Sandpaper 101: a guide to using it correctly

True grit

Sandpaper is the unsung hero of many D.I.Y. tasks. It comes in handy for a wide range of jobs, helping you achieve a professional-looking (and splinter-free) finish whether you’re painting, woodworking or preparing surfaces to be glued. Here’s what you need to know about this smooth operator.

Safety tip: Always wear the appropriate safety equipment (safety glasses, ear muffs and a mask, for example) and always follow the instructions for the product or equipment. Always sand in a well-ventilated area.

Grade expectations

The numbers on the back of the sandpaper refer to the paper’s grit rating. “The grit number is the number of holes per square inch in the sieve that sorts the abrasive material. The smaller the number, the larger or coarser the grain,” says Steven Hutchinson of Flexovit.

For jobs that involve sanding away large volumes of material (such as shaping timber or removing paint), opt for the coarsest grits of 40 and 60. For general sanding jobs, 80-grit is reasonably rough while still giving you plenty of control and not gouging or scratching the surface. By the time you get to 120-grit, you’re moving into ‘fine grit’ territory. For a satiny finish on timber, or a smooth-down after the first coat of paint on a timber workpiece, go with 180-grit. Although the details will vary depending on what you’re using it for, the general rule of thumb is to start with a coarse-grit paper such as 60 or 80, and then progress through 120-grit and finally 180- or 240-grit for a smooth-as-silk result.

It’s important to sand between coats of paint because some of the fibres on the surface of the timber can lift as they absorb the primer or first coat, creating a bristly surface. Giving your workpiece a quick once-over with 180-grit paper eliminates the bristling, while also ‘cutting’ the surface of the paint so that the topcoat can bind to it more effectively.

Tip: When sanding timber pieces, work in the direction of the grain for best results.

Rough and ready

Match the type of sandpaper to the particular job you need it for. Painter’s sandpaper is designed so that it does not accumulate paint dust that would clog ‘standard’ sandpaper intended for timber. Wet-and-dry paper won’t fall apart when saturated and is often sold in extremely fine grit ratings of up to 800 and beyond. “Wet-and-dry paper, which has a distinctive black appearance, can be used with a lubricant – usually water,” says Steven. “Typically made with silicon carbide grain, it is used to resurface or restore metal surfaces. The water assists by reducing clogging of the abrasive, helping to achieve a high-gloss finish.”

Pro tip: You can freshen up a clogged piece of sandpaper by giving it a once-over with a wire brush. When it is no longer abrading properly, throw it out and grab a new one.

Shape up

Sandpaper comes in wide variety of pre-cut shapes, rolls and sheets.

• Rolls of sandpaper: These are best used with a sanding block. Folding the paper back and forth ‘breaks’ it, allowing it to be easily torn.
• Sheets: In the standard size of 280mm x 230mm, sheets can be divided into thirds or halves and clipped onto orbital sanders. Some are available in extremely fine grades and can be used for hand-sanding to a perfect finish.
• Discs: These usually come with perforations for dust extraction, to suit random orbital sanders. They are attached to the sander’s pad with hook-and-loop backing.
• Triangles and finger pads: They are pre-cut to suit standard shapes of detail sanders and are ideal for getting into those tight spots.
• Rectangles: These have holes designed for one-third-sheet and one-half-sheet sanders.

Sand and deliver

From the humble sanding block to the high-performance belt sander, there’s a tool for every type of smoothing task.

• Sanding block: Made of cork, sanding blocks are used by wrapping sandpaper around them for sanding flat surfaces.
• Sanding sponge: Sponges are better suited to rounded and contoured objects that need to be sanded, conforming to the curves and hollows of items such as furniture.
• Detail sander: This is an electric sander with a triangular sanding pad, often with a pointy ‘finger pad’ extension, letting you sand right into corners and other tight spaces. “When upcycling furniture using a detail sander, it’s always better to take the job slowly,” says Jason Salmon of Ryobi. “You don’t need too much downward force on the sander; let the tool and the paper do the work for you.”
• One-third- or one-half-sheet sander: These use pre-cut sheets clipped to their bases or secured using hook-and-loop fastening. They oscillate rapidly to power through sanding jobs.
• Random orbital sander: “It uses an orbital action, while at the same time oscillating in a random pattern. This results in a highly effective sanding, from fine to very coarse stock,” says Jason.
• Belt sander: This removes more material than other sanders, using a belt tensioned between rollers. To change the belt, first disconnect the power or battery. “Release the belt tensioning lever to slide out the old belt and slide in the new, aligning the arrows on the inside of the belt with those on the sander,” says Jason. “Push the lever back and power up the tool. Holding it upside down, use the tracking dial to make fine adjustments so the belt tracks the centre of the base plate.”

Thinking of sanding your deck?

Follow our guide on how to sand back a deck and get it ready for resealing.