Concrete Dreams & Concrete Nightmares…
… are two white pillowcases snuggly sheathing two half-emptied bags of cement. About 80 lb (approx. 40 kg) mined from each are mixed as slurry and dumped / smeared across 4 equally sized panes of glass spread across a floor.
DRAG Dreams & Nightmares through wet mix. Spell out the action using a 4-letter word.