Hoardings, also known as bretêches, were walkways projecting out from the edge of a tower or wall with holes or doors in the floor in order to afford the defender the opportunity to drop offensive materials (missiles, molten lead, pitch) onto the attackers below. Machicolations (from the French machi = melted matter + coulis = flowing) were stone equivalents to bretêches...see if you think it could have referred to some kind of mortar cement.

bill, the way I read it, the 'flowing melted matter' refers to what was dropped as opposed to the makeup of the stucture. (if that's what you're asking)