Concrete Resources Inc.
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Concrete Resources Inc.
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Welcome to our Contractors Corner. Here you can find resources and helpful information for anything that deals with concrete and finishing concrete. To order Ready Mix Concrete click here.
To order, call 678-684-4500 or email sales@concreteresourcesinc.com
More helpful links for Residential Concrete installation Concrete Construction Online- Helpful columns and features that even the most experienced concrete contractor can find useful.
American Concrete Institute- Members of ACI have unlimited access; Non-members have limited access but can still find useful references from this site.
Concrete Info- A very helpful forum where customers and contractors alike ask questions about different aspects of concrete and installations.
Concrete FAQs Cracks in concreteQ. How do I prevent visible cracks in during the finishing process? A. So, you are going to put in a patio, driveway or sidewalk, and you are going to use concrete. One thing to know before you put in your concrete — all concrete cracks. Concrete typically consists of cement, rock, sand and water. In the fresh, or plastic stage, concrete is fluid. As it hardens, the cement and water begin to shrink, and the stresses created by this shrinking cannot be overcome by the small amount of strength developed by the young concrete. If you place the concrete on a windy day, the top may start to harden before the bottom, which will cause the concrete to shrink unevenly (plastic shrinkage cracks.) Also, if the ground underneath the concrete is not level, there will be an unequal dragging force while the concrete shrinks, also causing stresses the new concrete cannot withstand. So, how do you get concrete with no VISIBLE cracks in it? By following a few simple steps before and after you place the concrete, you will have a very nice looking structure that will require very little maintenance, and give you years of enjoyment. Before you place the concrete, make sure your subgrade (ground beneath the concrete) is thoroughly compacted and level. The absolute best thing to do is get a garden tiller, till the soil to a depth of 6 inches, then use a hand operated compactor and compact the soil vigorously. This will help ensure there are no soft spots. You can apply a layer of cushion sand if you want. This will help achieve a totally level surface and allow a consistent friction to the shrinking concrete. Four inches of washed sand ought to be plenty for the cushion. If you use a wire mesh for reinforcement, use panels and not rolls. The rolled wire mesh is extremely difficult to keep in the top half of the concrete, where it HAS to be in order to do its job. You can also use reinforcement bars (rebar) tied together with steel wire, but spacing and size requirements vary based on load and soil conditions, so it is hard to recommend a standard set up for that. If you do use rebar, it is essential that you keep it in the top half of the concrete. You can use stones, broken brick or you can buy plastic chairs that the steel will sit on to keep it in the proper position when you place the concrete. You can also have the ready mix concrete company supply fibers to the mix. These fibers are usually nylon or polypropylene. They help keep the cracking of the concrete on a micro level instead of a macro level (where you can see the cracks with your naked eye.) Steel reinforcement also helps keep cracking in check, but if cracking does occur, the steel, when properly placed in the concrete, will hold the concrete together, whereas fibers will not do that. When the concrete arrives, if you don't have a vapor barrier, wet the subgrade without creating puddles so that the water in the concrete will not be absorbed by the dry subgrade, thus causing uneven drying and the dreaded plastic shrinkage cracks. Once the concrete is placed, make sure to protect it from high winds and direct sunlight so the concrete will dry evenly from top to bottom. You are now ready to perform the most important step in preventing noticeable cracking. Contraction joints are the secret to no cracking! By placing contraction joints that are at least ¼th the depth of the concrete and on intervals of 25 to 30 times the depth of the concrete (usually easiest with a jointing trowel or tool while the concrete is still fresh), you will almost ensure there will be no visible cracking in your concrete. If your slab is 4 inches thick, the joints must be at least 1 inch deep and placed every 100 to 120 inches. If you cannot use a jointing tool to put the joints in, you can hire a concrete sawing contractor to do this for you. Make sure he cuts the joints a minimum of ¼th the slab depth. This jointing method helps the concrete crack at the weakest point. This is why it is so important for the joints to be deep enough. Variations in subgrade levels could cause greater stress in the concrete in an area where the joint isn't deep enough, and the concrete will crack outside the joint. Once your joints are in place, and the concrete has cured for about two weeks, you are ready to seal the joints. This will prevent water from migrating into the subgrade and expanding and contracting, or getting into the joints and freezing, causing the water to expand and breaking out the concrete around the joints. You now have a concrete structure that will serve you well. Removing spots from concrete Q. I have an unsightly rust spot and I have not been successful in removing it. Will you please advise me how to remove this? A. If the stain is fresh, use a heavy duty cleaning compound containing a large proportion of tri-sodium phosphate or TSP, available at any hardware store. Apply with a damp cloth or pad. Rub the discolored surface until the stain is removed and rinse thoroughly. If that doesn't work, make a paste of 1 part sodium citrate crystals to 6 parts water and enough whiting or talcum powder to make a paste. Spread the paste on the rust stains. Scrape the dried paste. The rust should be removed. Repeat if necessary. Another rust removing product is naval jelly, which is available from paint stores. Apply a small amount of the jelly with a soft paintbrush or cloth. Allow the jelly to cover the stain for 30 minutes to an hour or until the stain disappears. Then wash with clear water. Dusting, peeling, spalling, etc.Q. The top of the concrete is dusting, peeling up, spalling, or coming up in little spots. What causes this and how can I repair it? A. Several situations cause spalling, delamination, dusting or peeling. Water sealed under the surface of the concrete during the finishing process, dirty coarse aggregate, or applying too much water to the surface before the concrete hardens. To repair, make sure all loose material is removed, using a stiff broom or even a high-pressure sprayer. Remember, always use eye protection in those type situations. Once you have exposed the good concrete, you can apply a topping to cover the old, ugly concrete. The best material to use and which many companies manufacture, is epoxy grout. It is usually stronger than the in-place concrete, it bonds very well with the existing concrete, and can be applied as thick as several inches down to a feather's edge. Selecting the proper concrete mixQ. What strength concrete is normally used for the slab under a home? A. Typical mixes range from 2500 PSI to 4000 PSI, depending on the area of the country and the quality of the raw materials. Should there be a different weight used for the garage area? Not really. Usually the biggest load on a slab is the heaving from the subgrade and not the structure on top of it (or the car). Determining if the concrete can be placed directly from the truck or will need to be pumpedCan you get a truck up close to where the concrete's final destination is? Trucks can't get close enough to the pour for four reasons: 1. The ground surrounding the project is
too wet and the truck will sink. |
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