Mortar MCQ with answer and solution

Concept

Lime mortar compatibility in historic preservation

Formula

NONE

Step-by-step solution

1. Modern Portland cement mortars are stiff, brittle, and form impermeable barriers with high compressive strength. 2. Historic structures constructed of porous stone or soft lime-burned brick require mortars that match original substrate characteristics. 3. Lime mortar offers high vapor permeability (breathability) and lower elastic modulus (flexibility), accommodating foundation settling and thermal cycling without fracturing adjacent masonry. 4. Hence, lime mortar is preferred in historic preservation for flexibility and breathability. Answer: B

Explanation

Non-hydraulic and hydraulic lime mortars possess a low modulus of elasticity and significant vapor permeability compared to modern dense Portland cements. These characteristics allow historic stone and soft-fired brick structures to accommodate slight seasonal ground or thermal movements while breathing moisture naturally, preventing stress concentrations and face spalling of fragile historic masonry.

Why the other options are wrong

A) High compressive strength and rapid setting of cement mortars cause stress cracking and edge spalling in historic stones. C) Trapping water inside masonry causes accelerated freeze-thaw decay and salt crystallization; breathability is needed. D) Rapid hydration creates high internal stresses that damage delicate heritage materials.

Shortcut

Historic preservation = Lime mortar (flexible, breathable, prevents spalling of softer historic bricks/stones).

Common mistake

Believing restoration requires high-strength cement mortar, which actually destroys soft heritage masonry.