June 10, 2008
WaterstopsA waterstop is a pre-molded sealant that is applied across concrete joints to stop the passage of water where hydrostatic pressure exists. They are typically used for two types of joints:
1. Working joints: Joints where significant movement is expected.
2. Non-working joints: Joints where little or no movement is expected.
Most waterstops are provided in 6-inch, 9-inch or 12-inch widths. The type and shape of the waterstop should be based on the specific requirements of the existing joints. Common waterstops are manufactured from:
• Polyvinyl chloride (PVC).
• Styrene butadiene rubber (SBR).
In addition to the waterstops, the other application components include:
1. Backer rod (07910): Closed-cell polyethylene foam that has a diameter 25 percent greater than the joint width.
2. Sealant (07920):Sealant must be compatible with the joint filler.
• ASTM C 920: Polysulfide, polyurethane or silicone.
• Type S or M (one part or multi-component).
• Grade P or NS (pourable or non-sag).
Waterstops should be applied in accordance with the manufacturer’s requirements.
Working joints: Use a compatible waterstop that allows for concrete movement in both parallel and perpendicular directions.
Non-working joints: Use a dumbbell or flat, serrated waterstop. The dumbbell shape holds the waterstop in place and improves watertightness by providing a longer path for water to tunnel across the joint.
Sealant: For joints of ½ inch in width, the depth should equal the width of the joint. For joints of ½ inch in depth, joint widths should be ½ an inch to 1 inch. The sealant should not bond to the joint filler.