Best sponge grit for drywall corners is a different job

For drywall corners, use a medium-grit sanding sponge to smooth small ridges in joint compound and a fine-grit sponge for the final pass. Drywall compound is soft, and sanding too aggressively can expose or tear the paper face. The goal is to level the compound—not to sand deeply into the corner.

Choose grit based on the surface

• Medium grit: Use it for minor ridges or uneven compound after it has fully dried. Work lightly and check the surface often.
• Fine grit: Use it to remove light scratches and smooth the corner before priming. It is also the safer choice for a small touch-up when the surface is already close to level.
• Coarse grit: Usually avoid it on finished drywall corners. It can gouge soft compound, damage the paper, and leave scratches that show through paint.

Grit labels can vary between products, so follow the sponge’s packaging rather than assuming every brand’s grit feels identical. If a ridge is substantial, it is usually better to apply another thin coat of compound than to sand away a lot of material.

Use the sponge without rounding the corner

Let the compound dry as directed. Fold or position the sponge so it contacts the corner evenly, then make gentle, controlled strokes. Keep the sponge flat against each side instead of pressing hard into the seam. Check the corner with your hand and a work light; stop when it feels smooth and looks even.

A sanding sponge is useful here because it can conform to the corner, but that flexibility also makes it easy to round over the edge. For a crisp outside corner, avoid pushing the sponge across the corner’s point. If the corner bead or drywall paper becomes visible, stop sanding and repair the damaged area before painting.

Control dust and protect the surface

Drywall sanding creates fine dust. Wear eye protection and a well-fitting dust mask or respirator appropriate for the work, and ventilate the area. Use dust-control methods recommended for your sanding setup, and follow the compound and tool manufacturers’ instructions.

After sanding, remove dust from the wall before priming. If the surface feels rough after dusting, use a fine sponge lightly rather than repeating a heavy pass with medium grit.

When a sponge is not the right fix

A sponge is best for small patches and corners. For a broad, flat wall area, a drywall sanding block or suitable drywall sander can help keep the surface more even. If you have deep ridges, gaps, or exposed paper, correct the compound or repair the surface instead of trying to solve it with a coarser sponge.