Chloe Zhang
Sandpaper is graded based on the size of the grit, with each grade serving a different purpose. The lower the grit number, the coarser the sandpaper. Coarse sandpaper is used to shape wood and remove previous finishes, while fine sandpaper is used for final smoothing before the work is finished. When it comes to polyurethane plastic, sandpaper with a grit of 220 is often used to sand the material before applying a coat. Finer grits such as 320, 400, and 600 are also used for sanding between coats of polyurethane. However, sandpaper may not be the best option for polyurethane as the friction can cause the polyurethane to melt and block up the grit. Alternatives such as steel wool are sometimes preferred for this reason.
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What You'll Learn
Sandpaper grits for polyurethane
Sandpaper grit is what makes it abrasive. Manufacturers grade sandpaper based on the size of the grit, and the grade you need depends on the job. Generally, the lower the grit number, the coarser the sandpaper. Coarse sandpaper is used to roughly shape wood and remove previous finishes, while fine sandpaper is used for final smoothing before the work is finished.
When it comes to polyurethane, sandpaper is fairly useless on its own as the heat generated by the friction causes the polyurethane to melt and block up the grit. However, some sources suggest using sandpaper with a grit of 220 or 320 between coats of polyurethane. One source recommends using 320-grit sandpaper wrapped around a hard block to sand lightly between coats, with the first coat requiring the most sanding to appear smooth. After the third coat, you can move on to 400-grit and finally 600-grit sandpaper.
For sanding plastic, garnet sandpaper is a good option as it is slightly softer than flint and emery. Silicon carbide sandpaper is also a good choice for sanding plastic and is available in a range of 80 to 3,000 grit, making it versatile for many different projects.
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Sandpaper alternatives for polyurethane
Sandpaper is graded based on the size of the grit, with each grade serving a different purpose. While sandpaper is commonly used for sanding polyurethane, it is fairly useless as the heat generated by the friction causes the polyurethane to melt and block up the grit.
- Steel Wool: Using steel wool instead of sandpaper is a common practice for sanding polyurethane. The steel wool does not gum up like sandpaper and allows for better following of the grain as you have to go slowly. It is important to buy good-quality steel wool to avoid metal particles that can stain the wood. The grades of steel wool range from #000 (very fine) to #00000 (ultra-fine).
- Brown Paper Bag: A brown paper bag can be used for sanding polyurethane. It is not clear what grit this corresponds to, but it is known to be quite effective.
- Emery Cloth: Emery cloth is an abrasive glued to a cloth, making it more durable than sandpaper. It is suitable for removing corrosion, polishing steel, and paint removal.
- Garnet: A natural grain that is slightly softer than flint and emery. Garnet is used for polishing and fine sanding of wood, leather, and plastic. It tends to dull quickly when used for sanding metal.
- Silicon Carbide: Silicon carbide is a synthetic abrasive used for sanding a wide range of materials, including plastic, metal, hardwoods, and softwoods. It is available in a range of 80 to 3,000 grit, making it versatile for different projects.
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Sandpaper grits for plastic
Sandpaper is graded based on the size of the grit, with the coarsest grades ranging from 24 to 36 grit and the finest grades ranging from 800 to 1000 grit. The grade of sandpaper you need depends on the specific task at hand. For example, coarse sandpaper is used to roughly shape wood and remove previous finishes, while fine sandpaper is used for final smoothing before completing a project.
When it comes to sanding plastic, there are a few different approaches you can take depending on the type of plastic and the desired outcome. For softer plastics or projects involving tiny, fragile parts, higher grit sandpaper is recommended. Specifically, grits ranging from 400 to 600 are commonly used for sanding softer plastics. Starting with 400-grit sandpaper can help speed up the process, and 220-grit can be used if a lot of material needs to be removed, although more care is required to avoid damaging the workpiece.
For removing mould lines on plastic models, a range of grits can be used depending on the desired level of precision. Some model makers suggest starting with a grit file, such as a metal needle file or a fingernail file, before progressing to higher grit sandpaper. Others recommend starting with 800-grit sandpaper and working your way up to higher grits, such as 1000 and 1500, for a finer finish.
It is important to select the right grade of sandpaper for the job, as using sandpaper that is too coarse can leave scratches and damage the surface, while sandpaper that is too fine may not be effective. Additionally, when working with plastics, it is worth considering alternative abrasives such as emery cloth or garnet sandpaper, which are suitable for fine sanding and polishing.
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Sandpaper types for plastic
Sandpaper is graded based on the size of the grit, with the lower the grit number, the more coarse the sandpaper. Coarse sandpaper is typically used for shaping wood and removing previous finishes, while fine sandpaper is used for smoothing and removing scratches. Very fine sandpaper is often used between coats of paint or varnish, and extra-fine sandpaper is used for sanding finishes before polishing. Super-fine and ultra-fine sandpaper are used for polishing finishes on wood and metal.
When it comes to sanding plastic, not all sandpaper works well. Some abrasives cut too aggressively, leaving deep scratches and causing heat damage, while others wear down too quickly. Silicon carbide sandpaper is the best option for sanding plastic as it cuts efficiently without excessive friction or clogging. It has a sharp cutting ability and even wear, maintaining a consistent cutting surface which reduces the risk of uneven sanding. This type of sandpaper is available in a range of 80 to 3,000 grit, making it versatile for different projects.
When sanding plastic, it is important to start with a coarse grit for heavy material removal and then move to progressively finer grits for a smooth, polished result. Wet sanding is often used when working with plastic as it helps keep the surface cool and flushes away debris that could cause scratches. This is why silicon carbide sandpaper is commonly used for headlight restoration, acrylic finishing, and 3D print smoothing.
Another option for sanding plastic is garnet sandpaper, which is a natural grain that is slightly softer than flint and emery. It tends to dull relatively quickly when used to sand metal but creates a finer finish. Garnet sandpaper is best for hand-sanding plastic rather than power sanding. Emery cloth, on the other hand, is too coarse for plastic and can Sandpaper is graded based on the size of the grit, with the lower the grit number, the more coarse the grit. Coarse sandpaper (40 to 50 grit) is used to roughly shape wood and remove previous finishes, while fine sandpaper (100 to 120 grit) is used for final smoothing before the work is finished. Very fine sandpaper (150 grit or higher) is often used between coats of paint or varnish as well as for finishing. The coarsest grade, designated as extra-coarse, includes 24-, 30- and 36-grit paper, while the finest grade (i.e. ultra-fine) includes 800- and 1,000-grit paper.
When it comes to sanding plastic, not all sandpaper works well. Some abrasives cut too aggressively, leaving deep gouges, while others wear down too quickly. Silicon carbide sandpaper is the best choice for plastic as it cuts efficiently without excessive friction or clogging. It removes material without excessive friction, which helps prevent heat buildup. Silicon carbide also maintains a consistent cutting surface, reducing the risk of uneven sanding. Its open-coat structure minimises the problem of plastic dust and debris accumulation, allowing for longer sanding sessions without needing to change sheets frequently.
Other types of sandpaper include aluminium oxide, which is a synthetic material that is often tan, light grey or grayish brown. It works well for all types of sanding, especially wood and metals, and is effective when used with a power sander. Garnet sandpaper is made from natural materials and is reddish or golden-brown. It features a soft grit and wears out the fastest but produces the smoothest surface. It is the best sandpaper for wood hand-sanding. Emery cloth is glued to a cloth rather than paper, making it a little more durable than sandpaper. It is used for removing corrosion, polishing steel, deburring and paint removal.
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Sandpaper grit standards
Sandpaper grit refers to the size of the abrasive grains on the sandpaper. These grains are responsible for sanding down surfaces. The lower the number, the coarser the grit, and the higher the number, the finer the grit. For example, 40-grit sandpaper is much coarser than 400-grit sandpaper. The grit of sandpaper is measured by counting the number of abrasive grains per square inch.
There are two commonly used grit sizing systems: CAMI and FEPA. The United States uses CAMI (Coated Abrasive Manufacturers Institute), while Europeans use FEPA (Federation of European Producers of Abrasives). The numbers are fairly close for larger grit sizes but differ more with smaller grits. The FEPA system is the same as the ISO 6344 standard. In the CAMI system, sandpaper grits range from 24 to 1,000 (and sometimes higher), which corresponds to P12 to P2,500 in the FEPA system.
Other systems used in sandpaper include the Japanese Industrial Standards Committee (JIS), micron grade (generally used for very fine grits), and the aught system.
Sandpaper is available in a range of grits, from extra-coarse to ultra-fine. The coarsest grade, extra-coarse, includes 24-, 30-, and 36-grit paper. Fine sandpaper (100 to 120 grit) is the best utility sandpaper and is suitable for most DIY projects. Very-fine sandpaper (150 grit or higher) is often used between coats of paint or varnish and for finishing. The finest grade (ultra-fine) includes 800- and 1,000-grit paper, which is used for ultra-smooth polishing of wood and metal finishes and bare metal.
Different materials are used to create various types of sandpaper, and each material has unique properties that allow for targeted results on different surfaces. For example, garnet is a common choice for hand sanding, especially when working with wood to remove light scratches and prepare surfaces for finishing. Emery cloth is a durable sanding material used for tough sanding jobs, such as deburring or paint removal. Aluminium oxide is the most common type of modern sandpaper, with the widest variety of grits and the lowest unit cost. It can be used on metal or wood. Silicon carbide is available in a very wide range of grits, from very coarse to microgrits, and is common in wet applications.
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Frequently asked questions
Sandpaper grit is what makes sandpaper abrasive. The lower the grit number, the coarser the sandpaper. Manufacturers grade sandpaper based on the size of the grit, and the grade you need depends on the job.
Sandpaper is not the best tool to use on polyurethane as the heat generated by friction can cause the polyurethane to melt and block up the grit. However, if you do want to use sandpaper, a very fine grade (150-grit or higher) is often used between coats of varnish. For a fine finish, you could also try garnet sandpaper, which is softer than flint and emery and will therefore dull more quickly, creating a finer finish.
Steel wool is often used as an alternative to sandpaper for polyurethane. The #000 Steel Wool is recommended, but be careful to buy good quality steel wool as some can leave metal particles that stain the wood.
