Terrazzo flooring procedure: identify the incorrect step among the following commonly specified operations for laying a terrazzo floor.

Introduction / Context:
Terrazzo is a decorative, durable flooring made by embedding marble or stone chips in a rich cement matrix and finishing by grinding and polishing. A correct step sequence ensures bond, flatness, and appearance. This question asks you to spot the incorrect step among typical specifications.

Given Data / Assumptions:

• Traditional in-situ terrazzo over a concrete base.
• Use of divider (glass/brass/aluminium) strips to control cracking and create panels/patterns.
• Final grinding and polishing with oxalic acid slurry is standard in legacy specs.

Concept / Approach:
The terrazzo topping is not ordinary 1:2:4 concrete. It is a rich terrazzo mix (often 1:2 by volume cement to marble chips with pigments) of about 12–20 mm thickness laid over a base concrete layer (for example, 1:2:4 or 1:3:6) that provides support. Divider strips are set before the topping stiffens, and grinding/polishing reveal the chips.

Step-by-Step Solution:
Base course: correct—similar to cement concrete flooring base.Topping composition: should be terrazzo mix with marble chips, not plain 1:2:4 concrete, and usually much thinner than 32 mm.Divider strips: correctly installed to form panels/patterns and control shrinkage cracks.Final finishing: oxalic acid rubbing/polishing is a recognized traditional step.Therefore, the incorrect step is describing the topping as a 32 mm thick 1:2:4 plain concrete layer.

Verification / Alternative check:
Standard BOQ items specify terrazzo topping 12–20 mm (varies) with marble chips; thicknesses like 32 mm are atypical for topping and mischaracterize the mix.

Why Other Options Are Wrong:

• Base preparation, divider strips, and oxalic polishing are all standard steps.
• “None of these” is incorrect because one statement is indeed wrong.

Common Pitfalls:

• Confusing base concrete with the terrazzo topping mix.
• Skipping divider strips, leading to random cracking.

Final Answer:
a 32 mm thick layer of 1:2:4 cement concrete is laid as the terrazzo topping and trowelled smooth