@bonzer - I created a new sheet I called "WALL BACKGROUND" which I place above the grid. So the GRID sheet is sandwiched between FLOOR and WALL BACKGROUND.
@Towser - Mine is probably crisper because the other image is a blown up section of a PDF. I lost quality by doing that, but thanks just the same! And the icons are from DD3: Symbol Set 2, Bitmap B style. Except the "stairs" which I made in Photoshop and imported.