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Six steps to properly prepare and place exterior concrete that will be exposed to freeze-thaw Conditions

There are six steps to follow to achieve a high quality, durable exterior concrete project.
The following are six crucial steps that all go hand in hand with each other.
All six steps are required to obtain a professional, durable exterior concrete project.
It is not acceptable to follow some or most of the steps as listed. Anything less than following all six steps could result in an unsatisfactory project.
VanDerVart Concrete Products desires you to be fully satisfied with your concrete. We recommend that you review the following six steps with your contractor and discuss procedures before you sign a contract.
The proper handling and placement procedures of ready-mixed concrete is a skill. We do not recommend consumers place ready-mixed concrete without proper training, experience and adequate help at the worksite. This is to ensure a long lasting, high quality and durable concrete slab.

Step #1
PROPER SUBGRADE PREPARATION

  • The subgrade is the existing soil after the topsoil is removed.
  • Any pockets of soft soil that cannot be uniformly compacted must be removed and replaced with suitable material such as compactable gravel, compactable sand or fractured stone.
  • Slope the subgrade away from structures 1/4” per lineal foot to ensure good drainage.
  • Never place concrete on frozen or muddy subgrade.

Step #2
PROPER SLAB DESIGN

  • Use a minimum concrete thickness of 4 inches.
  • Control joints should be placed as soon as possible with a minimum depth of 1/4 the slab thickness never less than 1 inch.
  • Control joints should be spaced 2 to 2 1/2 times the thickness of the slab converted to feet.
    Examples:
    4” thick concrete x 2 times the thickness = 8 feet, 4" thick concrete x 2 1/2 times the thickness = 10 feet.
    Therefore concrete control joints should be cut at 8 feet x 8 feet or 10 feet x 10 feet maximum on a 4" thick concrete slab.
    The same math calculations apply as concrete is placed thicker, however control joints should never exceed 15 feet x 15 feet.
  • Aspect ratio of joints should be maximum 1:1.5 (length to width ratio). Make sure to incorporate restraint points into your joint layout.
  • As with the sub base, slope the concrete surface 1/4” per lineal foot.
  • Isolation joints are required at existing slabs, structures, and objects.
    Isolation joints should run the full depth of the slab.

Step #3
PROPER CONCRETE MIX DESIGN

  • The concrete mix should be designed to obtain 4500 psi. @ 28 days.
  • The concrete mix should have a maximum water/cementitious ratio of .45
  • The concrete mix must be an air entrained concrete mix. The air content when placed should be 6 percent, plus or minus 1 ½ percent.
  • The concrete slump should be approximately 4 inches, plus or minus 1 inch.
    [Assuming the customer does not request slump altering admixtures]
  • The concrete mix should include stone and sand that meet current Wisconsin Department of Transportation specifications.
    [Washed and properly graded aggregates]
    Note: The air content and strength of the mix will be affected by any re-tempering with water added at the jobsite.

Step #4
PROPER PLACING AND FINISHING

  • Place the concrete as near to final position as possible.
  • No finishing operations shall be performed when there is excess moisture or bleed water on the surface.
  • The only finishing operations required are: screeding or strike-off; bull floating prior to the appearance of any bleed water; a waiting period for the water sheen to disappear; edging and jointing; and a broom texture (the safest and most durable final finish).
  • Protection of the concrete from the hot sun, high winds, or freezing temperatures is required until the concrete has a chance to gain adequate strength and cure properly.
  • All concrete should be placed within 90 minutes from the time the truck was loaded. Hot-weather practices call for shorter placement time limits.
  • Hot weather concrete conditions reduce the placement time as the increased ambient air temperature and concrete temperature generate heat at a rapid rate. The chemical reaction that takes place is temperature sensitive, accelerating the mix "set time".
  • Placing concrete early in the morning is a common practice to provide a higher quality concrete mix and improved workmanship by the contractor.

Step #5
PROPER CURING AND SEALING

  • The concrete must be cured immediately after finishing. Curing greatly increases the strength and durability of the concrete surface. Proper curing increases the resistance to freezing and thawing as well as de-icing salts.
  • Curing is a process where a satisfactory moisture content and temperature must be maintained for a period of time.
  • There are several acceptable methods of curing; however the most common method is the use of a concrete cure and seal product applied at the manufacturer’s recommendation. VanDerVart stocks several types of curing compounds and curing products.
  • Note: In spring and fall when average temperatures are below 50 degrees, use cold weather concrete practices to maintain temperature and cure the concrete for a minimum of ten days.

Step #6
PROPER AFTERCARE

  • Keep vehicles off of freshly placed concrete for at least 7 days. In cool or cold weather conditions, a period in excess of ten days may be required.
  • Freshly placed concrete should be sealed after allowing a minimum of 28 days to air dry. Consider cleaning and resealing aged concrete every several years or as wear in high traffic areas begins to show. VanDerVart stocks several high quality concrete sealers for a variety of applications. Follow the manufacturer’s recommendations for the coverage rates to seal or reseal concrete.
  • Sealing is a process where a protective coating or penetrating water repellant material is applied to keep moisture and contaminates out of the concrete. This step can ensure years of attractive, trouble free and durable concrete.
  • The use of rain gutters and down spouts directing water away from both the building and the concrete is important. Downspouts connected to drain pipe should be pitched to a suitable area to ensure that water does not undermine concrete which can cause settlement of the concrete and/or settlement cracks in the concrete. It is desirable to maintain a dry subgrade under the concrete slab. Water or excessive moisture under the concrete will lead to significant frost heave during the winters of Wisconsin.
  • Prevent snow and ice from accumulating on the concrete especially during the first winter. Contact VanDerVart for a detailed explanation on this point if interested.
  • Don’t allow the use of de-icing chemicals, especially the first winter. Sand is available from VanDerVart and can always be used for traction.
  • Never use de-icers containing fertilizer ingredients such as ammonium sulfate, ammonium nitrate, calcium chloride, and magnesium chloride. These chemicals will chemically attack and destroy the concrete.
  • Prevent lawn fertilizers from accidently being placed on concrete. Some fertilizer ingredients contain chemicals that will stain or chemically attack the concrete.

These six steps insure a high quality, durable exterior concrete project.
VanDerVart desires you to be fully satisfied with your concrete. We recommend that you review the six steps with your contractor and discuss procedures before you sign a contract for work.

We request, that you request your contractor to use ready-mixed concrete and concrete products from VanDerVart. We have an experienced staff of professionals to ensure you receive high quality concrete, and we are available to assist you in the selection of aftercare products to protect your concrete.

Thank you,

The staff and management of VanDerVart Concrete Products



We provide service throughout all of Wisconsin.
We Provide ready-mixed concrete and aggregates through our locations in Calumet, Manitowoc and Sheboygan counties. We deliver concrete block, brick, retaining wall block and masonry products to the entire state of Wisconsin. Contact one of our sales representatives at 920-459-2417 (Sheboygan), 920-898-5771 (New Holstein) or 920-683-5585 (Manitowoc).