Can alkyd paint go over oil paint?

Yes, alkyd paint can go over oil paint because alkyd is essentially a modified oil-based paint and the two are chemically compatible. Both oil paint and alkyd paint cure by oxidation and use solvents, so alkyd adheres well to existing oil-based paint when the surface is properly prepared. To do it correctly, you should first clean the surface with soap and water or TSP to remove grease, dirt, and grime, then lightly sand the existing oil paint with 150 to 220 grit sandpaper to degloss the surface and create a mechanical key for adhesion, because glossy oil paint can be too slick for good bonding. After sanding, wipe off all dust with a tack cloth or damp rag. If the existing oil paint is in good condition, well adhered, and not peeling, you can apply alkyd paint directly over it without a primer, though a bonding primer helps if you are making a drastic color change, covering stains, or the surface is very glossy. Alkyd over oil is common for trim, cabinets, doors, and furniture where a hard, durable enamel finish is desired. You cannot apply water-based latex directly over oil without proper sanding and priming, as it may peel, but alkyd over oil works well.

Yes, alkyd paint can go over oil paint, as alkyd is essentially modified oil based paint and is compatible with oil paint. Alkyd and oil based paints are similar chemistry, both cure via oxidation and use solvents, so alkyd adheres well to existing oil paint if surface is properly prepared. To apply alkyd over oil paint, you should clean surface to remove grease and dirt, lightly sand with 150 to 220 grit sandpaper to degloss and create key for adhesion, wipe dust, and then apply alkyd paint. No primer is strictly needed if oil paint is in good condition and well adhered, but if oil paint is glossy, stained, or you are changing color drastically, bonding primer helps. Alkyd over oil is common for trim and cabinets. However, you cannot apply water based acrylic directly over oil without sanding and priming, as it may peel, but alkyd over oil is compatible. So yes, alkyd paint can go over oil paint with proper cleaning and light sanding, and it will bond well and provide hard durable finish, as both are oil based family. Ensure good ventilation as both have strong odor and VOCs.