Re-finishing old bowl with unknown gummy finish

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08-09-2019, 6:48 PM
Robert Marshall

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Re-finishing old bowl with unknown gummy finish
A friend of mine asked me to consider re-finishing an old turned bowl, that she would like to restore to use. Which would be massive green salads for church pot-luck suppers, mostly. I'm looking for guidance as to how to do this.

The bowl is about 25" in diameter and 9" tall; huge! Others at my woodturning club, Brasstown Woodturners Guild, think it might be chestnut. I have no opinion. I think it's probably a nice bowl, once you get past it's existing finish.

The existing finish on the bowl is what I would describe as 'gummy.' You can scrape a fingernail across it, and it gums up your fingernails. My guess is some sort of oil, perhaps also (or else) a wax. Press a fingertip to it, and you would say it is a bit sticky. But underneath that finish, there's some solid wood (chestnut?), and it's thick enough that removing a layer of finish, along with some wood, won't be a problem, structurally.

This (below) will give you an idea of the existing finish, and the underlying wood once the finish is removed.

Attachment 414121

Close-up of sanded area (test):
Attachment 414122

I'm considering 3 different approaches to removing the existing finish, prior to revealing the underlying wood and sanding out the implement scratches, and re-finishing the bowl. (Some previous owner paid no attention to the 'use wooden implements' advice, so the bottom of the bowl has some visible scratching that needs to be sanded out.)

Here are the 3 approaches, for which I'm soliciting comments and suggestions. Of course, if you think of other approaches, let me know:
1. Forget about how much sandpaper costs, just do it. Throw away lots of gummed up rough grit paper in the early stages, and then get on with the finer grits, until it's done. This is something I know how to do, and from the photo above, you can see that I've given it a test. I used 3" hook-and-loop disks on a drill, but I'm wondering if a random-orbit sander (5" disc) might be better, at least initially.
2. Use some sort of scraper to physically remove the top layer of gummy finish, then go to sandpaper. Save some money on sandpaper (but spend it on scrapers), and learn something new (to me, at least). If you think this is the way to go, give me some tips, please!
3. Go 'Chemical Ali' on it, and use something liquid to remove the old finish. Like what, and how?
I appreciate your thoughts on this!

Robert
08-09-2019, 9:15 PM
Chris A Lawrence

I cant look at the pics but if it were me i would start with good quality mineral spirits to see how much i could get off. Then go at it with sanding discs. Get a 5 inch interface pad from here to use on your ROS to help navigate the curves. His discs are great to they last a long time.
08-09-2019, 10:01 PM
Paul Williams

In my opinion the chemical stripper would allow you to wipe off the sticky stuff, but would also allow it to sink futher into the wood. If I was in a hurry I might still try chemicals. I purchased a set of scrapers that included several curved scrappers. They were cheap. I think the best would be to scrape out all of the sticky stuff. You shouldn't even need a burr on the scraper to do that. Then sand. In the event you decide to only sand, I agree with Chris that getting some of of the sticky stuff out with mineral spirits would be a good start.
08-10-2019, 7:29 AM
John K Jordan

3 Attachment(s)
Quote:
Originally Posted by Robert Marshall

Forget about how much sandpaper costs, just do it. Throw away lots of gummed up rough grit paper in the early stages, and then get on with the finer grits, until it's done. This is something I know how to do, and from the photo above, you can see that I've given it a test. I used 3" hook-and-loop disks on a drill, but I'm wondering if a random-orbit sander (5" disc) might be better, at least initially.
Use some sort of scraper to physically remove the top layer of gummy finish, then go to sandpaper. Save some money on sandpaper (but spend it on scrapers), and learn something new (to me, at least). If you think this is the way to go, give me some tips, please!
Go 'Chemical Ali' on it, and use something liquid to remove the old finish. Like what, and how?
Starting with sandpaper would be my last choice since it would gum up quickly.

A solvent that dissolves what's on the surface might pull some of it into the wood.

I would use hand scrapers and remove all or as much of the gummy junk as possible, before trying any solvent. Hand scraping down to the bare wood can also remove most scratches, requiring only fine sanding. After scraping for smoothing new wood I can often start with 400 grit or finer paper.

Scrapers are cheap. Scrapers with the right curvature are hard to find but easy to make. I buy rectangular card scrapers and grind curves as needed, using a 1" belt sander instead of a bench grinder to prevent overheating. A scraper must then be prepared properly to work effectively. File and hone the curved edges to 90-deg then turn a burr on both sides with a burnisher. Dec 18 FWW has an article on preparing and using curved scrapers.

These are some scrapers I've made and bought. I keep a variety of curved scrapers since I use them instead of coarse sanding and power sanding.

Attachment 414132 Attachment 414133

You can get an incredible surface on new wood.

Attachment 414134

I think removing the soft, gummy "finish" would be easy with scrapers. Scrape, sand a bit, wipe with solvent, then repeat. Possibly wet sand with the solvent. When removing unknown stuff I try mineral spirits, alcohol, naphtha, and acetone. If the gummy finish is from some oil which hasn't dried/set up, wiping with oil can also help.

JKJ
08-10-2019, 8:12 AM
Alex Zeller

If you go the chemical route I would be very leery of using anything that wasn't labeled as food safe. The last thing you would want is to have something soak into the wood that could harm someone. Maybe a citrus or alcohol solvent might work. Are you sure it's a finish on the bowl and not something like years of dressing residue from the salads? Maybe just warm water and dish soap might be a good place to start.
08-10-2019, 9:14 AM
John K Jordan

Quote:

Originally Posted by Alex Zeller

If you go the chemical route I would be very leery of using anything that wasn't labeled as food safe. The last thing you would want is to have something soak into the wood that could harm someone. Maybe a citrus or alcohol solvent might work. Are you sure it's a finish on the bowl and not something like years of dressing residue from the salads? Maybe just warm water and dish soap might be a good place to start.

Solvents like alcohol, naphtha, and acetone evaporate and don't leave any residue.
08-10-2019, 11:19 AM
Reed Gray

It was a labor of love..... A bowl that had a similar gummy surface to it. Water as hot as you can stand it, Dawn dish soap, one of those heavy duty metal scrub pads, and lots of elbow grease. You can get it down to wood, but the gummy stuff still comes back to the surface, and it may need a couple of treatments. Some lemon juice and salt can help too.

robo hippy
08-11-2019, 3:56 PM
Robert Marshall

2 Attachment(s)

A bit further along in this process . . .

I've taken the advice offered by Reed Gray, and attacked the gummy finish with hot water, suds, and a metal scouring pad, and it seemed to get almost all of it up. I've got a set of cabinet scrapers coming from Amazon, and I'll probably do that next, then final sanding.

In the meantime, there's another existing problem that I didn't bring up initially, because I was trying to focus on one problem at a time.

There is a crack that goes from about 2" below the rim, down to near the bottom flat area of the bowl. The crack goes from the inside surface of the bowl, to the outside. Something has been done to it before, but I think it needs to be re-worked, or else it will trap food and get foul.

Here are 2 photos: the first shows a closeup of the crack, with a penny placed there for scale. The crack is about the same width as the penny's thickness, which I understand is about 0.05", a bit less than 1/16". The second picture provides the location of the crack, relative to the rest of the bowl.

Attachment 414203

Attachment 414204

My thinking is that I should use some sort of carving tool, perhaps a Dremel, and "open up" the crack somewhat on the inside surface of the bowl. Then, fill with something, perhaps epoxy mixed with coffee grounds, or epoxy mixed with sanding dust from this bowl.

I'm asking for comments and suggestions for how to deal with the crack.

Thanks!
08-13-2019, 7:38 AM
tom lucas

The crack is part of its character. But if it needs to be stabilized, I'd clean it out from both sides with an awl or knife, or with a nylon wheel brush on a dremel tool, or maybe just a toothbrush. A small veining chisel would also open it up a bit. You could also put a bow tie patch in it (I wouldn't though). Then fill with CA. The trick will be controlling the spread of the CA filler so it doesn't stain the rest.
08-13-2019, 11:02 AM
Dave Mount

50/50 on CA v epoxy. Epoxy is my preference for a crack with much of a gap, but CA is great for wicking into tight cracks to keep them from moving further. I would think you'd be looking to hide this crack rather than emphasize it, so I would use wood flour as the filler rather than coffee. Sanding dust is fine too, I'm just usually too impatient to collect it. Buy a pound of wood flour and it will last you for years. I use medium brown and reddish brown Transtint to add color if I need to, though from the pics it looks like no colorant would be needed. Not sure what's in the crack now, if that's old finish/food residue or dust from the sanding you've already done. If the latter, you can just wick CA on top of it; if you're using epoxy, I would clean the crack and mix your wood dust filler into the epoxy.

To help avoid unwanted spread of the CA or expoxy, mask the crack with blue tape. CA really wicks, so you'll want to seal the edges of the tape down tightly if you choose CA. The crack looks straight enough to mask from both sides, but you can also mask by putting blue tape over the crack, then rubbing the tape until the crack telegraphs through -- this will allow you to take a marking knife, razor blade, or other sharp tool and cut away the tape right along both sides of the crack. Hand cutting the edges tends to give the mask a little more of an organic look (compared to straight lines) if you do get a little coloration difference.

I haven't seen a lot of chestnut, but from the pics I'm not convinced that's what it is. The scalloped end grain is a characteristic often present in butternut.

Best,

Dave
08-13-2019, 12:32 PM
tom lucas

Some professionals say that vinyl sealer on the surface will prevent the CA from staining. They suggest letting the sealer dry for at least a full day before filling. I haven't tried this, but plan to next time I need to control the staining. I've read that this also works with dyes other coloring techniques.
08-13-2019, 7:28 PM
John K Jordan

1 Attachment(s)

Quote:

Originally Posted by tom lucas

Some professionals say that vinyl sealer on the surface will prevent the CA from staining. They suggest letting the sealer dry for at least a full day before filling. I haven't tried this, but plan to next time I need to control the staining. I've read that this also works with dyes other coloring techniques.

I don't have much trouble with staining. I always use an extremely fine capillary tip to pinpoint the application area and limit the amount of CA. I apply CA to the area then IMMEDIATELY wipe the surface with the figure and away from the area to feather it out. If the wood has any variability this usually distributes any staining so it is not obvious. If the CA is applied and allowed to soak in without wiping there will in fact be a distinct line with some woods. When I do this with new wood, applying and wet sanding "danish" oil into the surface usually makes any marking go away on most wood.

Another thing I like to do with small voids and cracks is wet sand with thin CA glue - I learned this from John Lucas. Apply thin CA to a small piece of fairly coarse sandpaper (say 220 or 180) then sand with the grain (or more often, with the figure). This fills in the surface and usually makes the crack or void invisible. It is easy to get the sandpaper stuck to your fingers!

BTW, these are the capillary tips I almost always use when applying CA to woodturnings. They slide over the applicator tip of most CA bottles. I'd hate to work without them.
https://www.amazon.com/gp/product/B000H7H4NW
Attachment 414355

I'm concerned that CA might not work well with an existing crack in the bowl in question. Unknown substances forced into the crack may cause the CA to not stick to the wood. In addition, if the crack was formed by wood movement it might simply open up again with use. Unless the crack is large and threatening the strength of the bowl I might just leave it. Or fill it with beeswax or something after finishing.

JKJ