Young alluvial soils developed in recent fluvial, lacustrine, or marine sediments, commonly found in low landscape positions such as river valleys, deltas, and tidal marshes. They show weak horizon differentiation and stratification from recent sedimentation. In wet or poorly drained conditions, redox features may appear as greyish, bluish, or greenish reduced colours with reddish-brown mottles. “Eutric” indicates relatively good base status, where exchangeable Ca, Mg, K, and Na are equal to or greater than exchangeable aluminium. Used in this atlas for Mang Thit - Vinh Long

Thionic Fluvisols are a special type of Fluvisols, also known as Acid Sulfate Soils. They are young alluvial soils formed in recent fluvial, lacustrine, or marine deposits, but unlike ordinary Fluvisols, they contain pyrite-rich sulfidic material. When these sediments are drained and exposed to oxygen, pyrite oxidizes and produces strong soil acidity, often causing low pH, aluminium toxicity, phosphorus deficiency, salinity problems, and acidification of surface water. Thionic Fluvisols are especially important in the coastal lowlands of Southeast Asia, including Vietnam, and are specifically associated with wide depressions and brackish-water sediments in the Mekong Delta. Used in this atlas for Nhon Trach - Dong Nai

Fluvisols are young, azonal soils developed in recent alluvial deposits, mainly from fluvial, lacustrine, or marine sediments. They typically occur in periodically flooded landscapes such as alluvial plains, river valleys, deltas, and tidal marshes. Fluvisols are characterized by weak horizon differentiation, AC profiles, and clear evidence of stratification or recent sedimentation. Their properties are strongly shaped by flooding, groundwater, and sediment deposition, making them generally fertile but variable in texture. Flood control, drainage, or irrigation is often required for stable agricultural use.

Rhodic Ferralsols are deeply weathered tropical soils with low-activity clays and high iron and aluminium oxide content. The prefix “Rhodic” comes from Greek rhodon, meaning “rose”, and indicates a strongly red subsoil layer between 25 and 150 cm from the mineral soil surface. In simple terms, Rhodic Ferralsols are defined by their deep, intense red colour, caused by iron oxides within a highly weathered tropical soil profile. Used in this atlas for Ia Grai - PleiKu

Ferralsols are deeply weathered red or yellow tropical soils, typically found on old and stable geomorphic surfaces in humid tropical regions. They are characterized by diffuse horizon boundaries, low-activity clays mainly dominated by kaolinite, and a high content of iron and aluminium sesquioxides, which give the soil its red or yellow colour. Ferralsols generally have good physical properties and stable structure, but they are chemically poor, with low natural fertility, low pH, limited nutrient reserves, and strong phosphate fixation. They are often used for shifting cultivation, while sustainable permanent agriculture usually requires liming and full fertilisation.

Dystric Gleysols are wetland soils with gleyic properties caused by prolonged groundwater saturation, but with poor base status. The prefix “Dystric” indicates that exchangeable aluminium is greater than exchangeable base cations such as Ca, Mg, K, and Na in the specified mineral soil layer. This means Dystric Gleysols are generally more acidic and chemically less fertile than Eutric Gleysols. Used in this atlas for Tuy Hoa - Phu Yen

Wetland soils with gleyic properties caused by prolonged groundwater saturation. They occur in low landscape positions and show greyish, bluish, or greenish reduced colours with redox mottles. The prefix “Eutric” indicates relatively good base status, where exchangeable Ca, Mg, K, and Na are equal to or greater than exchangeable aluminium. Used in this atlas for Trang An - Ninh Binh

Gleysols are wetland soils with clear signs of excess wetness, usually formed in depression areas or low landscape positions with shallow groundwater. They develop from unconsolidated fluvial, marine, or lacustrine sediments and are saturated with groundwater long enough to form gleyic properties within 50 cm of the soil surface. Their typical feature is a gleyic colour pattern, combining greyish, bluish, or greenish reduced colours with reddish-brown or yellow mottles caused by redox processes and iron/manganese segregation. Wetness is the main limitation of Gleysols, but when drained they can be used for arable cropping, dairy farming, horticulture, and, in tropical and subtropical regions, rice cultivation.

Other Acrisols. Used in this atlas for Cao Phong - Hoa Binh

Acrisols with ferric properties, marked by iron-related redox features such as Fe/Mn masses, concretions, or nodules within the soil horizon. These properties indicate iron segregation rather than simply a uniformly iron-rich soil. Used in this atlas for Yen Son - Tuyen Quang

Acrisols are strongly weathered, acidic red-yellow soils with low base saturation, commonly formed on old acid rock surfaces in wet tropical, monsoonal, subtropical, or warm temperate regions. They are characterized by clay migration and accumulation in the subsoil, creating an argic horizon with low-activity clays. Acrisols are generally nutrient-poor, prone to aluminium toxicity, phosphorus fixation, surface crusting, and erosion, which makes them difficult for intensive agriculture. They are often used for subsistence farming or acidity-tolerant crops such as pineapple, cashew, oil palm, and rubber.

The World Reference Base for Soil Resources (WRB) is an international system for naming and classifying soils, developed from earlier FAO/UNESCO soil classification frameworks. It provides a global reference for comparing soil types across regions. In this atlas, it is used to ensure consistent soil type labeling and to make local soil data comparable within an international framework.

Mass per unit volume of a material, including voids. Lower density indicates higher porosity and typically less thermal mass. Used to assess CEB composition.

The capacity of a material to repel or limit the uptake of water. Critical for earthen construction exposed to rain or moisture. Measured by conducting immersion, contact, and absorption tests; as well as spray/erosion tests in tropical climates where the rainfall is significantly higher.

The ability of a material to resist bending forces before breaking. Also called modulus of rupture. Relevant for hybrid earthen construction, where the blocks are used as infill within a structural frame.

The maximum load a material can withstand before failure under compression. Measured in megapascals (MPa) or N/mm². Standard reference for load-bearing brick and block performance.

A biopolymer is a natural or biologically derived polymer composed of repeating molecular units. In the context of soil-based material research, biopolymers can function as bio-based binders, stabilizers, or water-resistance agents that help improve the cohesion and durability of compressed earth blocks.

Additives of natural origin—plant fibers, agricultural byproducts, or biopolymers added to earthen mixes to improve mechanical performance, reduce cracking, or enhance water resistance.

Building with earth-based blocks that have not been fired in a kiln. Includes adobe and compressed earth blocks. Lower embodied energy than fired brick or concrete.

A CEB in which a mineral stabilizer such as lime or cement has been added to the soil mixture to improve performance and durability.

An unfired masonry unit produced by compressing a mixture of soil, water, and optional bio-based additives like fibers or biopolymers using a mechanical press. CEBs are a low-energy, low-carbon, site-responsive alternative to fired bricks. At the end of their lifecycle, they can be reused to make new blocks, making them reversible.

A design and research principle emphasizing that building knowledge is inseparable from its geographic, ecological, cultural, and historical context. Material solutions developed in one region cannot simply be transferred to another without accounting for these situated conditions.

A concept used in this project to describe the atlas as simultaneously a technical material database (investigating soil properties and CEB performance) and a cultural archive (documenting vernacular knowledge, indigenous practices, and ecological context). The two layers are interdependent, not separate.

A geographic region defined by shared ecological characteristics such as climate, vegetation, soil type, and topography. The atlas covers seven distinct ecological zones across Vietnam.

Knowledge systems held and developed by indigenous communities through long-term relationships with their environments. In this project, the term refers to the knowledge of Mường, Jarai, Bahnar, Cham, Khmer, and other communities regarding soils, plants, materials, seasonal conditions, craft practices, and construction.

Regionally established building practices shaped over generations by local materials, climate, ecology, and everyday use. Vernacular construction refers to built forms, techniques, and construction logics that are not necessarily authored in a professional architectural sense, but transmitted through practice, adaptation, and collective experience.

The test consists of spraying the face of a prepared sample of the soil for a period of 1 hour or until the specimen is penetrated. This method is different from the Drip Erosion Test.

Immersion test is a method used to evaluate the water resistance of earth blocks by immersing the specimen in water and observing its stability, surface degradation, or loss of material.

Suction test is a method used to evaluate the moisture resistance of earth blocks by exposing the specimen to water suction and observing its resistance to water uptake and surface degradation.

Water absorption is determined by immersing dried brick specimens in water for 24 hours and calculating the percentage increase in mass after saturation.

The Flexural strength Test is a method used to determine the bending resistance of a brick specimen by applying a load at the center of the sample until failure occurs.

The Compressive strength test determines the load-bearing capacity of earth blocks by placing the specimen between two flat plates and applying a compressive load to the specimen until failure occurs.

Laboratory analysis of the proportions of clay, silt, sand, and gravel in a soil sample. Plotted as a gradation curve. Used to assess material composition and predict behavior in earthen construction.

A field test for cohesion. A small roll of moist soil is shaped as a cigar and allowed to dry. Length of crack-free roll indicates cohesion and suitability for earthen construction.

A field test for plasticity. A ball of moist soil is pressed flat and allowed to dry. A cracked, crumbling result indicates low plasticity. A smooth, firm result indicates higher clay content and plasticity.