Laterite in the Construction of Brick Prang-style Chedis of the Early Ayutthaya Period on Ayutthaya Island

Abstract

This study examines several early Ayutthaya period prang chedis or prang-style chedis located in the ancient city of Ayutthaya, highlighting the intriguing integration of laterite within their primarily masonry construction. This suggests a potential continuity in the developmental lineage of prang-style chedis that can be traced back to earlier structures, such as the principal prang at Wat Phra Si Rattana Mahathat in Lopburi. Since laterite is not a naturally occurring material in the area, large masonry chedis could have been constructed without its use. This article aims to present these perspectives through a case study analysis of prang-style chedis built with laterite and brick during the early Ayutthaya period within the ancient city.

The analysis indicated that historical documents from the Ayutthaya period reveal that builders selectively utilized laterite for specific types of structures. This suggests that builders were likely aware of the distinct characteristics of laterite compared to brick, influencing their material choices in structural construction. The laterite used may have been obtained as tribute or requisitioned from provincial cities under central authority for state purposes, possibly for the construction of chedis in royal temples of the capital.

Studies on the structural stability of buildings, based on contemporary architectural principles, suggest that the stability of chedis is influenced by multiple factors, including mass, form, and the application of suitable construction techniques. Among these, the choice of construction materials has a significant influence on structural integrity. Previous research has shown that laterite possesses greater load capacity and durability than brick.

Field survey data revealed that the laterite used in construction exhibits two types of rectangular block shapes: 1) newly quarried laterite blocks at the time of construction, and 2) laterite blocks reused from older, collapsed, or abandoned structures, which typically demonstrate more rounded edges, chipping, or breakage. The locations and patterns of laterite placement suggest that builders intentionally used laterite in the base level and chamber areas, forming the structural core that bears the greatest load. Physical evidence indicates that masons during the early Ayutthaya period possessed empirical knowledge of structural load distribution, leading them to selectively utilize laterite in areas subjected to higher compressive forces.

However, it is noteworthy that laterite is not naturally found in the local environment and was not as widely used as brick. The construction patterns of laterite masonry can be classified into three distinct types:

1) Rectangular laterite blocks, with layers that are horizontally uniform in thickness and notched to create a shoulder on the masonr block. These blocks are laid with staggered joints to enhance structural bonding strength, a technique that seems to have been inherited from the principal prang of Wat Phra Si Rattana Mahathat in Lopburi. However, the configuration in Ayutthaya appears to be more systematically arranged.

2) Rectangular blocks of approximately uniform size and thickness, laid in a pattern resembling the English bond technique. This may represent a later development in laterite masonry, specifically related to the prang structures of the early Ayutthaya period. This pattern is commonly found in early Ayutthaya masonry chedis but is not observed in the main prangs of any earlier case studies, and the use of laterite in construction is not found in earlier prangs in Lopburi.

3) Laterite blocks of various sizes and shapes, including both rectangular and square forms, laid in a non-uniform pattern across the wall, likely indicative of a reused and reassembled material. This requires supporting evidence from other contextual sources.

Thus, the development of construction techniques using laterite may have initially emerged alongside the principal prang at Phra Si Rattana Mahathat in Lopburi before evolving into a distinct form in later periods.