Frequently Asked Questions About Concrete

A redi mix concrete truck driving up to your house can be intimidating, but it doesn't have to be if your site is prepared, you have all your tools at hand, and you've ordered the right amount. Our dispatcher is quite helpful and our drivers are very experienced, but you should know the basics before you call so you don't wind up with unforeseen problems.

Contractors or homeowners should begin with excavating by removing all organic materials such as sludge, tree roots, leaves, wood, etc. Concrete should be placed on a graded granular fill and compacted (if necessary). This eliminates settlement and variations in thickness, and allows drainage under the slab. Shortly before placing the concrete, wet the forms and the subgrade. Do not make the sub-grade so wet that puddles form. Do not place the concrete in muddy, standing water or on frozen subgrade. Before concrete is placed, install expansion joint material wherever the concrete is placed against buildings, steps, walls, columns, existing slabs, etc. These joints allow movement of the slab and help reduce cracking caused when such movements are restrained. Additional water may be added to the concrete, when the truck first arrives, to a maximum 6” slump. However, excessive water is detrimental to achieving the design strength of the concrete. The concrete should be placed in a manner that keeps wheelbarrow or buggy movement to a minimum. Spread the concrete with a come along. Do not use any tool that will cause segregation. Use a wood or metal straight edge to strike off and to level the concrete.

Our trained dispatcher can help you with this by giving him/her your dimensions of length x width x depth or you can try it yourself by these two methods: Use this handy online concrete calculator: Concrete Volume Calculator Concrete is not cheap and nothing is worse than coming up short (except rain). A good rule of thumb is to order an extra 5 percent rounded up to the next 1/4 yd. to handle spillage and uneven bases.

Float the concrete as soon as possible after the concrete has been struck-off. This operation must be completed before bleed water appears. Do not perform any finishing operations when there is bleed water on the surface. The surface must remain open until all bleeding has occurred. Any finishing operations done while bleed water is on the surface will result in surface problems, such as scaling, de-lamination and blistering. Float surface after bleed water is gone. Do not “bless” or add any water to the surface of the concrete. This raises the water/cement ratio of the surface, causing it to be weaker and more porous. If maintaining surface moisture is a problem, apply an evaporation retardant (not surface retardant) to the concrete after initial floating. Evaporation retardant is especially effective if rapid drying conditions exist, such as low humidity, high winds, etc. Cut joints (if hand tooled) and edge while the concrete is still plastic. A light broom finish is recommended on exterior concrete to improve traction. Do not overwork or overfinish the surface of any exposed concrete slab. This tends to bring too much fine material to the surface and weakens it. Caution – Machine floating and/or troweling is not recommended. These procedures reduce the entrained air in the surface where it is needed most. Control joints may be hand tooled or sawed. In either method, they must be cut to a depth of at least one fourth the thickness of the slab and spaced so that the dimension in either direction does not exceed that shown in the following table: Thickness of slab longest between: 3 ½” 8 ft. 4” 10 ft. 5” or more 12 ft. In addition to lateral jointing, a joint must be cut down the center for the full length of a driveway that is 10’ wide and 3 ½” thick or for one that is 16’ wide and 6” thick. Joints must be straight and continuous, not staggered or offset. If control joints are sawed, this should take place after all finishing and curing applications are complete and when the concrete has hardened sufficiently to allow sawing without raveling. At Becker & Scrivens we have a wide range of concrete supplies to help you with any job, start to finish.

Curing is one of the most important steps in concrete construction and regrettably, one of the most neglected. Laboratory tests show that concrete in a dry environment can lose as much as 50% of its potential strength compared to similar concrete that is properly cured. The goal with curing is to maintain moisture and temperature so that the cement may fully hydrate with the water. If a slab is allowed to dry at the surface, hydration virtually stops and the result will be a soft surface with poor resistance to wear and abrasion. The most common method of curing new driveways is the use of a liquid membrane-forming compound, normally called curing compound or “cure and seal.” This must be applied at a rate not thinner than manufacturer’s instructions, often specified at 200 square feet per gallon. There are some variations in curing methods during different times of the year. In the warmer months, a cure and seal may be used immediately following finishing. This helps to retain moisture and fully hydrate the cement at the surface. It is suggested that a curing compound or a cure and seal is used, that the driveway be resealed with an acrylic sealer approximately one month after initial curing. In the colder months, a penetrating sealer should be used and applied only after finishing operations are complete and the surface can take foot load. This product lets your surface breathe, allowing water to bleed from the surface. Effective and timely curing will improve short term and ultimate strength, provide better durability, and increase resistance to scaling, all contributing to better concrete.

It is also essential that a slab be kept from freezing for at least the first week after it is placed. This must be done preferably with insulating blankets. If concrete freezes during the first three days after placement, permanent damage will occur. De-icing tips: Exposure to de-icing salts cannot be completely avoided. However, measures should be taken to limit the amount of de-icing salts applied directly and intentionally to the concrete, especially during the first year. Using these de-icers sparingly will extend the life of the concrete. De-icers containing ammonium sulfate or ammonium nitrate should not be applied. Even the safest de-icers are harmful to the surface. Sand is generally the safest way to reduce slip and fall accidents.

Discoloration of concrete comes from a variety of factors: Calcium chloride will cause discoloration every time. Concrete poured on different days will cause subtle variations in color. Different brands and different types of cements or aggregates will cause different concrete colors. Avoid switching on the same project. Concrete that is poured at different slumps will result in different colors.

A concrete contractor is a trained and experienced individual or team that can manage concrete from fluid state to the hard finished product that is produced. Usually the contractor takes care of preparing for, ordering, placing, and finishing the concrete. A redi mix supplier partners with reputable contractors to supply a quality mix that will last a lifetime.

We recommend a 4000 psi concrete with limestone aggregate. For concrete driveways, slabs and sidewalks, a pour of at least four inches is typical.

A well-poured concrete slab with a deep, sturdy foundation can last for 30 to 40 years. Pouring concrete over old concrete instead of directly over a new gravel foundation limits the ability to maximize the slab's lifespan. The condition of the existing slab is the primary factor that determines how long the new concrete will last.

You can fill over the dirt as long as it is compacted very well and has no organic matter that will be in contact with the concrete. You should also leave enough room to have a full four inches of concrete throughout the area of the pour.