agent.Typical residential installation of concrete is a 3000 PSI (pounds per square inch) mixture that is installed at a depth of four inches. This material will be poured over sub-grade of packed dirt or crushed stone depending on the makeup of the soil. We typically use 3500 PSI mix which makes for a stronger product and produces a better finish. In commercial application the PSI will typically be even higher due to heavier traffic and usage.

The two main types of concrete applications used in residential settings are broom finished and exposed aggregate. The choice between these two applications will determine the overall look of the finished project and cost of installation.

With broom finished, once the concrete is poured crew members will work the pour to flush out air pockets and provide for a consistent, even surface. This will take some time and several reworkings as the concrete begins to set up. As the top of the concrete begins to harden and dry, the crew members will brush the surface with a broom to give it a slightly rough texture. This texture will help prevent pedestrians from slipping when walking on the concrete after a rainfall.

Exposed aggregate is concrete that has had pea gravel or other small stones added to the mix before it is poured. As the concrete hardens some of the water and cement bonding agent will rise to the top. After the concrete has cured for a couple days, a power washer is used to remove this top coating thus exposing the gravel in the mixture. As with all concrete the finished product will be gray in color and bleach out over time. Much of the exposed aggregate poured in this region has had a red dye added to it to give it that reddish-brown tint so popular in the Williamsburg area.

Exposed aggregate is more labor intensive than broom finished and will therefore cost more to install. It is also highly recommended that a clear sealer be installed once it has cured. This will keep the surface looking new and the exposed rocks in place but will also add to the cost of the overall project.

Many people mistakenly use the term cement interchangeably with concrete, but they are not the same. Cement is made of lime and clay. When water is added it acts as a bonding agent. Cement is not used by itself but added to other ingredients to bond them together. In the case of concrete these other ingredients of sand, gravel, and crushed stone when bonded with the cement mixture produces a highly durable and long-lasting material for driveways, garage floors, patios and other applications.

Asphalt is byproduct of petroleum production from crude oil. It is a black liquid that is mixed with aggregate (gravel), heated and then spread down and compressed by heavy rollers as often seen in highway construction. The mixture will harden as it cools.

While asphalt is more economical per yard than concrete, it is not as durable a product and can move and crack over time. The amount of subgrade material needed to stabilize the asphalt can vary significantly based on the makeup of the soil. This will also add to the cost of the total project. Concrete is a little more expensive per yard for the raw material but requires less subgrade material. When installed properly to allow for expansion and contraction, concrete is more durable and will last for decades or longer.

Expansion from summer heat and contraction from winter cold can cause concrete to crack. For this reason, when properly installed, concrete will have expansion joints installed every 10 to 13 feet to allow for expansion and contraction without cracking. We typically use salt treated lumber for expansion joints in our driveways and sidewalks.

Concrete will look dry a few hours after installation. However, concrete must cure before it can be used. In five to seven days the concrete will have cured to about two thirds strength and can be used for normal daily activities of driving and parking regular sized vehicles. The concrete will fully cure in twenty-eight days and provide a strong and long-lasting surface.

Concrete can be installed in the winter months in this region. Virginia weather rarely gets too cold for extended periods of time to interfere with the installation and curing of concrete. If the daytime temperature is 40o or warmer, concrete can be poured.

New concrete looks medium to dark gray when first installed. As the sun bleaches it out, the color will lighten to nearly white. This will take approximately a month. After that any stains that get on the surface can be removed with a mixture of half bleach, half water. Oil stains from parked vehicles can by removed with commercially available products. Alternatives to these products are standard kitty litter or oil dry that will soak up oil and then washing the surface with a solution of grease cutting detergent and water. For best results stains should be tackled when they are fresh. Over time the oil will penetrate deeper and be harder to remove.

Once concrete has cured to full strength, a clear sealer can be applied to the entire surface. This sealer will prevent oil and other materials from penetrating the surface. If spills or leaks occur, the sealer can be washed clean with detergent and water.

The biggest culprit to cracking concrete is tree roots growing under the surface. While large roots and occasionally entire trees will be removed before installing new concrete, homeowners should not allow new trees to be planted too close to the driveway in the future.

Damage to your concrete can occur from road salts that are put down on bridges and overpasses during winter storms. Do not ever put these products on your concrete. They will cause pitting and destroy the look of the surface of your driveway. If you need to use a snow melting product, choose the pellets. These will dissolve over time and will not damage the concrete.