What happens if you paint over gloss without sanding?

If you paint over gloss or semi-gloss without sanding, you are very likely to experience poor adhesion and a failed paint job that peels, chips, or scratches off easily. Gloss and semi-gloss paints dry to a hard, slick, non-porous film with high resin content that is designed to be smooth and easy to clean, but that smoothness also makes it difficult for new paint to grip. When you apply new paint directly over unsanded gloss, the new layer sits on top of the shiny surface without bonding properly, almost like trying to stick tape to a greasy surface. At first it may look okay, but over time, especially with temperature changes, moisture, or any impact, the new paint will start to bubble, flake, or peel off in sheets. You may also see uneven sheen, poor coverage, and visible brush strokes. To avoid this, you should always clean the surface, scuff sand it with 120 to 220 grit sandpaper to dull the shine and create microscopic texture, wipe away all dust, and ideally apply a bonding primer before topcoating. Sanding is a critical step that ensures mechanical adhesion and long-term durability.