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Planning & Preparation
Before you begin your project, it is important to properly plan and prepare. Proper planning will save time in the end, and helps to assure your satisfaction with the finished product.
Volume Calculation
The general rule of thumb for a 4 inch thick pour is: 1 cubic yard will cover 81 square feet.
To calculate square footage multiply Length times Width in feet.
Length X Width = Square Feet
Below is a reference list of coverage for different thicknesses.
3” = 106 sq ft
3.5” = 93 sq ft
4” = 81 sq ft
4.5” = 72 sq ft
5” = 65 sq ft
5.5” = 59 sq ft
6' = 54 sq ft
If your dimensions do not fit these guidelines, you can figure most anything that has all straight sides with the following formula:
Length X Width X Depth, divided by 27 = cubic yards.
The values must all be in feet.
To convert inches to feet simply divide the number of inches by 12. For example: 4 inches divided by 12 is .33 feet. 6 inches divided by 12 is .5 feet.
To calculate square footage multiply Length times Width in feet.
Length X Width = Square Feet
Below is a reference list of coverage for different thicknesses.
3” = 106 sq ft
3.5” = 93 sq ft
4” = 81 sq ft
4.5” = 72 sq ft
5” = 65 sq ft
5.5” = 59 sq ft
6' = 54 sq ft
If your dimensions do not fit these guidelines, you can figure most anything that has all straight sides with the following formula:
Length X Width X Depth, divided by 27 = cubic yards.
The values must all be in feet.
To convert inches to feet simply divide the number of inches by 12. For example: 4 inches divided by 12 is .33 feet. 6 inches divided by 12 is .5 feet.
Thickness
For common household projects - driveways, walkways and patios - 4 inches thick should do the trick. You may require a thicker pour should the area have heavy traffic or if your ground swells and contracts (Clay soil).
Base
We recommend using a crusher run compacted base 2 inches thick. If you wish, you may pour directly on compacted dirt. Never pour over organic material as it will decay and leave a void.
Drainage
Industry standard for exterior concrete calls for a slope of 1 inch fall per 10 feet away from structures.
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Excavation
First and most important Call 1-800-522-6543 to locate any utility lines in the area. While taking care to only dig as deep as necessary (keeping an eye out for power lines), ensure you remove tree roots, leaves, wood and any other organic matter in the desired area, as they will decay causing voids or will continue growing and can crack your new concrete.
Compaction
To ensure your slab doesn't settle or vary in thickness, make sure to compact the soil/gravel base in the desired area.
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Forming
Take care to stake your forms securely to the ground, while paying close attention to the slope (for proper drainage). 2x4s are adequate for use as forms. Never use particle board or wafer board as the water from the concrete will break down the glue that holds them together. Check the accuracy of your base by pulling a string very tight across the top of your forms and measuring down to the base in several different areas.
Expansion
All concrete expands and contracts with heat and cold. The forces enough to cause buckling, cracks and can even collapse brick walls. Install premolded expansion joint material anywhere concrete will come into contact with existing slabs, steps or buildings. You can get this material from home improvment stores. However, most people prefer the shreddred rubber type over the fiber board type. You can get that at M&M Lumber at 46st and Mingo. The joint must cover the entire contact area where the concrete meets any other structure to ensure the new slab will be completely isolated. This allows for heat expansion to occur without causing damage.
Specification
Specifying the correct mix can be the difference between long-term satisfaction or dissapointment.
Concrete specifications consist ofStrength (in psi) (amount of cement included)Slump (in inches; basically the wetness)Chemical Additives (calcium chloride accelerator for example)Fiber (mixed in reinforcement).
Strength (psi)
Concrete Exposed to freezing and thawing temperatures should have a minimum compressive strength of 3000 psi and contain 4.5% to 6% air. You can choose better mixes. Higher psi. mixes have more Portland cement. This makes them stronger, more weather resistant and easier to smooth. We offer from 3000 to 6000 psi. in 500 psi. increments. Each 500 psi. upgrade cost $5 per yard more.
Slump (wetness)
For most pours we recommend a slump of 5 inches (+/- 1"). A higher slump will make the concrete more liquid and will be easier to place. If your pour is on a steep grade you may need a lower slump to prevent the concrete from running down the slope. Note: a slump greater than 5" may prolong the time you have to wait before finishing, particularly in cool weather. Also, less water added to the mix means stronger and more freeze resistant concrete.
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Consolidation
Placing
Concrete delivery should be closely coordinated with placing and finishing operations. Concrete should not be poured faster than it can be spread and screeded. Instead, concrete should be poured continuously as near as possible to its final position. You should never dump concrete into separate piles and work them together.
Using a concrete vibrator is recomended for optimum consolidation. The consolidation process uses vibration and gravity to consolidate fresh concrete within the forms and around embedded items and reinforcement. This process eliminates unwanted pockets of trapped air and stone while maintaining significant amounts of entrained air. The vibration temporarily suspends the natural friction between the aggregate particles, causing the concrete to behave as a liquid. Internal friction resumes as the vibration is stopped.
Finishing
Slabs exposed to the elements, driveways, patios, etc. - will need to be finished. You can finish your concrete in many ways, including color tinting and texturing. Patterned and stamped finishes are very popular on projects of all sizes.
Most surfaces will require strike-off or screeding to proper contour and elevation. In this process a straight edge (2X4 on edge) is moved across the concrete with a sawing motion.
Bull-floating eliminates high and low spots and embeds large aggregate particles immediately after strike-off. Jointing is required to eliminate unsightly random cracks.
Relief joints:
1. Can be made with a hand groover while the concrete is wet enough to work. The grooves should be at least 1\2 inch to 3\4 inches deep.
2. This can also be done by inserting strips of plastic, wood, metal, or preformed joint material into the unhardened concrete though this process is much harder to get right.
3. Another method of making relief joints and a bit cleaner look is to saw-cut joints after the concrete is hard enough to prevent chunking along the cut line.
After the concrete has been jointed, it should be floated with a wood or magnesium float or with a finishing machine using float blades. This embeds aggregate particles just beneath the surface; removes slight imperfections, humps, and voids; and produces the grout layer at the surface in preparation for additional finishing. Where a smooth surface is desired, floating should be followed a short time later with steel troweling. A slip-resistant surface can be produced by brooming before the concrete has completely hardened, but it should be sufficiently hard to retain the scoring impression from the bristles. If the surface grout moves in front of the broom, it is too soon.
Most surfaces will require strike-off or screeding to proper contour and elevation. In this process a straight edge (2X4 on edge) is moved across the concrete with a sawing motion.
Bull-floating eliminates high and low spots and embeds large aggregate particles immediately after strike-off. Jointing is required to eliminate unsightly random cracks.
Relief joints:
1. Can be made with a hand groover while the concrete is wet enough to work. The grooves should be at least 1\2 inch to 3\4 inches deep.
2. This can also be done by inserting strips of plastic, wood, metal, or preformed joint material into the unhardened concrete though this process is much harder to get right.
3. Another method of making relief joints and a bit cleaner look is to saw-cut joints after the concrete is hard enough to prevent chunking along the cut line.
After the concrete has been jointed, it should be floated with a wood or magnesium float or with a finishing machine using float blades. This embeds aggregate particles just beneath the surface; removes slight imperfections, humps, and voids; and produces the grout layer at the surface in preparation for additional finishing. Where a smooth surface is desired, floating should be followed a short time later with steel troweling. A slip-resistant surface can be produced by brooming before the concrete has completely hardened, but it should be sufficiently hard to retain the scoring impression from the bristles. If the surface grout moves in front of the broom, it is too soon.
Curing
Curing is an important step in concrete construction. Proper curing greatly increases concrete strength and durability. Concrete hardens as a result of the process of hydration: the chemical reaction of the components of cement after the addition of 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. The most common method of curing (and one of the simplest) is to utilize a liquid membrane which is sprayed or rolled on the surface of a slab after finishing to prevent premature drying of the surface. Waret sprinklers may be used when you are able to insure constant wetting for at least 3 days.
Curing in Extreme Weather
Curing is an important step in concrete construction. Proper curing greatly increases concrete strength and durability. Concrete hardens as a result of the process of hydration: the chemical reaction of the components of cement after the addition of 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. The most common method of curing (and one of the simplest) is to utilize a liquid membrane which is sprayed or rolled on the surface of a slab after finishing to prevent premature drying of the surface. Waret sprinklers may be used when you are able to insure constant wetting for at least 3 days.
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Curing Shortcut To Avoid
Avoid any curing method that lets the surface dry in a short time. Quick drying stops the hardening process, thus making a weak surface that is likely to scale.
Sealing
Water-repellent coatings or sealers can help prevent damage from freeze/thaw cycles and salting. They keep water from getting into the surface pores. Newly cured concrete should have a period of air-drying before being sealed. Follow the sealant manufacturers directions.
First Winter
Do not use salt or other deicers during the first winter. Use sand instead to improve traction. Even light applications of salt, or salt carried on cars may cause severe scaling of newly placed concrete. Fertilizers are not an acceptable deicer at any time.