Can I paint new paint over old paint?

Yes, you can paint new paint over old paint, and this is how most interior repaints are done, but success depends on proper preparation and compatibility. If the old paint is in good condition, meaning it is not peeling, chipping, bubbling, or flaking, and the surface is clean, dry, and dull, you can paint over it after light cleaning and possibly light sanding. You should clean walls to remove grease, dust, and dirt, repair any holes or cracks, and scuff sand glossy or semi-gloss surfaces to improve adhesion. If the old paint is oil-based and you want to use latex, or vice versa, you will need a bonding primer to ensure the new paint sticks, because latex does not adhere well directly to oil-based enamel. If there are stains, smoke damage, or strong color changes, primer is also essential to block bleed-through and ensure even color. If the old paint is peeling or chalky, you must scrape, sand, and prime before repainting, otherwise the new paint will fail. In general, you do not need to remove old paint completely unless it is failing, you just need to create a clean, dull, sound surface for the new coat to bond to.