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Forum topic by Karda posted 08-27-2018 06:41 AM 1089 views 0 times favorited 27 replies Add to Favorites Watch
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Karda

1832 posts in 1116 days


08-27-2018 06:41 AM

Hi, I was sand an ash bowl and noticed it started getting dark spots after I sanded for a while, any idea what causes this. Here is a picture of it best i can get


27 replies so far

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therealSteveN

4318 posts in 1136 days


#1 posted 08-28-2018 05:07 AM

Nothing I am aware of about Ash specifically that would cause it to darken with sanding. Now seeing that it is 90* here with a heat index of 104 today, any chance you were sweating on it a little? If so you found your cause. For now I would continue sanding until it has the look and feel of the smoothness you were looking to achieve. Don’t worry too much if it looks muddled.

Once you have it sanded so you are happy with the smoothness, and feel, all over both inside and out. I would suggest you take that damp cloth anyhow, to “raise the grain.”

You sand it down, then get it damp to raise the grain, which will happen with any fluid you put on it anyhow. So do it now, so your finish doesn’t raise it when you put it on later. Raising the grain when you finish is not usually going to lead to a nice finish, and causes a lot more work. Typically the grain only raises on that first wetting. If you look closely you can actually see it, like a fuzzy covering.

-- Think safe, be safe

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Karda

1832 posts in 1116 days


#2 posted 08-28-2018 05:55 PM

thanks for the suggestions, I’ll do that. I am using mostly wet and dry sandpaper wet to keep the dust down, could the sandpaper leave the dark marks

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therealSteveN

4318 posts in 1136 days


#3 posted 08-28-2018 06:09 PM

Not thinking it was the sandpaper per say, but any water. moisture, sweat, just wet will darken a light wood, for at least the time it remains wet, so if you are using a wet paper I’d say you found your culprit.

Never tried sanding wet to decrease dust, usually I sand over a home made downdraft table

If you use pegboard for a top it’s really just a shallow box, with a place to attach a dust collector. Many folks make them a lot bigger than their vacs can effectively pull in dust. Unless you are sanding very large pieces something 12” square will usually work.

I am wondering what effect your using moisture will have on grain raising? If it will still raise after you are done at all. Not that it would be a bad thing, just musing.

Good luck with it, I didn’t think it sounded like you had hurt the wood any. I sweated so much yesterday that was what came to my mind, everything I worked on got a little wet.

-- Think safe, be safe

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Karda

1832 posts in 1116 days


#4 posted 08-28-2018 10:54 PM

I don’t think it is moisture because it is kind of a gray and it never changed. I am doing a birch bowl I see if it has the same reaction. I am sanding a bowl on a lathe and they trough dust allover anything to keep dust down is good

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Lazyman

4180 posts in 1949 days


#5 posted 08-29-2018 03:24 PM

What brand of sandpaper are you using? Could be the adhesive from the sandpaper isn’t holding up to the heat from friction of sanding, is melting and is being deposited on the wood? Use the slowest speed possible when sanding. Or there is some resin or sap from something you previously sanded with the same piece of paper, perhaps. Try using some sort of solvent (mineral spirits, etc.) to see if that removes it—or try a different sandpaper.

BTW, I got a sample of the 3M Sandblaster Pro Ultra Flexible sandpaper in a package of regular paper and tried it on the lathe and it is great stuff. Once I use all my regular paper up I will probably use this almost exclusively for sanding on the lathe. It doesn’t clog and seems to almost last forever.

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

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Karda

1832 posts in 1116 days


#6 posted 08-30-2018 12:14 AM

The wet and dry I got at harbor freight, the dry I can’t remember, I’ll test it. an other sanding question. how do you prevent a mottled look. I power sanded the tear out now that spot is very light compared to the rest of the bowl. and there are other light areas. They don’t seem to be differences in wood color. any ideas

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therealSteveN

4318 posts in 1136 days


#7 posted 08-30-2018 05:47 AM

Not sure without seeing it? I think I would proceed, and it will all be wetted before you finish to see if you do raise any grain on areas where you haven’t raised it already. See if then it doesn’t even out. If not I’m not sure what to tell you. Typically harder woods like your Ash will uptake stain, dye, whatever finish you use fairly evenly. Differences now are likely just from exposure to an uneven wetting. Softer woods like Pine you might use a “sanding sealer” Either Shelllac in a 1# cut, or a marketed product that fills the grains so uptake will be more even for color. I’ve used a lot of Ash, and never needed anything like that though.

Are you certain it is Ash, and not Maple, which does tend to get splotchy sometimes, both are whitish colored woods which can have some browns, and greys mixed in. What is the grain of the wood like?

-- Think safe, be safe

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Lazyman

4180 posts in 1949 days


#8 posted 08-30-2018 01:57 PM

Is the wood dry enough? Could be that if the bowl sat for a while before you power sanded that spot it simply darkened with exposure to air and light, especially if this is a piece of wood you collected green. It could also be some sanding dust embedded in the grain. After you spot sand, you should then lightly sand the entire piece with a higher grit paper so that you have a consistent surface for your finish. Wiping down with some mineral spirits after sanding will get any sawdust out of the grain and help you see if the spots you are seeing are going to affect the finish.

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

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Karda

1832 posts in 1116 days


#9 posted 08-30-2018 06:54 PM

Hi the piece I am working on now is white birch but the problems are the same i’ll take some pics later when I am done with the honey dew list thanks Mike

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Wildwood

2767 posts in 2696 days


#10 posted 08-30-2018 08:42 PM

Think you’re right about that HF sandpaper being the culprit. Do you think that cheap sandpaper + CA glue which takes forever to get rid of could be the problem?

Might try getting little better aluminum oxide paper from Lowes or Home Depot. You definitely need better wet/dry paper to keep blue from staining wood. Been there done that!

-- Bill

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Karda

1832 posts in 1116 days


#11 posted 08-30-2018 11:50 PM

ok thanks

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Karda

1832 posts in 1116 days


#12 posted 08-31-2018 01:23 AM

Bill I thought aluminum oxide paper were only for dry sanding. I like wet, keeps dust down and cools the wood as well, as I replace I am going to use a better quality paper. here is picture of the birch bowl i am working on. I wiped it down with paint thinner the took a pic you can still see the mottling, the other pic of the inside, I haven’t sanded inside yet.

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therealSteveN

4318 posts in 1136 days


#13 posted 08-31-2018 03:23 AM

I think that is just the normal mottling, and color phases of wood in general. Most everything has some variation.

On the sandpaper causing it. I would think if it were glue from the paper it would be tacky feeling. Anything like that?

-- Think safe, be safe

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Karda

1832 posts in 1116 days


#14 posted 08-31-2018 03:52 AM

no tacky feel I didn’t get any dark spots yet on this bowl. I am watching for it. I noticed that ash seems to have grain that is lower that that next to it kinda like oak. there are dark and light grain next to each other. it is a pattern the lighter grain is between and lower that the dark streaks. some times the lighter grains will take on a soft gray tint. its hard to explain

View Lazyman's profile

Lazyman

4180 posts in 1949 days


#15 posted 08-31-2018 04:44 PM

I had a similar problem with a birch bowl I turned recently. I wound up wet sanding using Howard’s Feed and Wax and sanded to 600 grit. Took a while but after wiping it down with MS and applying a CA finish it was gone.

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

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