Concrete flooring specification: for cement concrete floor construction, what is the maximum permissible nominal size of coarse aggregate to achieve a smooth, defect-free finish?

Introduction / Context:
Floor toppings and thin floor slabs require tight surface finishes. Excessively large aggregate leads to trowelling difficulties, exposed stones, and surface defects.

Given Data / Assumptions:

• Flooring thickness typically 25–50 mm.
• Nominal sizes from 4–12 mm are considered.

Concept / Approach:
To secure smooth finishing and proper compaction in thin layers, the nominal maximum size of coarse aggregate is restricted to 10 mm in common practice and codes for floor concretes.

Step-by-Step Solution:
Check code recommendations for flooring concretes.Select the largest size that still ensures finishability without pop-outs: 10 mm.

Verification / Alternative check:
IS 2571 recommends using aggregates not exceeding 10 mm nominal size for floor work to facilitate finishing.

Why Other Options Are Wrong:

• 12 mm can impair finishing in thin toppings.
• 4–8 mm are acceptable but not the maximum permitted size; they may increase paste demand and cost.

Common Pitfalls:

• Using structural concrete aggregate sizes in floor toppings without adjusting mix design, leading to poor finish.

Final Answer:
10 mm