Jamieson, Fausset and Brown on Jeremiah 43:9

9. stones--to be laid as the foundation beneath Nebuchadnezzar's throne (Jr 43:10).

clay--mortar.

brick-kiln--Bricks in that hot country are generally dried in the sun, not burned. The palace of Pharaoh was being built or repaired at this time; hence arose the mortar and brick-kiln at the entry. Of the same materials as that of which Pharaoh's house was built, the substructure of Nebuchadnezzar's throne should be constructed. By a visible symbol implying that the throne of the latter shall be raised on the downfall of the former. Egypt at that time contended with Babylon for the empire of the East.