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Concrete

Justin Crain

2013-06-25 09:33:11

Q-What are the concerns in concrete basement construction?

A-A number of things affect the performance of concrete, such as climate and soil conditions, load, design, and the quality of material and workmanship. These issues present a number of concerns that should be observed throughout the process. First, site condition and excavation. It is essential to have a soil investigation to ensure proper design and construction of the foundation. The next important concern is the framework and reinforcement. All framework must be constructed and braced so that it can withstand the pressure of the concrete. Reinforcement is effective in controlling shrinkage cracks and is also important in uneven side pressures. Joints are another concern. If they are properly placed, they can control temperature and shrinkage cracks. Concrete must have a moderate slump. To avoid cold joints, place concrete in a continuous operation. Curing should start immediately after finishing. Waterproofing and drainage is another huge concern. Spray or paint needs to be applied to the exterior walls and foundational drainage provided. Finally, it is important that the backfilling is done very carefully to avoid damaging the walls. When possible, it is best to have the first floor in place before backfilling. All of the elements play a huge role in your basement construction. Always talk to a professional to make sure the job is done correctly.

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Concrete

Justin Crain

2013-05-29 11:00:48

Q-I have a crack in my patio. Is it possible to repair it without it looking like a patch job?

A-It is certainly possible to repair a crack to a condition that is very acceptable and sometimes even to a flawless finish. How visible it is depends on many factors, such as the size of the crack and age of the concrete and how much weathering has already occurred to the surrounding areas. There are many techniques, each appropriate for a particular type of crack. It is always best to consult a concrete professional who can fix the crack as well as address the problem that caused it in the first place. To fill a crack, a concrete professional will determine the size of the crack, and look for the factors that caused it, such as a lack of expansion joints. If there are underlying problems, it might be necessary to fix those issues so that the patio does not continue to crack in the same or other places. After determining the size and depth of the crack, you choose the appropriate type of filler. Choosing the right filler for the crack is very important not only to attain the best cosmetic results, but also for the best bonding. Then, you must prepare the area so that you can get a good mend. Sometimes this means just making sure it is clean, loosening surrounding material with a stiff wire brush. Other times you must enlarge the crack, making the bottom wider than the top. It also includes using a chemical cleaner of concrete adhesive to increase the adhesive properties of the concrete. Finally you install the repair matter, forcing it into the crack, and you are finished. When done professionally and skillfully, it is possible to achieve a beautiful finish.

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Concrete

Justin Crain

2013-04-30 09:01:42

Q-What types of cracks may occur?

A-Cracks are common in basement walls and happen for a number of reasons. First, you might have shrinkage cracks. Newly placed concrete has the largest volume it will ever have at the time of placement. Excessive drying or a significant drop in temperature increases the tendency for it to shrink. Also, if the footing and the walls are placed at different times, you will get different shrinkage rates that might lead to additional cracking. Another type of crack is the settlement crack. These cracks are caused by non-uniform support of footings or expansive soils. Another concern is structural cracks. Structural cracks in basements occur during backfilling, especially when heavy equipment gets too close to the walls. Finally, some of the common basement cracks are caused by a lack of joints or improper joint practices. There are many ways to control or minimize cracking in basement walls as recommended by the National Association of Homebuilders. Control joints are joints in the concrete that help prevent or minimize any cracking in the walls. These practices include such things as: • Providing uniform soil support. • Concrete being placed at a moderate slump. • Following proper procedures. • Placing control joints every 20-30 feet. • Careful backfill done when the first floor is in place. • Following proper curing practices. Thanks for the question and I hope I have helped.

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Concrete

Justin Crain

2012-08-02 10:24:54

Q- The walls in our basement are slightly bowed, and have developed a couple of cracks. Is it possible to repair this as a DYI job, and if so, what would you rate the level of difficulty?

A- While it is possible to patch cement walls as a DYI job, you likely have another problem you need to address—the cause of the cracking. Many things can cause cracking, but since you mentioned that the walls are slightly bowed, unstable soil is a likely culprit. Unstable soil can be a basement's (and homeowner's) worst nightmare and a problem you will want to address properly. Unstable soil issues can arise when the soil is either expansive clay or compressible or improperly compacted. This can cause the structure to be unevenly supported which then leads to settling and shifting soil. Ultimately, you will notice this from signature signs such as the bowing walls and cracks. Another issue may be a problem of uneven lateral loads, which can also be as a result of soil problems. Either way, you may want to have a professional look at the problem before proceeding. Fortunately, it is a fixable problem. One of the solutions that is often used is to install hydraulically driven piles or piers to help rescue settled foundations and then concrete stabilization processes to repair the cracks and stabilize and fortify the wall. As you probably already surmised, this is really not a DYI project. You will want an expert to get in there as soon as possible and help fix the problem and prevent further movement.

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Concrete

Justin Crain

2012-08-01 14:51:35

Q- Can you tell me about the curing process? How long does it take and what are my primary concerns?

A- Curing is process where the cement is kept under controlled environmental conditions until the process of hydration is complete. Cement requires time for the water to permeate the mixture and begin an exothermic chemical process during which it acquires the properties of strength and hardness. During this time, to keep the surface area moist. Keeping the cement under controlled conditions during curing is important because any disruption to the process will result in tensile stresses that lead to cracking. Proper curing, and proper hydration during the process results in a superior finished product. The effects of curing are primarily a function of geometry (the relation between exposed surface area and volume), the permeability of the concrete, curing time, and curing history. If you want to avoid cracks, scaling, and reduced abrasion resistance, give the concrete the time and proper conditions needed for proper curing. It is only a little more effort for a superior result. Good luck with your project!

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Concrete

Justin Crain

2012-06-01 11:21:06

Q: We just had a concrete patio put in and the contractor said to be sure to maintain it. I kind of let that breeze by as I thought concrete was fairly maintenance-free. Now, as I think of it, I am wondering what I should do to keep it in good shape. What do you recommend?

A: Of course one of the outstanding attributes of concrete is that it needs very little work to keep it in great condition. However, no material is ever completely maintenance-free. Remember, homeowner warranties covering exterior concrete are extremely rare. Proper care and maintenance is your responsibility. If you want to keep your patio in good condition and extend the life of your investment, here are some important tips: • New concrete must be given at least seven (7) days of curing time (at temperatures above 32 degrees) before vehicular traffic is allowed on it. Concrete takes 28 days of curing time to achieve its maximum strength. • Concrete surfaces must be kept as clean as possible. Remove snow and ice as soon as possible. Use sand for traction instead of salt. • Keep lawn fertilizers cleaned off of concrete surfaces. • Apply a quality sealer annually or according to the manufacturer’s directions. Sealer is easy to apply and the most important step to caring for your concrete. • Remove stains immediately. A sealer can protect from stain absorption, but it is still best to remove spills as soon as possible to avoid discoloration. • Annual maintenance is important! As you care for your lawn, trees, shrubbery, and your house, please take the time to care for your concrete pavements. It is a SMALL INVESTMENT for such a GREAT RETURN! Your concrete surface is like your wood deck or the siding on your house, in that they all must be protected from the environment to reach their expected service life.

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Concrete

Justin Crain

2012-04-20 09:57:01

Q: I am a DIY kind of guy and looking at pouring my own patio. I did a slab for my shed last summer and got a bunch of fine cracks on the surface. How do I avoid that for this project?

A: From the information you provided, I believe the cracks to which you are referring are plastic shrinkage cracking. These cracks appear 1 to 3 feet apart, relatively shallow, and generally do not enter the perimeter of the slab. While unsightly, these surface cracks do not impart the strength or durability of the concrete. These cracks form on fresh concrete while still in the plastic stage and caused when the rate of evaporation is faster than the rate of bleed water, causing tensile force in the surface layers. Some of the contributing factors may include: • Wind velocity in excess of 5 mph • Low humidity • High ambient and/or concrete temperatures It is important to remember that anything that delays the setting increases the possibility of plastic shrinkage cracking, like cool temperatures, cool subgrades and high water content. To avoid the problem, pour concrete under ideal conditions and minimize anything that would contribute to their formation. You might consider putting up temporary windbreaks to reduce wind velocity over the surface of the concrete or sun shades to control surface temperature. If it is very hot, consider using a fog spray to control evaporation. Other important things to consider would be having enough manpower on hand to finish the task promptly, and the proper materials available. Finally, consider your choice of materials. Consider using synthetic fibers which help resist cracking. The synthetic fibers do not replace rebar, but do replace wire mesh, as the fibers are mixed evenly through the concrete.

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Concrete

Justin Crain

2012-03-27 09:58:38

Q: What is concrete crazing?

A: Crazing is the development of fine random cracks across the surface of concrete or mortar, caused by the shrinkage of the surface layer. These cracks are sometimes referred to as shallow map or pattern cracking due to the appearance of the spider web network of cracks. The cracks are rarely more than 1/8 inch deep and usually most noticeable on steel-troweled surfaces. Crazing develops early in the life of the concrete, and usually apparent the day after placement or within the first week. There can be several causes, including: • Poor or inadequate curing • Adverse environmental conditions • Too wet mix • Finishing operations performed while bleed water remains on the surface • Sprinkling cement on the surface to dry bleed water In order to avoid crazing, start curing as soon as possible. Use moderate slump, or 3-5 inches of concrete. Do not sprinkle cement to soak up the bleed water. Finally, when you expect high evaporation rates, slightly dampen the subgrade prior to placement. Getting a good surface on cement can be difficult and involves careful attention and precision timing. Concrete professionals can help assure that your surface is free of crazing and ready for you to use and enjoy.

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Concrete

Justin Crain

2011-07-01 08:19:00

Question: What is the difference between cement and concrete?

Answer: One of the most interchanged words in the construction industry is concrete and cement. There is no such thing as a cement driveway or a cement curb; the correct terms are concrete drive way and concrete curb. So what is concrete? Concrete is a mixture of cementitious materials, water, rock and sand. Cement is a powdered ingredient that provides the glue that binds the rock and sand together in a mass called concrete. A concrete mix design is accurately weighed by a computer at the plant, and then the concrete is delivered to the customer in a freshly mixed and unhardened state. The concrete normally sets or hardens within two to twelve hours after it is placed. Concrete needs to cure, and will achieve its maximum strength twenty-eight days after it has been placed. Below are some tips to maintain your concrete surface: • New concrete must be given at least seven (7) days of curing time (at temperatures above 32 degrees) before vehicular traffic is allowed on it. Concrete takes 28 days of curing time to achieve its maximum strength. • Concrete surfaces must be kept as clean as possible. Remove snow and ice as soon as possible. Use sand for traction instead of salt. • Keep lawn fertilizers cleaned off of concrete surfaces. • Apply a quality sealer annually or according to the manufactures directions. Sealer is easy to apply and the most important step to caring for your concrete. • Annual maintenance is important! As you care for your lawn, trees, shrubbery and house, please take the time to care for your concrete pavements. It is a SMALL INVESTMENT for such a GREAT RETURN! • Homeowner warranties covering exterior concrete are extremely rare. Proper care and maintenance is your responsibility. Your concrete surface is like your wood deck or the siding on your house, in that they all must be protected from the environment to reach their expected service life.