Mastic Asphalt – Key Material Property Which statement best describes mastic asphalt as used for roofs, terraces, bridge decks, and damp-proofing layers?

Introduction:
Mastic asphalt is a dense, void-free asphaltic material used where watertightness and durability are essential. The question probes recognition of its defining performance characteristic in construction waterproofing.

Given Data / Assumptions:

• Application areas: roofs, terraces, podiums, bridge decks, damp-proof courses.
• Composition: bitumen binder with graded mineral aggregates and fillers.
• Service condition: compacted, cooled layer forming an impermeable sheet.

Concept / Approach:

The hallmark of mastic asphalt is impermeability to liquid water when properly laid at specified thickness and falls. Elasticity is limited compared with membranes; vapour permeability is also low.

Step-by-Step Solution:

Verification / Alternative check:

Engineering manuals specify mastic asphalt for zero-permeability details (e.g., upstands, gutters) confirming its non-porous nature.

Why Other Options Are Wrong:

Highly elastic: incorrect; that describes rubber/modified membranes. Allows percolation: opposite of design intent. Combustible surface: laid asphalt has acceptable fire performance in rated systems; the key property asked is impermeability. Vapor-open: false—mastic asphalt is typically vapour-tight.

Common Pitfalls:

Confusing mastic asphalt with polymeric membranes; assuming all asphaltic products are elastic; overlooking the need for movement joints and proper detailing.

Final Answer:

It is waterproof and non-porous under service conditions