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What is silaleng?

September 28, 2011

Most buildings in Thailand are made of ephemeral concrete, not looking much different from any other building in the west. Indeed wood has become rare due to deforestation and the 1989 logging ban, and prices are very high. What was the material of the poor has become the material of the rich. However, wood is poorly insulated and so noise and heat transfer through the walls like in a tent. In the old temple and chedi ruins in the city heart of Chiang Mai here in northern Thailand you can see a more sturdy building material. It is a reddish-brown stone, and the locals call it silaleng. Ketsanee said that simply means ‘stone’. What is it?

It is in fact laterite. The Latin word ‘later’ means brick. Laterite was coined by the Scottish naturalist Francis Buchanan-Hamilton (1762-1829) when he observed a laterite mine for making building blocks in India. Buchanan-Hamilton later succeeded the botanist William Roxburgh as the Superintendent of the Calcutta botanical garden.

Laterite rock and soil are typically tropical, and red due to the iron oxide (rust). Laterite is the result of the weathering of another rock, leaving insoluble iron and aluminium salt. A monsoon climate with wet and dry seasons is considered essential for the formation.

A single wet block is fragile, but cemented together a wall can stand for centuries. At Dokmai Garden we use laterite stone for walking paths and for the parking. The red subsoils you see in the jungles in the mountains surrounding Chiang Mai are laterite soils. The natural soil at Dokmai Garden is not laterite, but a more inert and neutral fine sand.

Text & Photo: Eric Danell

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