Can I get some advice from a luthier (wood treatment, offtopic)?

April 11, 2021, 6:41 PM · Hi, this is kind of off-topic but since luthiers work with wood and know a lot about it (I guess), I think some of you can help me. I am building a desktop which consists in two big high quality squared metal legs and a plain plank/table/board of wood, which happens to be pine.

My question is fairly simple: which treatment would you use to finish the board?

It's going to be a desktop for studying, writing, etc... I have basically 4 different "ingredients":

1. Wood sealer/varnish primer/seal coat: it's a white liquid that seals the wood (becomes transparent when you apply it), avoiding humidity to enter and affect the wood overtime. Helps as well the varnish to stuck well, be efficient and spread evenly.

2. A trick from a local luthier: paraffin oil, that you use in untreated wood, such as a fingerboard or fretboard, that basically is a wood sealer, like number 1. It is way more "oily" though, darkens the wood more, but it makes the wood look gorgeous and shiny, unlike the number 1, which barely changes the wood color and beauty.

3. Water-based varnish: I have heard about them a lot, but never seen or used one myself. I bought one the other day, and it's something I was not expecting. It's an opaque liquid, with a gel-like texture, like "cold" custard that is starting to solidify. Really weird, even after shaking it a lot, stayed the same. Nevertheless, once you apply it to the wood it becomes an easy to use varnish, but the texture really shocked me.

4. Your old time "regular" varnish, I guess it's called "synthetic" varnish, your typical translucid, honey-like texture varnish. I've just read that they are older and "worse" than water based varnishes. Apparently it is WAY more shiny than the water based one.

So, here's what I was going to do: first, sand the board so I have a very smooth surface. Then, I prefer the number 2 sealer, since it darkens a little bit the pine and makes it look "alive". The problem is, it's oily, unlike the other primer, at least for the first 2-3 days, and I am not sure if the varnish will work over that. I've always used the paraffin oil as the finish to raw wood. Or may be it's compatible with water based but not synthetic, or viceversa.

Once the sealer is applied, I pretend to use the water based varnish, 3 or 4 layers so I get a shiny finish.

I'd love to read some comments, if you knew about paraffin oil (not many people know about it), and basically if I am good to go.

Replies (61)

Edited: April 11, 2021, 7:13 PM · I'm afraid the ancient Cremona secret is supposed to have been buried with Guadagnini! But one characteristic it had: When you rested your hand on one of their violins and then took it off, the surface would be misty.
But I read of one modern luthier putting olive oil on before varnishing, saying it gave great beauty (he didn't specify whether that was beauty of tone or just beauty of appearance - I suspect the latter), rather than paraffin. Elsewhere I've read about water glass being used as an initial sealant.
I don't claim to be a luthier, and that's not out of modesty.
Edited: April 11, 2021, 7:45 PM · I'm not a luthier either -- not by any stretch. However I have made myself a few writing-desks and other pieces of simple furniture (end tables, etc.). My preferred surface wood is birch because that is readily available as a plywood veneer, and it takes finish beautifully.

I guess it's probably just my ignorance of all the possibilities, coupled with my general unwillingness to experiment with other finishes, but I have enjoyed reliable success with Minwax "Helmsman" Varnish. This is an oil-based urethane product -- basically boat varnish. So it gives you a very robust surface. It is vitally important to read and follow the instructions on the can for coating, drying time, sanding, and re-application. I recommend using it "as is" without any thinner, use a high-quality brush, and apply it fairly sparingly. I always sand lightly between coats with a fine abrasive such as an ordinary 200-grit garnet paper. This will knock down the tiny bubbles that will appear on the varnish surface. For my work, I put down at least three coats and then after the last coat is well hardened I sand it lightly with 200-grit paper and then polish it with finer paper like 320. 0000 steel wool will give it a nice gloss. Helmsman Varnish will yellow/darken over the years, which you might like, or you might not. If you don't want that to happen, then there is another product called BenWood "Stays Clear" that is sold at your local Benjamin Moore paint store. Ben Moore paints and varnishes are expensive but they are very good quality in my experience. "Stays Clear" is a water-based urethane product (curiously, it smells worse than the oil-based Minwax), so if you have knots and such in your wood then you need to be concerned about whether the grain will be raised unevenly. I have not tried it on veneered plywood. These issues can all be tested on scrap though.

The desk I'm working on right now is made from a large scrap of laminate-surfaced plywood that was left over from my kitchen remodel some years ago. It's all chipped on the edges from daily wear-and-tear, and totally abraded off where my microphone clamps onto my desk. In other words it's too fragile -- it's rubbish. Over the summer I am going to replace it with real wood. Well ... plywood (with pine screen molding that I cut myself and apply with glue and clamps).

Edited: April 12, 2021, 4:19 PM · I wouldn't use paraffin oil (which we call "mineral oil" in the US) for two reasons:

1. It will never dry, and no other product will adhere to it well.
2. Pine is a very soft wood, and paraffin oil will do nothing to harden the surface. It will always be vulnerable to dents or tracking, even from one pushing hard on a pen or pencil while writing.

I can't comment on the other products since I don't know specifically of what they are composed.

One thing that can work quite well is Zinsser Bulls-Eye Seal Coat. This is a Shellac product. If you use this, use the one which is dissolved in alcohol, not the water-based version. Practice on a scrap piece of wood first, because it's not the most consumer-friendly and easiest to apply.

With any of the sealers and finishes, apply them to both the top and bottom of the wood, so both surfaces will absorb and release moisture at the same rate, to minimize the curling which can occur during humidity changes if this is not done. On plywood, this probably wouldn't be necessary, but since you are using a plain board, sealing both sides is a good idea if you want it remain flat.

Edited: April 12, 2021, 8:48 AM · I wouldn't flatter myself to call myself a luthier—I've just fixed a couple instruments and built one. BUT:

I think the most beautiful "alive" look is achieved by a small amount of drying oil (linseed, tung) followed by a thin coat of shellac. If it were an art piece I would keep applying shellac. In the case of a pine desk I would go for those freaky ultra-hard water-based finished from the hardware store. No more than that is needed I think.

April 12, 2021, 10:32 AM · If you're going to consider instrument finishes consider something designed for high wear like guitar finish.
Edited: April 12, 2021, 2:18 PM · Pine is notorious for blotching. My suggestion, is use ZInnser sealcoat (dewaxed shellac) as a sealer. You may or may not want to dilute to to 50/50 with denatured alcohol. One coat. Then use General Finish Gel Stain. Then after a few days to dry, use General finish Gel Varnish, at least 3 coats. This should give you a no blotch, protective finish, that is easy to apply and predictable results. PRACTICE on a piece of scrap. I've refinished more new projects than I care to admit.
Edited: April 12, 2021, 3:52 PM · OK, I'll forget about the mineral (paraffin) oil. Quick question here: why is it then recommended when finishing fretboards and fingerboards?

These are plain solid wood chunks as well, same as my table.

Yes, I will apply it to the whole surface, up, down, sides... I know I must protect it everywhere so humidity stays the same all around.

Anyways, I'm facing a really annoying issue: twisting. In other words, I've joined the 2 legs, which are big and heavy, 3D solid metal rectangles with 6 screws, but the table is not perfectly flat, but twisted a little bit, and now it does not sit correctly on the floor. If you put one of the legs (the whole side of the rectangle) on the floor perfectly flat, the other leg is only touching with a corner (I hope you can imagine how it is).

This is harder than expected... I knew I needed some structural changes, but a twisted table was not in my mind. I've tried to flatten it with books, but it's 1 inch thick and looks complex to do. Even tried wet towels to put some humidity...

It looks amazing even untreated, I love the legs, the table, the colors and quality, nothing I've seen in stores is anywhere near this table in quality and beauty, only starting at $400-500 you see some tables that use high quality thick metal legs and raw solid wood.

Downside... I'm facing these issues.

Oh, I am not looking for a "violin finish" table, that would be way too much, like a wine glass carved from diamond or something like that. I am looking for a fine, light, solid pine color finish that fits a sturdy, elegant and modern desktop. Besides some hardware stores, this is the only site I know that I can ask wood questions.

April 12, 2021, 4:31 PM · Paul wrote:
" OK, I'll forget about the mineral (paraffin) oil. Quick question here: why is it then recommended when finishing fretboards and fingerboards? These are plain solid wood chunks as well, same as my table."

Fingerboards are usually made of a wood which is much harder than pine, such as ebony. Fretboards don't typically have wear from string contact. The string contacts the frets rather than the fingerboard.
But even on ebony fingerboards, i don't use mineral oil. I use a vegetable oil which polymerizes or "dries", like tung oil or linseed oil. Tung oil is the tougher of the two, but still won't harden the wood as much as a shellac sizing.

April 13, 2021, 6:12 AM · Oh, so with high dense hard woods such as ebony or rosewood, the paraffin mineral oil works, right?

But with softer woods such as pine or spruce, mineral oil would be less effective?

By the way, do you seal the wood of a violin before applying varnish?

Now that I think about it, I have in my mind the appliance of varnish directly, weird... I don't remember to have seen any white liquid applied to a violin.

April 13, 2021, 6:18 AM · no parrafin oil never works because it never dries
Edited: April 13, 2021, 8:47 AM · Of course the violin is sealed, otherwise the varnish would seep into the wood and make a mess of things. I once visited a local maker who used oil varnish and didn't use a ground... his entire lineup of instruments sounded like it was stuffed with socks. Just ruined. His wife, who did seal the plates, made very nice-sounding violins.

I believe a lot of makers use shellac as a sealer because it's pretty. On my project I used vernice bianca, which I liked. It would serve no purpose to a desk, though, unless you're also going to use it as a drum.

April 13, 2021, 10:50 AM · Lyndon, paraffin oil MUST work with ebony and such because my local luthier has personally told me that's what he uses to finish the fingerboards and fretboards of his instruments.

What do you mean it never dries, anyway?
I have tested it in an extra chunk of pine I had. While the water based sealer completely dried in a few minutes, the paraffin oil took 3-4 days. After that, you wouldn't get oil in your finger if you touched or pressed the wood. I have that chunk right now and it feels to the touch completely dried.

April 13, 2021, 11:12 AM · No respectable luthier uses parrafin oil on fingerboards.
April 13, 2021, 11:31 AM · It will never dry and will gum up the windings on the strings
Edited: April 13, 2021, 2:02 PM · Paul, what happened is that the mineral oil soaked in, and was absorbed to the point that you could no longer feel any on the surface. It didn't dry, unless you waited at least several hundred years.

While it can make the wood darker and appear more transparent (a cosmetic improvement), it will continue to move through the wood. Eventually, some of it will reach the gluing surfaces. This shouldn't make an already-glued joint come apart, but will reduce the adhesion if a part like a fingerboard or upper nut ever needs to be removed and re-adhered, or some sort of crack needs to be repaired. This will also increase the weight of the part with subsequent applications, until the wood is completely saturated..

These are the main reasons I use a true drying oil instead of a mineral oil. But if your luthier is satisfied with mineral oil, that's fine by me. I tend to be pickier than some others.

Products like linseed oil and tung oil polymerize upon exposure to oxygen and light, turning into a resinous or varnish-like substance. That's why they are referred to as "drying oils". These are plant products.

"Mineral oil", or "paraffin oil" is refined from the stuff pumped out of oil wells. It will dry about as well as any lubricating oil derivative of crude oil, which is about none at all.

Edited: April 14, 2021, 5:39 AM · Thanks for the explanation, I was imagining something like that about the term "dried". In hard woods, anyways, my luthier does not put an insane amount of oil that will soak the entire fretboard or fingerboard all deep through. It's just the surface, you put some of it along all the surface that's visible, let it "soak" for a few minutes, and then you start rubbing with a hard cloth, like jeans. There is no way at all that the oil is going to go all the way through the ebony or rosewood and reach the glue, spruce, maple... You do not deep fry the hard wood in paraffin oil.

To be fair and clear, my luthier does a first quick layer to "sanitize" the surface, rubbing thoroughly, and then he puts some oil more and pours pumice powder all along, and keeps rubbing, as pumice helps to seal and even sand and finish smoothly the surface. The results are always amazing.

Question is... isn't it even beneficial that you have a small layer of oil "forever", protecting the surface?

What do you guys exactly mean when you say "this oil is dried"?
It must not mean that it's no longer there anymore, becase that would mean you have to put it again.

Anyways, updates on the desktop, I'm managing to untwist it using water and flexing it the other way to counter the twist. It's a slow process but I am seeing changes, now it's almost completely flat.

I am thinking about the next step, and some questions come to my mind. Right now it's mounted solidly with the metal legs, and I am probably going to screw 2 metal beams all along, like a bass bar on a violin, so the steel forces the board to stay straight forever. The problem is... if I have to seal it and then varnish it, my heart is telling me to do it as it is right now, mounted, in its final form. If I unscrew it and let the board be itself again, I might face again some twisting or wrapping, and if I seal and varnish in that state, it might fight a lot when I try to screw it again to the legs and beams.

So what's the problem about doing it right now?

Well, in the bottom side, the legs and beams are there, and I can't seal and varnish those areas.

Can I do all the layers of seal and varnish in the top and sides, and when that's finished and dried, unmount it and do the bottom side?

I might be overthinking it, but if I do the sides and top face, and that is going to take 3-4 days, moisture can still go to the bottom side, making the board to curve down. Well, it wouldn't since it's mounted and the 2 beams won't let it curve, but there could be some internal tension that can unleash when doing the bottom face later. Uh?

April 14, 2021, 9:12 AM · David, I saw "Stand Oils" mentioned elsewhere - I believe these are drying oils that have been stood at a high temperature with comparatively little access to air (e.g, in a covered saucepan or pot), so that they polymerise, and then, when applied take longer to dry, but by the same token the dried surface takes far, far longer to be weakened by further oxidation. Is this, in fact, the case?
Edited: April 14, 2021, 10:11 AM · "Can I do all the layers of seal and varnish in the top and sides, and when that's finished and dried, unmount it and do the bottom side?"

Not only that, now that I am thinking about it, BIG question:
Why you don't varnish the whole violin so every surface is even and the same?
Or you do seal the whole pieces of wood of a violin (inside as well), but the varnish is only applied to the visible parts?

Since I've been recommended to seal and varnish both sides so humidity is balanced, idea that I already had in mind because it made sense to me when I thought about it, why this doesn't work in a violin and you can live with the insides untreated?

April 14, 2021, 11:17 AM · > There is no way at all that the oil is going to go all the way through the ebony or rosewood and reach the glue, spruce, maple

If it can absorb oil, oil can travel inside it. It will continue to travel around until it's evenly distributed everywhere. It might take a while, and the amount might be rather little, but it will definitely get to the other side eventually.

April 14, 2021, 1:56 PM · I mean, what are we even talking about here?

I feel like you are saying to me something like "don't touch or sniff money bills because there's probably cocaine in those and it will enter in your system". Come on...

I've indeed put "a lot" of mineral oil in the extra chunk I got, about 1 inch thick fyi, in pine wood which sucks way faster the oil as it's softer and much less dense, and it's not coming from the bottom at all, so I imagine that if that you claim ever happens in hard dense wood like ebony or rosewood, it will be so very little and after so many months or years that this is nonsense.

Let's please discuss the other things I did in my last message.

Edited: April 14, 2021, 4:05 PM · Paul, Han Jin is right. And you are also correct in that total through-penetration of mineral oil on a one-inch piece of wood won't happen right away, or nearly as quickly as on a piece of paper.

Regarding your other question(s): Some violin makers put some sort of "sealer" on the inside, and others do not. Any sort of sealer, varnish, or paint will still allow some water vapor penetration, unless it is a very thick coating of wax, or a paint which has a high density of metal (usually aluminum) flakes. Moisture even goes through fiberglass and epoxy resin.

Heavy wax coatings (like one millimeter thick) do not seem to enhance the sound of violins, and aluminum-colored violins have not yet established an enviable sales history. ;-)

April 15, 2021, 5:31 AM · Some woodworkers will use parafin oil on chopping boards and bowls because it is claimed to be food safe. And they end up with a surface that always feels a bit sticky or oily because the oil never hardens. It will serve the purpose of protecting the wood against (temporary) water contact, but it will always be sticky. Drying oils - like linseed oil, tung oil and walnut oil - will polymerize inside the wood (or on the surface if you apply too much) and give a similar protection while avoiding the sticky feeling. Varnish will build up a film on the surface.
Edited: April 15, 2021, 6:51 AM · It is not "claimed" to be safe for human consumption, it is safe, basically because I know it's used in pharmacy.

Anyways, none of my ebony or rosewood fretboards and fingerboards are sticky in any way, nor oily or anything weird.

You are not being fair because you are all assuming you apply an inadequate amount of oil that will "damage" the wood or make it inappropriate for its job. I could say you can't varnish a violin because it can cause a mess with the peg box, make the pegs sticky, the bridge sticky, or you can't bend the wood because you could burn it, etc... I don't know why this has become the topic of the thread because I even said I am not going to use it in my pine table as a sealer, I'm gonna use the water based sealer the seller suggested.

Again, lets focus on my actual problems:

"I am thinking about the next step, and some questions come to my mind. Right now it's mounted solidly with the metal legs, and I am probably going to screw 2 metal beams all along, like a bass bar on a violin, so the steel forces the board to stay straight forever. The problem is... if I have to seal it and then varnish it, my heart is telling me to do it as it is right now, mounted, in its final form. If I unscrew it and let the board be itself again, I might face again some twisting or wrapping, and if I seal and varnish in that state, it might fight a lot when I try to screw it again to the legs and beams.

So what's the problem about doing it right now?

Well, in the bottom side, the legs and beams are there, and I can't seal and varnish those areas."

Edited: April 15, 2021, 7:15 AM · It's a bit strange that you ask questions about mineral oil, and then seem to object when people attempt to answer them.

If I understand correctly, your board has some twist. Since you will be using a waterborne sealer, I suggest tweaking the board so it is twisted in the opposite direction immediately after applying the sealer, and keeping it that way until all the absorbed water is gone (which could take several days to a week).

April 15, 2021, 9:14 AM · I am sorry if I misused the word "claimed". What I mean is that it is marketed as food safe - basically implying that the alternatives e.g. linseed oil are not. Go ahead and use mineral oil on wood if you want to - I wont.

Why do you use a twisted board? Building something flat from something that is not by forcing it is asking for problems. I would either get a board that is not twisted or flatten it with a jointer and planer, which would off course give you a thinner - but straight - board.

Edited: April 15, 2021, 9:24 AM · Let me explain myself: I created this so I could receive some help with the wood problems. That is and was my main target.

After discarding paraffin oil myself to use in this soft wood, it somehow became the main topic, even constantly asking questions about the board; I was told that it was not adequate to use in hard woods neither, like ebony or rosewood, and that was questioning my local luthier which is an excellent professional. So of course I am gonna judge what you say about that very specific topic. You were all acting as if I said I deep fry the fingerboard and fretboard in paraffin oil and let it soak for days until it can't absorb more oil. That is not fair and that's what I am trying say. Not a single question I've asked about paraffin mineral oil had an answer like "you shouldn't use it because it can flow to the other side and unglue the woods or make the surface sticky forever".

I've been applying paraffin oil to rosewood and ebony for so many years to different instruments and absolutely never have found any problem, never a sticky surface or filtration problems that unglue woods, and all the things I've been told. It is the opposite, it always works fantastic. I've even cared to correctly describe the whole process so I don't keep getting the same answers that asume I deep fry the woods in a mineral oil pan.

Now, you've explained some things here and I appreciate that a lot. Thank you, let's get back on track:

I have already the table mounted with the legs and twisted the opposite way using books and metal pieces to twist or tilt the legs. Right now, without any weight, it almost sits flat. One question here:

Does applying a water based sealer softens the wood the same way water does, which is what I have used to fix and flatten the board?
In other words, if I put water based sealer on just the top surface of a board and let it act... Will the sealer make the board concave as water would do?

Actually I'm gonna try it on one side of a balsa lumber, which reacts very quickly to uneven water distribution to check if it goes concave.

April 15, 2021, 9:36 AM · It seem you didn't come here to learn anything at all, but rather to lecture us with nonsense!!
April 15, 2021, 9:45 AM · If you want to un-twist a board just wetting it will not do. You need heat. Steam the board, force it into place and let it cool.
But you probably did not want to hear that either. Good luck with your desk - I shall comment no further.
Edited: April 15, 2021, 10:43 AM · It will probably initially go convex. Upon thoroughly drying, it may end up concave. Part of this will depend on how much the product contracts upon drying. Good idea to test first.
April 15, 2021, 10:34 AM · A related question, which has always puzzled me: why is the interior of a violin never varnished, and is always left untouched?
April 15, 2021, 10:57 AM · Trevor, some makers do put something on the inside. When it is not done, the notion behind this is often that the added mass is bad for the sound, since there is not enough of an increase in stiffness to make up for the added mass.

Simone Sacconi, the famous restorer in the Wurlitzer shop was of the opinion that Stradivari put SOMETHING on the inside of his violins. I haven't had nearly as many apart as he did, but my opinion has been more that whatever was on the inside was an accumulation of air-borne contamination which would be expected for a violin of that age.

April 15, 2021, 11:04 AM · David, thank you!
Edited: April 15, 2021, 11:29 AM · Lyndon, the only one talking nonsense and even trolling here is YOU, and only you. Stop coming to say one stupid sentence to provoke, you always behave like this for what I've read, I don't know why are you here.

Bo, I am not just wetting it and that's it, I am wetting it and applying force to counter the twist, even twisting it the other way and letting it dry with this force applied. It has worked really well and I almost got it flat already. It is not quite there yet, there's a very subtle twist still, but it's almost gone.
Don't play the victim now, I repeatedly said to drop the mineral oil topic, it was indeed never the topic, let alone judging what my local luthier has told me, and I have already done and tested dozens of times. I don't want you to be quiet (well, only Lyndon), indeed if you explain to me how can I steam a board of 5.7 x 2 feet and 1 inch thick, I might try it out.

David, I was thinking... if the water based sealer behaves like wetting with water a wood board, then unless you do all the faces and sides at the very same time, you will face twisting and wrapping. In floors you only apply it in one surface, so if it had the same effect as water, no floor could be sealed because you would make it convex without a solution, because you can never access the bottom or sides... unless, you put always already sealed, straight pieces of wood. That can't be the case because I've seen people first do a sealer layer on the floor and then apply the varnish. That first sealer didn't make the floor convex. If it does, it must be so very little it's not a problem at all.

Trevor is right, I asked that already. If you left the insides untreated, humidity will go there and if we apply extreme thoughts, that would behave like wetting the insides with water, which would make the violin to "shrink", to fight the convex shape of the top and bottom to straighten them, which would end up in ungluing the top and bottom from the sides. So... what's the catch?

Edited: April 15, 2021, 12:43 PM · The catch is tonewood is seasoned and doesn't instantly twist into a knot when introduced to moisture. There are examples of historic violins with twisted necks and things because they were carved from "green wood"... either that or luthiers were drinking a little too much back then.
Your pine desk was evidently not thoroughly air-dried before it was cut.

Hardwood floors are made of, well, hardwood. And pretty thick slabs of it. You'd have a hard time making hardwood slats warp with one measly coat of sealer. Bo's right about the twist, too: you need to heat the wood to make it hold its shape. You might get it straight under force, but it will dry back into its original shape.

Edited: April 15, 2021, 1:23 PM · But if I let it dry, with the forces of course applied in the opposite direction as I have done, it's like heating the wood but at a very slow rate, isn't it?

Proof is I have straighten it a lot, as I said, now it's almost plain and straight, although there is a little bit still.

What do you suggest, to wet all the wood all along, all faces, and then use a hairdryer?

If I wet the wood I fear it's gonna twist where now it is straight, it will appear this concave area, then that convex area. I don't want that, that's why I am doing it slowly.

I hope you can imagine the board: 5.7 x 2 feet and 1 inch thick. Basically like this picture:

April 15, 2021, 1:32 PM · Floors:
A traditional hardwood floor is nailed to the sub-floor. I you were to use a water-based sealer, you might find that each individual narrow board has gone slightly convex, if you checked it carefully with a straightedge. Once all the extra water is gone, it would presumably return to being flat, although any time wood is moistened, or even humidity-cycled, it can release stresses remaining in the wood and result in an altered shape.

The moisture content of wood in violins and flooring will rise and fall (with some time lag), according to the relative humidity of the surrounding air. Since violins have arched tops and backs, they are a little more forgiving of expansion and contraction than a flat board. Since the tops and backs are secured at the perimeter, the expansion from increase moisture content tends to manifest as an increase in the arching height, and a decrease in moisture produces a decrease in the arching height.

Why don't seams come unglued if these stresses get too high? Ideally, they do, if they are glued with a deliberately weak glue, as they are supposed to be. It's much easier and less expensive to glue an open seam, than it is to repair a crack resulting from the seams failing to give, and a re-glued seam won't devalue a violin like a repaired crack will.

Edited: April 15, 2021, 1:45 PM · Phew! Reading this thread makes me downright glad that I'm an inferior woodworker relegated to making every large, flat surface out of veneered plywood!

My wife and I got a lovely wood salad bowl for our wedding, over 20 years ago. It came with a little bottle labeled "Wood Oil" (no snickering!) which is light mineral oil. After treating the bowl with the mineral oil and wiping it off again (which we do rarely), the surface will feel slightly oily to the touch for about a week. We have no hesitation about using it in that state, as mineral oil is harmless in such trivial quantities.

David mentioned epoxy and fiberglass resins as permeable to water. That could be a slow process, but it really depends on the resin. I learned this the hard way. I have an inert-atmosphere chamber ("glove box") in my lab that maintains a very dry, oxygen-free environment inside so that materials reactive toward air can be handled and transferred safely. I noticed that all the caps on the bottles and jars were shrinking and becoming brittle over time. Turns out the small amount of water inside the plastic softens (plasticizes) the resin material of the caps (phenol-formaldehyde), and over time (years) the water was leaching out in the "dry" environment.

There has been some discussion of oils that "dry." Vegetable based oils have C=C double bonds that are reactive toward oxygen leading to new C-C bonds among the oil molecules. (Traditionally favored oils like tung oil have many of these C=C double bonds, sometimes arranged in groups, which increases their reactivity.) This polymerization process makes the oil much more viscous over time until it forms, for all practical purposes, a solid ("dry") substance. Paraffins do not have these C=C double bonds, and that's why they can't "dry" in the same way. The drying process can be catalyzed (accelerated) by various formulations (generically called drying agents or "Japan drier") that often include soluble metal salts. Some Japan driers (not all) can impart a slight tint to the dried oil, and sometimes that effect is desirable. I'd be curious to know whether luthiers ever use driers.

Edited: April 15, 2021, 4:52 PM · Paul D, some makers use chemical "driers" in their oil-based varnishes. I don't, because questions remain about many of them ever ceasing to do their thing, which raises the prospect of a varnish more quickly reaching a nice state, but also going downhill more quickly after that. Some of them are also poisonous or toxic. Lead is one example, which is no longer allowed in paint.

Many makers prefer to use direct sunlight or UV light to speed up the drying of an "oil" varnish. By using that to bring the varnish to the "plateau" stage in the drying curve, that strong light-source accelerant can be removed at will, and any continuing drying and embrittlement slowed down considerably.

The printing industry has been using UV drying for a long time, partly because the drying can be done more quickly, and partly because it can be considered safer than incorporating potentially toxic substances into the ink constituents of products like magazines and newspapers which will be regularly handled by humans.

April 15, 2021, 3:51 PM · OK, wait a second.
I have done this many times: if you wet wood, then force it to bend one way, let it dry forced to be in that way, and then it's dried (to a considerable amount) after a few hours (no heat), it will stay like that, forever, unless you re-introduce water in the structure. Of course it will come back to it's original shape just a little due to internal tensions balancing. That's why I always have to go a little further to correct a problem.

When you use heat you are basically accelerating the process of that drying, so you can get to the shape you want real quick, and may be almost eliminate that come back (can you?). So, I don't understand how what you said about floors coming back to its shape fits that explanation.

If you pour water on wood, it will twist and wrap, unless there's something holding it. Oh wait... may be the wood of the floors is held by something... hahaha, of course it must be. Then that question is solved. Untreated wood floors can be wet a little bit and nothing will happen because they are supposed to be stuck or held to the base or under floor.

Paul, I can't reach your chemistry level so your detailed information can't be really processed by my brain right now, hahaha, little rusty. I "really" hate plastic veneers on artificial wood. If I am spending my time on designing a desktop with custom dimensions, legs, materials and everything, I will get solid real pieces of wood, as long as my money allows me. If I start to give up these things, then I cancel the whole project altogether and go to Ikea to "build" the desktop. Of course I will be cursing and criticizing the design, materials, etc...

April 15, 2021, 4:06 PM · To permanently bend wood - so it will retain its shape without being bolted to a steel frame - you need to soften the lignin by heating it, bending it while hot and let it cool. This is done with the ribs of a violin and it is done with the 2" thick oak boards of a wooden fishing boat. The difference is the time it takes to heat that wood and the force it takes to bend it. A large board such as yours is difficult. You would need to build a box to surround the board. This could be done with construction plywood. And then feed steam into that for a few hours. Finally clamp the board in place and let it cool.
The picture shows a table top made of staves and with breadboard ends. But as I understand your top is one big board? Impressive! But with a board twisted from the beginning I would be a bit worried that with changes in humidity that table will be lifting a leg....
Edited: April 16, 2021, 6:33 AM · Now that's way more helpful, appreciate it! Nicely explained!

OK, so I had this first conception that if you wet the wood, you soften it so you can deform it. The question now is:
Then what's the difference between wetting it and heating it?
How do you propose to heat a table like you see in the picture (I've already said the dimensions)? Hairdryer?
I "don't have" the space or time to build a chamber and create a steamer... that's why I was wetting the table, looking not to bend areas or surfaces that were straight.

My actual table is exactly like that one you see above, the legs have the same color, dimensions and material (metal, steel I guess), but my table is made from pine and it is composed by 6 long pine trims/beams stacked and pre-glued:

I am also worried about wrapping and curving, that's why I'm gonna reinforce it with 2 or 3, probably 3, laminated steel squared profiles all along it so it stays straight forever. To avoid unnecessary internal tensions I want the table to be as straight as possible before screwing the 3 beams, and with 0% twist.

Oh, another question here, lots of questions I am throwing... if you have a supposedly nice "tonewood" that's been drying for 20 years, and you wet it a little to correct a little bit of curvature... are you completely messing those 20 years of waiting?

April 15, 2021, 4:46 PM · Paul N. wrote:
"When you use heat you are basically accelerating the process of that drying, so you can get to the shape you want real quick, and may be almost eliminate that come back (can you?)."

Not really. Wood contains bonding ingredients which act somewhat like a hot-melt adhesive. Melt them, and wood cells or fibrils can slide over each other. Cool them, and things stick in their new position.

When the curve is bent into bows, this is done with heat, and without adding moisture.

Edited: April 15, 2021, 4:57 PM · Oh, very nice! That is amazing!

So if heat "melts the glue", then what water does?

Where would you apply heat, by the way?

Imagine I had an "U" shaped wood veneer. I would correct that by adding water to the top surface of the "U", and that would make it go the other way, straightening it. So where do you apply heat here? Top? Bottom? All around as if it were a piece of glue that you have to melt altogether and reshape it?

If the answer is the whole thing, I don't know how I can correctly heat a huge board like mine... May be once I've straighten it with water (basically almost now), I should go ahead and use the hairdryer all along the top and bottom of the whole board so I force it internally to stay that way?

Edited: April 15, 2021, 5:26 PM · I often straighten warped bridges by moistening the concave side (which will expand it), and heating the convex side, which will dehydrate and contract that side, while also softening the "internal glue".

No clamping or other physical force required.

April 15, 2021, 5:33 PM · The lignin I mentioned is the "glue" inside the wood. You basically have to heat it all the way through. That's why it is quick with a violin rib but takes a long time with a big board like yours. I am afraid a hair drier is not going to cut it.
You mention that you straighten it with water. What exactly do you do - apply water to one side of the board? Absorbing water on one side will cause that side to expand a bit which might change the twist of the board, but it will probably twist back once it dries again if you don't heat it.
Edited: April 15, 2021, 8:09 PM · David I agree that the UV-curing approach sounds much better. But I appreciate knowing that driers have been employed too.
April 16, 2021, 5:00 AM · To fix the slightly concave surface of the table I wet with water the top area. After a few minutes/hours you can see the differences, which can be a lot if you don't do it carefully.

To untwist it, I wet both sides top and bottom a little, so I don't get uneven humidity and new curves appear, and then put a ton of books in one corner on the table, another ton on the opposite corner of the table (the ones that are up), and put a small piece of metal in each other corner, under the leg this time. Since the legs are solidly screwed to the whole side of the table (look picture above with metal legs, I am basically using them to twist it the other way.

So, what you guys are saying is that I have to do that, and then, instead of letting it dry in a few minutes/hours, I have to heat it, right?
The only thing I can think of is a hairdryer, I don't have anything else.

April 16, 2021, 5:13 AM · Perhaps you could try an iron? With a wet towel between it and the table.
April 16, 2021, 6:14 AM · Paul, your strategy of moistening and tweaking alone may do the job. It's hard to know, since when lumber is dried from its living water-content state, stresses are inevitably incorporated which further moisture cycling can release, and these are not always fully predictable.
Edited: April 16, 2021, 6:33 AM · Or an iron, that's right!

David, I've done quite some projects with solid wood and I've always corrected these things with water, force and patience, although I have never tried to fix something 1 inch thick. I always read things about heating the wood, but since it was working for me just with water, I didn't mind to try that.

I'm definitely gonna try to iron it this time, to make sure the table stays that way.

By the way... I asked this question but got no answer I believe. When you work with wood that's been drying for years or decades, and you wet it... do you destroy all those years of patience?
If not, then, what's the difference between waiting for 25 years for a wood to be dry, and dry yourself in an oven during some hours or days pieces of wood?

April 16, 2021, 8:28 AM · Since wood air-dries from the outside in, the outside will initially dry in expanded state, held in that state by the not-yet-contracted wood on the inside. Later, when the inside dries, it will be held in an expanded state by the drier wood on the outside. It may take several moisture cycles to get the wood to it's final contracted state. (I've oversimplified this a bit.)

Another thing is that when wood is cut into flat boards and then dried, there will be some distortion and cupping, the degree and direction depending on the direction of the cut, relative to the annual growth rings. During drying, the boards are normally shimmed to maintain flatness, but the stresses trying to deform the wood are still present with many sorts of cuts.

The picture linked below shows some of the types of cuts, and the shrinkage and distortion which can be expected from each.

April 16, 2021, 10:32 AM · Yeah, I'm familiar with those cuts. So... how would you proceed with an iron?

I've thought about covering the top with a thin blanket, wet it evenly, and just start ironing?

All that WHILE it's twisted the other way to counter the natural twist. I have not worked on the table for 2 days and I have noticed that the twist has come back a little bit more. So the twist thing is hard to fix like I was doing it. Nevertheless, the concave or convex curves are easily fixed with what I was doing and they are not coming back.

April 16, 2021, 11:16 AM · Since your board appears to be made of glued-together strips, which could have the grain running all sorts of directions, it's hard to know what to recommend next. Before using heat though, do you have a way of knowing that the glue holding these strips together won't release when heated?
April 16, 2021, 1:50 PM · Oh... you are right. I didn't even think of that, that's why you are a luthier and I am not, hahahaha. The glue looks pretty good, the pieces are joined really well as far as I can tell. If I am not wrong I think I saw yellow traces of glue, really similar to those from the great Titebond glue, but I highly doubt they used a glue that expensive. I mean, even though I bought real wood, the whole piece was like $40 or so.

Should I risk heating it?

I don't know if it's my mind betraying me, but I would swear the twist is coming back even more. Not like the original state, but 2 days ago I had it almost leveled to the floor, and now the wood is doing "so much" force one of the legs is not touching the floor with one end. Not that it's really difficult to do that, because it gets flat if I press a little bit in the center with my bare hand and just a little pressure.

Thing is... I would like to apply the sealer and varnish once I check the normal state in rest is straight and flat. I still have not screwed in the steel beams, I'm pretty sure those will keep the revel wood in line so easily, but still, I'd love to make it flat and nice.

Edited: April 17, 2021, 3:45 AM · Titebond is often used in modern guitar construction, and heat, or some combination of heat and moisture, is used to release it.

One of the potential beauties of natural wood, and hand work, is that it looks different from what is produced to machine-age standards. Could you be OK with that, leaving some twist?

April 16, 2021, 4:19 PM · I thought it was one board. If it is glued of several strips with PVA glue forget about what I said.
Depending how big the twist is you could just decide to live with it? Add shims between the legs and the top to keep it from rocking.
Edited: April 16, 2021, 4:51 PM · Hahaha, so I forget about heating it?
I was hoping it was the key to perfection!

Yes, it is one single board, but not from a single cut. I hardly think you can find a pine, or actually any tree, that allows you to have one piece all together with such dimensions. It's always the same with wood objects: whenever you want 1 feet or more width and 1 feet or more length, commercially, you are gonna find mostly trims or cuts glued together. I don't know, unless you are a really professional wood worker that knows where to get single cuts of such dimensions.

So I do the same process?
Wetting top and bottom and apply a twist in the other direction?

April 17, 2021, 5:27 PM · Nothing, I think the iron even at maximum is not enough to correctly heat a 1 inch thick board.

I've tested, in the extra chunk I had, water + max temp ironing and the glue won't get affected at all. Basically the other side of the board doesn't care that there's an iron at 240ºC on the other side, the temp won't rise a single unit.

So... I've gone crazy and put "a lot" of counter twist force (it's basically noticeably twisted the other way) while wetting both sides and only parallel to the current twist axis, so it can only go concave or convex in that axis. In other words, I'm trying to soften only the wood that is in the middle of the table and perpendicular to the twist axis that is naturally occurring.

I'm gonna leave it like that for 20-30 hours while it dries, and hopefully it will balanced to a perfectly flat board.

My God I didn't thought it would be this hard (with my tools) to correct such a common and "trivial" problem.

April 17, 2021, 7:24 PM · "I didn't thought it would be this hard." You are working against the forces of nature. I also didn't know your board was joined. That certainly doesn't make the problem any easier.

How much deformation are we talking about? 1/16" or less? I thought for a moment that you could cut the board in half, feed it through your planer, and re-join the two halves, but I bet removing twist with a planer is nigh impossible.

April 18, 2021, 7:30 AM · Don't underestimate the forces of wood. Oak floors that have been laid down with too little distance to the walls have been known to move the walls when expanding as humidity rises. Even when screwed to the floor joists!
April 18, 2021, 9:07 AM · Guys, I finally made it, I wetted both sides and applied a counter twist that was the most extreme of all of the ones I did. I also ironed the bottom side although I don't believe it did anything important. Now it's finally sitting flat naturally, though it is still conserving some internal twist force because two corners get lifted way easier than the other two.

Nevertheless, now I have a bit of a curve in the middle, convex, so I'm gonna apply the counter twist again and then wet the bottom side so it goes concave.

I think I know what I did wrong previously. There was one time I managed to almost completely fix the twist (not as perfectly as it is now, but almost), but encountered the same problem: the board had went concave. So, WITHOUT reinforcing with the counter twist, I tried to fix the concave problem alone, simply wetting the top side. Since there was no counter twist forces and I wetted the wood, yeah, I fixed the concave curve, but the naturally occurring twist was free with the wet wood to again twist it.

So, now I am going to fix the concave problem WHILE I apply a counter twist at the same time, that way I believe everything will work out just fine.

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