During the years of the slate trade the FR track was ballasted with the material which returning sailing vessels brought back to Portmadoc as ballast. The tonnage of slate shipped out of Portmadoc by sea was much greater than the limited quantity of freight brought in to the port and so sailing ships putting in to Portmadoc had to carry enough ballast to keep them stable. Because the predominant trade was to Hamburg where ballast was obtained from the gravelly banks of the river Elbe, this material was known as Hamburg ballast. That there was an abundance of this ballast available at Portmadoc is illustrated by the creation of Cei Ballast (Ballast Bank), the island of ballast material just offshore from South Snowdon Wharf. Hamburg ballast was typically made up of smooth yellowy brown pebbles and smaller shingle. In the early years of the reopened FR it was just below the turf that had spread everywhere over the ballast. Wherever the FR mainline was relaid for the first time post 1954, platelayers came upon it, with the last significant stretch being from Tanygrisiau to Glan-y-Pwll. De-turfing of this section was completed in November 1974. Gradually, Hamburg Ballast has disappeared under layers of modern granite ballast, only to be revealed when serious digging is done.
These facts are supported by the following sentence in an article about the FR published in Railway Magazine in August 1900:
"The ballast is 6ft. wide and 1ft. deep, being 6in. under the sleepers, and composed of gravel brought in vessels to Portmadoc, there being no material suitable for the purpose on the line."
- Railway Magazine, August 1900, ILLUSTRATED INTERVIEWS, No. 34.-MR.JOHN SYLVESTER HUGHES, General Manager, Festiniog Railway