These two services share a cavity and a material (refractory mortar) and differ in everything else, and because the chamber hides above the damper, homeowners can’t referee quotes with their own eyes. Here’s the clean split, plus the findings that pick sides:
Parging: the surface play
What happens: after thorough cleaning, refractory mortar is troweled over the chamber’s interior, corbel steps filled smooth, joints sealed, the funnel finished as a continuous surface. What it buys: the full parging dividend, slower fouling, better launch draft, heat containment, at a modest, single-visit cost. Its prerequisite: sound structure underneath. Parging is a finish, and finishes inherit their substrate’s future.
Rebuild: the structural play
What happens: failed masonry comes out, dropped corbels, through-cracked walls, fire-eaten sections, structure relays or reforms, and then the smooth refractory finish goes on (every rebuild includes parging’s endpoint; the reverse isn’t true). What it buys: a chamber that’s structurally trustworthy over your fires and under your flue. Its price: a real multiple of parging, access and reconstruction labor, the pricing anatomy.