Why is the word 'brick' singular in the phrase "a hunk of brown brick?"

Question

The following is an excerpt from the New Yorker:

The Newkirk Avenue building was nondescript, a hunk of brown brick. “Wow, it’s bleak,” Grant said, standing in the courtyard, which was covered in patchy grass. “The contrast between here and Point Dume of Malibu couldn’t be more extreme.” Grant, who has kept a diary for more than fifty years, has published two gossipy volumes littered with boldface names. “Who, and how, and where people come from so informs everything about them,” he said. “So now I’m in actual Streisand Land.”

-- From Richard E. Grant Hearts Barbra Streisand

Given that we usually say 'a pile of bricks,' my question is why is it 'a hunk of brick' instead of 'a hunk of bricks.'

Similarly, I am not sure if we should say:

1. A wall of bricks / a wall made of bricks
2. A wall of brick / a wall made of brick

Answer 1

Brick, as an uncountable noun, refers to the material.

The Newkirk Avenue building was nondescript, a hunk of brown brick.

The term hunk refers to the building, which is singular.
Hence a hunk of brown brick = the building was a solidified mass of brick. If we change the material to rock it becomes

The fort was a hunk of grey rock.

As to 1. A wall of bricks and 2. A wall of brick I suspect that both forms are grammatical, but I wouldn't say “a wall of brick” by itself. Instead the wall would be part of a building or construction

• a house that has a back wall of brick
• a building with a foundation wall of brick

A single wall that divides a property or land would be (for me)

3. a brick wall

Answer 2

From Oxford, definition 1.1:

mass noun Bricks collectively as a building material.
‘this mill was built of brick’
as modifier ‘a large brick building’

In your example, the expression "hunk of brown brick" is language purposefully meant to convey that the building was not pretty. The surrounding context emphasizes that, where the building is described as both "bleak" and "nondescript".

Given what the author has described, I believe they chose the better wording. I suppose we could describe a building as a "hunk of brown bricks," but this almost emphasizes the individual bricks of the building. By using the noun hunk, the author doesn't want to do that; instead, the author is trying to emphasize the building's lack of beauty, and contrast it with the presumably elegant building in upscale Malibu.

In short, it was a stylistic choice, not a grammatical one.