How to Repair and Seal Expansions Joints in Concrete
Concrete expansion joints are cuts in concrete slabs that go completely through the slab to the base material. Expansion joints can also be the joints between walls and concrete slabs. The purpose of an expansion joint is to allow the concrete slab to expand and contract with temperature changes…without cracking the slab.
Concrete expansion joints must be sealed with a flexible sealant or an expansion joint strip, to prevent water from penetrating the joint and deteriorating the sub base. As with any concrete repair, proper attention to joint preparation is essential to achieving a successful result.
Expansion joints should be swept out to ensure that any pebbles, dirt or loose debris are removed.
If oil or grease are present, a concrete cleaner should be used so that a strong bond can be made between the sealant and the edges of the joint. Before applying a sealant, the joint must be completely dry.
The best option for sealing horizontal expansion joints is a polyurethane sealer. A polyurethane sealant is a highly fluid and flexible sealant that will stretch up to 800 percent without failing. This allows for ground movement and expansion and contraction from temperature change.
For joints over 1/4 inch, Backer Rod, which is a foam rope, should be placed in the expansion joint before applying the sealant. The Backer Rod should be pressed into the joint allowing a sealant depth of between 1/8 inch and 1/2 inch.
Polyurethane sealants work best when they are bonded only to the inside edges of the crack or joint.
Always wear eye protection and waterproof gloves when working with polyurethane sealants, and work in a well-ventilated area.
To apply a polyurethane sealant, first cut the tip of the nozzle at an angle with a utility knife, matching the width of the crack, and insert the tube into a standard caulk gun.
Move the nozzle slowly along the length of the joint, allowing the sealant to settle. The sealant is highly fluid and may require an additional application. This should be done immediately so that the two applications will mend into each other. No additional tooling is necessary.
A polyurethane sealant will be tack-free in two hours and will dry to a smooth gray finish. Excess sealant should be cleaned up immediately with a commercial solvent or a citrus based cleaner.
Polyurethane Sealants are temperature sensitive and should not be used when temperatures are below 50 degrees.
For vertical expansion joints in concrete, masonry or stucco walls, the best option for joints over 1/4 inch wide is a non-sag polyurethane sealant.
A non-sag polyurethane sealant is a multi-purpose, permanently flexible sealant that seals and waterproofs vertical joints. For joints over 1/2 inch, Backer Rod should be placed in the joint before applying the sealant. The Backer Rod should be pressed into the joint, allowing a sealant depth of between 1/8 inch and 1/2 inch.
To apply a non-sag polyurethane sealant, first cut the tip of the nozzle at an angle with a utility knife, matching the width of the crack, and insert the tube into a standard caulk gun. Move the nozzle slowly along the length of the joint, pressing the sealant into the joint. The tip of the nozzle can be used to smooth the sealant.