Repairing cement cracks using foam and caulk to protect against water and sun

Some concrete patches do not provide flexing, and cement caulk can shrink.

Advantages of urethanes:
1. Polyurethane is flexible to deal with temperature change and seasonal movement
2. It expands to completely fill the crack, even large ones
3. It dries fast, so a second coat can be applied after a couple of hours
4. The foam forms a strong bond to the cement – in does not leak away
5. DIY homeowners find it easy to use
6. The cracks do not need structural strength

For deep cracks, stuffing in fillers – sand, stone, backer rod, dry foam tubes – then covering with a sealant will not stop the materials from moving because the sand underneath settles breaking the sealant water seal.

Silicone caulk will loosen as the cement absorbs water along the repair, in time the caulk will lose its bond and start peeling. And hydraulic cement has a weak bond with concrete.
An elastic epoxy may work.

Just be sure to clean the area first.