26th November 1836

Death of the inspiration for Tarmac

John Loudon McAdam was born in Ayr in September 1756. He is remembered for inventing the process that took his name – macadamisation – which reduced the cost of road building. The process did away with the rock foundations that until then had underpinned major byways in favour of a bed of crushed stone laid directly on the underlying soil.

The crushed stone was put down in at least two layers, with larger stones beneath and smaller stones, of 2cm or less, on top. McAdam settled on the 2cm limit because it was smaller than the width of most carriage wheels which were, at that time, 4cm.

McAdam was adamant that the stones should be broken by hand, rather than crushed by machine, and it is said that workers knew a stone was small enough for the upper layer if they could fit it in their mouth. Once laid, the stone would be compacted and, over time, the road would become ever more stable as it was further pressed down by passing traffic.

A later patent

McAdam didn’t invent Tarmacadam, or tarmac, despite the name, which is derived from the fact that it uses the macadam process to combine small stones with tar and sand. It was patented in 1902, when McAdam had been dead for over 65 years, by Welsh inventor Edgar Hooley. McAdam himself had decreed that, ideally, nothing should be laid on top of the crushed stone used in macadamisation, although this could result in dust being thrown up in dry conditions, and ruts forming in the road by the passage of traffic along similar paths.

Where McAdam’s invention of the macadamisation process had come about through years of careful study and thought, Hooley’s ‘discovery’ of tarmac came out of chance when, on a walk close to an iron works in Derbyshire, he came across a smooth stretch of road. Upon inquiring, he was told that a barrel of tar had been spilled and, in an effort to dry it, slag, used in the smelting process, had been poured over it. Inspired by this happy coincidence, Hooley patented the process of mixing tar and aggregate, which would be laid down on the road surface and pressed flat. He patented his invention and founded the Tar Macadam Syndicate in 1903, which later became Tarmac Group.

John Lound McAdam’s death

Although he had moved first to America, and then to England, where he spent the majority of his working life, John Lound McAdam died in Moffat, Scotland, on 26 November 1836 while returning from a visit. He was 81. In later life he had been offered a knighthood, which he had declined. It was later accepted by one of his sons.

Reporting his death, the Perthshire Courier of 8 December 1836, quoting the Dumfries Courier, noted that “in manner and address, no man could be more agreeable: in place of being a mere roadmaker, he was a man of science generally, conversed most intelligently on almost every subject, kept pace with the advancing knowledge of the age, and composed with all the accuracy of a professed litterateur.”