Understanding the Problem
This question is about historic masonry restoration - specifically, repointing deteriorated mortar joints in soft-brick buildings.
Historic bricks, especially those made before the early 20th century, are often much softer and more porous than modern high-fired bricks. The mortar originally used was also softer, usually lime-based, which allowed for thermal movement, moisture permeability, and protection of the brick units.
Why the Correct Answer is "Duplication of Original Mortar Strength"
* Best practice in preservation (as outlined in the Secretary of the Interior's Standards for the Treatment of Historic Properties) is to match the original mortar in strength, composition, permeability, and appearance.
* A mortar stronger than the original can cause the softer brick to crack or spall under thermal or moisture stresses, because the brick will end up being the weaker link and take the damage.
* Duplication ensures that the new mortar works compatibly with the old masonry system - allowing for similar vapor transmission and structural flexibility.
Why the Other Options Are Incorrect:
* B. Increased mortar strength over the original mortar - This is harmful in historic soft-brick construction. Stronger cement-based mortars can trap moisture in the brick, leading to freeze-thaw damage and spalling.
* C. A bond stronger than the brick - This would cause the brick to fail first when stress occurs, which is undesirable in preservation work.
* D. Deeper joint profiles - Deeply raking out joints unnecessarily can damage surrounding brick edges and change the visual proportions; repointing depth should only be enough to remove deteriorated mortar (typically 2-2.5 times the joint width).
NCARB ARE 5.0 PDD Study Guide References:
* Content Area: Integration of Building Materials & Systems - Historic Preservation Techniques
* Key Resources:
* The Secretary of the Interior's Standards for Rehabilitation & Illustrated Guidelines for Rehabilitating Historic Buildings
* National Park Service Preservation Brief 2: "Repointing Mortar Joints in Historic Masonry Buildings"
* Building Construction Illustrated - Masonry Restoration
* Key Preservation Principle: "New mortar should match the historic mortar in composition, strength, and vapor permeability."