Using the proper compound solves half the equation; execution determines whether the repair shows under raking light. Every compound requires tailored handling during application and smoothing.
When applying all-purpose mud over seams, keep knives clean and flex them at a 30-degree angle. The first coat embeds the tape; the second feathering coat extends the boundary by several inches; the third coat refines the edge to zero thickness. Trapping dry air under tape causes blisters. If a bubble appears after drying, cut the blister out with a utility knife and re-apply mud; never simply slap spackle over a floating pocket of paper tape.
Sanding technique also differs dramatically across these materials. Ready-mix mud sands effortlessly with standard 150-grit sandpaper or an open sanding screen attached to a pole. Spackle, especially vinyl-rich varieties, gums up standard paper quickly; pros prefer fine-grit sanding sponges dampened slightly to knock down edges without generating clouds of airborne dust. Setting compounds dry harder than the surrounding gypsum core, requiring precise knife work during application to minimize sanding afterward.
