The Importance of Grain Size in Abrasives: Achieving the Perfect Floor Finish

When it comes to floor sanding, grain size in abrasives plays a critical role in determining the final outcome of your project. Whether you’re removing old finishes, levelling an uneven floor, or applying the finishing touches to create a perfectly smooth surface, selecting the right grain size for each stage of the sanding process is essential. In this blog, we’ll explore why grain size matters, how to choose the right grit for each phase of sanding, and how understanding abrasive grain sizes can help you achieve a flawless finish every time.

What Is Abrasive Grain Size?

Abrasive grain size refers to the size of the particles embedded in the abrasive material. These particles, or “grits,” are responsible for cutting into the surface being sanded. The coarser the grain, the more material it can remove in a single pass, while finer grains are used for creating smooth finishes​. Grain sizes are classified using a standardised numbering system developed by the Federation of European Producers of Abrasives (FEPA). This system labels abrasive grains with a “P” number, such as P40, P80, or P120. The lower the number, the coarser the grain, and the higher the number, the finer the grain​.

Why Grain Size Matters in Floor Sanding

The grain size you choose for your sanding project has a direct impact on the smoothness of the finish, the speed of material removal, and the overall quality of the job. Using the wrong grain size can lead to issues such as scratches, uneven surfaces, or an overly aggressive cut that removes too much material.​

Here’s how grain size affects your floor sanding project:

• Coarse Grains for Material Removal

In the initial stages of sanding, coarse grains (typically P24 to P40) are used to quickly remove old finishes, varnishes, or paint. These grains are highly effective at levelling uneven floors and stripping away material fast. Coarse abrasives are perfect for removing deep scratches, high spots, and imperfections in the wood​. However, coarse grains are too aggressive for the final stages of sanding. If used too late in the process, they can leave behind deep scratches & gouges that require additional sanding to smooth out. That’s why it’s essential to use coarse grains only for the early stages of sanding​.

• Medium Grains for Refining the Surface

After the initial rough sanding, it’s time to move on to medium-grit abrasives (typically P60 to P80). These grains help refine the surface, removing the deep scratches left behind by the coarser grains and preparing the floor for finer sanding​. Medium grains also known as intermiate grits strike a balance between material removal and surface smoothness. They are aggressive enough to smooth out the floor without leaving noticeable scratches, making them ideal for preparing the floor for finishing​.

• Fine Grains for Finishing

The final stage of floor sanding requires fine-grit abrasives (typically P100 to P120) to create a smooth, even surface that’s ready for staining, sealing, or varnishing. Fine grains remove the last traces of scratches and imperfections, leaving the floor with a polished appearance​ but also still leaving the grain and pores of the wood open for the finish to be able to be absorbed by the week; hence, the reason why we don’t go too fine for our final passes. Using fine grains is crucial for achieving a professional-quality finish. However, it’s important to remember that fine grains don’t remove material as quickly as coarser grains. For this reason, you should only use them after the floor has been properly levelled and refined with coarser abrasives​.

How to Choose the Right Grit for Your Project

Selecting the correct grain size at each stage of the sanding process is essential for achieving the desired finish. Here’s a guide on how to choose the right grit for your specific sanding job:

• Initial Rough Sanding (P24 to P40):

Start with a coarse grit if you’re dealing with an uneven or heavily worn floor. Coarse grains are ideal for removing old finishes or paint, levelling high spots, and stripping down to the bare wood​. Remember to revisit our blog about direction sanding to get the best and fastest results with your first initial rough cut.

• Intermediate Sanding (P60 to P80):

Once the floor has been levelled and the old finish removed, switch to medium grit. Medium grains help refine the surface by removing scratches left by the coarse grains and preparing the floor for final sanding​. Check out our other blogs to find out what material best suits which floors.

• Final Sanding (P100 to P120):

For the last pass, use fine grit to achieve a smooth, polished surface. Fine grains create a scratch-free finish, making the floor ready for staining or sealing​. The idea here is not to close the pour of the wood too much. But remove any existing scratches from previous grit passes.

It’s important to gradually progress through the grit sizes rather than jumping directly from coarse to fine grains. Skipping grit sizes can leave behind scratches that may become visible once the floor is stained or sealed, resulting in more work to correct the problem​.

Why Skipping Grits Can Lead to Problems

One common mistake that professionals sometimes make is skipping intermediate grits and moving too quickly from coarse to fine sanding. Sometimes, when you feel that you may be saving time with a process and money on a different abrasive, you will only find when you put your finish down that you have not saved any time or money but allow yourself to sand the floor again.  This can result in an uneven finish, with deep scratches from the coarse grains still visible under the fine finish​. The purpose of each grit is to remove the scratches left behind by the previous one. Skipping a grit can leave these deeper scratches behind, and fine abrasives alone won’t be able to remove them. That’s why it’s important to follow the recommended progression through the grits for the best results​.

The Role of FEPA Standards in Grain Size Consistency

The Federation of European Producers of Abrasives (FEPA) has established a grain size classification system that helps professionals choose the right abrasive for their needs. They label abrasives classified under the FEPA system with a “P” followed by a number corresponding to the grain size. This standardisation ensures that you can reliably select the right abrasive grain for your project, no matter the brand​. The consistency of FEPA-classified abrasives allows you to achieve predictable, professional results every time, knowing that each grit will perform exactly as expected.

Why Grain Size Matters in Floor Sanding

The grain size of your abrasive plays a crucial role in the success of your floor sanding project. From the initial rough sanding stages to the final finishing touches, choosing the right grit at each step ensures that the floor is smooth, even, and free of imperfections. By understanding how abrasive grain sizes work and following the correct grit progression, you can achieve a flawless finish that is ready for sealing, staining, or varnishing. So, next time you’re preparing for a floor sanding job, remember that selecting the right grain size is key to professional results.