How to Prepare Redwood Lap Siding for Paint

Power wash the surface thoroughly with a wood cleaning product if the siding has been allowed to weather without a primer or protective sealer. Take care not to get excess moisture under the siding lap joints or to damage the surface with too much pressure. Allow to dry thoroughly.

Replace or reset any fasteners that have surfaced and fill holes with wood putty as required.

Sand the surface of the siding as required with 80-grit or finer sandpaper to level any repairs or to even out surfaces. Weathered redwood will have to be sanded completely to expose the surface of the wood again so it will take the primer coat well.

Caulk as needed around any vents, windows or door frames.

Spot prime any obvious knots or sap veins with an alkyd primer or shellac-based product using a brush.

Prime the surfaces completely using a thick nap roller cover and a brush to smooth out, or "back brush" lap marks. Apply one coat of quality, oil-based alkyd resin primer. Alternatively, apply two coats of a quality water-based, latex acrylic, stain blocking primer, allowing the recommended time to dry between coats. Be sure to work the primer under all the lap joints and into all the exposed ends.

Decide on either paint or solid color stain depending on how much of the wood grain showing through is desired. Both have excellent opacity and protective qualities but paint will leave a fuller body film surface.