How To Choose The Right Sandpaper Grit

Whatever the DIY project, there’s always a certain amount of preparation involved. Sanding is one of the most common preparatory tasks in home decorating and is sometimes taken for granted. However getting this part of the process right is essential to achieving a great finish, and there may be more to it than you think.

From removing rust on patio furniture to sanding down wooden floors, in the simplest terms, the process of sanding is smoothing a surface by rubbing it with something rough or abrasive.

It’s a practice that dates back to 13th century China and for many years has proven its usefulness in making surfaces smoother, removing layers of unwanted material e.g.old paint or rust and in some cases making a surface rougher to allow paint, glue or filler to adhere better.

Sanding can make little imperfections and signs of wear and tear on furnishings, doors, wooden floors and walls in your home disappear.

When embarking on home improvements, the temptation is to dive straight into the most rewarding part. However, while it can be a laborious task to sand down a surface in preparation for painting, it’s a vital step to ensure a good quality finish. For example when applied to old flaking paint a new coat will not adhere properly.

On the other hand, where a surface is too smooth or glossy, the paint will have difficulty attaching so sanding with sandpaper or steel wool is used to roughen the surface to make it a little easier for the paint to adhere to.

Why Choosing the Right Abrasive Is Important

Steel wool and sandpaper are the most commonly used abrasives and the process can be undertaken manually or with an electric sander.

For the purposes of this guide, we will look at different types of sandpapers and their specific uses. It’s very important to use the right type of sandpaper and the appropriate grade or grit. Using sandpaper that is too coarse can cause damage not easily remedied, like leaving deep scratches on the surface.

Similarly, playing it safe by using too fine a sandpaper, will not only be labour intensive, it can also result in failure to remove the imperfections on the substrate entirely. Either way, using the wrong grit sandpaper will leave an imperfect finish.

Sandpaper Types

There are a variety of different sandpapers on the market each designed for specific tasks.

Emery paper is used to sand metal surfaces and is available in boards, cloths or discs for use with electric sanding tools.

Aluminium Oxide is commonly used in dry sanding and is available in a wide range of grades. It is suited to manual sanding or it comes in disc belt or sheet form for electric sanders

Garnet Paper comes with a paper backing for dry abrading and a cloth backing for wet abrading. Wet abrasion also called wet sanding is used to achieve a very fine finish, it involves using water or some lubricating liquid when sanding to remove the smallest of particles.

Glass Paper is made, as the name suggests, from ground-up glass, It is used predominantly for dry sanding timber. It comes in various grades ranging from coarse to fine and can be bought on paper or cloth backing.

Note; each abrasive will wear out at a different rate depending on the hardness or softness of the surface being sanded.

Sandpaper Grits or Grades

It’s useful to familiarise yourself with the three main grades or grits of sandpaper and their uses before choosing the right sandpaper for the job you are doing. Sandpaper coarseness is graded by number, the higher the number the smaller the grain and the finer the sandpaper.

For most DIY home jobs you will want sandpaper grades ranging from 80 up to 360. The grade or grit you will need is determined by the surface.

Coarse sandpaper is ideal for removing rough paint and stripping rust from the substrate fast. It’s not good for getting a fine finish as it can abrade small chunks out of the surface and leave deep scratches.

Medium grade sandpapers are more versatile and gentle and are suitable for use in a variety of tasks.

Fine grades are used to achieve polished finishes and will remove traces of coarser sanding.

On the far ends of the spectrum, you have extra coarse sandpaper which is exceptionally abrasive and should only be used for the toughest jobs. Extra fine sandpapers are usually confined to polishing jobs. Sometimes you will need to use different grades in succession, starting with a coarse sandpaper grit and moving to a finer grade as work progresses.

We can break down the coarseness of the sandpaper grit further by looking at the graded numbers in the chart below and their corresponding uses.

Sandpaper Grit Chart

The Sandpaper grit chart is a numerical system that measures the coarseness of sandpaper. In the UK, sandpaper grit is graded by the Federation of European Producers of Abrasives (FEPA). Grit on the FEPA scale is indicated by the letter “P” before the number. In the US they use the CAMI scale.

It can be a bit confusing but the grit chart guide below should give you all the information you need.

TypeP GritUses
Extra Coarse24-36The toughest of the tough, this grit is used to remove hardcore paint and varnish and for old floors. Use with caution – this grit is aggressive.
Coarse40-50Ideal for heavy stripping of old coating and material fast, shaping wood, bare wood sanding, preparing for primer paint, cleaning wood, plaster, filler etc. Used on wood, plaster, fibreglass, plastic and metal. Leaves scratches on surface.
Medium60-100Can be used for light stripping, primary sanding of rough surfaces or final shaping in preparation for fine sanding, can smooth out shallow scratches.
Fine120-220Commonly used for final sanding of surface in DIY projects, plaster patches, softwood. Useful also for eliminating watermarks or other slight imperfections. Eliminates traces of coarser sanding.
Extra Fine240-600Suited to delicate sanding, polishing and removing dust and minor marks between coats of varnish. Wet sanding. Leaves a smooth finish.

What Grit Sandpaper for Wood?

When working with softwood you need to employ a light hand, use a fine grit sandpaper and sand diagonally across the grain of the timber. If you’re preparing to apply paint, you should finish with a light sanding, with the grain, to create a slightly roughened surface for paint.

Note: if you plan to stain or varnish the softwood do not sand across the grain otherwise the marks will show through the clear finish.

For hardwood timber use a fine grit sandpaper, sanding with the grain.

A basic guideline to help decide which sandpaper grit suits the DIY task you are undertaking:

  • Strip wood – coarse 40
  • Sand wood – medium 80
  • Finish wood – fine 120

What Grit Sandpaper for Metal?

Metal is easily scratched by coarse abrasives and scratches on metal are actually more difficult to remove than on wood. When stripping rust or deburring a metal edge a fine or even extra fine grade sandpaper is recommended.

Extra fine sandpaper is suited to polishing metal and will give a smooth surface. Emery sandpaper is ideal for metal surfaces.

What Grit Sandpaper for Plaster?

Plaster is an easy surface to sand, and sanding can be handy to remove imperfections like splashes, uneven surfaces or dirt and grit embedded in the surface.

Note: vigorous or aggressive sanding can damage your wall so take your time and use the right grade of abrasive.

When sanding plaster surfaces a medium grit is ideal, a 60 grit paper will work well on rough or textured plaster. A fine, 120 grit paper or even extra fine grit sandpaper will be required to achieve a smooth plaster finish.

Tools You Can Use for Sanding Down Surfaces

If you are sanding by hand use a cork or rubber block to wrap sandpaper around. This will make it both easier to use and more efficient.

If you have a large amount of work to do you might want to consider using an electric sander. Electric sanders require a certain degree of skill to use but they get the job done more quickly and effectively than by hand.

The following sanding tools are available to buy from any good hardware store, or you can hire them as needed:

Orbital sander

Suitable for various types of sandpaper, this lightweight sander moves in small circles or orbital motions, to abrade the surface. It produces a finer surface than a rotary sander.

A high-quality Makita orbital sander.

Rotary sander

This sander has a flexible rubber head that spins in circles. It is most suited to removing rust from curved surfaces. Using a rotary disc sander takes practice and can cause damage to surfaces in novice hands.

Belt Sander

This versatile sander has a moving belt of sandpaper, with adjustable speeds. It is faster than an orbital sander and comes in various sizes, from heavy duty ones for sanding floors to smaller versions suited to stripping light rust from metal surfaces. Belt sanders are also great for the rapid removal of wood like levelling rough boards.

Final Thoughts

In conclusion, whether you’re planning a home improvement paint project or restoring old wooden floors, removing old paint, blemishes or rust is an essential first step. When it comes to selecting the right tools and abrasives, it can seem a little overwhelming.

This comprehensive guide is here to help you figure out, step by step, the best approach for the job at hand. You will never regret putting in the time and research to get this preparation stage right as it really shows up in the end result.