**Bare drywall: yes—prime it before painting.** Once the joints are finished, dry, and sanded, remove the dust and apply a drywall primer, commonly PVA. This equalizes absorption between the drywall paper and joint compound, helping prevent patchy color and sheen. [Sherwin-Williams primer guidance](https://www.sherwin-williams.com/homeowners/how-to/painting/interior-painting-how-tos/sw-article-dir-intchooseprimer).

**Existing painted, textured walls: you don’t always need primer before mudding.** If the paint is firmly attached, clean, and dull, joint compound can generally bond to the prepared surface. Remove loose paint or texture, clean off grease and dirt, let dry, and lightly sand glossy paint to dull the sheen. [USG surface-preparation guidance](https://www.usg.com/content/dam/USG_Marketing_Communications/united_states/product_promotional_materials/finished_assets/sheetrock-wall-ceiling-texture-application-tips-en-J1828.pdf).

If the surface has adhesion problems, stains, or exposed torn drywall paper, use an appropriate bonding primer, stain blocker, or problem-surface sealer before mudding; follow its instructions for compatibility with joint compound. Ordinary PVA drywall primer serves a different purpose.

**After skim-coating, prime again before painting.** Let the compound dry completely, sand, remove dust, then prime the entire skim-coated surface for an even finish. [USG finishing instructions](https://www.usg.com/content/dam/USG_Marketing_Communications/united_states/product_promotional_materials/finished_assets/sheetrock-lightweight-settingtype-joint-compounds-easy-sand-submittal-J621.pdf).