Concrete Questions Answered

Plus do it yourself tips

What is a slump?

The slump is the consistency of the concrete. (how wet or dry the mix is)

What do you use a tamp for?

A tamp is used to blend the aggregate downward into the mix and bring the “cream” to the top. The use of a tamp will provide a more workable mix and allow for a proper finish.

How long does it take for concrete to dry enough to walk on?

Wind, humidity, and sunlight are all factors in how long it takes for concrete to cure, walking, normally about 1 to 2 days.

How long does it take for concrete to cure enough to drive on?

Again, wind, humidity, and sunlight are all factors but the standard is about 5 to 7 days.

Should I put cure or water on the concrete?

Yes, after the initial 12 hours applying a cure of water for 5 days every morning and night is recommended.

Do I need to use base rock for my subgrade?

Baserock is often needed, but not always, dependant upon conditions and expected use of concrete. When used, it will always need to be compacted.

What is a control/construction joint and where are they needed?

It is a groove joint used to control concrete cracking.

What is an expansion board and where are they needed?

It is material placed in the concrete to allow for expansion and contraction of the concrete.


Of Concrete Terms

Accelerator – A chemical substance added to a concrete mix reduces the set time by increasing the rate of hydration.

Aggregate – Concrete is a mixture of water, Portland cement, and aggregates (sand and/or stone).  Sand is considered a fine aggregate, while any stones are coarse aggregates.

Bull Float – a tool comprising a large, flat, rectangular piece of wood, aluminum, or magnesium usually 8 inches wide and 48 inches long, and a handle 4 to 16 feet in length used to smooth unformed surfaces or freshly placed concrete.

Cubic Yard – Unit of measure for ready mix concrete.  Concrete is ordered, sold, and batched by volume.

Curing – The maintenance of the proper moisture and temperature of concrete in its early stages so that desired properties may develop.

Portland cement – A hydraulic cement that sets and hardens by chemical interaction with water.

Sack mix – The number of sacks of cement in a cubic yard of concrete.  Specified when ordering, concrete is typically referred to as a 5-sack mix.  The sacks of cement needed in a mix are usually specified in either the plans or the specifications of a project.  More sacks = more strength.

Screeding – The operation of forming a surface by the use of a screed or strike-off and screed guides.  (typically, the forms)

Set time – A measurement in hours and minutes of the hardening of concrete to resist a measure of penetration.

Slump – A measure of the consistency of freshly mixed concrete, measured in inches.  It is the distance that freshly mixed concrete subsides when a conical mold (slump cone) is lifted from the test specimen.  Increasing the slump is typically done by increasing the batch water.  This method also will begin to erode the strength of the concrete if the slump is raised higher that its designed level.

Subgrade – The prepared and compacted soil made to support a structure or pavement system.

Mobile (Volumetric) mixer – A concrete mixer that measures and produces ready-mix concrete by volume rather than weight.  Volumetric mixers meter their concrete output as they produce the concrete, also known as continuous batching.

Mike's Concrete Tips

Do It Yourself Guide

STEP ONE: Site Preparation & Planning
  • The subgrade must be compacted and free of standing water.
  • Forms must be secure and capable of withstanding the load pressure of fresh concrete.
  • Arrange enough help to place and finish the concrete.  Start with a minimum of 2 people for a 1 cubic yard pour.  Add one person for each additional cubic yard of concrete.  If you are using wheelbarrows to move the concrete from the truck to the forms, add an additional person.
  • Assign specific responsibilities to helpers before the concrete arrives.
  • Provide acceptable access for delivery:
    1. The pathway must be of stable soil (able to support 85,000 pounds)
    2. The pathway must be at least 10 feet wide and 14 feet high
    3. Avoid bringing trucks over curbs, sidewalks, and driveways
  • The discharge chutes can reach approx. 20’ straight back or 15’ to the side.
  • Determine what type of control joints will be used to control cracking; hand-tooled or saw-cut.
  • TIPS: Concrete used for residential applications should be at least 4 inches thick.
    1. Control joints should be placed no more than 10 feet apart
    2. Sections should be square or nearly square
    3. The joint depth should be at least ¼ the thickness of the concrete
    4. Avoid creating triangles or odd-shaped panels when placing joints
STEP TWO: Placement
  • Concrete must be discharged as close to the final position as possible (eliminate “dragging” concrete long distances).
  • Concrete must be discharged in a timely manner upon arriving at the job site.  If you are using wheelbarrows to move the concrete from the truck to the forms, make sure you have enough help to finish the project in a timely manner.
  • During the placement process, follow these easy steps:
    1. Strike off or “screed” the concrete to the proper elevation or form height with a wood or magnesium straight edge (2”x4” works fine).
    2. Immediately after striking off and before bleed water appears, the concrete must be bull floated and the edges formed with an edger.
    3. After bull floating, no finishing practices must take place until the bleed water has completely evaporated.
    4. Concrete will be glossy when bleed water is present and will dull when it evaporates.
STEP THREE: Finishing
  • Finishing is the process of texturing the concrete.  If you are using hand-tooled control joints, these must be completed prior to final texturing.  The following textures may be applied:
  • A broom or brush finish is recommended for exterior applications that require maximum skid resistance such as; sidewalks and driveways.  To achieve a broom finish; simply push or pull the concrete broom across the concrete when it reaches the desired consistency; timing is a judgment call based on the desired depth of broom texture.
  • A porous trowel finish is recommended for exterior applications that require minimal skid resistance such as; patios and porches. To achieve a porous trowel finish; trowel the concrete when it reaches a consistency that supports our weight but leaves footprints approximately ¼ inch deep.
  • A hard trowel finish is recommended for interior applications that require a non-porous surface such as shop floors and garage floors.  To achieve a hard trowel finish the concrete must be finished with a power trowel.
  • For decorative or architectural finishes we recommend that you hire a qualified licensed contractor that specializes in decorative concrete. (Accu-Con Concrete Services are a great choice for this type of work.)
  • Curing is the most important step in concrete placement, yet is typically the most neglected. To ensure that concrete reaches its maximum designed strength and durability, it must be properly cured. This process must begin as soon as the concrete will accept the process without damage to the surface. There are two methods for curing concrete.
  • Wet curing is the process of keeping the concrete surface saturated. A garden sprinkler is typically used for this type of curing.