Sunday, October 1, 2023

Automotive sandpaper: advantages of dry sanding vs water sanding

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The automotive sandpaper It is an abrasive specially designed for use on automobiles (and other surfaces with similar characteristics), generally fine grains are used and a substrate suitable for metals and putties, the support is a disc, a tape or a sheet and it prevents smearing.

Now, within the set of automotive sandpaper There are two possibilities: wet sandpaper and dry sandpaper; It is important to know the differences and the advantages of each of them.

Automotive sandpaper: differences with common sandpaper

We can think of the automotive sandpaper as a subset of sandpaper designed to work specifically on metal surfaces coated with a certain type of paint, on bare metal surfaces, and on sheet metal and putty mixes.

automotive sandpaper

Comparison and advantages of each method

Characteristics of wet sanding

This method is useful in the preparation stage of the bare sheet (matching and polishing process), since as the sheet is a waterproof material, there is no risk of generating stains or absorbing moisture.

By using water in the process, the suspension of particles in the air is avoided, which can be harmful to the health of the operators.

water sandpaper

water sandpaper

Characteristics of dry sanding

On the contrary, dry sanding is essential for operations on putty, since this material is sensitive to humidity and must be dry to avoid later problems in rigging and painting.

Dry sanding is a process that will inevitably generate particles in suspension in the atmosphere, so it is necessary to use personal protection elements such as chinstraps and goggles.

Advantages and comparison of both sanding systems

Wet sanding prevents particles resulting from abrasion from being suspended in the air; At the same time, form a pasta that helps a more uniform and neat polishing.

Dry sanding, on the other hand, does not alter the chemical composition of some materials such as filler, which is susceptible to the presence of water.

What are the right degrees for automotive work?

This depends a lot on the type of work to be done. Here we will see in detail each graduation and its applications.

  • 32 and 40: Along with files and rasps, this graduation is used only for a first coarse abrasion (to remove old paint or to remove excess material in welds. It is recommended to use dry sandpaper for this type of work. For its application, it is It is possible to carry out this first sanding by hand, directly using the sandpaper.
  • 80: coarse roughing of the putty and smoothing of the first coarse work of sandpaper 32 to 40 in metals. In both cases, only the use of dry sandpaper mounted on wooden or plastic blocks is recommended for a more neat and uniform work.
  • 180: fine sanding of putty (dry). Intermediate polishing of metallic surfaces (can be dry or water-based). Sandpaper can be used mounted on blocks of wood or plastic or on orbital sanders.
  • 320: optional finish before applying an anti-rust substrate, both on metal and on putty.
  • 400: anti-rust substrate polishing.
  • 600: Fine polishing of the anti-rust substrate. Here it is advisable to start using water-based sandpaper, as this will prevent the removed particles from re-entering the pores of the substrate layer.
  • 1000: final polishing of anti-rust substrate before applying color paint. As in the previous step, it should be done with wet sandpaper without allowing the sheet to dry.
  • 1200: polishing of areas to be painted over. It should only be done with water sandpaper.
  • 1500: polishing of the colored paint layer before applying clear lacquer. Use only wet sandpaper.
  • 2000: final polishing of the lacquer layer with water-based sandpaper, as a previous step to polishing with a cloth.

Useful accessories and add-ons

abrasive sponges

They are useful for wet and dry abrasion of hard to reach areas. They also allow small parts that may have been scratched from a previous process to be retouched.

abrasive sponges

abrasive sponges

abrasive fibers

Their use is similar to that of sponges, although they provide additional ease for removing oxides and surface dirt. They can be used dry and wet.

abrasive fiber

abrasive fiber

Backings for sanding discs

They are used in conjunction with discs when doing final finishing and polishing using orbital sanders.

Backings for sanding discs

Backings for sanding discs

varnished gauze

Sometimes it is necessary to remove loose particles that end up adhering to the recently polished surface, this can occur when using dry sandpaper to finish. If that happens, the varnished gauze allows you to remove any particles by thoroughly cleaning the material.

It also has practical use as a supplemental cleaning agent after the use of wet sandpaper.

varnished gauze

varnished gauze


The use of chinstraps and goggles is very important when working with dry sandpaper, since suspended particles can cause damage to the respiratory system.

Face mask

Face mask

general tips

If you notice that the automotive sandpaper pastes up shortly after starting a polishing job, replace with the immediately previous graduation; For example, if using 600-grit sandpaper you notice that it cakes within a minute of working with it, replace it with 400-grit sandpaper.

Always use dry sandpaper to work with fillers, fiberglass and other porous filler materials. Avoid at all costs that these materials absorb moisture, since the kiln drying process can cause the absorbed water to turn into steam, causing breakage, spattering or blistering.

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