Limewash bonds by soaking into a porous mineral surface, and latex paint and bare drywall paper are neither. That is why painted walls get a mineral or bonding primer approved by the limewash maker, and fresh or patched board is sealed with a drywall primer first. A primer tinted toward the final color keeps any thin spot from flashing white.
Before priming, nail pops and dents are filled, hairline cracks above doors and at corners are filled and sanded, and the walls are wiped free of dust and grease. Flat builder paint that rubs off on a damp cloth needs extra attention, because the lime can only be as sound as the layer under it. A few limewash products are meant only for bare masonry, so indoors we choose one whose instructions cover painted walls.