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finishing walnut question

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Forum topic by MsDeltaGuy posted 02-04-2018 03:27 PM 357 views 0 times favorited 9 replies Add to Favorites Watch
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MsDeltaGuy

3 posts in 134 days


02-04-2018 03:27 PM

Hello all,

I have a question about some walnut lumber im working with. I am located in MS and I recently built a desk from 2” thick walnut. I sanded with 60,120,220,320 then applied a thick coat of tong oil. after drying for 12 hours I wet sanded it with 0000 steel wool. I somewhat dried the desktop but three hours later I returned and the desk has black spots all over it !! does anyone have any ideas what this could be? The only way to remove it is by starting over with 60 grit sanding with my orbital sander.

Any ideas ??


9 replies so far

View mahdee's profile

mahdee

3888 posts in 1789 days


#1 posted 02-04-2018 03:37 PM

Walnut soaks things up pretty good. Probably used too much tong oil and didn’t seal it before hand. I would use some mineral oil or something that would thin the oil and wipe it for several days until it stop bleeding. Usually if you expose it to heat (sun) it will ooze out a lot faster.

-- earthartandfoods.com

View OSU55's profile

OSU55

1693 posts in 2011 days


#2 posted 02-04-2018 04:00 PM

I assume you mean tung oil, but exactly what product did you use – ther are many fakes and then there is raw and polymerized or cooked. How dry is the wood? Some pics would help- black spots all over can mean a lot of different things. Walnut is usually not one to blotch, but depending on the piece can have o lot of color variation. You may just be seeing some of the dark purplish hue that is there. Wetting wood with ms or naptha gives a good idea of what it will look like with finish, which will usually be darker than as sanded.

View Kazooman's profile

Kazooman

1024 posts in 1974 days


#3 posted 02-04-2018 04:06 PM

“Wet sanded it with 0000 steel wool”. I assume you mean you used water, not more oil. Water, steel, and the tannins in the wood could generate a black color.

View Aj2's profile

Aj2

1420 posts in 1820 days


#4 posted 02-04-2018 04:28 PM

Sure sounds like you left steel wool behind. I use 0000 but only dry.

-- Aj

View Lazyman's profile

Lazyman

2036 posts in 1409 days


#5 posted 02-04-2018 04:55 PM

You said you applied the tung oil (assuming it was really tung oil) but you didn’t say anything about wiping off the excess. True tung oil is supposed to be a applied and then wiped off an hour or two later. And you should wipe vigorously to sort of buff it and generate a little friction. Directions on the package should explain that in most cases.

Need more information on the wet sanding. It should not be done with water and certainly not with water and steel wool. I wouldn’t use steel wool on walnut at all because steel wool will usually leave little flecks of steel behind which will eventually oxidize (rust) which will react with the tannins in the wood and stain the wood black. Look up “ebonizing wood” to see a process that uses this reaction to stain wood black. It may only take a few minutes to react and turn the wood black once the steel rusts. If those little black spots are small, they are probably caused by the steel wool and sped up if you sanded with water. If you are trying to smooth out any nibs after applying a finish, synthetic steel wool (3M or even scotch bright pad) is a better way to do it but with no water.

Note: Sometimes wet sanding is done on walnut to seal the pores of the wood to get a smoother finish. This is done with the finish itself, such as Danish oil, to get a slurry of wood, oil and the varnish that is in in the Danish oil to fill the pores. You could use a synthetic steel wool but I think a fine grit wet/dry sand paper is more effective.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View MsDeltaGuy's profile

MsDeltaGuy

3 posts in 134 days


#6 posted 02-04-2018 07:38 PM



I assume you mean tung oil, but exactly what product did you use – ther are many fakes and then there is raw and polymerized or cooked. How dry is the wood? Some pics would help- black spots all over can mean a lot of different things. Walnut is usually not one to blotch, but depending on the piece can have o lot of color variation. You may just be seeing some of the dark purplish hue that is there. Wetting wood with ms or naptha gives a good idea of what it will look like with finish, which will usually be darker than as sanded.

- OSU55

I used a big box product Formby’s tong oil high gloss. What i did was used 2000 grit sandpaper with some water and wet sanded it and a few hours later the spots appeared.

View MsDeltaGuy's profile

MsDeltaGuy

3 posts in 134 days


#7 posted 02-04-2018 07:40 PM



You said you applied the tung oil (assuming it was really tung oil) but you didn t say anything about wiping off the excess. True tung oil is supposed to be a applied and then wiped off an hour or two later. And you should wipe vigorously to sort of buff it and generate a little friction. Directions on the package should explain that in most cases.

Need more information on the wet sanding. It should not be done with water and certainly not with water and steel wool. I wouldn t use steel wool on walnut at all because steel wool will usually leave little flecks of steel behind which will eventually oxidize (rust) which will react with the tannins in the wood and stain the wood black. Look up “ebonizing wood” to see a process that uses this reaction to stain wood black. It may only take a few minutes to react and turn the wood black once the steel rusts. If those little black spots are small, they are probably caused by the steel wool and sped up if you sanded with water. If you are trying to smooth out any nibs after applying a finish, synthetic steel wool (3M or even scotch bright pad) is a better way to do it but with no water.

Note: Sometimes wet sanding is done on walnut to seal the pores of the wood to get a smoother finish. This is done with the finish itself, such as Danish oil, to get a slurry of wood, oil and the varnish that is in in the Danish oil to fill the pores. You could use a synthetic steel wool but I think a fine grit wet/dry sand paper is more effective.

- Lazyman

Thanks for the information I did buy some snythetic finishing pads today and going to give them a try

View OSU55's profile

OSU55

1693 posts in 2011 days


#8 posted 02-04-2018 08:09 PM

Formby’s is one of the fakes, its just thinned poly varnish. My guess is you have water spots from sanding through the finish in some ares and the wood getting wet, as well as the slurry formed depositing in those areas, and /or black oxide from the steel wool and water. You say steel wool then 2000 gr sandpaper, but it doesnt matter. I would wipe it down well with mineral spirits and use a synthetic pad with the ms, then wipe off while still wet. Let dry and see what you have. If that doesnt do it, wet the wood again with ms and do the spots show? If yes sand it down, if no add more Formbys.

You can wet sand a finish but use ms unless it is a thick film finish. I wet sand thin poly finishes often useing ms. Can also wet sand with the varnish/Formbys itself to fill pores, just wipe it down after – dont let it dry that way. If it gets stickey while sanding ad a little varnish or ms.

View dhazelton's profile

dhazelton

2771 posts in 2318 days


#9 posted 02-04-2018 08:48 PM

The black spots could be from the steel wool or mold if the board wasn’t completely dry.

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