Selecting the right type of sandpaper and grit size is essential when sanding metal as it’s all too easy to make mistakes if you’re not careful. So what sandpaper should you use on metal?
It’s recommended to use aluminum oxide or silicon carbide sandpaper with a 320-grit or higher to sand metal. In order to prepare metal for priming and to remove rust, it’s best to use sandpaper with a coarser grit. For polishing metal, it’s best to use fine-grit sandpaper to obtain a smooth finish.
For your ease, I’ve included links throughout this post to the different types of sandpapers that I recommend to get the best results.
What Is the Best Sandpaper for Metal?
Before painting metals, you need to remove dirt, rust, and old paints from the surface with sandpaper. You can choose from a range of sandpaper grits, from aggressive to gradual smoothing. The lower the value of the grit, the rougher the sandpaper, and the more material it will take off with each pass.
You need several grit sizes for sanding metal, so it’s best to purchase an assorted pack of sandpaper. Sandpaper with coarse 220-grit particles works better on rust and for preparing the surface for priming.
Larger grits with grades lower than 100 can leave deep scratches, though this does make a good surface for primer adhesion.
A finer grit of 1000 will leave you with a smoother surface for painting, but it will take more passes to remove any imperfections. It is less common to use a grit level higher than 1000 unless you want to clear coat the surface.
Aluminum Oxide vs Silicon Carbide Sandpaper
The most popular sandpapers for metalwork are aluminum oxide (Al2O3) and silicon carbide (SiC). Aluminum and silicon sandpapers work best on harder metals, like steel and iron, and during the final stages of polishing the metal.
Aluminum oxide works well on grinding discs and electric sanders. Brown aluminum oxide sandpapers are the toughest and the most suitable for metalwork. The crystals that form the grit break down with each pass and create a sharper new layer for sanding.
Silicon carbide is ideal for finishing off sanding and making it ready for painting. The friable coating of silicon carbide means that its grain will stay more consistent than aluminum oxide while sanding. Silicon carbide is better for hand sanding as it will wear down too quickly on sanding discs and belts.
Sandpaper for Metal Rust
Aluminum oxide is the best sandpaper for rust since you can be more aggressive on the rust without ruining the sandpaper. This compound of aluminum works well with sanding discs and belts in the quick removal of rust, but it is more expensive than silicon carbide.
Most people start with a 320-grit aluminum oxide sandpaper, but it depends on how bad the rust is on the surface of the metal. Then for finer polishing, you will want to move up to 1000-grit or higher. If you are going to prime the metal after sanding, a few passes of 600-grit should be more than sufficient.
- Protection Tip: You should wear eye protection and a mask anytime you are sanding metal. Rust particles and pieces of grit will become airborne, which can damage your eyes and lungs.
What Tool Is Used to Sand Metal?
Sanding blocks are cheap and fine for quick preparation work but not for large sections of rust removal. Though, sanding blocks do give you a level of control that is not possible with a power tool.
Power tools with grit are by far the fastest way of removing rust from metal. There is an enormous range of discs, belts, and sandpapers, which will bring down the time of removing rust from hours to minutes.
What Is the Best Method of Sanding Metal?
The best type of sanding tool for the task will depend on the dimensions and orientation of the surface. Corners are difficult to get into, and you will need to use small grinding tools. For box tubing and metal plates, you will need something more industrial, like a grinder or a disc attachment for your power drill.
The simplest of sanding tools are sanding blocks, where the block gives you a flat surface to push the sandpaper against the metal. Sanding blocks are fine for small and difficult-to-reach areas, but this will take far too long on thick rust.
Sanding blocks are cheap, and you can use all the same sandpaper that you would use if sanding by hand. Coarse sandpaper of lower than 320-grit can be effective with hand sanding, enough to get the metal ready for paint.
And if you want a polished finish, hand sanding with wet paper is the best way of removing scratch marks and small blemishes. Hand sanding is also a safer method for removing rust from metal and for those unfamiliar with power tools.
The random movement of an orbital sander helps to prevent deep scratching and obvious sanding lines. Most orbital sanders will use coarse grits of less than 320, which is fine for rust and old paint removal.
These sanders are dustier than hand sanding, but you will finish much faster. Modern orbital sanders will also have vacuum attachments so that you can suck the dust away before it gets into the air.
It can be difficult to use a belt sander on metal, but these are fantastic at shedding rust and paint. Small narrow band sanders are great on box steel and in the corners of joints. Wide-band sanders work well on large flat metal surfaces, but they create a lot of dust.
Band sanders can be difficult to control, and it is easy to tear these types of sandpaper. The sandpapers for sanding machines are the most expensive choice for sanding, but they are effective and fast.
Coarse grit grinding discs are the best way of getting the rust off of metal fast. The discs are inexpensive, though the grit tends to be below 100. Most metal projects will get a coat of primer and paint, which will cover up the scratches left behind by the disc.
When it comes to smoothing off lumpy welds, nothing else will work as well as a grinding disc. A single pass with a grinder is enough to remove light rust, and old paint, to the point that you can repaint it.
Grinders will throw rust and dust into the air, so it is better if you use these tools outdoors while wearing a mask and goggles. Grinders can also jump out of your hand, making them one of the more dangerous methods of sanding.
Frequently Asked Questions
Can You Use Normal Sandpaper on Metal?
Yes, and the most common types of sandpaper are also the ones that work well on metal. Though you do want to make sure that you work your way up in grit. Regular sandpapers will tear faster than sanding papers designed for metal if they are paper rather than cloth-backed.
Do I Need to Wet Sand Metal?
Wet sanding is a necessary process of preparing the metal bodywork of your car for painting. Wet sanding with grit higher than 1000 will give you a mirror finish, leaving your paint with a smooth and even surface to dry on.
Do I Need to Sand Aluminum?
Aluminum will polish to a shine if you sand it with a high enough grit, though it will continue to dull as it oxidizes. A grit of 5000 will produce a mirror finish, but then you will still need to use a polishing compound to prevent it from dulling.