How to sand a deck

Start by clearing everything off the deck, including outdoor furniture, pots and mats. Give the entire area a thorough sweep to remove dirt, leaves and loose debris. If the deck is particularly dirty or has mould and grime build-up, wash it down with a deck cleaner and allow the timber to dry completely before sanding.

Check the surface carefully for any loose or damaged boards and inspect all nails and screws. Hammer in raised nails and tighten screws so they sit slightly below the timber surface. Any fixings sitting proud can tear the sandpaper, damage the sander and leave unwanted marks across the deck.

Using the correct grit sandpaper will make the sanding process easier and help produce a smoother finish. If the deck only has light weathering or a thin coating, begin with a medium grit such as 60 grit. For older decks with peeling stain, paint or heavy weathering, start with a coarser grit like 40 grit to cut through the surface coating more effectively.

Fit the sanding belt to the drum floor sander following the manufacturer’s instructions, making sure the belt is secure and running in the correct direction. It’s also a good idea to check the dust bag is fitted properly before you begin to help minimise airborne dust while working.

When starting the drum sander, keep the sanding drum lifted off the deck surface until the machine is moving forward. Gently lower the drum onto the timber as you begin sanding. This helps avoid gouging the timber or creating deep sanding marks at the start of each pass. Work with the grain of the timber in long, smooth passes along the full length of the boards when sanding timber decking. Try to maintain a steady walking pace and overlap each run slightly so the finish stays even across the deck. Avoid stopping in one spot with the drum lowered, as this can quickly leave noticeable low spots in the timber. For decks with uneven boards or stubborn coating patches, you may need to complete additional passes with a coarser grit before moving to finer sanding stages. The goal is to remove the old finish evenly without taking off more timber than necessary.

Once the old coating has been removed, vacuum or sweep away the sanding dust before switching to a finer grit. Working progressively through grit stages helps remove scratches left by the previous sanding pass and creates a smoother surface ready for coating. For most decks, finishing with around 80 grit provides a good balance between smoothness and coating adhesion. Sanding too finely can sometimes reduce how well oils and stains soak into the timber, so there’s usually no need to go beyond this for exterior decking. Cleaning away dust between sanding stages also makes it easier to spot any remaining rough patches, coating residue or uneven areas that may need additional attention.

Use an edging sander to sand along the edges of the deck and around posts, balustrades and walls where the drum sander can’t reach. Work with the grain of the timber and keep the sander moving lightly across the surface to avoid swirl marks or uneven patches.

For tight corners or detailed areas, switch to hand sanding using a sanding block or folded sandpaper. Feather the edges between the hand-sanded sections and the machine-sanded boards so the entire deck blends together evenly. This is also a good time to inspect the deck for splinters, rough edges or damaged sections that may need extra sanding before coating.

Sanding generates a significant amount of fine dust, so it’s important to manage it throughout the process. Empty dust collection bags regularly and vacuum between each sanding stage to keep the workspace clean. This also makes it easier to monitor your progress and spot any areas that may need extra attention during your D.I.Y. deck sanding project.

Once all sanding is complete, thoroughly vacuum or sweep the entire deck to remove dust from the surface and gaps between the boards. Any remaining dust can affect how evenly the new coating absorbs into the timber. If needed, lightly wash the deck with water and a stiff-bristle broom to remove the last of the fine dust, but make sure the timber is completely dry before applying any oil, deck stain or exterior finish. Drying times can vary depending on weather conditions, so allow extra time if the deck has been washed or if conditions are cool or humid. With the sanding complete, your deck is now ready for its new finish.

Check out our guide on how to stain a deck to preserve the timber.