Concrete is often the foundation for other flooring surfaces, such as vinyl tile. Concrete floors provide a stable subfloor on which the more comfortable tile can be laid. However, cracks in the concrete floor should be completely sealed before the vinyl tile is installed. Polyurethane caulk is an effective way to fill the gaps and cracks in concrete. The sealing compound will fill the targeted areas and properly prepare concrete for the tile.
Cut open a tube of urethane caulk at the tip using a sharp pair of scissors or a utility knife. Use a nail or stiff wire to puncture the seal, then load the tube into a caulking gun.
Squeeze a bead of caulk 1/4-inch thick or less directly into a crack in the concrete. Maintain continuous pressure as you draw the caulking gun along the length of the crack, smoothing the sealant with the tip of the tube as you go.
Apply a foam backer rod to cracks larger than 1/4 inch. Use a backer rod slightly thicker than the targeted crack so it conforms to the gap.
Insert the backer rod into the crack and push it firmly below the surface of the concrete floor. Repeat the same process for sealing the concrete, with the foam as support for the urethane caulk.
Smooth the caulk with a spatula or another slick tool such as the back of an old spoon. Level the sealant with the concrete and allow it to dry overnight.