CLICK HERE to download the pool deck plan.

The Challenge

Lay out all control joints, construction joints, and isolation joints to provide for shrinkage and eliminate the possibility of cracking (assuming the concrete doesn't have a mind of its own). Mark construction joints with "CJ" and isolation joints with "IJ." The winner will receive a free one-year subscription to Concrete Construction magazine.

Project Information

  • The deck concrete is 4 inches thick. There is no reinforcement included in the slab, neither steel or fibers added to the concrete
  • The pool coping is cast separate from the deck and is anchored to the top of the concrete pool walls.
  • Coping around the spa is also cast separately
  • The artificial rockwork doesn't rest on the pool deck, it has its own footings.
  • The pool deck meets up with the house foundations
  • Walkway and riser entrance into house is placed separately. Include joint layout details for this area also.
  • The pool deck is either pitched to the drains indicated on the drawing or to deck edges
  • After all the control joints are laid out they will be cut into the deck with diamond blade saws
  • The contractor casts the deck in two days, approximately half the square footage each day

Hint: Joint layout

Here are some basic rules for laying out contraction joints:

  • Keep panels as close to square as possible, don't exceed length to width ratios of more than 1.5.
  • To lay out joints multiply the thickness of a slab times 2 feet. For example, if a slab is 4 inches thick, multiply 4 times 2 and lay out joints every 8 feet in both directions. Don't exceed 15 feet regardless of slab thickness.
  • Control joints intersecting formed edges should be at 90 degree angles or less
  • Control joints intersecting other control joints should be at 90 degree angles or less
  • Never intersect other joints, construction joints, or form-lines at acute angles less than 60 degrees.
  • When "dog legs" are used when laying out joints that intersect with form lines or other concrete placements at angles less than 90 degrees, make them 12-inches to 18-inches long.
  • Make joint lines bisect box-outs or drains
  • Pavement shapes that cause planes of weakness, such as inside corners, should be considered in joint layout plans.
  • Provide isolation joints where deck concrete meets objects that respond to subgrade or freeze/thaw movement differently

Hint: Construction Joints

These are joints in concrete pavement created by forms to end one concrete placement and start another. If a placement is too large to cast at one time, workers set forms to complete the placement and then remove them to join the next placement to the old one.

Hint: Isolation joints

"Isolation joint" is now the preferred term instead of "expansion joint," even though you order "expansion joint" at supply houses. The function of these joints is to isolate your work from structures, other pavements, and objects considered to be non-movable. For all practical purposes, concrete is at its most expanded state when it's placed, so expansion material isn't needed in the body of a placement and is unsightly. Isolation joints provide space for slab movement around perimeters. The joint material should be resistant to deterioration, should be wide enough to extend to the full depth of the placement, and it should be ½-inch to 1-inch in thickness.