Wet sanding

[Doomwolf]

I'm doing a finishing course at the local college, and the instructor has had us do a lot of wet sanding. I'm curious - what's the highest grit you typically wet-sand your top coat to?

I did my story board to 1500, but a couple of students took it to 8000 and then used a buffing wheel. 

[TerryMcK]

Doom when doing guitars I like to wet sand to around 4000 using water with a little detergent. A high gloss finish always looks great with such high grits. It's hard work and you have to watch for burn through at the edges but the results are spectacular.

When doing furniture I would rarely go above 800 dry as I personally prefer a satin finish. Only lightly hitting it with 2000 to 4000 well after curing is complete primarily to remove dust nibs and make it feel ultra silky.

[wdwerker]

For high end finishes like a guitar maybe wet sand, for a car or high end piece of furniture sure, but for most woodwork its a bit too much. You can't wet sand and make any money when finishing unless it's a really high end product.

[TerryMcK]

Yes if I'm completely honest I can't remember the last time I wet sanded furniture. I do try to get it straight off the gun and as I previously said hit it with 2000 to 4000 very lightly or a brown paper bag.

[Tom King]

0000 steel wool and Pledge

[Jim DaddyO]

I only went to 600 on my  guitar, but I was leveling shellac between rounds of french polishing.   I would go much higher if I was working with laquer.  Depending on the intended use for the piece of course.

[rodger.]

0000 steel wool and paste wax for oil based topcotes and water with a pinch of dishsoap with a white scotchbrite pad for water based topcoat.

[Rick Mosher]

I only wet sand for buffed, high gloss finishes. Then 1500 scratches will buff out just fine but I usually take it to 2500 or 3000 just to cut down on the buffing time. For rubbing out a finish (not high gloss) I use Abralon pads on a DA sander with a spritz of water and match the grit to the sheen I am after. 1000 is an almost flat finish 5-10% sheen, 2000 is around a 25% sheen , 4000 is 50-65% sheen.

[AceHoleInOne]

I have a question for you? Just curious...is this a woodworking "finishing" class? Wondering why the focus on "wet-sanding"  

 

-Ace-

[dwacker]

We were taught with pumice, rottenstone with paraffin oil although really never found the need in the real world.

[Freddie]

I use the 3m perfectit system now and go to 5000 on my sprayed urethane finishes that warrant it. The best scenario is a finish with no dust and no peel that doesn't need to be cut and polished. Think about it, why would you want to sand off all that clear you just applied? The top coat is also stronger when it hasn't been cut by abrasives, but every project will dictate whether or not it is needed. 

[Doomwolf]

To clarify, most of the sanding in the course was surface prep before we applied stain*. However, wet sanding was something I'd heard the existence of, but that was about it, and I was surprised at home it could be used to increase the shine of the piece. 

 

The wet sanding as shown and practiced was 2-3 passes with light hand pressure, rub out the surface**, and then apply more topcoat. I like the visual and tactile effect that it gave, and will probably use some version of this method on my next table top, or similar surface that people are likely to feel; his first rule he gave us after demoing technique was that you didn't necessarily need (or want!) to do it all over the entire piece. 

FWIW, the guy teaching does woodwork himself, but by trade is a professional finisher.

*And to go further into detail, limitations of time, money, and space mean that a lot of the course is theory/explanation of different finishes and methods of application. It's still highly enjoyable.

**Is this the correct use of the term?

[AceHoleInOne]

Cool thanks for the reply...so Im assuming you actually used water as a lubricant to sand a freshly applied finish?

 

To speed the re-coat time of some finishes such as lacquer or shellac, you can wet sand a mid-coat with 600 paper to knock down the high spots. The reason we wet-sand is because the finish is still very young, but hard enough to wet sand. If we were to dry sand the paper would clog and pill-up.

 

-Ace- 

[Trip]

I'm a bit thick... Can we clarify: is this pole about wet sanding? about the finest grit abrasive regardless of technique? or some combo of the two?

 

==>We were taught with pumice, rottenstone with paraffin oil although really never found the need in the real world.

PB's spot on... This was the 'standard' schedule for rubbing-out hard film finishes (i.e. shellac and lacquer) for many years -- decades, in fact... I was taught exactly the same thing... The fist step in the schedule was wet sanding with 400/600 to level the surface.

 

The technique was supplanted as techniques and products from the auto finishing industry were adopted by woodworkers... The initial leveling step with 400/600 wet still remains in many schedules. After leveling, some schedules continue with successive wet grits. However, many finishers switch to automotive finishing products like Abralon, auto glaze, etc.

 

On a high-gloss piano lacquer finish, I typically top-out at 6000/8000 auto glaze.

[AceHoleInOne]

I guess it depends on how you were taught terminology. I think of it in terms of:

 

Wet-sanding = wet-sanding between the coats typically 400/600 grit of young finishes to speed re-coats

 

Rubbing out = wet or dry sanding to gain a sheen of fully cured finish, polishing with high grits typically starting at 1000 (satin) and up to 4000 (gloss). 

 

 

-Ace-

[Rick Mosher]

I am not a fan of wet sanding between coats of finish.Too fine sanding can cause adhesion issues especially with oxidizing type finishes like varnish and polyurethane which depend on mechanical bonding (sanding scratches) for adhesion. It will work on finishes like lacquer and shellac which chemically re-wet the surface and bond with the next coat but while wet it is impossible to see the shiny spots (low spots) that still need to be addressed until all the water has evaporated. also water and wood or MDF don't get along well and can penetrate into joints and cause swelling. (Especially in tables between leaves) I dry sand between coats and will go as high as 600- 800 grit but that is extremely rare. 400 grit between coats will not telegraph scratches if a proper film thickness is applied. Only if I am rubbing out or polishing to a high gloss do I wet sand and then only after all coats have been applied and properly cured.

[Freddie]

Good point Rick about waiting for the finish to fully cure before wet sanding and polishing. Any finish applied has specific guidelines to follow; flash time, sand time, cure time. This becomes more important as you start layering different types of finishes on and essentially trapping the previous layer of finish. Especially if you are working with solvents, you can trap unevaporated solvents beneath a fresh coat. As for wet sanding and polishing, if you do not follow appropriate cure times, your sheen will die back, and you run the risk of having sanding scratches telegraph through the finish as it final cures. I am working in a commercial auto body shop again, and we are using a PPG Refinish system. In the spray booth, after the final coat of clear is applied, we can run a short bake cycle for 10 minutes at 140f and the car is ready and sent to detail. These products we use are specifically made for a high volume commercial setting. 

 

When I finish projects in my garage shop with a wipe on varnish, there is always the damn dust that likes to fall in the wet finish. My lacquered and urethane finishes are done in a down draft spray booth, and I am fortunate enough to say that none of those jobs have ever required to be wet sanded or polished. 

[Trip]

==>sanding between the coats typically 400/600

You use 600/800 for inter-coat sanding? I've never heard of that. I typically go 320 and rairly, if ever, wet. What finishes benefit from 400/600?

 

The first time I go wet is the leveling-step of the rubbing-out schedule. I use 400/600 to level.... And now that Abralon is available down to 320 (I've just ordered a pack of 320, 400, 600, and 800 to give it a whirl), I'll probably phase-out all wet sanding all together...

[AceHoleInOne]

400 =  If I have thick build of a solvent lacquer or solvent shellac. I will hit it with a wet 400 grit paper (freshly applied and dry enough to wet sand) for a rough or orange peel surface. Sometime if you spray to heavy and want a fast build, say a table-top, they can orange peel on you. 

 

600 = If I have a thin build of solvent lacquer or solvent shellac I will hit it with a wet 600 grit paper (freshly applied and dry enough to wet sand) to knock down nibs and smooth a surface that doesn't require a lot of sanding.

 

Water-based topcoat is a whole different story. Mid-coat sanding's are dry and with 320 paper same goes with oil based topcoats .

 

Water-based topcoat rubbing of fully cured surface. Yes will use a little water and dish soap if the finish manufacture approves. I think Target Coating recommends rubbing without a lubricant.

 

Word of caution using Albralon or those types of pads. Just make sure your pads are fresh. Frugal Woodworkers tend to use sanding pads or sand paper that is worn-out. Using a pad that is worn out (say a 1000 grit pad for a satin sheen) will actually buff your surface to a higher sheen. So be careful.  

 

-Ace- 

[Trip]

So you inter-coat wet sand 400/600 lacquer? Interesting...

 

For solvent-based nitrocellulose lacquer (if I'm not in a hurry): shoot a tac coat, then a wet coat, wait overnight & scuff w/320, shoot a wet coat wait an hour or three & scuff w/320, then a light dust coat. Wait a couple of days and knock-down any nibs. Done. I aim for 3-4mil total. If I'm in a hurry, a fine coat, then a wet coat -- wait an hour or so, scuff w/320 then a fine coat, done...

 

I do change things for pre/post cat, retarder, accelerator, temp, humidity, temp, etc. When conditions get funky, I just kind of wing it... I've gotten-away with a lot of funky stuff, which is a credit to the chemists who invented the stuff - it's way more forgiving then one might think...

 

I agree w/ your points on Abralon... I've been using the 1K-4K since it was first introduced for rubbing-out, then switch to auto glaze. And your right about over using it -- it's not exactly cheap, so the temptation is there. I also found that I get much better results/lifespan when I dial the RPMs back signifigantly. This will be my first use of low-grit Abralon, so should be interesting.

[dwacker]

We spray solvent lacquer exclusively. Its nearly impossible to see how the final finish is going to lay down until about hour 6  unless your running a hot box and in cooler temps hour 18. There is way to much shrinkage to jump the gun and sand before the finish has dried. That being said we only sand the sealer never between coats unless a bug or something happens to land on the finish.

[AceHoleInOne]

It's not jumping the gun, I'ts ok to mid-coat sand a solvent lacquer or solvent shellac before it has fully cured. You don't have to wait till the paper powders. If your paper is clogging, wet-sand. Dry the finish and shoot another coat.

 

Remember one coat will dissolve the coat underneath and open it up to become one and dry down as one.  Not implying to wet-sand your final coat that hasn't fully cured.  

 

The goal here is to sand the surface should you shoot some total crap like runs,sags maybe some orange peel. And get another coat to the piece to build a finish, allowing you enough finish on the piece to finish sand then shoot a nice full wet-coat and call it done.

 

-Ace- 

[bob493]

This poll is useless without knowing what type of finish you're going to be using; AS WELL as the type of buffers and compounds you have available. 

 

Assuming an arbor buffer and medium and fine cut polishers ->

 

For nitrocellulose lacquers, you only need to go up to 1000 before buffing. Nitro heats up quickly, is relatively soft, and therefore incredibly easy to buff. Burn throughs are easily fixed with drop fills and more sanding too. Gets mirror shine without swirls (with proper technique) very easily. Unfortunately nitro isnt the most durable of finishes...

 

For catalyzed finishes, the buffing process is much more straight forward but much more time consuming. when I used 2k urethanes, I always go to 2000, and start with a medium cut compound. Going beyond 2000 isn't really required for anything, but if you only have a fine cut finishing compound, it may be required to not have "swirls". I always have to shake my head when I see people use micro mesh THEN jump to a buffer. Its quite pointless and simply a waste of money. The end product does not look any better (I've tried it!).

 

For oil finishes -> 0000 steel wool and beeswax buffed on

 

 

Polyurethane, enamels, and latex  lacquers should not be used on a guitar for any reason (yes I'm aware some use it with success, but it's not "worth it" for one reason or the other) 

 

Polyurethane -> Doesn't get the "wet glass" look, and is ridiculously difficult to buff without melting. For the wipe on poly's; its replicating an oil finish... so why not use an oil finish? 

Enamel -> .... just a horrible paint that doesn't need to exist any more. It can "look good", but the question is "for how long" as its not very durable. Better off just using nitro. 

latex -> barring the waterborne "safety" paints, latex's just don't shine that well. They always have a slight haze, and it's really detrimental to a guitars finish.