As Professor Silpa Bhirasri pointed out, the Thai were the direct successors of the Khmer culture in Southeast Asia and one could expect Thai architecture to follow the Khmer style. But the purpose of the religious buildings erected by the Thai was different from that of the Khmer.
In Buddhism, second to the symbolic Stupa, the most important structure is the Chaiya Hall, in Thai called Bot or Ubosot. Here the monks meditate, study the Doctrine, ordain novices and perform all other ceremonies. The Bot must be spacious because it has to accommodate a congregation of one or two hundred monks.
Structurally, a wide span cannot be roofed with the Khmer vaulting system. The Khmer temples were formed by narrow corridors and by relatively small square cells; the former were vaulted with horizontal layers of stones while the sanctuary was covered with a tower-like structure originating from the Sikhara of the northern Indian temples: here, too, horizontal layers of stones were used.
In contrast, it was quite natural for the Thai to roof their larger halls with timber. And the halls had to be large because after Hinayana Buddhism had become the official religion of the kingdom of Sukhothai (1257 A.D.) Thai men retired in droves into monastic life.
This meant that not only a large number of monasteries needed to be built but also that each one needed to accommodate a large number of monks. As timber was easier to get than bricks or cut stone, the Thai shifted from the Khmer structures entirely built of stone to mixed structures for which wood was increasingly used.
Difference of materials engenders a difference of architectural style. This was the very cause from which the Thai style emerged. It was not due to any reaction against the Khmer art; in fact, for the sake of tradition the Thai retained many architectural features of the Khmer even when they were no longer constructive.
Among the materials used by the Thai in their religious structures, aside from cut stone and bricks, were wood, glass mosaics, gold leaf, porcelain, stucco, lacquer and mother-of-pearl.
Wood was not only used as a general material for building and the roofing of brick buildings but also extensively for ornamental and decorative parts. Wooden parts were then generally gilded and enriched with glass mosaics.
Glass mosaics in dark red, green, blue and violet were used to decorate gables, pillars and all other wooden and stucco ornaments.
Gold leaf was used to gild ornaments made either of wood or stucco, architectural moldings and lacquer designs.
Porcelain or glazed terra-cotta ornaments were used to decorate old temples. Later, especially in the Bangkok period, small different colored pieces of porcelain, often from broken vessels, were used to form ornamental patterns to enrich the surface of all kinds of brick structures.
Stucco was extensively used to enrich architectural molding, to model ornaments of window and door frames and to decorate gables when this decoration was not made in wood.
Lacquer was commonly used for the designs of window and door panels. The designs were often gilded while the background was left in black lacquer.
Mother-of-pearl was inlaid to decorate window and door panels.
The term Wat refers to a group of religious buildings generally enclosed by a wall with several gateways. According to artistic importance, the principal religious buildings in Thailand are: the Phra Chedi, the Bot, the Vihara, the Phra Prang, the Mondop and the Prasat. The other structures architecturally not very important are: the Kuti, Ho Trai, Sala Kan Parien, ordinary Salas and the Ho Rakhang.
A Wat may contain just some of these structures or all of them. The most essential is the Bot, also called Ubosot. In general, with the exception of the Bot or of the Vihara, whose plan is conceived as a single unity within its enclosing gallery, the rest of the monuments are added little by little without special consideration of the general planning. But because of the contrasting forms of the large Bot or Vihara and the slender pinnacle of the Stupas or the solid vertical mass of the Phra Prangs, the resulting effect is always harmonious.
The Bot (also called Ubosot) corresponds to the Indian Chaiya Hall, and like this it may have one large nave or one nave and the lateral aisles. Its classic type has a rectangular plan and at its end it enshrines a large gilded sitting Buddha image modeled either in stucco or cast in bronze. The image is placed on a high pedestal whose rich ornamentation contrasts sharply with the plain modeling of the image and seems to symbolize the restlessness of the earthly life in comparison with the serenity of the Enlightened One.
Because of the limited light the interior receives and also because in general the walls are decorated with paintings having a rather dark tone, the large image often seems to shine - an effect apt to add mysticism to the holy interiors.
The shape of the Bot may have originated from the thatched Indonesian-Thai house. Of course, the roof of the Bot has in time become more complex than the roof of a common house because of lateral additions and the superimposed roofs. The lateral additions are meant to widen the interior. Thereby (as usually is the case) a feature dictated by functional necessity had become a characteristic of a style.
The roofs of the front and rear porches which are not as high as those of the main structure add movement and beauty to the mass and outline of the building. In central Thailand, at the end of each ridge of the roof of the Bot there is that graceful finial called Chofa. It may be a reminiscence of a horn of some animistic protective mask as those seen in the houses of Indonesian clubs used for animistic ceremonies, or it may be a reminiscence of the Makara motif made in glazed terra-cotta used for the same purpose in Sukhothai art.
The gables are enriched with wooden carved ornaments which are gilded and often have a glass mosaic as background. The triangular wooden framing of these gables, as well as those of the other superimposed roofs, are decorated with the universal design of the Naga (mystical serpent) as it was in the Khmer temples.
In old Ayutthaya architecture, the Bot had, instead of panelled windows, narrow vertical openings rather high up in the side walls - a reminiscence of the fine windows of the Khmer temples. At a later period series of windows with wooden panels were added laterally at the height of about one meter from the level of the inner floor.
The Bot (or Ubosot) may have one, two or three doors, both in front and at the back of the building. Outside, the doors and windows are decorated with ornamental frames in stucco, gilded and enriched with glass mosaics. The panels of the windows and those of the doors are decorated outside with gilded lacquer ornaments while, in general, the interiors have mythical figures of guardians painted in vivid colors. Some Bots instead of lacquer decoration have ornaments in inlaid mother-of-pearl.
Some Bots such as that of Wat Na Phramane in Ayutthaya (ca. 16th century A.D.) have between the two lateral doors a large and high niche containing a standing Buddha image. Both front and rear facades have the same niche.
In old Thai architecture, the pillars of the interior and exterior of the Bots are octagonal. The interior ones are generally enriched with painted ornaments. The capitals of these columns have a lotus form. If the inner columns were in wood, then their natural circular form was respected; the shaft was often painted in red and enriched with gilded ornaments.
Like the old Christian Basilicas, old Thai structures had no ceilings. The wooden ceilings added later are painted in red and enriched with gilded studs.
The mass of the building is in brick, plastered and whitewashed. The large sloping roofs are covered with glazed tiles which in general have dark orange, green or violet color and contrast with the plainness of the main white mass. This white mass is relieved at its lower part by the series of the gilded window frames.
Wat - Khae Hindu Temple, this temple is the most Hindu Temple in thailand located on Silom Road,the decorete in Hindu style. And the most Colour-Full - Decorated by Stucco and Merble as well.