Dinamitek presents the definitive guide to sanding

Everything you need to know about sanding: abrasives, substrates, grits, and use with Dinamitek

Sanding is the most common operation that needs to be done when doing repair and maintenance work, or when doing a DIY project.

This guide aims to clarify the choice of support , provides basic information for the correct choice of abrasive and provides some guidelines to be able to operate effectively immediately.

If you need to rough-sand, sand, clean surfaces, or finish to prepare a piece for painting and gluing , you need to use the right abrasive. Whether you use sandpaper by hand or with a power tool, the things you need to know are the same. By paying attention to a few details, you'll achieve perfect work you can be proud of.

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The abrasive is nothing more than a support to which the abrasive grains are glued.
There are three main types of abrasive grains:

•          Corundum: Crystallized aluminum oxide. Suitable for sanding very hard wood and removing old paint, it sticks well to paints, varnishes, and sealants.
•          Emery: A mixture of minerals bonded to a cloth. Suitable for use on metals, it smoothes and polishes. Suitable for heavy-duty rust removal.
•          Flint: Replaced glass chips. Used for smoothing paint, wood, resin, or plaster.

The abrasive grains are glued on different supports:

• Nylon fiber : found on self-adhesive sheets with Velcro. It's used with power tools like sanders and handheld mouses.
• Cloth : the very resistant abrasive cloth, ideal for sanding corners and less accessible points of the piece.
• Paper : functional if soft but not too fine. Use dry or wet, depending on the situation. On new wood, it's used dry for simple sanding; when wet, it becomes "auto bodywork paper" and is suitable for removing paint.

Let's start with the basic concept: sandpaper is a sheet with a smooth surface and an abrasive surface .

Let's start by focusing on the product's name: sandpaper comes in several different forms. Although in common parlance, the terms "sandpaper" and "abrasive paper" are used interchangeably, they aren't necessarily the same thing.

THE SANDPAPERS

• Sandpaper has an abrasive surface made of crystalline glass grains. In modern versions, glass has given way to flint. It's recognizable by its yellowish color and is perfect for sanding softwood. It's the most popular type of sandpaper due to its affordable price and ease of use. The paper is soft and suitable for many applications.
• Sandpaper or emery cloth has a mineral base. It is recognizable by its brown-red color. Being a harder paper, it is suitable for all types of wood.
• Aluminum oxide paper doesn't have a specific color that distinguishes it; it's available on the market in various colors. Since it's a very durable paper, its primary use is for hand sanding hardwoods.
• Silicon carbide paper called "wet and dry" is the paper suitable for sanding paint when used wet and for fine sanding hardwood when used dry.

When it comes to sandpaper, one factor matters most: the grit size , or number of grains, which should be chosen based on the intended use of the sandpaper. If you need to sharpen, smooth, or finish, you need to use a different grit sandpaper. There's no universal grit that works for everything : with the wrong grit, you risk damaging the material too much and scratching the piece, or not being effective enough to remove the material, thus preventing effective cleaning.

The higher the grit number, the finer the grains . Grit numbers range from 40 to 2500. The coarser the grit, the lower the number.
What you need to remember is that the coarse grit is used for roughing , the medium grit for intermediate operations, the fine grit for finishing and the very fine for smoothing and polishing.

• Very coarse grain papers are indicated by the numbers 50 and 60,
• the coarse-grained ones with numbers 80 and 100,
• the medium grits are 120, 150, 180,
• the ends have 220, 240, 280 grit,
• the very fine 320, 260, 400, 500, 600.

The general rule is to work gradually : starting with a coarse-grained sandpaper, you should use it first to effectively remove the material, then gradually move on to a fine-grained sandpaper to perfectly smooth the surface.

The time has come to provide some practical examples of application , because there is no better school than practice in the field.

To remove something from a surface, you can start with an 80-grit paper, since it's quite coarse and will penetrate the surface well. Obviously, start with a hidden portion of the surface , and based on the results, decide whether you need to change the grit, opting for one that's rougher or one that's less damaging. For removing paint, 120-grit paper is fine.

To sand the wall, start with 150- or 180-grit sandpaper . The 80-grit sandpaper, suggested above, could create deep scratches in this case, forcing you to repair them with a filler. This is quite a paradox because with 180-grit sandpaper, you perform exactly the opposite process: you remove the excess filler from the wall.

For finishing, choose thin sandpaper. A 220-grit sandpaper might be suitable, but 320-grit sandpaper can also work. It's always recommended to test the sandpaper; the grits listed here are only indicative, giving you an idea of how to use the various sandpaper grits.

1000-grit sandpaper, the kind used by auto body repairers , produces a surprising result. When applied wet, it smooths almost without the user noticing. When applied, it creates a white cream on the surface, which must be removed with a cloth. It smooths perfectly , but you may end up with a dull surface.

Here are some useful tips to avoid making mistakes:

• When sanding, you should wear gloves to protect your hands, a mask to avoid inhaling sanding dust, and goggles to avoid getting any residue in your eyes.
• You need to sand the wood in the direction of the grain or the grain. Sanding in the opposite direction will scratch the wood.
• Work by gradually changing the paper grain, from rough to smooth.
• If you sand dry, you will have to vacuum up the residue; if you sand wet, you will have to remove the resulting substance with a cloth.
• If you sand by hand, fold the sheet of sandpaper into thirds or fourths, so you can use one side after the other, without wasting the sheet.
• Using the buffer allows you to optimize the sandpaper, because it allows for more precise use and uniform consumption

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