Pug: To pack or fill the space under a floor with mortar, clay, sawdust, or other material for the purposes of fireproofing or soundproofing a room or space.

1820 At the White House in Washington, "the garret and second story floors have been laid of best 5/4 heart pine, and the whole of these stories counter-floored and pugged, to guard against fire."

Daily National Intelligencer

Source: An Illustrated Glossary of Early Southern Architecture and Landscape. Oxford Press

I have this book. Awesome Resource. Gives all the primary sources from building documents of the period. Ill look see, if I can add to the Wiki.