1. What is Concrete vs. Cement?
Although the terms “cement” and “concrete” are often used interchangeably, cement is actually a component of concrete.
Concrete is made up of approximately…
- 6% air
- 11% portland cement
- 41% gravel or crushed stone (coarse aggregate)
- 26% sand (fine aggregate)
- 16% water
“Portland cement” is the generic term for the type of cement used in virtually all concrete. In its simplest form, concrete is a mixture of paste and aggregates. The paste (portland cement and water) coats the surface of the aggregates. Through a chemical reaction called “hydration,” the paste hardens and gains strength to form the rock-like mass we know as concrete.So, there is no such thing as a cement sidewalk; the proper term is concrete sidewalk.
2. When is the best time to pour concrete? Can you replace concrete in the winter?
Temperature extremes make it difficult to properly pour and cure concrete. On hot days, too much water is lost by evaporation. If the temperature falls too close to freezing, hydration slows to a near standstill. While too much water weakens the concrete causing peeling and chipping, too little water causes the concrete to cure too fast and will result in cracking. When pouring concrete, the best results are achieved in temperatures between 50 and 80 degrees Fahrenheit. Concrete can be poured in both colder and warmer temperatures, but may require additives.
3. How soon before we can walk on the new concrete? Drive?
This is the most commonly asked question. And the real answer is this; concrete is not fully cured (dried and settled) until after 28 days. However, most situations do not allow for that kind of cure time. So after years of experience and many jobs offering a variety of different conditions, we recommend the following:
- Walking: We suggest you wait at least 24 hours after the concrete has been finished. For stamped and decorative finishes this time frame will likely increase.
- Driving: We recommend that you not drive on the new concrete for 7 days.
Please keep in mind that these time recommendations are temperature driven. There are different concrete mix designs available that allow us to substantially increase the psi or compressive strength of the concrete which will allow for a faster curing time and earlier use. We can discuss this and any other questions you may have when we come to provide your free estimate.
4. How is concrete measured?
To measure concrete you will need to know the cubic feet of the area in which you wish to place the concrete.
5. Why does concrete crack? How much is normal?
Unfortunately, cracking is pretty common in concrete, especially during the first 30 days, while it’s curing. There are a number of reasons why concrete cracks. The most common is because concrete shrinks as the excess water evaporates and it hardens. Concrete can also crack if it dries too quickly. Weather conditions – extreme temperatures, rapid temperature changes or conditions that are too wet or too dry – also play a major factor in how well concrete cures. When the width of a crack exceeds 1/4” in width, it is probably time to seek professional assistance.
6. Why would new concrete chip or flake off?
Most likely, the concrete was not mixed correctly. The concrete should be mixed with the correct amount of water, and ideally the mix kept as dry as possible. High water content will weaken the material. The concrete also needs time to cure properly and should be handled with care during the curing process. Sealing the concrete can also shield it from the elements that break concrete down.
7. When do you need rebar or wire to support concrete?
There are varied opinions among professionals about when to use rebar or wire to reinforce concrete. Adding rebar or wire to concrete provides additional strength and support and helps to minimize cracking and separating. How do they do this? Rebar and wire actually help to absorb and distribute the strain put on concrete when it expands and contracts. We recommend using rebar in concrete if there is a concern for cracking, weakness or instability. Use wire mesh instead of rebar when dealing with smaller jobs.
8. Can you get the new concrete to match the old concrete?
Certainly. We understand the need for repairs to appear as seamless as possible. There are a few different approaches we can take to match existing, aged concrete.
- Use one or more muriatic acid washes to artificially weather concrete
- Etch the surface, and then wash it with a mixture of carbon black and water
- Use a diluted black or brown concrete stain to darken the color
9. Do you do stamped concrete? Exposed aggregate?
Yes we do! We’d be happy to meet with you to discuss your options and to help you make a decision as to which may be the best for your property.