I can't speak for crushed brick or lava rock, but I have several
places in my yard that are mulched 3-4 inches thick with river rock,
and it's nothing but a royal PITA. It's almost impossible to shovel
it out of the way when I want to plant something new, and weeds have
absolutely no problem sprouting through it at all. Since the rocks
make it impossible to use any kind of hoe, every single weed has to be
plucked by hand (and I would think this would be a real knuckle-
scraper with brick or lava rock). In fact, the weeds seem to really
like the rock mulch, growing big and hearty virtually overnight....

Jo Ann

The problem (and my question) is whether or not weeds are a big problem if
you use that product as a mulch subtitute. I would think that if you got
it 3 or 4 inches deep, weeds would not grow through it, like it will with
mulch. My thinking is that mulch retains moisture, and promotes weed
growth, and that the brick product would not hold moisture. By the way,
this is in a shady area, and the "mulch" would be more for looks that for
preserving moisture for the plants. That is not a concern or problem in my
situation.