Is Wet Sanding Dangerous or Bad Practice?

[Todd@RUPES]

Is Wet Sanding Dangerous or a Bad Practice?

I have read, recently, that some high-end detailers are advising against wet sanding paint finishes. Their opinion, to which they are entitled, is that wet sanding can remove too much clear coat/paint which reduces the paint systems overall protection against UV radiation, it alters the appearance of the paint finish, and it is bad practice in general. For years, body shops, professional detailers (including high-end detailers), and adventurous enthusiasts have taken sandpaper to their paint in order to increase its appearance. This begs the question, is wet sanding dangerous or a bad process to practice?


How Much Paint Is Removed?

The first question to tackle, in our question for knowledge, is how much clear coat or paint is removed by wet sanding. The answer: It depends!

Any abrasive method removes material (top-coat paint, whether it is clear coat or single-stage color), including any grade of machine polishing, using an aggressive detailing clay, or improper washing techniques. In fact, washing your car with a dirty rag can be very abrasive to the paint. Think of the hours of machine polishing required to remove the damage caused by just one really bad wash! It is possible to cause scratches that are 1-to-3 microns deep from just one bad wash. Machine polishing 1-to-3 microns of paint can require hours!

Using coarse grade sandpaper (400-1000 grit) is going to remove far more material then using a fine grade sandpaper (2000-3000 grit). Technique also plays a huge factor in the rate of material removal as well. Using a firm sanding block with a lot of pressure is going to considerably increase the amount of material removed versus using a light touch and a soft sanding block.

As with machine polishing, the hardness of the paint will play a role. Hard, scratch-resistant paint finishes will often show less material removal compared to a soft-paint finish we subjected to equal methods.

This leads us back to the original question, how much material is removed????

The answer is: As much material as needed to remove the paint defect.

When machine polishing, your results are often hidden under the polishing film which can hide the finish of the paint until you remove the residue. Also, most polishes must be worked through a polishing cycle in order to achieve a high-quality finish (the abrasive grains must break down). Sanding a finish allows for more precise control because you can stop sanding as soon as the defect is removed.

Paint defects range in depth. To remove them means that you need to remove all of the surrounding paint that is above the deepest part of the paint defect. Your paint does not concern itself with the method this was achieve, whether it be hand polishing, machine polishing, or sanding. Because of the ultra-fine grade sand papers available today (3000 to 5000 grit), it is possible to sand leave a sanded finish that only requires a minimal amount of polishing to fully remove that sand marks and restore close.

Sanding, just like machine polishing, is a process that when performed with good technique will remove just enough material to leave a pristine finish.


Sanding The Paint Removes Too Much Of The Paint`s UV Protection

Since, in the above section, we established that sanding the paint correctly only removes the required amount of material (and in some cases offers greater control), we can easily deduct that removing any material reduces the paint`s UV protection. Precisely sanding the paint with sand paper DOES NOT remove any more material then polishing the paint if the goal is to remove scratches and paint defects.

With modern paints, the UV protection is found through-out the clear coat layer. Removing the clear coat reduces the amount of UV protection as the coat becomes thinner. Some of the UV inhibitors are believed to migrate towards the top half of the clear coat during the curing process, although paint chemists tend to have different opinions on how much this occurs. Most paint manufacturers recommend maintaining at least 70% of the original clear coat thickness in order to maintain optimal levels of UV protection.

However, the practice of keeping a maximum amount of clear coat on the paint at all times is a good practice, whether you are polishing the paint or sanding it. Because, in the case of deep defect removal, sanding offers more precision, it could actually be a safer practice for maintaining paint thickness.


Orange Peel Reduction

Orange peel is a bumpy texture on the paint that resembles the texture of an orange`s skin, hence the creative name. Because machine polishing doesn`t generally offer the planing ability to remove the extreme changes paint texture, wet sanding is often used to level the paint`s surface. This is a fairly aggressive method that will remove a measurable amount of clear coat/paint. The question is whether it is advisable to remove orange peel from a factory finish.

In most cases, the answer is no. Factory paint is thin. Like all decisions in detailing, and perhaps in life, the pro`s must be weighted against the cons.

Wet sanding the paint to remove orange peel will create a surface that is much flatter then the factory can apply. This will a more brilliant shine with amazingly accurate reflections, far more then what could be accomplished by polishing alone.

However, the risk involved is much higher. Removing sanding marks from the entire surface of a car and leaving the finish perfect is extremely time consuming. There will be a reduction in clear coat thickness which lead to premature sun fade.

Wet sanding a new car in order to improve the finish is done purely for aesthetic reasons. If the car is a weekend driver where is appearance takes a precedent over other factors, it is an option. However, if the car is a daily driver, then it not likely worth the reduction in UV protection and paint thickness (having material to remove future swirls, scuffs, and scratches).

I have removed the orange peel from several new cars, and in each case I was able to do so while maintaining over 70% of the original paint thickness. However, these cars were weekend only cars so their exposure to the elements was minimal.


So Is Wet Sanding Dangerous or a Bad Practice?

My personal conclusion is no. Like any other process in a detailer`s tool bag, wet sanding (done correctly) has a time and a place. While some high-end detailers, who are misinformed due to their own lack of experience in wet sanding may disagree, it is simply a process that is done when needed.

Removing too much material from any finish, regardless of it is accomplished, is bad practice. However, when performed with care and patience, wet sanding allows precise remove of material. This is extremely beneficial when removing deep scratches were precision is required. Whatever methods you choose to use in your own personal question for paintwork perfection, never attempt to exceed your own limits!

Try wet sanding on a scrap panel or a junk car first. With enough practice you may find yourself correcting deep paint defects while maintaining more material thickness and increasing your results!

[mrclean81]

Excellent article Todd.

[Bunky]

Thanks for the write up.

[Addicted2Bling]

Thanks for the great write up Todd, I needed to hear this.

[Custom Care]

Now I have the urge to order some megs Unigrit paper and give wet sanding a try. Is there a "starter pack" recommendation for grits to get?

[ihaveacamaro]

Thanks for the article Todd!!! Do you think 5000 grit is enough to remove orange peel?

[juliom2]

Explendid topic Maestro.
Is hard to tell by aspiring detailers when to and when not to use a sanding procedure.
Like everything else in life, if its done in excess is not good.
Is not necessary to sand out every little defect, spot, panel ect...
Although, theres no doubt is the best/only method when correcting tuff defects
when high ending results are the goal to achieve.

[mrclean81]

Thanks for the article Todd!!! Do you think 5000 grit is enough to remove orange peel?

Your arms would fall off first

[Todd@RUPES]

Thanks for the article Todd!!! Do you think 5000 grit is enough to remove orange peel?

Yes, technically 2000000000 grit could remove orange peel. Follow me for a second.

When you are removing orange peel you have to use a firm backing to the sandpaper so that you can focus the abrasive power on the peaks (high spots) of the paint. If you use a softer backing, one that allows the paper to flow over the texture of the paint, then you will not really remove orange peel as much as you are just removing material.

In either case, the coarseness of the paper effects the rate of material removal. If you cannot focus the cutting power on the high spots you will not effectively remove texture.

So 5000 grit could remove orange peel. However, even when used with a very firm sanding block, it is going to take a long time.

[GearHead_1]

Todd this is a well written and well thought out article. I`m a firm believer there is a time and place for wet sanding. This might sound like I only reserve it for that special car and now days that`s the case. When your shoulders go, wet sanding is one of the worst exercises I`ve found for them. Heck, even polishing can be a chore.

[Evan.J]

Very nice informative write up Todd!

[Todd@RUPES]

Todd this is a well written and well thought out article. I`m a firm believer there is a time and place for wet sanding. This might sound like I only reserve it for that special car and now days that`s the case. When your shoulders go, wet sanding is one of the worst exercises I`ve found for them. Heck, even polishing can be a chore.

What about DA sanding?

[Don Porter]

Great article

[Evan.J]

Great article Todd Very informative!

[ihaveacamaro]

Yes, technically 2000000000 grit could remove orange peel. Follow me for a second.

When you are removing orange peel you have to use a firm backing to the sandpaper so that you can focus the abrasive power on the peaks (high spots) of the paint. If you use a softer backing, one that allows the paper to flow over the texture of the paint, then you will not really remove orange peel as much as you are just removing material.

In either case, the coarseness of the paper effects the rate of material removal. If you cannot focus the cutting power on the high spots you will not effectively remove texture.

So 5000 grit could remove orange peel. However, even when used with a very firm sanding block, it is going to take a long time.

Missed this explanation the first time around, thank you sir