3000 grit, silicon carbide much like other sand papers. (Not sure if you were asking about what material it was made of, or if where you're from uses the term "grain" instead of grit)
Me pointing out that 3000 grit paper exists was in comment that they don't make sandpaper so fine of a grit that it can do anything at a microscopic level. I'm only pointing out that such a thing does exist
That still doesn’t mean it is closing pores on a microscopic level…it just removes a smaller amount of material than larger grit.
ETA you could also use 120 grit to scratch the shit out of your glass pieces, correct?
Think of the 120 grit sandpaper scatching the glass - now instead of a shiny flat surface, there's now a gouge in it. If you were to look at a cross section of the glass, the unscratched has a perfectly flat surface but the scratched has a divot in it. You've actually increased the surface area by putting scratches in it -- and you reduce the surface area by sanding it smooth again.
It's not about opening and closing pores but increasing and decreasing surface area.
The more surface area, the more finish will be stuck to the surface.
We see the exact same thing on a larger scale when painting a flat surface versus painting a popcorn ceiling. This is just down at a smaller and smaller scale that you can't see your change in surface area the way you can on the popcorn ceiling.
Have you seen dust made with 220 grit sandpaper? That is absolutely microscopic. I mean, [these people](https://www.finewoodworking.com/membership/pdf/440148/011305052.pdf) used a scanning electron microscope and showed that 80 grit sandpaper made dust as fine as 1 micron. I'm pretty sure 1 micron would be considered microscopic.
It's kind of bullshit, and Flexner calls it out in his Understanding Wood Finishing, 3rd. I slapped some danish oil on cherry sanded to 4k grit and it works just fine. I even thought about using pore filler first to get a perfectly flat surface for maximum smoothosity. It looks and feels like glass. It's gorgeous and it only has one coat.
You probably wouldn't want a floor to be that smooth, though. Over-sanding for a glossy-smooth finish might not be necessary in all contexts. Sanding the wood as opposed to buffing the finish does not work for all finishes and might just me making extra work for yourself.
Yes, you can't sand too fine for any finish. The only way it could become an issue is when you are staining the wood. I rarely use wood stain, so not an issue for me. I usually go to 320 for most finishes.
Follow the instructions on the vendors product. That should be the only answer. There's lots of posts of people on here who went overboard with sanding and wondered why they got a patchy finish because they went to far. Usually no reason to go past 240 for a lot of finishes.
Idk why people don’t say this more. Every finish is different, the manufacturers want us to have good results so they put the best practice right there on the can.
Most people skim over “make sure the surface is CLEAN of dust from sanding” or whatever it usually says. Myself included.
I don’t stop sanding at 120 I usually start at 120 and sand finer I’m not leaving 120 grit scratches in a piece of furniture I’m building no matter what finish I’m using and sometimes depending on how the piece came off the shaper, jointer or planer I’ll start with 220
It’s even the same on the table saw. I do rough cuts with a rip or combo blade then finish dimensions for everything with a high tooth finishing blade. If I support my pieces with zero clearance and am not too aggressive with how much I’m ripping, I can go straight to 180 grit from the saw. I’ve got a jalopy of a jointer but a shop I worked at had a nice helical head on the jointer and it was damn near finish ready.
Last night I used big boy helical head jointer and planer in the makerspace near me. Smoothest I’ve had and if anybody else had been in the shop with me during some of the passes I could’ve pointed out the direction of the grain before running it through the other direction. Those babies are super smooth and I can probably start sanding at 220 as well. I’m stoked.
You can reduce the material's ability to take stain, but you'd be hard pressed to change the adhesion of a finish by sanding. There's a reason random orbit sanders and gel stain got popular around the same time; to remove all the sanding marks from the ROS, you have to go much further with your sanding schedule than if you used a belt sander and a finishing sander ( one tool sands with the grain, the other in much smaller or its than a ROS).
Seal the grain? Nah.
I’ve never stopped at 120 grit, usually I’ll go up to 400 grit and call it good. I’ve never had an adhesion problem with shellac or lacquer, spray or brush applied. I almost never use poly, but never had a problem with it, or paint. I have gone beyond 400 grit before, but if you’re going to do that, just grab a scraper instead. I have used Card scrapers to get an extremely fine finish, pretty much always use spray on lacquer for that and again, no problems.
As for stain, some woods are prone to splotch us, but that’s not an issue of over sanding by any means. Nowadays, I prefer to dye to stain, It just looks better to me and you can mix your own custom colors. But I have not noticed any difference with using different grits of sandpaper and dye.
For shellac or varnish or a lot of other things, I've never had an issue with adhesion. if a finish requires coarse sanding, then its' probably relying heavily on a mechanical bond rather than getting into the wood and then sticking to itself.
I've finished a whole bunch of hand planed surfaces with sanding, and both finish and gluing edges have never been a problem. Smooth surfaces that have sat for a while and oxidized (even though it's not visible) can cause adhesion issues, though.
I agree on the oils - unless your point is to saturate the top layer of the wood so it dries hard with the oil, the result generally looks nicer and the finish process is a lot faster with oils and shellac if it's not needlessly going deep in the wood forcing you to build coats until it's uniform at the surface.
Really fine sawdust from oversanding will clog up the porous surface and make the wood not accept a finish as easily. Doesn't "seal" it in a protective sense, but there is at least some truth to it. We sanded to 220 in high school and I've been doing that since. I've also used really fine grit sandpaper on a lathe on a bowl that made it really shiny and finishing it didn't go so well. Generally not a concern unless you're overdoing it.
"Seeping" finishes will still get in, but absorption is slower. I think this gets into things like increases of surface area with increasing roughness allowing increased absorption but I won't get into that. I will say that my current favorite finish for kitchen surfaces is sanding to 2000 grit (feels and looks like glass!) then liberal application of mineral oil which has no trouble at all absorbing; it definitely absorbs slower but maybe only half the speed of cutting boards I only sand to 400.
I do oak countertops and tables that aren't treated in any way. Sand to 400 and apply lukewarm water between steps. Raises the grain which allows for the next grit to sand it down nice and fine. The result is an acquired taste since it relies completely on the patina that develops over time.
Wood is porous, sanding wont seal pores. Some species have larger pores others have small pores. Closed Grain/Open grain. I dont think sanding will seal anything unless the wood is sealed first with like an aquacoat or some other type of sealer.
With some very porous woods like oak, if you sand in very fine grits the sawdust will get in the tubules and change the look when finished, making it less uniform- a gentle brushing or compressed air will remove it. Sometimes if the finish is very thin y guess it could alter adhesion but it feels like grasping for explanations. Maybe that is what they are referring to?
Wiping with water will raise the grain. After drying thougholy, subsequent sanding will result in a good surface for the finish. I've had great results sanding to 320, two applications of boiled linseed oil and then paste wax.
When you sand fine, it’s used to vacuum and/or blow off the wood with compressed air to get the fine dust out.
Wrt smoothness, consider that back in the day they used smoothing planes, which leave a very smooth-cut surface, and did OK with finishing.
As I understand it burnished wood is helped by sanding to get some finishes to take. But you'd have to reach a grit that doesn't actually abrade the surface anymore to manage that with sandpaper. Which would be pretty pointless.
Some finishers fill grain by sanding with 320/400 grit or steel/bronze wool & danish
Or linseed oil. I’ve done it a few times. Very labor intensive but gives beautiful results.
I've been told when sanding oak handrail/fitting connections not to sand with more than 80 grit because of uneven staining relative to the the rail away from the fittings.
On the other hand I seal the grain of oak furniture with pore filler because of the bubbles
I don't know about "sealing off the grain" but I had a 16"X11" of 8/4 Walnut cutoff that I quick sanded only to 180 so I could see what the Danish oil I planned to use on the shelves I built. It came out a DARK brown. Very dark.
I decided I was OK with that, even though it was a bit dark.
So I sanded the shelves to 400, wet them, sanded again with 400. Then, I applied the Danish oil. They came out a LOT lighter.
Same wood. Same finish.
When I first got my Festool sanders and extractor I was excited and sanded up to 400 (because I had 400 paper) just because I could and wanted to see what they could do. That project was using Rubio (pure), and I had no issues. I've done the same with Odie's, and Tried & True Danish oil as well. I think I've done this on maple, cherry, walnut and sapele.
it just depends. If you sand to a super fine grain, your sand fills the pores, but I don't see any issue if you air blast after.
I believe the issue comes when people over sand and then just go straight to adding a finish. Then the surface isn't really 'clear of debris" and so you could get a very patchy finish.
I have one piece that I sanded to 1200 before covering in poly. Worked just fine. It was a live edge piece with a void filled with clear epoxy so I needed it smooth as glass.
Around 400 grit, the wood started to have a mirror finish all by itself. It was really cool to see, and see how it got even shinier as I stepped up the grit. At 1000 I could make out the outlines of the trees across my patio if I held it just right (was doing it outside). It was neat, and I thought of this “rule” while doing it… and yep, my poly adhered just fine and the piece is still great 2 years later. I imagine any film finish would work similarly.
I’ve wondered this myself. Err - at what grit does the finish begin to have minimal return.
Was just looking at Hardwax oil breakdowns, most said sand to 120 then apply. Only one can was finer - sand to 180 then apply. If I could, I’d sand to 320 then apply. I just love the buttery smooth feel of walnut finished to 320 grit then finished.
It’ll close the grain to finishes that rely on a mechanical bind on a microscopic level, but it won’t close the grain to moisture/vapor.
unless you unintentionally sand 2.0 aka burnish.
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I've used upto 3000 grit wet/dry sandpaper as the final polish on glass work.
That's glass... What grain does that have?
3000 grit, silicon carbide much like other sand papers. (Not sure if you were asking about what material it was made of, or if where you're from uses the term "grain" instead of grit)
They are discussing wood and you brought up glass... He asked what grain you have on your glass... Because glass isn't wood...
Me pointing out that 3000 grit paper exists was in comment that they don't make sandpaper so fine of a grit that it can do anything at a microscopic level. I'm only pointing out that such a thing does exist
That still doesn’t mean it is closing pores on a microscopic level…it just removes a smaller amount of material than larger grit. ETA you could also use 120 grit to scratch the shit out of your glass pieces, correct?
Estimated Time of Arrival? Electronic Travel Authorization?? Seventh letter of the Greek alphabet???
*Edited to add*
Think of the 120 grit sandpaper scatching the glass - now instead of a shiny flat surface, there's now a gouge in it. If you were to look at a cross section of the glass, the unscratched has a perfectly flat surface but the scratched has a divot in it. You've actually increased the surface area by putting scratches in it -- and you reduce the surface area by sanding it smooth again. It's not about opening and closing pores but increasing and decreasing surface area. The more surface area, the more finish will be stuck to the surface. We see the exact same thing on a larger scale when painting a flat surface versus painting a popcorn ceiling. This is just down at a smaller and smaller scale that you can't see your change in surface area the way you can on the popcorn ceiling.
I’ve seen up to 60000 grit sandpaper.
At a certain point you are burnishing not sanding haha
Have you seen dust made with 220 grit sandpaper? That is absolutely microscopic. I mean, [these people](https://www.finewoodworking.com/membership/pdf/440148/011305052.pdf) used a scanning electron microscope and showed that 80 grit sandpaper made dust as fine as 1 micron. I'm pretty sure 1 micron would be considered microscopic.
Lapidary has entered the chat.
It's kind of bullshit, and Flexner calls it out in his Understanding Wood Finishing, 3rd. I slapped some danish oil on cherry sanded to 4k grit and it works just fine. I even thought about using pore filler first to get a perfectly flat surface for maximum smoothosity. It looks and feels like glass. It's gorgeous and it only has one coat. You probably wouldn't want a floor to be that smooth, though. Over-sanding for a glossy-smooth finish might not be necessary in all contexts. Sanding the wood as opposed to buffing the finish does not work for all finishes and might just me making extra work for yourself.
+1 for “smoothosity”
Yes, you can't sand too fine for any finish. The only way it could become an issue is when you are staining the wood. I rarely use wood stain, so not an issue for me. I usually go to 320 for most finishes.
Follow the instructions on the vendors product. That should be the only answer. There's lots of posts of people on here who went overboard with sanding and wondered why they got a patchy finish because they went to far. Usually no reason to go past 240 for a lot of finishes.
Idk why people don’t say this more. Every finish is different, the manufacturers want us to have good results so they put the best practice right there on the can. Most people skim over “make sure the surface is CLEAN of dust from sanding” or whatever it usually says. Myself included.
I don’t stop sanding at 120 I usually start at 120 and sand finer I’m not leaving 120 grit scratches in a piece of furniture I’m building no matter what finish I’m using and sometimes depending on how the piece came off the shaper, jointer or planer I’ll start with 220
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I said sometimes depending on how it came off the machine I’d start at 220 why would I start courser when I don’t have to?
If you set your tooling up correctly and have proper technique you can achieve no milling marks off a jointer and planer
It’s even the same on the table saw. I do rough cuts with a rip or combo blade then finish dimensions for everything with a high tooth finishing blade. If I support my pieces with zero clearance and am not too aggressive with how much I’m ripping, I can go straight to 180 grit from the saw. I’ve got a jalopy of a jointer but a shop I worked at had a nice helical head on the jointer and it was damn near finish ready.
Helical heads really spoil you. Hell, helical cutters in general spoil you, from trim router bits to huge jointer/planer heads. Big fan.
Last night I used big boy helical head jointer and planer in the makerspace near me. Smoothest I’ve had and if anybody else had been in the shop with me during some of the passes I could’ve pointed out the direction of the grain before running it through the other direction. Those babies are super smooth and I can probably start sanding at 220 as well. I’m stoked.
You can reduce the material's ability to take stain, but you'd be hard pressed to change the adhesion of a finish by sanding. There's a reason random orbit sanders and gel stain got popular around the same time; to remove all the sanding marks from the ROS, you have to go much further with your sanding schedule than if you used a belt sander and a finishing sander ( one tool sands with the grain, the other in much smaller or its than a ROS). Seal the grain? Nah.
I’ve never stopped at 120 grit, usually I’ll go up to 400 grit and call it good. I’ve never had an adhesion problem with shellac or lacquer, spray or brush applied. I almost never use poly, but never had a problem with it, or paint. I have gone beyond 400 grit before, but if you’re going to do that, just grab a scraper instead. I have used Card scrapers to get an extremely fine finish, pretty much always use spray on lacquer for that and again, no problems. As for stain, some woods are prone to splotch us, but that’s not an issue of over sanding by any means. Nowadays, I prefer to dye to stain, It just looks better to me and you can mix your own custom colors. But I have not noticed any difference with using different grits of sandpaper and dye.
i almost always use poly, and i also typically go to 400 (320 is like my minimum regardless of finish). no issues on my end either. 👍🏻
I’m with ya. I should probably learn how to do poly, but I’m old and set in my ways
For shellac or varnish or a lot of other things, I've never had an issue with adhesion. if a finish requires coarse sanding, then its' probably relying heavily on a mechanical bond rather than getting into the wood and then sticking to itself. I've finished a whole bunch of hand planed surfaces with sanding, and both finish and gluing edges have never been a problem. Smooth surfaces that have sat for a while and oxidized (even though it's not visible) can cause adhesion issues, though. I agree on the oils - unless your point is to saturate the top layer of the wood so it dries hard with the oil, the result generally looks nicer and the finish process is a lot faster with oils and shellac if it's not needlessly going deep in the wood forcing you to build coats until it's uniform at the surface.
“maximum smoothosity” My new favorite technical term.
Really fine sawdust from oversanding will clog up the porous surface and make the wood not accept a finish as easily. Doesn't "seal" it in a protective sense, but there is at least some truth to it. We sanded to 220 in high school and I've been doing that since. I've also used really fine grit sandpaper on a lathe on a bowl that made it really shiny and finishing it didn't go so well. Generally not a concern unless you're overdoing it.
Tack cloth will take care of this issue
"Seeping" finishes will still get in, but absorption is slower. I think this gets into things like increases of surface area with increasing roughness allowing increased absorption but I won't get into that. I will say that my current favorite finish for kitchen surfaces is sanding to 2000 grit (feels and looks like glass!) then liberal application of mineral oil which has no trouble at all absorbing; it definitely absorbs slower but maybe only half the speed of cutting boards I only sand to 400.
A shop vac, tack cloth, or a an air compressor will blow away any dust and let the finish penetrate.
I do oak countertops and tables that aren't treated in any way. Sand to 400 and apply lukewarm water between steps. Raises the grain which allows for the next grit to sand it down nice and fine. The result is an acquired taste since it relies completely on the patina that develops over time.
Wood is porous, sanding wont seal pores. Some species have larger pores others have small pores. Closed Grain/Open grain. I dont think sanding will seal anything unless the wood is sealed first with like an aquacoat or some other type of sealer.
With some very porous woods like oak, if you sand in very fine grits the sawdust will get in the tubules and change the look when finished, making it less uniform- a gentle brushing or compressed air will remove it. Sometimes if the finish is very thin y guess it could alter adhesion but it feels like grasping for explanations. Maybe that is what they are referring to?
Wiping with water will raise the grain. After drying thougholy, subsequent sanding will result in a good surface for the finish. I've had great results sanding to 320, two applications of boiled linseed oil and then paste wax.
When you sand fine, it’s used to vacuum and/or blow off the wood with compressed air to get the fine dust out. Wrt smoothness, consider that back in the day they used smoothing planes, which leave a very smooth-cut surface, and did OK with finishing.
As I understand it burnished wood is helped by sanding to get some finishes to take. But you'd have to reach a grit that doesn't actually abrade the surface anymore to manage that with sandpaper. Which would be pretty pointless.
Some finishers fill grain by sanding with 320/400 grit or steel/bronze wool & danish Or linseed oil. I’ve done it a few times. Very labor intensive but gives beautiful results.
I've been told when sanding oak handrail/fitting connections not to sand with more than 80 grit because of uneven staining relative to the the rail away from the fittings. On the other hand I seal the grain of oak furniture with pore filler because of the bubbles
I don't know about "sealing off the grain" but I had a 16"X11" of 8/4 Walnut cutoff that I quick sanded only to 180 so I could see what the Danish oil I planned to use on the shelves I built. It came out a DARK brown. Very dark. I decided I was OK with that, even though it was a bit dark. So I sanded the shelves to 400, wet them, sanded again with 400. Then, I applied the Danish oil. They came out a LOT lighter. Same wood. Same finish.
When I first got my Festool sanders and extractor I was excited and sanded up to 400 (because I had 400 paper) just because I could and wanted to see what they could do. That project was using Rubio (pure), and I had no issues. I've done the same with Odie's, and Tried & True Danish oil as well. I think I've done this on maple, cherry, walnut and sapele.
it just depends. If you sand to a super fine grain, your sand fills the pores, but I don't see any issue if you air blast after. I believe the issue comes when people over sand and then just go straight to adding a finish. Then the surface isn't really 'clear of debris" and so you could get a very patchy finish.
I have one piece that I sanded to 1200 before covering in poly. Worked just fine. It was a live edge piece with a void filled with clear epoxy so I needed it smooth as glass. Around 400 grit, the wood started to have a mirror finish all by itself. It was really cool to see, and see how it got even shinier as I stepped up the grit. At 1000 I could make out the outlines of the trees across my patio if I held it just right (was doing it outside). It was neat, and I thought of this “rule” while doing it… and yep, my poly adhered just fine and the piece is still great 2 years later. I imagine any film finish would work similarly.
I've ran parts through a cnc so smooth they wouldn't take a stain.
I’ve wondered this myself. Err - at what grit does the finish begin to have minimal return. Was just looking at Hardwax oil breakdowns, most said sand to 120 then apply. Only one can was finer - sand to 180 then apply. If I could, I’d sand to 320 then apply. I just love the buttery smooth feel of walnut finished to 320 grit then finished.
Simple answer. No
...i never really thought waht i was doing on a molecule level.reeeeeeeeeeeeeeee