wet sanding for good finish

wet sanding for good finish · 07-28-2009, 10:28 AM

Hello All;

Some years ago I read an article in Wood magazine about how to wet sand between coats of any brush on finish. I've used the method quite sucessfully a few times, and I wonder if anyone else has used it. Also, I have a question about the final step. At the time, the magazine stated that this process was borrowed from auto body shop techniques.

Steps are:

1) after 1st coat is dry, put water with "Dawn" dishwashing liquid in shallow container, and use 500 grit wet/dry sandpaper on sanding block in rotary motion. Rinse off with damp sponge with clean water. Dry off with clean rag. The purpose of the Dawn is to cut down on the friction between the wet/dry sandpaper and the work piece.

2) Do subsequent coats the same way as #1

3) Final coat, same process, but start with 1500 grit and work up to 2000 grit wet/dry.

4) final polish - use Turtle wax or similar car wax, and buff with cotton pad either by hand or with power buffer.

I think this works great for a brush on finish, such as polyurethane. I've also used it on water based varnish.

My question is, though, I tried the final step with the Turtle wax a couple of times, and I wonder if there might be another wax that might be better to use.

Any thoughts? Has anyone else tried this method? It seems to me that the article is in the archives of the Wood magazine web page, or at least used to be.

Thanks,

John

steelwheel1999 · 07-28-2009, 01:01 PM

I hav ent tried it as of yet but I am very interested in this process. Thanks for sharing

Thanks Mark

SteveHall · 07-28-2009, 03:04 PM

I have been wetsanding water-based polyacrylic (Minwax Polycrylic) with great results, using Johnson's Paste Wax for the final:

1. De-whisker wood by lightly wetting and after 5 minutes sanding (120 grit).
2. Apply first coat. Dries in an hour or two.
3. Sand with 220 (do not use steel wool).
4. Clean with damp cloth.
5. Apply second coat.
6. Lightly sand with 320-400 (do not use steel wool).
7. Clean with damp cloth.
8. Apply third coat.
9. Lightly sand with 600-800 grit. Use higher if desired.
10. Clean with damp cloth.
11. Apply two coats of paste wax (Johnson's or similar). Buff after each coat.

ErnieM · 07-28-2009, 04:02 PM

John,

Your process is quite similar to the way I've been finishing harpsichords for years. Although I'm working with a paint finish instead of clear, there is really very little difference in the two. I start with a courser grit (usually 320, sometimes 220). It depends on how much of the pore you want to eliminate (I want to eliminate all of it), and how fast you want to get it done. I've never used water based finishes and I'm curious - do you wet sand it with water?

At any rate, if I'm going for a shiny hi-gloss finish (which I almost never do), I would try McGuire's Mirror Glaze #7. It's available at most auto parts outlets and does a great job. In addition, it's paintable so its use doesn't stop you from adding another coat of finish if you feel you need it.

Here's a link to my post on finishing a harpsichord - maybe you'll find something of use there.

Ernie

Gregory Paolini · 07-29-2009, 08:14 AM

Well, I do wet sand, but I actually wet sand the finish. I make my own wipe on finish, and flood it on, then wipe it off after a few minutes. After the first coat dries, I use a red scotch brite pad, and flood a second coat of finish on, wipeing the finish with the grain, using the red scotch brite - This applies finish, and sands at the same time. Then I'll wipe off the excess, and let it dry. I'll repeat this process untill I get the build I'm looking for, for the specific project - It could be 2 coats, it could be a dozen.... Usually around 4 though...

Ragtimeman · 08-01-2009, 08:32 AM

Thank you all for the fine replies;

I have some comments, and an additional question, and problems with a current project perhaps you can help me with.

1) Ernie - It's been a few years (maybe 3) that I tried the wet sanding process with a water based varnish, but as I recall it worked fine. And, according to Steve on this post, he has good success with it too. As long as it dries good before the wet sanding, there should be no problem, but perhaps Steve will have a comment about that. I'm going to try the McGuire's Mirror glaze #7 that you recommend too; thanks for that tip.

2) Gregory - Your process sounds very interesting. What, though, do you mean, exactly, when you say "flood" on the finish? Pour it on? And how do you "make your own finish"? That may be proprietary information though, and if so, I would certainly understand and respect that.

3) Steve - I'm going to try the Johnson's Paste Wax too. It seems you start with courser wet sandpaper than I'm used to using, and I'll bet if I try that it would help in the overall process. Thanks for that.

4) Mark - I found a copy of the article in the "Wood" magazine archives on their website for a couple of bucks. But years ago I printed out a copy for myself, before they were charging for it. If you send me your address, I can mail you a copy if you like.

5) My current project and my problems with it -

I'm refinishing a dining room table top for my daughter. In my garage shop, I have windows on both sides. I usually open both windows, and place an exhaust fan in the window in the side that I do the finishing on. That way, the fumes from the varnish or solvent do not build up. I generally leave them open for a couple of hours after brushing on a coat. I'm using Minwax Polyacrylic high gloss quick drying varnish.

The humidity is very high right now, and according the Greenville (SC) newspaper this morning, it is around 94%, and I assume that is an average for the day.

After a coat of varnish dries, and I wet sand, even with as fine as 1500 grit, I get a "milky" look to the varnish, in the higher spots moreso, I guess. Great smooth finish, but this milky look.

I've just tried more coats to see if I can eliminate this problem, and I just did coat #8 this morning. I tried something different this time, though. I closed the window on the opposite side of the shop so that I won't pull in the outside air, and bring it over the table top. I was thinking that I might be bringing in the moisture from the air. I didn't think about doing this until after I had put this varnish coat on, so maybe, if it helps at all, it was too late.

So, should I be doing this process with just the one window open? The one with the fan in it to dissapate the fumes? Is the milky look a problem with humidity?

Any thoughts?

Thanks in advance - John

SteveHall · 08-01-2009, 09:15 AM

John, I have no problem wet sanding my water-based finish. As you said, as long as it has dried (cured) there is no difference between water-based and others.

As for opening the windows, I do not find any issue with fumes with water-based Minwax Polycrylic. Although I still usually open the garage door, they are so minor that I could imagine myself doing minor finishing on a small project without ventilation. (Imagine the middle of the night in dead winter.) Not that I would actually recommend anyone do this--for context my shop is nearly 500 square feet x 12' high, about 6,000 cubic feet of volume for dissipation.

Regarding grit, I'm convinced most people start too high and finish too high to make finishing efficient. There's no point in sanding wood past 180 if it will have a finish. Likewise, I've not found any appreciable improvement in sanding finish past 800 if you intend to wax it. Of course, you can always start higher and finish with 5000 (there are plenty of recommenders for doing so

) but the x4 energy expended has a negligible effect on the final piece in my estimation.

Bob Flexner's book on finishing, Understanding Wood Finishing, Revised 2005, was the breakthrough for me. He has a lot of good explanation on finishing chemistry but also a lot of clear discussion on things like wet sanding, grits, sheen, setup, product applications, etc.

Gregory Paolini · 08-01-2009, 09:45 AM

John,

When I say flood the finish, I just mean put a bunch of finish on the wood... I usually use either a foam brush, or one of those cheap china bristle brushes, and start liberally applying finish. I'm not concerned about runs, or drips or anything, I just want to get a bunch of finish on the wood, as quick as possible, so I can start wet sanding it.

Hmm, My own finish... I could tell you, but then I'd have to... Just kidding.

I use a bunch of different home made finishes... here's a link to one of them

http://www.gregorypaolini.com/Woodwo..._on_finish.htm

Another I use is just diluted oil base poly with some linseed oil added. Mix the Poly with linseed oil in a 2:1 ratio - Then cut that with paint thinner 1:1. It takes more coats to build, but on woods like cherry, and maple, the feel is incredible!

Ragtimeman · 08-02-2009, 06:57 AM

Thank you again, gentlemen.

I looked for the book you mentioned, Steve, "Understanding Wood Finishing" by Bob Flexner, while at Barnes and Noble yesterday. While they didn't have it, they did have one called "Foolproof Wood Finishing" by Teri Masaschi. In his chapters on topcoating, he recommends a cure time after the final coat of a minimum of 200 hours with polyurethane like I'm using. Interestingly, HE also recommends the Flexner book in his book. He also says to do the final rubdown with rottenstone and mineral oil or another type of oil. I think that's what I'm going to try next; 200 hours curing, with a rub down with rottenstone and oil. Also, I'll be ordering the Flexner book.

After thinking about it, most of the finishes I've used this method on in the past has been a light colored finish, either golden oak or birch. This time around, I'm using it on dark Walnut. Maybe I just didn't see the milkyness before due to the color.

On a future project, I'm going to try your wipe on method, Gregory. Thanks for the link to that. Sounds like a lot less curing time.

For this project, though, 200 hours is 8 days +, so I'll post how it all turns out in a couple of weeks. In the meantime, I have the legs to strip and stain, so plenty to do.

John

PChristy · 08-02-2009, 09:41 AM

I have done some wet sanding on the lathe when I have turned green wood with great results - but have not tried it yet on dry wood - I will need to get some finer grit paper - all I have is up to 400

steelwheel1999 · 08-02-2009, 10:47 AM

Phillip I have looked for your thread cause I have a piece on the lathe right now that I thought would be a prime target for wet sanding but I caint find the thread(the piece is persimmion). I dont remember where you started.

Thanks Mark

PChristy · 08-02-2009, 12:08 PM

Mark if your turning is already somewhat smooth - start with 220wet/dry paper and work your way up from there - use a couple of wet paper towels and hold them on the piece while sanding with the other - wetting the towels often - this will keep the heat down from the sanding - be sure to wipe down the piece after each sanding before starting the next step

steelwheel1999 · 08-02-2009, 12:43 PM

I got a lot of rough patches and I have started with 80g dry for now almost ready to move up. Question do you wet sand Inside?

PChristy · 08-02-2009, 02:25 PM

Originally Posted by steelwheel1999

I got a lot of rough patches and I have started with 80g dry for now almost ready to move up. Question do you wet sand Inside?

Yes

Ragtimeman · 08-10-2009, 01:47 PM

Steve;

I received my copy of "Understanding Wood Finishing", and am still in the early part of the book, but I want you to know that I've already learned a lot from it. I can see where it is a great book, and I highly recommend it to anyone. I'm looking forward to reading the rest of it.

Thanks for the tip!

John

Originally Posted by SteveHall

John, I have no problem wet sanding my water-based finish. As you said, as long as it has dried (cured) there is no difference between water-based and others.

As for opening the windows, I do not find any issue with fumes with water-based Minwax Polycrylic. Although I still usually open the garage door, they are so minor that I could imagine myself doing minor finishing on a small project without ventilation. (Imagine the middle of the night in dead winter.) Not that I would actually recommend anyone do this--for context my shop is nearly 500 square feet x 12' high, about 6,000 cubic feet of volume for dissipation.

Regarding grit, I'm convinced most people start too high and finish too high to make finishing efficient. There's no point in sanding wood past 180 if it will have a finish. Likewise, I've not found any appreciable improvement in sanding finish past 800 if you intend to wax it. Of course, you can always start higher and finish with 5000 (there are plenty of recommenders for doing so ) but the x4 energy expended has a negligible effect on the final piece in my estimation.

Bob Flexner's book on finishing, Understanding Wood Finishing, Revised 2005, was the breakthrough for me. He has a lot of good explanation on finishing chemistry but also a lot of clear discussion on things like wet sanding, grits, sheen, setup, product applications, etc.