"Wooden plugs of the same diameter as each through-hull fitting were cut out and placed on the mold in the exact position where the future through-hull fitting was to be installed later. These were cut from doweling and made one inch (25.4 mm) deep. A hole was drilled in the center of the doweling to ensure that the plug did not split when nailed to the mold. The mesh was cut away under the plug and trimmed neatly at the edges. Some attempt was made to place the doweling in a position clear of the intersecting rods."
January 1, 1970
https://en.wikiquote.org/wiki/Ferrocement