🔍 Key Concepts

• Difference between castable and insulating refractories • How a material’s strength and abrasion resistance affects its use as a backing surface • The role of a rigid, straight surface behind insulation block when casing is warped

💭 Think About

• Which option would set hard enough to support and keep insulation block straight if the steel casing isn’t perfectly flat? • Which materials are mainly for lightweight insulation versus for structural backing in hotter, more abrasive areas? • Think about which material can be poured or troweled, then cured, to form a durable, flat surface for the insulation to rest on.

✅ Before You Answer

• Identify which choices are primarily insulating/low‑density products versus dense, structural refractories • Check which material is commonly used as cast-in-place lining or backing in furnaces and boilers • Verify which option can provide a hard, wear-resistant, straight surface rather than just filling voids with soft insulation