Concrete expansion joints are placed in concrete slabs in order to allow for trouble-free expansion and contraction of the concrete during temperature changes. By placing expansion joints when laying concrete, you prevent the cracks and breaks that may otherwise occur in the concrete if the safety margin of the joints were not added. Unfortunately, either through a mistake when cutting the joints, or simply with the passage of time, these joints may become damaged. When the joints have grown wide over time, pulled away from adjoining structures, or developed cracks, the joints can be repaired using a joint sealer, preventing the spread of damage to the rest of the concrete, or the adjoining structure.

Instructions
Things You'll Need:

* Screwdriver
* Putty knife
* Mortar and patch repair
* Closed cell pipe insulation
* Masking tape
* Joint sealer

1.
Step 1

Remove any dirt or debris from the joints. If an elastic joint sealer or caulking compound was already applied to the joint remove this as well using a screwdriver and putty knife.
2.
Step 2

Seal any cracks or gouges coming from the expansion joint using the mortar and patch repair. Allow the repair material to set overnight before continuing with the expansion joint repair.
3.
Step 3

Place the closed cell pipe insulation into the expansion joint, filling the joint completely using the putty knife to push the insulation into place. The closed cell insulation will prevent water from flowing through the insulation between the slabs on both sides of the joint. Leave room at the top of the joint for placing joint sealer level with the concrete surface.
4.
Step 4

Mask off the edges of the expansion joint using masking tape to create a uniform edge for the joint sealer.
5.
Step 5

Place a layer of joint sealer into the expansion joints covering the insulation, level with the concrete surface. Spread the sealer on the top of the joint using the putty knife. The joint sealer should fill the expansion joint while remaining flexible enough to expand and contract as the temperature of the concrete changes.
6.
Step 6

Allow the sealer to set to a solid according to the manufacturer's instructions. Remove the masking tape to leave a sharp edge.