Wall Preparation Before Painting: Filling Holes, Fixing Cracks, and Sanding

Colour Selection and Planning

The difference between a professional paint job and an amateur one is almost entirely in the preparation — smooth walls produce smooth results.

Small nail holes are the most common wall imperfection in existing homes. A lightweight spackling compound applied with a flexible putty knife, allowed to dry, and sanded flush produces an invisible repair. Resist the temptation to use standard drywall joint compound for nail holes — it shrinks more as it dries and may require two applications.

Preparation Is Everything

Cracks in plaster or drywall require different treatment depending on their size and pattern. Hairline cracks can be bridged with 100% acrylic paint, which forms a flexible film. Cracks up to 3 mm wide should be filled with setting-type compound (durabond), which hardens chemically and resists shrinkage. Cracks wider than 3 mm should be taped with paper tape set in compound before filling.

Skim coating is the professional approach for walls with widespread texture, multiple repairs, or surfaces where previous paint layers have created uneven texture. A thin coat of diluted joint compound applied with a wide trowel over the entire wall surface, sanded smooth after drying, produces the flat, glass-like finish that paints and reflects light evenly.

Professional Results That Last

Sanding between coats with 120 to 150-grit sandpaper levels any stipple or brush marks from previous paint coats and provides mechanical adhesion for the next coat. This step is most important when applying semi-gloss or high-sheen topcoats, where surface imperfections are most visible.

Priming is required after any significant repair work. The patched areas absorb paint differently than the surrounding wall, creating visible 'flashing' — sheen variations visible when looking across the wall in raking light. A coat of PVA primer over all repairs equalizes absorption and prevents flashing in the topcoat.