Exposed aggregate mixes should not include what type of aggregate?

• A. Sand
• B. Quartz
• C. Iron
• D. Gravel

Answer: (C)

Exposed aggregate finishes rely on aggregates that will stay stable and keep their appearance once the top paste is removed to reveal the stone. Iron-containing aggregates are avoided because they oxidize when exposed to moisture and air, causing rust stains on the surface and potentially compromising both look and durability over time. Sand, quartz, and gravel are common choices because they are stable and resist staining, helping the finished surface remain uniform. So, iron is the type to avoid in exposed aggregate mixes.