For exterior tile installations, which condition necessitates a moisture barrier?

• A. Wet or exterior exposure conditions requiring crack isolation and moisture control
• B. Dry interior walls
• C. Low humidity interior spaces
• D. Any painted surface

Answer: (A)

In exterior tile work, moisture management is the key idea. A moisture barrier is needed whenever there are wet or exterior exposure conditions where water can reach the tile assembly. That barrier protects the substrate from water damage, helps control moisture vapor, and works with crack isolation to reduce the transfer of movement that could crack tiles.

The other scenarios—dry interior walls, low humidity interior spaces, or a painted surface—do not inherently create the moisture exposure that requires a barrier in exterior installations. They lack the ongoing water exposure that moisture control and crack isolation address.