Wetsanding is the act of using a very product (such as sandpaper) combined with a lubricating liquid to sand away a certain amount of the surface. This needs to be done with care and should not be done by beginners.
In some cases, it might be necessary to remove a large layer of the surface. For example, a scratch that is 10 microns deep. Polishing might take an hour or longer to fully polish away. Wetsanding can do this in minutes. Another example would be the removal of orange peel. Wetsanding will remove a layer in a different way then polishing, giving you new possibilities in affecting the surface of the object you are working on.
Wetsanding vs polishing
When you polish a surface, you are rubbing around particles over a surface. These particles are moved in a circular motion. Either by rotary (making circles) or by (making loops). In both cases, the particles are rubbing over the surface locally. The advantage of this, is that they have a little bit of effect on a very small area, which helps to remove a very even layer of the surface. If the surface is uneven, polishing will almost remove the same amount everywhere, maintaining much of the unevenness.
Wetsanding works very differently. The sandpaper you are using makes much bigger strokes then the polish does. With wetsanding, the particles move over a large area, instead of just being rolled around by the polisher. you could say that with wetsanding, you very evenly cut away the tops of the entire area. If that area is uneven, you will start at sanding away the peaks, and slowly work your way down to the flat surface.
Important to keep in mind
When wetsanding, the quality of your finish is partially dependent on the quality of your technique and your equipment. A slight investment in the tools and products used might be very much worth the effort.
A few things to keep in mind when considering (or preparing for) wetsanding.
- Use plenty of lubricant. Water is the most common used lubricant
- Wetsanding paper from the hobby shop is not as good as professional wetsanding paper for the automotive industry
- Use different grades of paper. Work your way up from the one you are using to the finest one
- To get the finish you want, you will need to do a 2 stage or a 3 stage polish
- A block of hard foam is often used to wrap the sandpaper around, this prevents that you apply to much pressure on one spot
- Your sandpaper will get clogged up by paint-particles, rinse them clean regularly
The danger of wetsanding
Wetsanding can be very effective when done by a pro. It will flatten the surface, improving the reflection of light (which results in more gloss), and remove imperfections at the same time. But mistakes can be made. There are a few things that can go wrong when wetsanding improperly.
- Pigtails. These are caused by an particles that cut deeper into the paint then the other particles. This could be due to bad quality sandpaper, dirt that got stuck in the sandpaper or applying uneven pressure
- Strike through paint. This happens when you sand away to much paint and actually sand all the way down to the primer
- Deep scratches, something big was caught in your sand paper, and by sanding you dragged it over the surface and made a deep cut through the paint
- Removed the clear coat. This will mean there is nothing left to protect the colored coat of paint on your car. Oxidation might occur in time and the surrounding edges of the clear coat can start to flake in time
The risk of wetsanding
Wetsanding is risky. And it shouldn’t be done without proper practice. When a bad technique is using, or mistakes are made, the results can be very costly. In same cases, the only repair is a complete respray.
- Too much paint is removed and you hit the primer layer. Only solution is a respray
- While wetsanding, you hit a corner and sanded off to much paint. Only solution is a respray
- You applied to much pressure and you made deep scratches. The only solution is either to carefully wetsand it again to remove the imperfection, or to polish it back up so the imperfection is less visible
- You didn’t keep your sandpaper clean, or used to little lubricant, and now you have made long deep scratches. Wetsanding again might not help, so you will probably just polish it so the imperfection is less visible
- You sand away the clear coat. This won’t be very visible right now, but eventually the edges might start to flake of you can have local oxidation in the paintwork. Onl solution to really fix this, is a clear coat respray
Wetsanding can deliver beautiful results, and can turn light surface imperfections into very nice, glossy surfaces. However, mistakes are easily made, and those mistakes are costly to repair. Wetsanding certainly has its place in the world of detailing, but it should be taken seriously and only be done by practiced professional.
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