FAQs

Yes. The rate at which concrete hardens is very much affected by temperature, moisture and wind. Wind can cause the surface to crack. Rain will significantly weaken the surface. That’s why it’s important to work with the right concrete mix for your application.

Curing is the procedure for maintaining an acceptable moisture content and temperature profile in the concrete to ensure desired properties of the concrete are achieved. Testing demonstrates improper or lack of curing that can cut the strength of a proper concrete mix by as much as 50%. The potential for concrete shrinkage, cracking, and dusting increases significantly when concrete is not cured correctly.

While a curing compound acts to prevent moisture from leaving the concrete during initial stages of strength development, a concrete sealer is designed to prevent moisture from entering the concrete matrix, to assist in limiting surface deterioration due to cycles of freezing and thawing. New concrete should air dry for 30 days prior to the application of a concrete sealer. Follow the manufacturer’s directions for application rates and intervals. Many sealer applications are effective for a two-year period.

The use of deicing chemicals during the first year of service is not recommended, especially if concrete is installed late in the year. Sand is an acceptable alternative anytime. Deicing chemicals used for snow and ice removal can cause and aggravate surface scaling. Therefore, judicious use of these products with regard to amount and frequency of application is strongly advised. Remember deicers can also reach concrete surfaces other than by direct application — for example, drippings from the under-carriage of vehicles. During and after the concrete’s second winter, deicing chemicals containing sodium chloride (common salt) or calcium chloride may be used judiciously. NEVER use deicers containing ammonium sulfate or ammonium nitrate, as they will chemically attack and rapidly disintegrate concrete. ALSO NOTE: common garden fertilizers often contain ammonium sulfate and/or ammonium nitrate, and can cause disintegration of your concrete. Avoid loading or cleaning your fertilizer spreader on your concrete slab and follow best-spreading practices by applying fertilizer around the periphery of your lawn first, without crossing pavement, then run the spreader back and forth within the area bounded by your perimeter fertilizer run. This practice both ensures consistent fertilizer application around the edge of your lawn and, because the spreader never crosses pavement, minimizes the potential for fertilizer damage to your concrete.

Frequent cleaning keeps your new concrete looking good and does wonders to improve the curb appeal of your home. By keeping your concrete clean by frequent sweeping and occasional hosing, you can also significantly reduce fall risks to family and guests. Wet leaves left on a driveway will have a tendency to stain, so be prepared to clean your driveway often in fall. Leaf stains can be cleaned away with a pressure washer (light pressure) or with hot water mixed with tri-sodium phosphate (one pound per gallon is recommended).

Temperature extremes make it difficult to properly cure concrete. On hot days, too much water is lost by evaporation from newly placed concrete. If the temperature drops too close to freezing, hydration slows to nearly a standstill. Under these conditions, concrete ceases to gain strength and other desirable properties. In general, the temperature of new concrete should not be allowed to fall below 50 Fahrenheit (10 Celsius) during the curing period.

Yes. Topsoil and any other organic matter must be removed before placing concrete. Organic materials are unstable and unable to provide uniform support for concrete slabs. A properly prepared subgrade contains no organic material and is crucial to constructing a quality concrete pavement or slab on grade.

In most instances, the answer is no. Very narrow “hairline” cracks are superficial and do not indicate any structural problem. Cracks that have movement where one side of the crack moves relative to the opposite side should be evaluated by a professional engineer.

Consider the cost of the driveway over its lifetime. A good quality concrete driveway will last more than 30 years with little maintenance. Asphalt driveways need regular periodic sealing coats to retard age-related cracking. Deterioration of even properly constructed residential asphalt driveways will occur more quickly due to environmental influences than due to vehicle traffic. If you factor in the cost of surface and crack sealers and the shorter life-span of the asphalt, concrete will cost much less over the life of the structure. Furthermore, the concrete structure will not harden in sunlight, resulting in a more consistent surface over time.

Brooming of the concrete surface provides a safe, attractive, non-slip surface for exterior concrete flatwork. Broom finishes are created by pulling a special dampened, stiff-bristle concrete texturing broom across freshly floated concrete, and can be applied in many ways, including straight, curved, and wavy lines. Most broom finishes for concrete sidewalks and driveways are straight-line textures broomed at right angles to the anticipated traffic direction. Broom finishes are not incorporated into most decorative concrete finishes.

Curing is one of the most important steps in concrete construction, because proper curing greatly increases concrete strength and durability. Concrete hardens as a result of hydration: the chemical reaction between cement and water. However, hydration occurs only if water is available and if the concrete’s temperature stays within a suitable range. During the curing period-from five to seven days after placement for conventional concrete-the concrete surface needs to be kept moist to permit the hydration process, new concrete can be wet with soaking hoses, sprinklers or covered with wet burlap, or can be coated with commercially available curing compounds, which seal in moisture.

Mechanic’s liens exist to provide collection rights to contractors and material suppliers who supply construction services or materials for improvements to real property. Waiver-of-lien forms provide protection for homeowners who pay their home improvement bills. With a mechanic’s lien, the concrete supplier or concrete contractor has the right to serve the homeowner with notice of lien and to record it as part of the county land-title records, should payment not be made for materials or services provided. A lien is a claim of partial ownership of your home. If the mechanic’s lien is not paid, the material supplier or contractor can commence court proceedings to foreclose the lien and sell the property in payment of the obligation. A waiver-of-lien form provides a homeowner proof that subcontractors and material suppliers have been paid and relinquish their right to serve the homeowner with a notice to place a lien on the home. The case history that follows, taken from the Wisconsin Department of Agriculture, Trade, and Consumer Protection web site, explains why lien waivers are important to homeowners: Mr. Jones signed a contract with ABC Contractors for the construction of an addition to his home. When the work was done, Jones paid the contracted price and started enjoying his new addition. A month later, he received a “Notice of Intent to File I Claim for Lien” in the mail from the lumberyard where ABC Contractors obtained building materials. What happened? Although Jones had paid his bill, ABC Contractors did not pay the lumberyard. The law allows a subcontractor or supplier of materials to place a lien on the property where the work was done, if the contractor doesn’t pay his bills. This can happen even if the homeowner has paid the contract in full.

Air-entrained concrete contains billions of microscopic air cells per cubic foot. These air pockets relieve internal pressure on the concrete by providing tiny chambers for water to expand into when it freezes. Air-entrained concrete is produced through the use of air-entraining portland cement, or by the introduction of air-entraining agents, under careful engineering supervision as the concrete is mixed on the job. The amount of entrained air is usually between 4 percent and 7 percent of the volume of the concrete, but may be varied as required by special conditions.

Concrete, like all other materials, will slightly change in volume when it dries out. In typical concrete this change amounts to about 500 millionths. Translated into dimensions-this is about 1/16 of an inch in 10 feet (.4 cm in 3 meters). The reason that contractors put joints in concrete pavements and floors is to allow the concrete to crack in a neat, straight line at the joint when the volume of the concrete changes due to shrinkage.

Concrete surfaces can flake or spall for one or more of the following reasons: In areas of the country that are subjected to freezing and thawing the concrete should be air-entrained to resist flaking and scaling of the surface. If air-entrained concrete is not used, there will be subsequent damage to the surface. The water/cement ratio should be as low as possible to improve durability of the surface. Too much water in the mix will produce a weaker, less durable concrete that will contribute to early flaking and spalling of the surface. The finishing operations should not begin until the water sheen on the surface is gone and excess bleed water on the surface has had a chance to evaporate. If this excess water is worked into the concrete because the finishing operations are begun too soon, the concrete on the surface will have too high a water content and will be weaker and less durable.

Portland cement is a hydraulic cement which means that it sets and hardens due to a chemical reaction with water. Consequently, it will harden under water.

The easiest way to add strength is to add cement. The factor that most predominantly influences concrete strength is the ratio of water to cement in the cement paste that binds the aggregates together. The higher this ratio is, the weaker the concrete will be and vice versa. Every desirable physical property that you can measure will be adversely effected by adding more water.

Color may be added to concrete by adding pigments-before or after concrete is place-and using white cement rather than conventional gray cement, by using chemical stains, or by exposing colorful aggregates at the surface. Textured finishes can vary from a smooth polish to the roughness of gravel. Geometric patterns can be scored, stamped, rolled, or inlaid into the concrete to resemble stone, brick or tile paving. Other interesting patterns are obtained by using divider strips (commonly redwood) to form panels of various sizes and shapes rectangular, square, circular or diamond. Special techniques are available to make concrete slip-resistant and sparkling.