A city of decaying grandeur
Downtown Yangon holds the largest collection of colonial-era buildings in Southeast Asia. Hundreds of structures from the late 19th and early 20th centuries stand in various states of decay. This slow-motion collapse offers a large-scale laboratory for materials scientists. They study the chemical and physical toll that a tropical monsoon climate takes on building materials originally suited for temperate Europe. The primary agent of this decay is water, relentlessly delivered by Yangon's high humidity, which frequently exceeds 60%.
Porous materials like brick, plaster, and traditional lime-based mortar are especially vulnerable. Water vapor from the humid air penetrates deep into the masonry. This constant dampness provides the perfect environment for two destructive processes to begin: salt weathering and biodeterioration.
The chemistry of crumbling
Salt weathering is a powerful force of decay in tropical environments. Moisture moving through the pores of bricks and mortar dissolves naturally occurring mineral salts within them. When the water evaporates from the surface, it leaves behind salt crystals. This visible white powdery stain, known as efflorescence, shows deeper trouble.
As these salt crystals grow, they exert immense physical pressure within the pores of the masonry. This crystallization pressure can be strong enough to fracture the material from the inside out, causing the surface of bricks and plaster to flake off and crumble—a process called spalling. Sometimes, the crystals grow just beneath the surface, a more destructive phenomenon called subflorescence, which pries off the outer layer of the material.
The high humidity also promotes biological growth. Surfaces covered in algae, fungi, and bacteria become common. These microorganisms are a surface stain; they form biofilms that can produce acids, which chemically break down the lime in mortar and plaster. Over time, larger plants can take root in cracks, their root systems physically dismantling the structures they inhabit.