In the origins of tarmacadam John Loudon McAdam, the Scottish inventor, is remembered for designing roads using broken stones laid in tight symmetrical patterns covered with further layers of smaller stones which had been crushed, broken and then compacted to create a hard surface. He discovered that the best results were obtained by grading the various layers of stones into similar sized pieces and compressing them into the road surface.
McAdam’s invention became known as a method of macadamising roads or macadam roads and it was considered the greatest advancement in road construction during the late eighteenth century – fine for horses and carriages. Along with the effects of rain and freeze / thaw cycles during winter damaging the surface however, the newly developed motor cars also caused the surface to break up, spitting stones into the air together with accompanying clouds of dust.
There are a number of differing stories of how macadamized roads became tar-mac roads, some of them dating back to the 1830’s (though these involved the addition of tar to existing stone roads). And although tar or pitch was said to be used on highways thousands of years ago, the following version seems to have acquired credibility over the years.
