Concrete Joint types
- Freshly placed concrete is always prone to cracking off inside corners.
- Spacing Recommendations no more that 2-3 times the size in inches
- 4 inch thick slab need joints that are 8-12 feet on center
- 2” slab = 4 to 6 foot joints
- 5 cm slab = 2 meter squared joints
- 4” slab = 8 to 12 foot joints
- 10 cm, slab = 3.5 meter squared joints
- 6” slab = 12 to 18 foot joints
- 15 cm slab = 5 meters squared joints
What is the difference between a construction joint, isolation joint and control joints?
Joints in concrete pavement are created by forms to end one concrete pour and start another. If a pour is too large to cast at one time, workers set forms to complete the pour and then remove them to join the next placement to the old one. The cleanest way I have ever seen a construction joint placed is by using a small edger (the smallest you can find) on the first pour. This edger will be used to create a slightly rounded edge on the exterior formwork of the slab. From there your next pour will be finished to the existing height of the first pour and not edged. The next morning come back and use a framing chalk line to mark a straight line on the construction joint and saw cut the joint open. This will look like the two slabs were poured at the same time and saw cut later.
"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. An old concrete guy once told me concrete is not going to get any bigger than at the time of placement, so expansion material is not 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 1/4 inch to 1 inch in thickness.
Control joints allow for movement and proper cracking. Temperature change and poor sub base preparation contribute to slab movement. When the concrete cracks,we want to have an active role in deciding where it will crack and that it will crack in a straight line instead of randomly. Control joints can be cut at the time of placement or the next day with a diamond saw blade.
Cut joints deep enough. Cut joints 25% of the depth of the slab. A 4" thick slab should have joints 1" deep if cut the same day. Control joints are cut a minimum of .33 times the concrete thickness if cut the next day.
How to cut joints- Saw cut joints using a diamond blade and high rpm diamond saw. When Saw cutting joints, the concrete should be cured enough as to not ravel or destroy the edges of the saw cut. Hand jointers can be used to tool joints into fresh concrete, but this is not as architecturally pleasing for Decorative Concrete.