Importance of Wet Sanding in Touch-ups

[Bornin1992]

Hi, all,

I wang to repair numerous rock chips and deep scratches and, while I understand perfection is not always possible, I am looking for the best possible results.

Most of the tutorials I have read online involve wet sanding to level/blend the touch-up paint with the existing paint. The Toyota pen is pretty poor such that I am looking for other options (available in Canada). Here we have 'Scratches Happen', which reads, 'It's a waterborne paint and wet sanding will remove it almost immediately' as well as ChipFixx that uses its own solution to remove excess touch up paint, meaning wet sanding is not recommended.

A local body shop can make a body of acrylic enamel, but feels wet sanding is not advisable

How important is wet sanding to get professional results when using touch up paint?


Thanks!

[Rsurfer]

If you choose wet sanding you must be patient. It will take a week or two of applying thin coats to build up the scratch before wet sanding. Search on Youtube, I'm sure there are a lot of videos.

[Calendyr]

When done correcly, a touch up that is wet sanded will disapear and looks as if nothing has ever happened to the paint.

The difficulty with that is you need to let the paint cure before wet sanding. With modern paints, that is at least 24 hours.

The paint repair kits from places like ChipFixx are way too expensive to use IMO. Unless it's for your own car, then ok sure. But if you want to do this as a business, you can't be spending 100$+ on a bottle of paint to fix one car.

As a mobile detailer, I pretty much never wet sand the paint touchups. They show but it's much less visible than a rock chip and the main goal is to protect the pannel from rust.

On occasion, if the customer wants them less visible, I will ask the customer to apply the touch up paint himself 2 days before I come for the detail and I do the wet sanding. In these cases it pretty much comes out perfect.

[2black1s]

Here's my take... Wet sanding touch-ups can be beneficial but there is some risk involved, especially if you have little wet sanding experience.

When wet sanding is desired, it should be done within a certain window of time relative to the touch-up paint dry time. Obviously, the paint needs to dry long enough that it is sandable, but not so long that its hardness approaches the hardness of the original finish. As the touch-up paint hardness nears that of the original finish it becomes more difficult to level it without removing too much of the original finish surrounding the touch-up.

One of the most important aspects to doing a high-quality touch-up, whether wet sanding or not, is to keep the touch-up paint to the minimum required to fill the scratch/chip, while minimizing any paint application beyond the boundaries of the defect being repaired. Doing this will minimize the amount of any wet sanding required.

Here'a link to a thread where I describe my method for touch-ups... https://www.autogeekonline.net/forum/how-to-articles/125096-discerning-paint-chip-touch-up-not-everyone-every-chip.html?highlight=discerning+chip+repair

[Bornin1992]

Here's my take... Wet sanding touch-ups can be beneficial but there is some risk involved, especially if you have little wet sanding experience.

When wet sanding is desired, it should be done within a certain window of time relative to the touch-up paint dry time. Obviously, the paint needs to dry long enough that it is sandable, but not so long that its hardness approaches the hardness of the original finish. As the touch-up paint hardness nears that of the original finish it becomes more difficult to level it without removing too much of the original finish surrounding the touch-up.

One of the most important aspects to doing a high-quality touch-up, whether wet sanding or not, is to keep the touch-up paint to the minimum required to fill the scratch/chip, while minimizing any paint application beyond the boundaries of the defect being repaired. Doing this will minimize the amount of any wet sanding required.

Here'a link to a thread where I describe my method for touch-ups... https://www.autogeekonline.net/forum/how-to-articles/125096-discerning-paint-chip-touch-up-not-everyone-every-chip.html?highlight=discerning+chip+repair

Thanks for your response and for sharing that other thread. I ended up trying it on my grandparent's Nissan Altima with a bottle of acrylic enamel mixed by Rondex. I put approximately 5 or 6 thin coats over the span of two days and wet sanding after letting the final coat dry for 24 hours. Unfortunately, I could not source a bottle of clear coat and did not want to try a spray can. The end result: as for the feel, the transition from the factory paint to the touch-up paint was smooth. As for the appearance, it came a fair bit darker than the rest of the paint (though blends in from certain angles). Based on further reading (including yours), it seems that metallics might be challenging.

My personal vehicle is a metallic black (Toyota's Black Sand Pearl), and I am wondering how necessary an airbrush is for metallic paints. If I had to guess, I have likely 40 rock chips on the hood of my car ranging from the size of a grain of salt to ones the size of a rice grain: with the black, all are very obvious. Thoughts?

[2black1s]

Thanks for your response and for sharing that other thread. I ended up trying it on my grandparent's Nissan Altima with a bottle of acrylic enamel mixed by Rondex. I put approximately 5 or 6 thin coats over the span of two days and wet sanding after letting the final coat dry for 24 hours. Unfortunately, I could not source a bottle of clear coat and did not want to try a spray can. The end result: as for the feel, the transition from the factory paint to the touch-up paint was smooth. As for the appearance, it came a fair bit darker than the rest of the paint (though blends in from certain angles). Based on further reading (including yours), it seems that metallics might be challenging.

My personal vehicle is a metallic black (Toyota's Black Sand Pearl), and I am wondering how necessary an airbrush is for metallic paints. If I had to guess, I have likely 40 rock chips on the hood of my car ranging from the size of a grain of salt to ones the size of a rice grain: with the black, all are very obvious. Thoughts?

Skip the airbrush. It's impossible to keep the paint within the confines of the chip using an airbrush. You could try masking around each chip, but to me, that would be a lot more work for only a marginally better, if better at all, repair.

For the spray can clear, spray the clear into the spray can cap, and then apply it with a brush (or whatever tool you're using for the touch-up, i.e., toothpick, syringe, etc.)

On your metallic black car, you might be surprised... Black is one of the easiest colors to touch up. Obviously, metallic black is tougher to touch up than straight black, but even so, it can be quite forgiving. Much moreso than lighter metallic colors.

[Bornin1992]

Skip the airbrush. It's impossible to keep the paint within the confines of the chip using an airbrush. You could try masking around each chip, but to me, that would be a lot more work for only a marginally better, if better at all, repair.

For the spray can clear, spray the clear into the spray can cap, and then apply it with a brush (or whatever tool you're using for the touch-up, i.e., toothpick, syringe, etc.)

On your metallic black car, you might be surprised... Black is one of the easiest colors to touch up. Obviously, metallic black is tougher to touch up than straight black, but even so, it can be quite forgiving. Much moreso than lighter metallic colors.

Thanks for your response, again. I had a follow-up question after re-reading your guide. How does it work for chips that are "shallow"? As I understand it, you are to put several layers of paint such that it is still below the surface of the surrounding area's paint, and top it up with clear coat to make it level with the surrounding paint. But, for shallow chips, I struggle to see how I could have any more than two layers of paint and have it reaching the surface level of the surrounding paint. Hopefully this question makes sense.

[2black1s]

Thanks for your response, again. I had a follow-up question after re-reading your guide. How does it work for chips that are "shallow"?

If a chip is very shallow, then it is quite possible that color is still intact and only the clear is compromised. If that's the case, you can simply use clear for the touch up.


As I understand it, you are to put several layers of paint such that it is still below the surface of the surrounding area's paint, and top it up with clear coat to make it level with the surrounding paint. But, for shallow chips, I struggle to see how I could have any more than two layers of paint and have it reaching the surface level of the surrounding paint. Hopefully this question makes sense.

When applying the color coat, you do not need "several" layers. You only need enough color to provide "hiding". Hiding is a term that describes the transparency of the color coat... Once you can no longer see through the color coat you have achieved hiding. In many cases hiding can be achieved in a single coat when doing touch ups.

Once you've achieved hiding, finish the touch up using the clear.