Updated: Nov 21, 2019
By Matt Shields
Sanding is often overlooked by many woodworkers, myself included. Rushing this process is guaranteed to create more issues during the varnishing process.
Below are a few tips and tricks that will help ensure the slab you just got from Urban Wood Lab will look and feel its best. We’ll start with the basics today, but this section will be continued in later newsletters with more advanced techniques.
Understanding What’s Happening:
Sandpaper is made when fine particles (that resemble sand) are adhered to a cloth backing material with special ‘glue.’ The higher the grit number, the smoother it is. Conversely, the lower the number, the rougher it is. Sandpaper makes tiny cuts or scratches to wood. As finer papers are applied, the scratches become smaller and eventually invisible to the naked eye.
The scratches are very important because they allow varnishes to adhere to the surface better.
The Basics: Tool Selection
The key to a smooth and scratch-free surface starts with choosing the right tool. While any of these items could achieve the same result, people new to the hobby will find more consistent success with a Random Orbital Sander. This is because the sandpaper spins at varying speeds and the entire block that holds the sandpaper also spins. The result is a scratch pattern that is imperceptible to the eye.
Other options include: Handheld belt sander, Palm Orbital Sander, ¼ sheet Palm Sander (Finishing Sander).
The Basics: Sandpaper
There are many types of grit materials that makeup sandpaper. Aluminum Oxide and Zirconia Alumina are the most common and are perfect for sanding hardwoods. They last long, aren’t terribly expensive and can handle hard, dense materials.
Other options include: Garnet, Flint, Silicon Carbide and Emory.
The Basics: Technique:
1. After the slab has been flattened, it will be important to remove any marks or gauges made by the planer or router sled. These are called ‘milling marks’ or ‘machine marks.’ Coarse sandpaper will help remove them.
2. Stick 60 or 80 grit paper to the Random Orbital Sander and place the unit on the surface before starting the tool. Use a consistent speed and make equal passes across the entire surface. Avoid the temptation to sand in one spot and completely removing deep scratches, this will make ‘craters’ or ‘cups’ in the surface and will make varnishing very difficult.
3. Put on some headphones because removing machine marks with even sander passes can take a while, even with very coarse sandpaper. Trust me, it’s worth the time investment.
4. After all the machine marks have been removed, it’s time to change the paper to a higher grit. Vacuum the surface off using a brush-head attachment to remove dust and any 60 grit particles left on the surface. Avoid using an air compressor to blow the surface clean; it will kick the dust up, which will often fall right back down onto the wood.
5. Avoid skipping grits. While this might sound like a good way to save time and sandpaper, it will actually burn through both. If I were to use 120 grit after 60 grit (instead of 80 grit and then 100 grit), I would need to sand up to 8 times longer than normal to get the same level of smoothness. I will also burn through 2-4 sanding discs if used correctly.
*Some sandpaper manufacturers will say that it is ok to skip one grit at a time. For example, after sanding with 60 grit, use 100 grit next, then 150, then 220 (or 80, 120, 180).