What item was commonly used to scrub stoops in New Orleans?

Brick or brick dust.

From
Kristina Brooks, writing about Alice Dunbar-Nelson's "Local Colors of Ethnicity, Class, and Place" at
http://www.findarticles.com/cf_0/m2278/2_23/54543094/print.jhtml said:

"Dunbar-Nelson's stories recording the practice of washing the doorstep include "The Goodness of St. Rocque" (Works 1) and "Cupid and the Phonograph" (Works 3). Dunbar-Nelson notes only that the custom stems from a superstition, but Robert Tallant explains that the most common protection from evil gris gris (hoodoo charms) in New Orleans was to scrub the front stoop with brick dust (199). "

Very informative article (above) for those interested in such things. There's a good bio of Dunbar-Nelson (1875 - 1935) at http://www.edwardsly.com/dunbarnelson.htm

For an except from "The Goodness of St. Rocque" see the pontchartrain history site at http://www.stphilipneri.org/teacher/pontchartrain/content.php?type=4&id=567 . An entire e-text of "The Goodness of St. Rocque and Other Stories by Alice Dunbar" can be found at http://www.infocentral.com/texts/etext96/stroq10.txt