harling is what they call wetdash in Scotland.. Ive done a fair bit up Aberdeenshire for Historic Scotland.. if you still need to know the method, let me know pal.. but its basically 1. scratch coat.2. render coat, and whilst it is nearly set, the wet dash is thrown ( harled ) on for the finish... you can add colourants etc to the finish dash.. its way more weather resistant the dry dash... used on castles, and historic buildings,,,