Should I Sand Primer?

When It Makes Sense

• Good fit: You are repainting a surface that was previously primed with a glossy or semi‑gloss primer and the new paint is a different color or a matte finish. Sanding removes the sheen and creates a key for the new coat.
• Good fit: The existing primer shows surface imperfections such as brush marks, roller stipple, or light sanding scratches that you want to eliminate before the topcoat for a flawless, professional look.

When You Should Avoid It

• Warning sign: The substrate is delicate (e.g., soft drywall, plasterboard) and aggressive sanding could damage the surface, making repair work necessary before painting.
• Warning sign: You are using a high‑quality, self‑levelling paint that specifically states no sanding is required on primer, and time or labor constraints are critical.

Pros and Cons

Pros

• Improves adhesion, reducing the risk of peeling or flaking after the paint dries.
• Creates a smoother, more uniform surface, which enhances the final appearance of the topcoat.

Cons

• Adds an extra step, increasing labor time, dust generation, and the need for protective equipment.
• Over‑sanding can thin the primer layer, exposing the substrate and potentially requiring a fresh primer coat.

Decision Checklist

• Is the existing primer glossy, uneven, or otherwise unsuitable for the new paint type?
• Will the benefits of better adhesion and a smoother finish outweigh the extra time and cleanup?
• Do you have the proper sanding tools, respirator, and a dust‑controlled workspace to do the job safely?

Alternatives to Consider

If sanding seems excessive, you can lightly de‑gloss the primer with a fine‑grit synthetic pad, or use a high‑adhesion paint formulated to bond to existing primer without surface preparation. Cleaning the surface with a mild detergent and a tack cloth is often enough for well‑applied, flat primers.

Final Recommendation

For most DIY projects where the existing primer is glossy, uneven, or you are changing color dramatically, a light sanding pass followed by thorough cleaning is advisable. When the primer is already flat, the surface is delicate, or you are using a paint that explicitly requires no sanding, skip the step to save time and avoid unnecessary dust. When in doubt, especially on historic or high‑value interiors, consult a professional painter to confirm the best preparation method.