When ground refractory material is shaped into bricks by hand moulding, the approximate water content required in the mix is closest to which value?

Introduction / Context:
Forming refractory bricks can be done by hand moulding, soft-mud, stiff-mud extrusion, or pressing. The moisture content of the mix directly affects plasticity, workability, drying time, and the risk of cracking. This question tests typical moisture ranges for hand moulded bricks.

Given Data / Assumptions:

• Method: hand moulding (soft, highly workable mass).
• Objective: sufficient plasticity to fill the mould and release cleanly.
• Drying and firing will follow to remove moisture and sinter the body.

Concept / Approach:

Hand moulding generally requires a higher moisture content than stiff-mud extrusion or dry pressing. Typical values for hand moulding are on the order of about 20% (sometimes a bit more depending on clay/plasticity). Values like 5% are far too low to provide plasticity; extremely high values such as 40–55% would cause severe drying shrinkage and cracking.

Step-by-Step Solution:

Verification / Alternative check:

Manufacturing references list soft-mud/hand-moulding moisture contents near 20–30%, with 20% as a typical target for many bodies.

Why Other Options Are Wrong:

5%: Too dry for hand moulding. 40% or 55%: Excess water leads to high drying shrinkage, cracking, and long drying cycles.

Common Pitfalls:

Confusing dry-pressing low-moisture mixes with hand moulding; underestimating shrinkage risks at very high water contents.

Final Answer:

20%