How should joints be treated to prevent water intrusion in slabs?

• A. Seal expansions and control joints with appropriate sealants (e.g., polyurethane or silicone) and use proper installation.
• B. Coat joints with epoxy only
• C. Leave joints unsealed to improve drainage
• D. Fill with sand

Answer: (B)

Joints in slabs must be treated with a flexible sealant so they can move with the concrete and still stop water from sneaking through. Temperature changes, drying shrinkage, and loads cause expansion and contraction, so the material filling the joint needs to accommodate that movement rather than crack or pull away.

Using a proper sealant such as polyurethane or silicone is key because these coatings bond well to concrete and stay elastic over time, forming a watertight barrier even as the joint widens or narrows. The joint should be prepared correctly—cleaned, and a backer rod placed to set the right depth—then the sealant applied so it adheres to the sides and remains flexible.

Coating the joint with epoxy is not suitable here because epoxy becomes rigid once cured and cannot handle movement; it can crack and fail, creating paths for water. Filling the joint with sand won’t seal it at all and will not stop water intrusion. Leaving joints unsealed also invites water ingress and damage.

In short, treat joints with a compatible, flexible sealant installed properly to maintain a watertight seal while allowing movement.