Short answer: Start with the mildest cleaning method, test it on a hidden spot, and let the wood dry fully before you refinish. Cleaning removes grime, wax and silicone, which can otherwise ruin a new finish.
Why cleaning comes first
Years of grease, wax, polish and grime stop a new finish or paint from bonding. Silicone is the worst offender. Many spray polishes contain it, and it causes fisheyes, the craters described in common furniture refinishing problems. Clean before you strip, sand or finish, even if the piece looks clean.
Start with dust and a soft brush
Vacuum loose dirt with a soft brush attachment. Include carvings, crevices and the underside, where dust builds up. Work from the top down, so dust doesn’t settle on areas you’ve already cleaned.
Mild soap and water, barely damp
Mix a few drops of mild dish soap in warm water. Dip a cloth in the mix, wring it out until it’s barely damp, and wipe the surface. Dry it right away with a clean cloth.
Don’t soak the wood or hose it down. Water swells wood, lifts veneer and softens hide-glue joints. Test on a hidden area first, because some finishes react to any moisture.
Mineral spirits for wax and silicone
Odorless mineral spirits on a rag or on 0000 steel wool will dissolve wax, polish buildup and grime without harming most finishes. Work along the grain.
Silicone polish residue, from many spray polishes, causes fisheyes. Wash it with mineral spirits, then with naphtha for any residue that remains. Change rags often, because a dirty rag just moves the contamination around.
Heavy grime
For heavy grease before stripping, use TSP or a TSP substitute, then rinse with clean water and dry. TSP is a strong cleaner, so wear gloves and rinse well. If you use an oil soap, rinse thoroughly, because oil soaps can leave a film that interferes with finishing.
Sticky gunk usually responds to mineral spirits first. For tougher residue, try naphtha.
Mildew and musty smells
Wipe mildew with dilute white vinegar or a mild detergent, then let the piece dry fully in a ventilated space.
For musty drawers, air them out, leave them in the sun for a few hours, and use baking soda or activated charcoal to absorb the smell. Seal bare interior wood with dewaxed shellac to block odor from coming back.
Remove hardware first
Take off knobs, pulls and hinges before you clean. Clean brass separately, and don’t soak hardware that has original patina if you want to keep that look. On antiques, don’t polish the original hardware to a bright shine.
Check for active woodworm
Small holes with fresh, pale dust (called frass) underneath can mean a live infestation. Deal with it before you spend time refinishing, because a new finish won’t stop the insects. Repairing woodworm damage explains how to check and treat it. Ask a professional if you’re unsure.
Let the wood dry fully
Let the wood dry completely before sanding or finishing. If any water reached bare wood, allow at least 24 hours. Finishing over damp wood traps moisture and can cause problems later.
What not to use
- Soaking or hosing the piece. Water damages the wood and joints.
- Pledge-type polishes. Silicone and oils build up and cause finishing defects.
- Strong acids on everything. Vinegar is fine for mildew, but strong acid solutions can dull some finishes.
- Ammonia and alcohol on shellac. Alcohol dissolves shellac, and ammonia can damage it.
- Ammonia with bleach. Never mix ammonia cleaners with bleach. The fumes are dangerous.
Safety: mineral spirits and naphtha are flammable. Ventilate well and keep them away from ignition sources. Don’t mix cleaning products.