Q: Every summer we have several large family braais and as a result our pressure-treated deck is, basically, trashed. It’s covered in grease stains, muddy footprints and mouldy leaves. Can you help me get it back to good health?
A: Before you clean, make repairs. Replace splintered and rotted parts, and sand down any rough spots. Be sure to use stainless-steel or weatherproof fasteners, not drywall screws or plain steel fasteners, which rust. If you haven’t checked your deck for structural soundness, now is a good time. For detailed guidance, download the Deck Evaluation Checklist from the North American Deck and Railing Association (nadra.org).
Grab the family and get to work. Protect adjacent surfaces with dropcloths or sheet plastic taped in place, and use a broom, leaf blower and putty knife to remove debris from the deck’s surface and between individual deck boards. Wash the deck with a cleaner formulated for exterior wood. Rust stains and tannin stains from leaves, berries and nuts are among the toughest to remove from a deck, and cleaners that contain chlorine bleach can make them worse. Instead, use a cleaner containing oxalic acid (wood bleach). In most cases, apply it with a paint roller, paintbrush or garden sprayer. Scrub heavily soiled areas with a deck brush; for really stubborn grease stains, apply a water-rinsable degreaser, and let it sit for a few hours first.
Rinse the deck thoroughly with a garden hose or a low-power pressure washer. The procedure is much the same if you’re removing a finish, but you apply a finish remover formulated for decks. Whether cleaning or stripping finishes, don’t overdo it. If the wood begins to look pulpy as you clean or pressure-wash, you’re going at it with too much force.
After the deck has dried thoroughly, apply a clear water-repellent finish that contains an antifungal agent. A well-sealed deck resists stains from fallen leaves and nuts.