Grit numbers on abrasive materials like sandpaper are a rating system indicating the size of the abrasive particles used. Essentially, the higher the grit number, the finer the abrasive particles, which results in a smoother surface finish. Conversely, lower grit numbers correspond to coarser abrasive particles, designed to remove material more quickly.
Understanding the Grit Scale
The grit number tells you about the density and size of the abrasive grains on the sandpaper. It's an inverse relationship:
- Low Grit Numbers (e.g., 40-80): These have large, widely spaced abrasive particles. They are very coarse and aggressive, excellent for removing material quickly, shaping, or stripping old finishes.
- Medium Grit Numbers (e.g., 100-180): These have smaller, more densely packed particles than low grits. They are good for general sanding, smoothing out imperfections left by coarser grits, and preparing surfaces for initial coating.
- High Grit Numbers (e.g., 220-400): These feature fine abrasive particles that are closely packed. They are used for final sanding before painting or staining, smoothing between coats, and preparing surfaces for a very smooth finish. As the reference states, a higher grit number is equivalent to a finer abrasive, which creates smoother surface finishes.
- Very High Grit Numbers (e.g., 600+): These are extremely fine and used for polishing, achieving ultra-smooth finishes, and sometimes for wet sanding applications.
The rating systems (like CAMI in North America or P-grade in Europe) use sieving processes to determine particle size. A higher number typically means more particles can pass through a sieve with a certain number of holes per inch.
Practical Applications of Different Grit Levels
Choosing the right grit is crucial for achieving the desired result on your project. Using a grit that's too coarse can scratch the surface excessively, while using one that's too fine can be inefficient for material removal.
Here's a simple breakdown:
| Grit Range | Abrasive Coarseness | Typical Use | Material Removal Rate | Surface Finish |
|---|---|---|---|---|
| 40-80 | Very Coarse | Heavy material removal, stripping, shaping | High | Very Rough |
| 100-180 | Medium | General sanding, smoothing, preparing surfaces | Medium | Moderately Smooth |
| 220-400 | Fine | Final sanding before finishing, between coats | Low | Smooth |
| 600+ | Very Fine | Polishing, achieving ultra-smooth surfaces | Very Low | Very Smooth |
Key Takeaways
- Grit numbers measure the size of abrasive particles.
- It's an inverse scale: Higher number = smaller (finer) particles; Lower number = larger (coarser) particles.
- Coarser grits (lower numbers) remove material faster.
- Finer grits (higher numbers) create smoother finishes.
- Typically, you progress through grits, starting with a lower number to shape or smooth roughly, and moving to successively higher numbers to refine the surface.
Understanding how grit numbers work allows you to select the appropriate abrasive for each stage of your project, from aggressive material removal to achieving a perfectly smooth, ready-to-finish surface.
