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finish, covering up sanding marks, etc?

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Aug 7, 2020 - 1:07:14 PM
893 posts since 2/21/2011

I am thinking that Tru-Oil, for a final finish, is not going to cover up even the smallest imperfections, like sanding marks, on a neck, right?

Deft Polyurethane, clear, gloss probably would be better for that, right?

Aug 7, 2020 - 1:41:35 PM
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Jbo1

USA

949 posts since 5/19/2007

Using finer and finer grades of sandpaper will be your best bet for removing sanding marks. And then you apply the finish. And the finish can take several thin coats, sanding and scraping in between. Depending upon the wood you would also want to use a sealer coat to fill the pores of the wood. That may help for some of the imperfections, but really, those shouldn't be there under the finish anyways.

Aug 7, 2020 - 2:24:31 PM
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Bill H

USA

1364 posts since 11/7/2010

There should be no sanding marks by the time you finish. Each finer grit in progression will remove the coarser marks of the previous grit--up to 500 or 600.

Aug 7, 2020 - 2:45:53 PM

44 posts since 5/27/2019

Remove imperfections up your personal level of perfectionism before applying any finish. There's probably no need to sand to higher than 220 before you start finishing. After you've applied and leveled a few coats, you'll be seeing and feeling the smoothness (or lack thereof) of the finish, not the wood.

Aug 7, 2020 - 2:48 PM

beegee

USA

21825 posts since 7/6/2005

Finishes will only amplify mistakes. Preparation is 90% of finishing. Hand sanding and scraping will remove scratches. Always sand with the grain when possible. I use oil-free steel wool that is finer than #0000 to help smooth the surface along with 1200 wet /dry paper on bare wood. Up to 2000 wet/dry followed by meguiers ultra-fine polishing compound on lacquer.

Aug 7, 2020 - 2:49 PM

rcc56

USA

3091 posts since 2/20/2016

If you want a good looking finish, sand, sand, and sand some more. Sand to 400. Give your arm a rest for a day or two, then sand some more.

I think Deft still makes a nitro based lacquer. If not, Stew-mac and Mohawk nitro spray can lacquers are still available.

Aug 7, 2020 - 4:36:35 PM

rmcdow

USA

852 posts since 11/8/2014

Deft does make a nitro based lacquer. I’ve used it in a bit of a different way lately with pretty good success. I sand to as fine as feasible, sometimes to 3000, but mostly to 600 or 1200, then steel wool with the oil free 0000 (Liberon). I then go over the entire surface with an N50 magnet to get all the steel off that shed. I spray a coat of Deft, steel wool again and use the magnet, then depending on the piece I’ll repeat this. Then I brush coat the piece with the same lacquer by Deft for brushing, two coats without steel wool or sanding at right angles to each other, good wet coats, drying in between. I let this dry a few days, then sand it with 400 until smooth (sometimes wet sanding, depending on the piece), then up the grit to 600, 1200, or higher, followed by a quick pass with the steel wool if needed. I can then get a good spray on finish that is flat and smooth with the good lacquer buildup that the brush on coats give me. I do this because it just takes way too many spray coats, at least for me and my skill level, to get a good solid finish with spraying alone. I don’t like to use sanding sealer. The other advantage of this method is that if there are any places that need a bit more filling with lacquer, you can use a small artist brush to fill them in a bit at a time until they can be sanded level, then spray the whole piece and finish it out with one of several polishing compounds I use.

Aug 7, 2020 - 7:02:43 PM

Fathand

Canada

11636 posts since 2/7/2008

Tru Oil makes a good finish especially on necks where nitro lacquer can feel sticky for months when warmed by your hand. Tru Oil or Shellac will highlight your sanding scratches more than most clear finishes but that is part of why they make your grain pop so nicely.
I have used Watco aerosol nitro in the past. It works ok but all nitro is highly toxic and I don't want to use it anymore.

Sand with 60 or 80 grit to shape your wood then use 100 followed by 150 then 220 for painted finishes or go to 320 for clear nitro or tru oil.

I wouldn't let polyurethane near an instrument, it's for floors.

If you want a finish that covers sanding scratches try autobody putty followed by paint.

Aug 7, 2020 - 11:10:38 PM

893 posts since 2/21/2011

Deft Polyurethane is not a Nitro Cellulose lacquer, is it?

What the heck is Polyurethane?

Aug 7, 2020 - 11:20:50 PM

rcc56

USA

3091 posts since 2/20/2016

Correct. Deft Polyurethane is not a nitro lacquer.

Polyurethane is a glassy plastic finish, commonly used on floors, inexpensive furniture, wooden gift shop do-dads, and inexpensive instruments. Exterior versions are used on boats.

Edited by - rcc56 on 08/07/2020 23:21:37

Aug 8, 2020 - 4:16:17 AM

13140 posts since 6/29/2005

Going back to the original question, I don't know of any finish that will hide even little scratches.  Much to the contrary, they accentuate them. 

I normally use dewaxed shellac as an initial sanding sealer and it has a slight amber color, which reveals every little scratch and enables you to final sand it to get rid of all of them.  In the case of a piece that will be stained, an application of thinned down aniline dye stain will accomplish the same thing.

You should never assume that more coats of finish, whether it's nitro, oil, or water-borne will hide scratches.

Aug 8, 2020 - 6:17:50 AM

rmcdow

USA

852 posts since 11/8/2014

The Deft I use says lacquer on the can, not polyurethane. One of the ingredients is cellulose nitrate propanol, which I believe is what nitro lacquer is based on. It dries to a waterproof finish on the pieces I have finished, and has not been sticky in my experience. It is much easier to apply than the Cremona violin finish from Germany that I do really like, but none of the finishes are going to cover scratches if they are transparent, they will only fill them if applied thick.

Aug 8, 2020 - 9:30:26 AM
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44 posts since 5/27/2019

quote:
Originally posted by Fathand

Tru Oil makes a good finish especially on necks where nitro lacquer can feel sticky for months when warmed by your hand. Tru Oil or Shellac will highlight your sanding scratches more than most clear finishes but that is part of why they make your grain pop so nicely.
I have used Watco aerosol nitro in the past. It works ok but all nitro is highly toxic and I don't want to use it anymore.

Sand with 60 or 80 grit to shape your wood then use 100 followed by 150 then 220 for painted finishes or go to 320 for clear nitro or tru oil.

I wouldn't let polyurethane near an instrument, it's for floors.

If you want a finish that covers sanding scratches try autobody putty followed by paint.


Tru Oil and polyurethane are both varnishes.  That is, they're both mixtures of oils and resins that polymerize when the finish cures.  It's just that they start with a different mix of ingredients that actually accomplish a somewhat similar result.  Tru Oil contains some linseed oil, and I'm guessing that if you mix some linseed oil into wiping polyurethane (just poly thinned with mineral spirits), there wouldn't be much functional difference between them. 

The instrument below was finished with one coat of boiled linseed oil followed by 3 or 4 coats of satin polyurethane diluted with mineral spirits to achieve wiping consistency (light rub with 0000 steel wool after each coat cured for 24 hours, but not touched after the final coat).  If polyurethane is applied correctly to a reasonable film thickness, it doesn't take on the thick plastic-like appearance that people associate with polyurethane.  However, it has the advantages of having the best scratch, wear, and moisture resistance of any finish that is readily available to the small workshop and can be applied without specialized equipment. 

Final note:  If you look at the Safety Data Sheet for Tru Oil, it's about 50% stoddard solvent, which is similar to mineral spirits.  If you took that away, it would act a lot like standard polyurethane straight out of the can.  That is, it would be hard to apply smoothly and it would build to an excessively thick, plastic-like coating if you put on more than two coats.


 

Aug 8, 2020 - 9:31:33 AM

beegee

USA

21825 posts since 7/6/2005

I like Deft a lot. It seem to have a good amount of solids and it dries quickly. It polishes out well. it's gotten kinda pricey from where it used to be. Lowe's used to sell it, but not now.

Aug 8, 2020 - 9:58:44 AM

Fathand

Canada

11636 posts since 2/7/2008

quote:
Originally posted by beegee

I like Deft a lot. It seem to have a good amount of solids and it dries quickly. It polishes out well. it's gotten kinda pricey from where it used to be. Lowe's used to sell it, but not now.


The first banjo I built, I used Deft Nitrocellulose aerosol and I liked it a lot. It does not seem to be available in Canada any more and I have not found anywhere I can pick it up cross border shopping. I can only find Deft Polyurethane in aerosol.  I did buy a can of Deft brush on Nitro from Lee Valley and tried it but it was like brushing on thick Tar.  Maybe I got an old can. 

Aug 8, 2020 - 10:29:14 AM

rcc56

USA

3091 posts since 2/20/2016

Nitro is great stuff. I will use it as long as it is available. It is toxic, and is fading out of use because of its toxicity.
Again, spray can nitro is available in the US from Stew-mac, Mohawk. Mohawk took over Behlen, and their instrument lacquer is the same as Behlen's was.

If you want a flawless finish, you must sand all the scratches out of the wood. It can be helpful to wipe naphtha over the sanded surface to find any scratches that you have missed. It's an old-fashioned cabinet maker's trick.

If a brush on lacquer is too thick, thin it slightly with high grade lacquer thinner.

Edited by - rcc56 on 08/08/2020 10:30:03

Aug 8, 2020 - 11:21:20 AM

rmcdow

USA

852 posts since 11/8/2014

quote:
Originally posted by beegee

I like Deft a lot. It seem to have a good amount of solids and it dries quickly. It polishes out well. it's gotten kinda pricey from where it used to be. Lowe's used to sell it, but not now.


Ace carries it.

Aug 8, 2020 - 12:10:50 PM

128 posts since 12/21/2012

I would personally just keep using finer and finer grit paper until you can no longer see marks in the raw wood.

I am struggling to remember any home built banjo that's come through the shop without sanding marks visible through the finish.

For a little extra time it will pay off in the long run. It will look a lot more professional.

Aug 8, 2020 - 1:38:21 PM

13140 posts since 6/29/2005

quote:
Originally posted by rcc56

Nitro is great stuff. I will use it as long as it is available. It is toxic, and is fading out of use because of its toxicity.
Again, spray can nitro is available in the US from Stew-mac, Mohawk. Mohawk took over Behlen, and their instrument lacquer is the same as Behlen's was.

If you want a flawless finish, you must sand all the scratches out of the wood. It can be helpful to wipe naphtha over the sanded surface to find any scratches that you have missed. It's an old-fashioned cabinet maker's trick.

If a brush on lacquer is too thick, thin it slightly with high grade lacquer thinner.


I hear you about the nitro—I used it for 50 years and it definitely has its strong points, and the spray guns are easy to clean to boot.  It makes a beautiful finish.

I finally had to stop using it for 3 reasons: (1) toxicity, as you say, (2) the smell, which became impossible since my shop is not in a separate building, and it was making my wife sick and very angry, and (3) the extreme danger of fire or explosion, and if my insurance company thought I was using something like nitrocellulose lacquer my rate would go sky high or they would make me buy an industrial type policy—heaven forbid what would happen if there was a fire and the investigators found evidence of what I was using.  I just had to give it up, like it or not.

I think those oil based things like tru-oil are very dangerous as well.  I remember (all too clearly) a person I worked with having the old floors in his 1700s colonial house in New Jersey stripped, sanded, and finished with Minwax, hand rubbed, which looked beautiful.  The refinisher left a bunch of rags they had used to rub in the finish in one room, and overnight, they spontaneously combusted, burning down half the house, which was not replaceable in kind because of its age and historic status.

To this day, if I use tung oil finish or any kind of oil finish, I take the rags outside and burn them at the end of the day.

Aug 8, 2020 - 3:55:19 PM

44 posts since 5/27/2019

quote:
Originally posted by Ken LeVan
quote:
Originally posted by rcc56

Nitro is great stuff. I will use it as long as it is available. It is toxic, and is fading out of use because of its toxicity.
Again, spray can nitro is available in the US from Stew-mac, Mohawk. Mohawk took over Behlen, and their instrument lacquer is the same as Behlen's was.

If you want a flawless finish, you must sand all the scratches out of the wood. It can be helpful to wipe naphtha over the sanded surface to find any scratches that you have missed. It's an old-fashioned cabinet maker's trick.

If a brush on lacquer is too thick, thin it slightly with high grade lacquer thinner.


I hear you about the nitro—I used it for 50 years and it definitely has its strong points, and the spray guns are easy to clean to boot.  It makes a beautiful finish.

I finally had to stop using it for 3 reasons: (1) toxicity, as you say, (2) the smell, which became impossible since my shop is not in a separate building, and it was making my wife sick and very angry, and (3) the extreme danger of fire or explosion, and if my insurance company thought I was using something like nitrocellulose lacquer my rate would go sky high or they would make me buy an industrial type policy—heaven forbid what would happen if there was a fire and the investigators found evidence of what I was using.  I just had to give it up, like it or not.

I think those oil based things like tru-oil are very dangerous as well.  I remember (all too clearly) a person I worked with having the old floors in his 1700s colonial house in New Jersey stripped, sanded, and finished with Minwax, hand rubbed, which looked beautiful.  The refinisher left a bunch of rags they had used to rub in the finish in one room, and overnight, they spontaneously combusted, burning down half the house, which was not replaceable in kind because of its age and historic status.

To this day, if I use tung oil finish or any kind of oil finish, I take the rags outside and burn them at the end of the day.


The solvents typically used in or to thin varnishes, as well as oil-based finishes like BLO and tung oil, (e.g. stoddard solvent and BLO in the formulation of Tru Oil, mineral spirits - especially the "odorless" variety, etc.) are less toxic than the solvents traditionally used in lacquer.  (Newer formulations of lacquer or lacquer thinner may be less toxic than the old stuff, but I haven't looked into that lately).  Obviously, you still don't want to drink them or get them in your eyes.  I've found that odorless mineral spirits triggers my eczema, so I use gloves to avoid that.

As you noted, rags soaked in oil-based finishes can self ignite due to an exothermic reaction as the finish cures.  To avoid that, you just spread the rags out.  You can lay them out flat on a concrete floor, hang them over a metal rail, etc.  The heat can only build up if there are multiple rags bunched together in a pile, bucket, garbage bag, etc.  Once they're fully dry (I leave them out to dry a few days, personally), it's absolutely safe to just throw them in the trash.  That refinisher you were talking about must have been an idiot, as the possibility of self-ignition and how to prevent it should be well-known among anyone doing professional refinishing.

Aug 8, 2020 - 5:13:38 PM

13140 posts since 6/29/2005

quote:
Originally posted by Uke-alot
 

I think those oil based things like tru-oil are very dangerous as well.  I remember (all too clearly) a person I worked with having the old floors in his 1700s colonial house in New Jersey stripped, sanded, and finished with Minwax, hand rubbed, which looked beautiful.  The refinisher left a bunch of rags they had used to rub in the finish in one room, and overnight, they spontaneously combusted, burning down half the house, which was not replaceable in kind because of its age and historic status.

To this day, if I use tung oil finish or any kind of oil finish, I take the rags outside and burn them at the end of the day.


The solvents typically used in or to thin varnishes, as well as oil-based finishes like BLO and tung oil, (e.g. stoddard solvent and BLO in the formulation of Tru Oil, mineral spirits - especially the "odorless" variety, etc.) are less toxic than the solvents traditionally used in lacquer.  (Newer formulations of lacquer or lacquer thinner may be less toxic than the old stuff, but I haven't looked into that lately).  Obviously, you still don't want to drink them or get them in your eyes.  I've found that odorless mineral spirits triggers my eczema, so I use gloves to avoid that.

As you noted, rags soaked in oil-based finishes can self ignite due to an exothermic reaction as the finish cures.  To avoid that, you just spread the rags out.  You can lay them out flat on a concrete floor, hang them over a metal rail, etc.  The heat can only build up if there are multiple rags bunched together in a pile, bucket, garbage bag, etc.  Once they're fully dry (I leave them out to dry a few days, personally), it's absolutely safe to just throw them in the trash.  That refinisher you were talking about must have been an idiot, as the possibility of self-ignition and how to prevent it should be well-known among anyone doing professional refinishing.


This happened in the late 1970s, in an area of New Jersey near Princeton, where there were a lot of old 18th centyury houses.  I lived in Bucks County at the time, where there were also a lot of old houses.  It was customary practice among the people who would work on them to use Minwax or some self-made "Sam Malloof" mixture of tung oil, linseed oil, mineral spitits, spar varnish, and naphtha, rubbed in oil finish on the floors of old houses, as opposed to ready made thick varnishes like Polyurethane. Some of these specialists would add some kind of dirt to their oil mix for effect.  Old house contractors in that era would actually use crankcase drainings on earthenware tiles, like the ones made by the Moravian Tile Works.

I don't think the guy was an idiot, he was actually a professional—he just got distracted and forgot to take his rags out of the house that day.

Since knowing about that disaster, I burn them—laying them out to dry just makes them as hard as a rock and they can never be used again anyway.

Edited by - Ken LeVan on 08/08/2020 17:14:51

Aug 8, 2020 - 5:33:04 PM

44 posts since 5/27/2019

quote:
Originally posted by Ken LeVan

This happened in the late 1970s, in an area of New Jersey near Princeton, where there were a lot of old 18th centyury houses.  I lived in Bucks County at the time, where there were also a lot of old houses.  It was customary practice among the people who would work on them to use Minwax or some self-made "Sam Malloof" mixture of tung oil, linseed oil, mineral spitits, spar varnish, and naphtha, rubbed in oil finish on the floors of old houses, as opposed to ready made thick varnishes like Polyurethane. Some of these specialists would add some kind of dirt to their oil mix for effect.  Old house contractors in that era would actually use crankcase drainings on earthenware tiles, like the ones made by the Moravian Tile Works.

I don't think the guy was an idiot, he was actually a professional—he just got distracted and forgot to take his rags out of the house that day.

Since knowing about that disaster, I burn them—laying them out to dry just makes them as hard as a rock and they can never be used again anyway.


Preventing something that could burn down your customer's house would seem to be a critical priority that was missed.

And correct, you can't use the rags again.  Laying them out flat to dry is just a convenient way to handle them until they're dry and safe to throw away in the trash.  I live in a dense neighborhood where open burning isn't permitted, and burning oil-soaked rags in my back yard would likely bother my neighbors and possibly draw a visit from the FD.  Your mileage my vary. ;)

Aug 8, 2020 - 7:30:23 PM
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118 posts since 2/12/2017

Wood does not need to be sanded any finer than 280 grit to have a mirror finish in the final clear coats.

Steve

Aug 8, 2020 - 8:17:06 PM

11067 posts since 6/2/2008
Online Now

quote:
Originally posted by rcc56

Again, spray can nitro is available in the US from Stew-mac, Mohawk. Mohawk took over Behlen, and their instrument lacquer is the same as Behlen's was.


There's also a place called The Guitar ReRanch that sells its own private label aerosol spray can lacquer. I have no idea who the actual manufacturer is.

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