Scrub your redwood furniture or deck with soapy water, using a soft brush to remove most of the debris. Should heavy debris remain, move up to a stiff-bristled brush. Allow the redwood to dry thoroughly before continuing.
Sand the redwood gently with 150- or 180-grit sandpaper if there are rough spots on the wood. Brand-new redwood need not be sanded, as it should still be in good condition. Older redwood that has begun to show its age can be renewed by sanding.
Replace any fasteners that have begun to rust, as the rust will stain the redwood and leave unsightly marks. Try to replace the fasteners with the same kind so all of them will match.
Dust the redwood thoroughly with a soft cloth to remove any debris from the sanding. Dampen a cloth with paint thinner and rub it over the redwood to finish removing any substances that may compromise the effectiveness of the sealer.
Apply one coat of water-repellent, pigmented redwood sealer to the furniture or deck with a paintbrush and allow it to dry for four to six hours before applying a second coat. Remember to seal the undersides of furniture, and particularly the bottoms of table and chair legs. This stops the moisture from traveling up the legs of the furniture to damage the redwood.
Clean and reseal your redwood furniture or deck on a yearly basis. In harsh climates, it is advisable to move your redwood furniture into a covered storage area when it is not in use.