Leirthart notices that bricks are typically associated with idolatry in Isaiah. He writes:
Babel is the first brick construction in Scripture (Genesis 11:3). They burn earthy clay to make it into building material for the city and teh tower that reaches to heaven. Egypt also deals in brick, and puts Israel to work making the bricks for its storage cities, its neo-Babels (Exodus 1:14; 5:7, 8, 16, 18-19).
The next time bricks are mentioned in Scripture is Isaiah 9:10, where the men of Ephraim respond to the collapse of “bricks” with the plan to build instead with hewn stones (Isaiah 9:. They are Babelites, constructors of a new oppressive Egypt, from which the faithful remnant will have to be redeemed. In context, the word “brick” (lebenah) puns with the “great hearts” (leb) of the men.
What are they building from bricks? The only other use of the word in Isaiah may help: Isaiah 65:3 refers to idolatrous offerings of incense upon “altars of brick.” In chapter 9, they are building brick altars; Yahweh makes them “fall” by His word that “falls” on Israel (v. 8); no matter, say the brick-hearted Babegyptians of Samaria, we’ll build it again, better this time.