The Gritty Guide to Sandpaper

Almost everybody knows what sandpaper is. That gritty piece of paper or block comes in all sizes. It is used to remove defects and create a smooth surface. But there’s a lot more to this toothy surface. The right (or wrong) sandpaper can make or scratch your next project.

Let’s face the facts; most of us wish we could skip the whole sanding process. Tedious, repetitive, and boring come to mind. However, skip this precious step, and any imperfections will be magnified when a job is done. It happened several times when admiring a final project that I wish I had just sanded a little more thoroughly.

How does sandpaper work?

Thousands of tiny particles work together to scratch away imperfections. The bigger the particle (or grit), the larger the scratch. But the scratching is not just determined by the grit. The density or spacing of the grit, the strength of the adhesive, the flexibility of the backing materials, and, let’s face it, the pressure administered all come together to play in your project’s outcome.

Let’s get sanding.

Select a sandpaper with a coarse grit, enough to remove surface imperfections, and follow with incrementally finer grits. Each successive effort erases the scratches of the coarse one before the scratches themselves become undetectable to the eye and the touch. Knowing what grit to start with and when to stop is the key to a perfect sanding job. Starting with too fine a grit eats up paper and time but using too coarse a grit in the beginning can leave scratches that are too tedious to sand out.

So, let’s talk gritty.

When shopping for sandpaper, a general rule of thumb is the higher the number, the smaller the grains, and thus the finer the sandpaper grit. Lower numbers alternately mean larger grains and coarser the paper. Note: think of less grains- lower- courser: more grains, higher-smoother.

In the US, grit is determined in manufacturing using the CAMI scale (Coated Abrasive Manufacturers Institute) which is measured in microns. To understand how small a micron is, check out a piece of 100-grit sandpaper. The tiny grains on the sandpaper measure approximately 141 microns in size, equivalent to .00550 inches. That’s tiny! The European measurement system is known as FEPA (Federation of European Producers of Abrasives) standards, the latter of which is preceded by a “P.”  You might come across the FEPA standards when buying some sandpapers online.

Stay the Coarse.

To make choosing sandpaper easier, manufacturers will label packaging with a coarseness grade description in addition to the grit number. What’s the difference? The grade is a broader term used to describe a range of grits. Coarse, medium, fine, and extra fine. They are the most common categories and include a range of grit numbers. Sometimes you’ll see these categories broken down even further into Micro and Macro categories. The finer sandpapers (fine, extra fine) fall into the micro category. Think wood and drywall. Macro grit-sized sandpapers are commonly used on tougher wood and metals.

• Coarse is typically used to remove previous paint finishes and polyurethanes. Coarse grits generally are in the 40- to 50-grit range.
• Medium sandpaper is typically used for the primary sanding of raw wood or to remove planing marks. 60-80 grit is standard in this category.
• Fine sandpapers are used in finishing work and fall into 100-1200 grit.
• Very fine is often used between coats of paint or finish to remove minor imperfections. Extra fine grits can start at 150 grit -220
• There are also “micro grits” – those that go above 240.  They are used for polishing metals and sanding wood when you need a glass-smooth finish and go up to 3,000 for fine polishing jobs.

The coarseness of the sandpaper makes a difference in your project, but so do the abrasive materials used to make the sandpaper. For example, some materials are better suited to wood vs. metal. Most manufacturers will list the material on the package.

Whatever sandpaper you are using, if it no longer feels rough to the touch, it’s time for a new sheet.  Don’t skimp on sandpaper and try to use it until it rips.  Your project will sand much quicker if you change out the sandpaper often.

Have more questions on the gritty choices of sandpaper? Stop by one of our three Cardinal Home Center locations and ask one of our Cardinal Specialists.