A Comprehensive Guide to Sandpaper: Types, Uses, and Features

Sandpaper is a common type of abrasive tool that has a wide range of applications in our daily life. However, how do you choose the right sandpaper for your project or client? This article will provide a detailed introduction to the common shapes of sandpaper, the types of abrasive materials used, their characteristics, backing types, and the appropriate applications for different grit sizes. We hope that this article will be helpful to you in making informed decisions.

Common Shapes of Sandpaper1

1. Sanding Sheets

The commonly used size is 9 × 11 inches (23 × 28cm), but there are also other sizes available. Customers can fold or tear them to the appropriate size according to their needs.

2. Sanding Belts

These are suitable for belt sanders and come in different sizes. They are typically used for heavy-duty work, such as removing old paint or sanding large rough surfaces. They can quickly remove a large amount of material.

3. Sanding Discs

These are suitable for various models of disc sanders and random orbital sanders. Depending on the model, they may also have holes (Hook and loop Sanding Discs).

4. Sanding Sponges

Sponge sand blocks, covered with sandpaper, are flexible and available in different shapes. They are perfect for sanding tight spaces and edges, making them ideal for surface grinding.

These blocks have water absorption capabilities, serving as an alternative to wet sandpaper. They come in various shapes and sizes, suitable for polishing furniture, treating plastic products, paint repairs, and rust removal on metal and plastic surfaces. They possess water, acid, and alkali resistance.

Common Types of Sandpaper and Their Characteristics

1. Corundum

A natural abrasive commonly used for removing corrosion and polishing steel and other metals. It is not suitable for use on wood due to its sharp edges.

2. Garnet

A natural abrasive that is slightly softer than corundum. Its round edges can produce a smoother finish. However, it is slower in the grinding process and paper wear faster. It is suitable for final polishing.

3. Alumina Zirconia

A synthetic abrasive that is durable and suitable for removing burrs on metal and for initial rough sanding of wood.

4. Aluminum Oxide

A synthetic abrasive that is durable and the most commonly used type of paper in power sanders. It is suitable for sanding and polishing various metals (such as bronze and alloy steel) and also for woodworking projects.

5. Silicon Carbide

A hard abrasive mainly used for sanding metal woodworking tools, using water as a lubricant for metal shaping or "wet sanding". It is usually mounted on waterproof backing. It is commonly referred to as wet/dry sandpaper, used for wet sanding, polishing between coats, and sanding metals or plastics.

6. Ceramics

A hard and durable abrasive, but expensive. It can be used for quickly removing wood material but may not produce a very smooth surface.

Common Backings for Sandpaper

1. Paper Backing

Abrasives with paper backing are relatively smooth and have unique bonding strength, elasticity, weight, moisture absorption characteristics, and waterproof properties. They are suitable for low-pressure applications and need to conform to the surface of the workpiece. The weight grade ranges from "A" to "F," with A being the lightest and F being the heaviest.

2. Cloth Backing

Generally made of cotton, polyester cloth, polyester nylon, synthetic fibers, or a blend of cotton and polyester cloth. Polyester nylon is stronger and smoother than polyester cloth, but it is more expensive. Polyester blend cloth is a blend of polyester cloth and cotton cloth, providing good strength, water resistance, and flexibility. Cotton cloth is made of natural fibers, but it lacks waterproof properties while offering lighter weight and better flexibility. Synthetic fibers are stronger than cotton cloth and can be mixed with natural fibers to provide waterproof capabilities. Polyester cloth is made of fibers that are stronger than cotton cloth and synthetic fibers, offering waterproof properties, excellent load-bearing performance, and wear resistance. Cloth backing is commonly used in sanding discs and sanding belts.

3. Composite Backing

It is formed by bonding E-paper backing and cloth backing. It has good load-bearing capacity and a flat bottom surface, with better flexibility compared to paper backing.

4. Screen Backing

Made of polyester fibers, it is bonded with abrasive minerals. The mesh structure effectively prevents clogging during grinding. The mesh specifications are generally 18x18 and 21x21.

5. Polyester Film Backing

Made of smooth polyester film and coated with fine-grained abrasive minerals. It is often used as a backing for very fine grits.

6. Fiber Backing

Made by blending hardened paper and cotton cloth, it is commonly used to produce rigid sanding discs. Thicker fiber backing is suitable for manufacturing rigid sanding discs for heavy cutting, while thinner backing produces more elastic sanding discs. The thickness of fiber backing is usually 0.6mm, 0.8mm, and 1.0mm.

Common Grit Sizes and Applications

1. Extra-coarse grit (24-, 30-, and 36-grit)

Typically used for material removal and initial sanding, such as removing stubborn finishes on wood, paint and varnish, or rust on metal. It is commonly used with drum sanders' belts or discs for edge sanders.

2. Coarse grit (40-, 50-, and 60-grit)

Used for rough processing and sanding wood surfaces or deep grooves, allowing for quick removal of a large amount of material. Coarse grits are commonly available in sheets (9 x 11 inches), belts for drum and belt sanders, and disks for disk sanders.

3. Medium grit (80-grit)

Usually used as the first step in fine processing and the final sanding before painting. It can be used for hand sanding or with a belt or track sander, and also helps to remove rust and corrosion from metal.

4. Fine grit (100- and 120-grit)

The most practical grit that can smooth out scratches and paint surfaces left by coarser grades. It is suitable for the final sanding before painting or for drywall sanding. It can be used for hand sanding or with a track sander. This is the most commonly used grit grade for most households.

5. Very-fine grit (150-, 180-, and 220-, 240-grit)

Used for sanding varnish, polyurethane, and other surface paints, creating an ultra-smooth finish on wood.

6. Extra-fine grit (320- and 360-grit)

The first type of micro-abrasive used for fine surface treatment, especially for sanding between coats of paint or varnish. It is suitable for pre-polishing.

7. Super-fine grit (400-, 500-, and 600-grit)

Used for polishing wood and metal finishes as well as exposed metal, with waterproof backing. It can be used for wet sanding.

8. Ultra-fine grit (800-, 1,000-grit and beyond)

Used for super-smooth polishing of wood and metal finishes as well as bare metal surfaces.

Choosing the right sandpaper involves considering the shape, abrasive material, backing type, and grit size that best suits your specific needs. By understanding these factors and their characteristics, you can ensure successful sanding results for your projects or clients.