How to Prep Exterior Trim for Painting

Surface preparation is the foundation of any exterior paint job. If you apply high-quality paint over loose flakes, grime, or rotting wood, it will fail within a single season regardless of how much you spent on the gallon. Successful exterior painting is ninety percent preparation and ten percent application, and skipping the grunt work is the fastest way to double your future labor. Done well, your prep work removes the barrier between the wood and the new finish. You want a surface that is clean, dull, and structurally sound. Once the old, failing layers are gone and the wood is smoothed out, the primer can bite into the grain, ensuring your new coat stays locked in place through years of sun and rain.

1. Clear Your Work Zone. Trim back any bushes or tree branches that touch the exterior trim. Use drop cloths to cover the foundation and garden beds to catch debris and paint chips.
2. Strip Away Loose Paint. Use a carbide-tipped paint scraper to remove all loose, bubbling, or peeling paint. Work systematically, pulling the scraper toward you and applying steady pressure.
3. Fill Gaps and Rot. Dig out any soft, punky wood with a screwdriver or chisel. Fill deeper gouges or rotted spots with a two-part epoxy wood filler, then smooth it level with a putty knife.
4. Smooth Every Edge. Use 80-grit sandpaper on a sanding block to smooth out the edges where paint met bare wood. Finish with 120-grit to create a uniform surface for the new paint to grip.
5. Wash Away Grime. Wash the trim using a mixture of mild detergent and water, or use a pressure washer on a low setting. Scrub off any mildew with a stiff-bristle brush and rinse thoroughly.
6. Lock in Your Foundation. Brush a high-quality exterior oil-based or bonding primer onto all bare wood spots and repaired areas. Ensure the primer works its way into the edges of the existing, well-adhered paint.