The sandpaper is often used to clean and smooth metal in preparation for either its finishing or painting. There are a variety of sandpapers with specific uses, and each type of sandpaper also wears out differently since each type is made of different materials with distinct characteristics. Therefore, it is vital to use the right sandpaper to achieve the desired sanding outcome.
The best sandpaper for metal depends on the sandpaper grit size, coarseness level, abrasive type, backing material, and the extent of grit on the backing material that will meet your sanding needs.
Selecting the right sandpaper for your metal can be confusing, especially when you have no idea where to start. This article provides a guide to help you understand the different sandpaper grit sizes, coarseness, grit material, and more. Read on to get the information you need to choose the best sandpaper for your metal project.
Table of Contents
Choosing the Right Grit Size
The sandpaper is made up of abrasive particles (grains or grit) from natural or synthetic sources. The grain is sifted and sorted by size then bonded with either paper, sponge, or cloth-type backing. The result is an abrasive material for sanding.
You should be able to distinguish the grit sizes as different sandpaper projects require different sandpaper grit sizes. The grit size you choose depends on the kind of work you need to do.
Grit is determined based on a gradation scale. Numbers such as 100-grit, 200-grit, are usually indicated on each sandpaper package. These numbers indicate the size of the grains and range from 24 to over 1,000.
Higher Grit Numbers
The higher the grit number, the smaller abrasive particles and the finer the sandpaper coarseness. Such sandpaper will not remove much material from your metal surface. However, using this kind of sandpaper leaves a finer and more polished appearance.
Lower Grit Numbers
Lower numbers indicate larger abrasive particles and a coarser sandpaper. The coarser the sandpaper, the more material it will remove from the metal as compared to the finer sandpaper. However, the coarser the sandpaper, the more noticeable scratches it will create.
The Best Sandpaper Grit Size for Your Project
The lower grit numbers in the grading system indicate very coarse and rough abrasive, higher numbers such as 1,000 grit number, shows very fine sandpaper with tiny abrasive particles. However, most people never use sandpaper with grit sizes at the top or bottom of the grading system.
Therefore, to use sandpaper properly and to achieve best results, you need to know the appropriate grit size for your project. If you use very coarse sandpaper, your metal surface will be too rough for painting, or the finishing will not be smooth.
However, this coarse sandpaper is best when you need to remove a lot of material from the metal surface, remove old paint, or shape an edge. On the other hand, using sandpaper that is too fine requires a lot of sanding and effort to achieve the desired outcome.
It is therefore recommended that you use several grit sizes when sanding your metal in preparation for painting or finishing, sand with progressively finer grits starting with coarser sandpaper moving up to higher-number grits until you achieve the desired level of smoothness. Each higher-number grit used removes scratches left by the previous sanding, hence creating a progressively increasing surface smoothness.
Selecting the Appropriate Sandpaper Coarseness for Your Project
The coarseness level and specific grade of sandpaper are usually included in the sandpaper package. It is, therefore, easy to identify the coarseness of sandpaper. The coarseness level is a range of grit sizes that work similarly for the same sanding project. Projects usually call for a specific coarseness level rather than a particular sandpaper grit size.
It is essential, therefore, that you know what each sandpaper level or range includes.
Sandpaper grit numbers range from 24 for heavy material removal to 2,000 and beyond. However, for household sanding projects, grit numbers between 60 and 220 are most preferred. The specific grit range to use will depend on whether you are sanding the metal in preparation for painting or finishing, and the state of the metal.
If you are sanding metal to remove rust or to smoothen its edges, it is recommended not to use sandpaper with grit less than 220. The reason being, sandpaper easily scratches metal, leaving behind marks that are not easy to remove.
Additionally, 220 grit numbers should also be the coarsest grits to use when sanding metal finishes between coats. The finest grits are between 320 to 1,000. The sandpaper with these grit numbers is best for polishing finishes on metal to achieve the smoothest surface.
For the best sanding results, follow the sandpaper’s manufacturer recommendation.
Most sanding projects, however, require the use of sandpapers in the following grit ranges:
Extra Coarse Sandpaper
Extra coarse sandpaper is sandpaper in the 24 to 36 grit range. Extra coarse sandpaper is tough and is best for substantial stripping and removal of rough and built-up paint and varnish. Use this sandpaper on only the toughest jobs.
Coarse sandpaper is in the range of 40-50 grit numbers. Best suited for the removal of rough surfaces, previous finishes such as paint or varnish, and rust on metal. This sandpaper will cut through old paint, rough surfaces, and edges with much ease. However, do not use this sandpaper on corners and edges you want to remain sharp.
This sandpaper is in the 60 to 100 grit range and is the most often used. Medium sandpaper is best suited for the removal of surface imperfections such as planning marks. Apply more pressure on your metal to remove difficult material or let up on the pressure to preserve fine metals.
Fine sandpaper has a grit range of between 120 to 220 grit and is usually used for the second or third sanding. Fine sandpaper is hardly used on the first sanding unless the surface is smooth when touched. Use this sandpaper for sanding your metal before applying the first coat of paint or varnish. You can also use Fine sandpaper to roughen glossy paint before applying another coat.
For home projects, fine sandpaper can be used for final sanding.
Extra Fine Sandpaper
Grits in the range of 240 to 400 are extra fine. Extra fine sandpaper is often used to smooth light surface imperfections and to achieve a level of smoothness necessary for final paint or vanish. Additionally, you can use extra fine sandpaper between coats of paint and varnish for perfect results.
This is a very delicate sandpaper. Superfine sandpaper has grits of up to 600. Superfine sandpaper can be used to wipe away small inconsistencies and for polishing metals with thick finishes. However, this sandpaper is not strong enough for effective removal of built up pain, vanish, or very rough surfaces.
Ultra Finishing Sandpaper
Ultra finishing sandpaper has grits up to 1,000 in number and is extremely fine because of the very small abrasive particles. Use this sandpaper for sanding finishes on your metal. Ultra finishing sandpaper can also be used to sand and remove light clear coat scratches that are impossible to remove through buffing or using a rubbing compound.
Choosing the Best Grit Type
Sandpapers are made of different materials and, thus, different characteristics. Sandpaper type that is good for removing rust from your metal will not work well for creating a smooth finish. Therefore, the grit type you use will determine the sanding outcome you will achieve.
Below are the types of abrasive grains that you can use to sand your metal:
Flint is a natural, durable grain that is well suited for sanding off old varnish or paint. This sandpaper type is not as expensive as compared to other types and, therefore, economical for removing paint or sticky substances from metal. However, sandpaper coated with Flint dulls quickly
Emery is also a natural grain, just like Flint. This sandpaper is commonly used to remove corrosion, rust and to strip or polish metal. Emery usually features cloth backing for durability. Emery can also accommodate any wet or dry metal sanding application. However, Emery wears out quickly.
Yet another natural grain but softer than Flint and Emery, therefore ideal for lighter work. Garnet sandpaper provides finer finish when used on metal. When sanding, these sharp abrasive edges will fracture, giving you new cutting edges.
However, when Garnet is used to sand metal, it tends to dull relatively faster as it wears quickly. Garnet is usually reddish or golden brown and most ideal for hand sanding.
Zirconia alumina is a long-lasting synthetic grit made of a mix of Aluminum Oxide and Zircon. This abrasive product is best suited for grinding away rough edges of metal.
When using zirconia alumina to sand metal, the grit particles become sharper by breaking down over time. You, therefore, won’t need to change your sandpaper frequently.
Aluminum oxide, also known as the workhorse of modern sandpaper, is yet another durable synthetic grit type. Aluminum oxide is most useful for stripping, sanding, and polishing metal.
Furthermore, this sandpaper product is available with a waterproof backing. Waterproof backing is a technique that allows moistening sandpaper for wet sanding.
Wet sanding provides for achieving the smoothest surfaces. This sandpaper type is durable as it can fracture under pressure to produce fresh cutting edges. Aluminum oxide provides quality results when used on both power sander and hand-sanding.
Of all the synthetic abrasives, Silicon carbide is the most durable. This synthetic abrasive is suitable for sanding metal for repainting, sanding between coats, prior to adding a primer coat and polishing smooth surfaces.
Silicon carbide can be used on both wet and dry surfaces as it features a waterproof backing. Wet-sanding with water or oil reduces clogging and makes the abrasive more durable.
This sandpaper is reddish-brown and made of synthetic material. Ceramic sandpaper is ideal for rough sanding as it is considered the hardest and sharpest sandpaper. This sandpaper is highly durable and can last four to six times longer than other sandpapers. Ceramic sandpaper is ideal for use with sandpapers.
Choosing the Right Sandpaper Backing Material
The most common sandpaper backing materials are cloth backing and paper backing. Your choice of backing material depends on the level of flexibility and resistance to tearing required by your sanding project.
Paper backing comes in four weights; A, C, D, and E, with A being the lightest and E the heaviest. A is designed for light sanding and is very flexible. C and D weights are for heavier sanding while E is designed for the toughest sanding. If you need flexible sandpaper, choose a lighter weight paper. However, a heavier weight is more durable and less likely to wear out quickly.
Cloth backing comes in various weights; Y, X, J, F with Y being the stiffest, and F the most flexible. Y is a heavy-duty cloth used for tough sanding while X is a heavy cloth backing recommended for ordinary machine sanding. J is a flexible, lightweight cloth for use where more flexibility is necessary. F is highly flexible and lightweight. They are used where extreme flexibility is required.
Cloth-backed sandpaper is ideal for heavy material removal and gives excellent durability, flexibility, and resistance to tearing.
For sanding by hand, paper backing is good enough. However, if you are to use a power sander or any other power tool, cloth backing is preferred because it is stronger and has better flexibility.
Choosing Between Open-Coat and Closed-Coat
A closed coat abrasive product has its particles closely spaced and cover the entire backing surface. There are more particles per given area; thus, the sanding is quicker and produces smoother results. However, the backing material is easily clogged.
Open-coat, on the other hand, has its particles placed further apart, creating some space on the backing material. This kind of construction creates some room for the waste material; thus, less clogging of the sandpaper. This sandpaper is well suited for sanding soft metal and for removing finishes. However, the cutting process is slower as compared to closed-coat.
Sanding can be done either by hand or with power- sanding tools. Power-sanding tools include Pole sanders, Orbital sanders, handheld belt sanders, Detail sanders, and Random-orbit sanders.
When you want to prepare metal for painting, power sanding is most effective. These tools help remove unwanted material such as rust and blemishes from metal faster and efficiently. The sandpaper used for power-sanding is available in sheets, discs, and belts designed for specific power tools. Hand sanders, however, come in sheets that you cut to your preferred size.
Hand sanders allow for better control of the sanding process, and you can reach areas that power sanding tools cannot reach. These sanding tools are best for finishing and for use between finishing coats as they can make scratches less visible.