How to damp-sand?

[Mary S]

Hi, I have seen several examples of people doing damp sanding but am interested in tips on how to do this.

Here is my understanding so far. When you are sanding with an electrical DA, you can't do the traditional wet sanding because water and electricity don't mix.

An article I saw by 3M said it is damp sanding when you spray the sanding disk to moisten it, and when you are sanding along a vertical panel there should not be enough water for the water to drip down the side of the car.

This is the part of the process I am interested in, mainly, how much spraying is required, how often you do it or know when to spray, how wet you get the sanding disk, do you soak the sanding disk first, that kind of thing.

If I were to do it, I would probably not use less than 2000 grit, possibly only 3000 and 4000, either using Meguiars Unigrit or Mirka Abralon or both, because this is factory paint/clear.

Thanks!

[CieraSL]

Re: How to damp-sand?

Here are some videos from one of the Advanced Classes (I think):

[cnfowler]

Re: How to damp-sand?

Damp sanding is when you moisten the sandpaper and sand with just damp paper. Wet sanding is when you saturate the area you're sanding and continue to flood the area while sanding.

Colin

[Michael Stoops]

Re: How to damp-sand?

Damp sanding vs wet sanding involves not only differing techniques, but different abrasive media as well.

True wet sanding involves use of special papers, discs, etc that should be soaked in water for at least 24 hours prior to use. The surface to be sanded is then sprayed with water or, in some cases, continually flooded with running water. There are even tools created to hold both a sheet of sand paper and a small hose to keep the water flowing over the paper.

The reason for the amount of water used here is basically two fold - it adds lubrication and keeps the surface clean. Nonetheless, constant cleaning of the abrasive medium is required for good housekeeping and the prevention (or at least minimizing) of "tracers", those random deeper scratches that can be caused by a build up of debris between the abrasive media and the paint.

Damp sanding is pretty much what the name implies - you are working with far less water than in a traditional wet sanding process. Hence, damp. Generally speaking you want to use abrasive media designed for damp sanding. In the case of Meguiar's new Unigrit Sanding & Finishing Discs, damp sanding is the rule (our Unigrit Sanding Papers, as well as our Unigrit Sanding Blocks, are designed for true wet sanding applications). This is due to the functional characteristics of the abrasive media. Rather than a simple binding of abrasive material to a backer of some sort (waterproof paper, essentially) these discs make use of a slurry that is bonded to the backer. Heavy use of water will reduce the ability of this abrasive to cut, so all that's needed is a small amount of water. Generally speaking, all you need is a spritz or two of water onto the surface to be sanded, and a similar amount sprayed onto the abrasive disc. No soap is added to the water, nor should any sort of quick detailer spray be used.

Meguiar's offers these discs in 3" and 6" sizes in both sanding and finishing formats. What's the difference between these formats? The sanding discs are basically a flat disc, or just the abrasive slurry bonded to a synthetic film backer. The finishing discs bind the slurry to a thin foam interface that essentially cushions the blow and allows the abrasive to conform to even fine contours, including orange peel. This foam interface reduces the cut provided by a given grit, meaning that a 1500 grit sanding disc will cut faster than a 1500 grit finishing disc, even though both utilize the same 1500 grit slurry. In this case, the finishing disc will better follow contours, including orange peel.

But why follow the contours of the orange peel? Aren't you sanding in the first place to get rid of the orange peel? Not necessarily. In the case of a panel that has been damaged in some way where a full repaint isn't needed but sanding will remove the defect, you do not want to fully level the paint on that panel while leaving the factory peel intact on an adjacent panel. Visually they would appear different when finished, and that's not a good thing. So rather than just mowing down the paint to remove the defects and flatten the orange peel, you can sand out the defects and retain the original factory orange peel when using a finishing disc. Subsequent compounding will remove your sanding marks and leave you with a repaired panel that is visually no different from the original.

Of course you could use this process to level and flatten orange peel, if you so desire. This assumes, of course, that you're not working on factory paint with the intention of fully removing the orange peel because, as we all know, that involves the removal of an unsafe amount of clear coat. But in the case of a repaint or custom paint job, using a sanding disc of the appropriate grit can indeed reveal a perfectly flat finish via damp sanding with a sanding disc. Naturally you would then follow with a finer grit of finishing disc, if only to further refine your sanding scratches so that final buffing is done more easily.

Damp sanding has been done via electric D/A by some experienced people but you must use extreme caution if you choose to go this route. We do not actively encourage this process but we also know that sooner or later someone new is going to give it a go. If you decide to go this route, please understand that electricity and water do not mix. The Meguiar's G110v2 is not UL approved for use in or around water (and I don't personally know of a D/A on the market that is) so, even though you aren't flooding with water you are still using water with an electric power tool. A pneumatic D/A tool is a far safer choice.

[Mary S]

Re: How to damp-sand?

Here are some videos from one of the Advanced Classes (I think):

Thanks, Shane, it has been a while since I saw those videos, but it would be a good time to review them.

[Mary S]

Re: How to damp-sand?

Damp sanding vs wet sanding involves not only differing techniques, but different abrasive media as well. ...

Wow, thanks for the very helpful and detailed explanation as usual, Michael. You really should take posts like this and put them in a library for other people's reference.

My goals are not to completely remove factory orange peel but to level it "some." So far I have held off on compounding and polishing my paint because nothing has been done to it yet, and once I do this I plan to take really good care of it so it never needs much else in the way of correction.

I don't plan to do anything more aggressive than regular wet sanding with 3000 grit (by hand), followed by damp sanding with 3000 grit then 4000 grit.

I had seen some posts and pictures on this but no explanations. Mike Phillips just finished a Show Car Garage on this that he posted pictures here a few days ago. He said he is working on getting the video edited and will have it available soon.

Thanks again! Your explanation is very helpful.

Mary

[Michael Stoops]

Re: How to damp-sand?

It should be noted that the series of videos show true wet sanding, not damp sanding. At the time those videos were shot we did not have our sanding and finishing discs on the market. Yep, when things change they can change pretty quickly!!

[Mary S]

Re: How to damp-sand?

It should be noted that the series of videos show true wet sanding, not damp sanding. At the time those videos were shot we did not have our sanding and finishing discs on the market. Yep, when things change they can change pretty quickly!!

Understood!

So Unigrit 3000 disks are only sold as finishing foam-backed disks, not as sanding disks? Searching around, it seems that is what I am finding with all the brands. I think using 3000 hand wet sanding and maybe following with 3000 and 4000 finishing pads on a DA with damp sanding will be the way to go. I will test the process on my test hood.

I already have the wet sanding paper, I guess I could give that a spin on the test hood and see if it does what I am looking for. I already know, 2000 took the orange peel right off with 8 hand strokes, so that is not what I want.

But I'm not in a hurry. I think a prerequisite is a paint thickness gauge when I get to my car.

[Michael Stoops]

Re: How to damp-sand?

But I'm not in a hurry. I think a prerequisite is a paint thickness gauge when I get to my car.

Smart move. Very smart.

[InfiniteDetail]

Re: How to damp-sand?

I've been using the Meg's system for about a month now...currently sanding out a truck with a *ton* of orange peel.

You get the feel for how much water to use pretty quickly. I moisten the sanding disc and lightly mist the panel. I might re-mist the panel during the pass to keep the disc spinning freely.

3000 is very fine, I can't imagine much benefit going higher than that. The rotary with wool pad and M105 easily polishes out the 3000.

Keep in mind that 3000 isn't going to remove orange peel or even moderate scratches. I tend to start with 1500 foam disc and if I need more aggressive combo go to the 1500 film disc. I follow either of those with 3000 foam finishing disc.

Good luck

[paul.segovich]

Re: How to damp-sand?

Just as a follow up, what is the benefit to damp sanding, over wet sanding?
Michael, you explained why one would use lots of water, and some soap, but not as to why one wouldn't want the benefits of doing it that way.
Honestly, I've never heard of damp sanding, before right now, so please excuse my naivety.

[dope92cc]

Re: How to damp-sand?

I've done more damp sanding than wet sanding. It's a production thing. It's all very quick and easy to keep track of, especially on large, flat panels. The reason you don't let water run over the panel is so the paper doesn't hydroplane (this is a big concern with 3000).
Most painters won't tell you this but; removing all orange peel will shorten the life of your clear if too many mils are removed. The factory lays down enough clear to protect.

[Andrew C.]

Re: How to damp-sand?

Just as a follow up, what is the benefit to damp sanding, over wet sanding?
Michael, you explained why one would use lots of water, and some soap, but not as to why one wouldn't want the benefits of doing it that way.
Honestly, I've never heard of damp sanding, before right now, so please excuse my naivety.

Right here:

But why follow the contours of the orange peel? Aren't you sanding in the first place to get rid of the orange peel? Not necessarily. In the case of a panel that has been damaged in some way where a full repaint isn't needed but sanding will remove the defect, you do not want to fully level the paint on that panel while leaving the factory peel intact on an adjacent panel. Visually they would appear different when finished, and that's not a good thing. So rather than just mowing down the paint to remove the defects and flatten the orange peel, you can sand out the defects and retain the original factory orange peel when using a finishing disc. Subsequent compounding will remove your sanding marks and leave you with a repaired panel that is visually no different from the original.

Of course you could use this process to level and flatten orange peel, if you so desire. This assumes, of course, that you're not working on factory paint with the intention of fully removing the orange peel because, as we all know, that involves the removal of an unsafe amount of clear coat. But in the case of a repaint or custom paint job, using a sanding disc of the appropriate grit can indeed reveal a perfectly flat finish via damp sanding with a sanding disc. Naturally you would then follow with a finer grit of finishing disc, if only to further refine your sanding scratches so that final buffing is done more easily.

[Mary S]

Re: How to damp-sand?

Just as a follow up, what is the benefit to damp sanding, over wet sanding?
Michael, you explained why one would use lots of water, and some soap, but not as to why one wouldn't want the benefits of doing it that way.
Honestly, I've never heard of damp sanding, before right now, so please excuse my naivety.

One advantage is that you can use a power tool to damp sand, such as a pneumatic 6" DA. Using the DA will create more even sanding marks and be milder than hand sanding. Mike Pennington in a video of a training class said that using a DA at 2000 grit was more like using a 3000 grit by hand. Plus, of course, it makes the job easier to do. Mr. Stoops cautioned about the use of the electrical DA to damp sand because of the presence of water in the process, and for this reason regular wet sanding with an electrical DA would be out of the question. I would think the misting of the sandpaper would need to be done with the paper off of the polisher.

[Andrew C.]

Re: How to damp-sand?

One advantage is that you can use a power tool to damp sand, such as a pneumatic 6" DA. Using the DA will create more even sanding marks and be milder than hand sanding. Mike Pennington in a video of a training class said that using a DA at 2000 grit was more like using a 3000 grit by hand. Plus, of course, it makes the job easier to do. Mr. Stoops cautioned about the use of the electrical DA to damp sand because of the presence of water in the process, and for this reason regular wet sanding with an electrical DA would be out of the question. I would think the misting of the sandpaper would need to be done with the paper off of the polisher.

Mary, you can also you a pneumatic DA to wet sand as well. Damp Sanding and Wet Sanding can both be used with DA's.

In a nut shell, you would want to damp sand if you are fixing a specific defect in a car that require sanding, but you don't want to wear down the orange peel because the rest of the car and panel has orange peel. Otherwise if you wet sanded the area, there would be a spot that has no orange peel and the rest has orange peel and that just wouldn't look too great.