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I've noticed this, I'm sure all of have. I just don't quite understand why it's such a great technique. For most of my wet sanding, I use mineral spirits. Does anyone have the info on this?

My wet sanding starts at 1000G so I guess it's more like wet polishing. Yes, it does a great job.

My wet sanding starts at 1000G so I guess it's more like wet polishing. Yes, it does a great job.

Should I keep going?

Hmm, mineral spirits.
I need to try that.
Water swells holes, and soap leaves a nasty white scum in the places you can't get to.
Thanks for the tip.

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I believe the slurry has a lot to do with it, similar to creating a slurry with a nagura stone on a waterstone when we sharpen.

I'm not sure what the slurry actually does, which is at the heart of your question. I suspect it washes away the dust and debris and leaves the grit at it's most aggressive, but I'm just speculating.

Interestingly, when I sanded some fully cured Royal-Lac with basic 600 grit dry a few weeks ago, it was literally like sanding a block of chalk. I chalk my hands all the time when I work out, and the cured Royal-Lac behaved exactly the same. I've never had something level so easily.

Water sculpts the entire world.

It's the slurry and it helps flow out the build up too.

I don't know why exactly mineral spirits works so well. For the finishes I've used (nitro, em 6000, and enduro-var) I get the same kind of slick emulsion. Water on em 6000 creates an unexpected stickiness or suction. Hard to describe. Maybe mineral spirits stays "slippery".

I've had the same thought that it's the emulsion or slurry that adds to the polishing effect. It doesn't feel more aggressive to me, rather the opposite. It seems to remove pressure point effects. The paper is evenly drawn to the surface wherever my fingers are. Definitely some kind of physical process going on.

Btw, maybe it's similar to pebbles in a stream? Rolling rocks in a tumbler without liquid does not result in the same finish as with liquid.

Agreed Mike, I use light mineral oil (lemon oil) on EM6000 and it works 100% better than water for the reasons you describe...

As Dan says, water swells holes. Wouldn't any liquid do that..including mineral spirits? Lately I have been dry sanding around holes to avoid the swelling problem but the paper loads up very quickly.

Michael

What holes are you all talking about? If you have sealed the surface, there are no holes. I'm confused on this

Machine head holes and in the case of my harp guitars, super treble zither pin holes. I drill these holes prior to finishing for various reasons.

Michael

Another benefit that hasn't been mentioned yet is that it prevents the paper from loading.

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I don't believe so. Wood will absorb water which causes it to swell or raise the grain. It won't absorb oil, at least not in the same sense like water.

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Wet sanding is good, but dry sanding works well too and has some other benefits (such as being able to see your progress as you work). But you have to use a good, non-loading abrasive to make this work correctly.

I wet sand water-based finishes with mineral spirits. On nitro or Royal Lac I use water with just a drop of dish soap. Both work well. I used to dry sand but now for initial leveling I wet sand with 800 and after the final finish coats I level by wet sanding with 1000. This is just what I'm doing now, may change next month The only thing that really matters is that you find a process, wet or dry, that works for you.

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Steve Smith
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"Lubrication" is often given as the reason for using water or other liquid, but it never made any sense to me. The amount of friction with dry sanding doesn't seem to be a problem, and anyway the liquid doesn't seem to reduce it, at least when I sand. Keeping the paper from loading up has been the main benefit I noticed, but I can see that the slurry and the vacuum effect evening out the pressure are other benefits, I can see.

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Tim Allen
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Sorry, I was talking about solid body guitars.
I drill all holes prior to finishing to minimize cracks and marring.
I tried the mineral sprits yesterday, works like a charm!

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Wet sanding also keeps the sanding dust down.

Alex

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Wet sanding with oil creates a slurry that cuts the wood into ultra fine particles and leaves a glass like surface. Some folks do this using pumice and shellac to pore fill prior to a french polish.

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I suspect it's a combo of the above -- it keeps the paper from loading so it can cut better, it presents a more uniform medium to the surface (spot-loaded paper creates problems), and the slurry is an active abrasive of smaller particles to even out the heavier scratches. And as Alex said, less dust!

If the surface material is hydrophilic, water will swell it.

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David Malicky

I think Bob and David's explanation fits my experience. I've also noticed that you can experience more aggressive sanding with wet sanding. Probably due to the non-loaded aspect of the process.

Wet sanding a finish keeps the paper from loading. What little abrasive is lost from the paper is suspended in the lubricating liquid, so does not aid or detract from the paper's cutting action. Like a dry, pere-lubricated paper, a properly prepared piece of wet/dry will resist loading for as long as the lubricant is present. Renewing the lubricant frequently removes dead finish and other contaminates, so aids cutting action. The slurry is largely composed of lubricating liquid (water, mineral spirits) and particles of finish, so there is little or no abrasive action from the slurry itself.

My mentor keeps a couple of tubs of different wet/dry grits handy in water/dish detergent (the detergent kills surface tension and keeps the dead finish suspended), and any new paper is soaked for at least 24 hours before use. Some of the 3M and good Japanese papers have been in the tubs for 2-3 years and still cut like new. Paper is only tossed when the backing loses it's waterproof properties and degrades.

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Wet sanding helps to remove, or keep mobile, particles abraded from the surface so that they themselves do not become abrasive.
The same effect can be achieved with air extraction through perforated abrasive papers as in the polishing of Corian