Do you sand paint before top coat?

Yes, you often sand paint before applying top coat, depending on type of paint, condition, and time since previous coat, to improve adhesion and smoothness. For house walls, if you applied primer or first coat of paint and it has dried, has bumps, drips, or rough texture, you should lightly sand with fine 220 grit sandpaper to smooth surface, then remove dust with tack cloth before applying top coat, as this gives professional smooth finish. If you are applying second coat of same topcoat within recoat window, usually 2 to 4 hours for latex paint, you can usually apply without sanding if surface is smooth. If previous paint is glossy, oil based, or has been drying more than 24 hours, light sanding is recommended to degloss and create key so new top coat adheres and does not peel. For wood trim, furniture, and cabinets, you should always sand lightly between coats of paint and before topcoat clear coat. For car painting, you may wet sand base coat lightly to remove imperfections before clear topcoat. So yes, sanding paint before top coat is good practice when surface is rough, glossy, or has dried long, but not always necessary for quick recoat of flat latex on smooth walls.