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Oil-Varnish Over Shellac

BurrDodd's picture

Has anyone had experience using an oil-varnish finish over a shellac coat. I've recently tried it out and find it gives a very smooth finish. But I'm wondering about it's long-term durability. Will the oil-varnish continue to stick to the shellac base?

I'm using shellac flakes dissolved in methylated spits (denatured alcohol) as undercoat with a satin poly varnish-boiled linseed-napthalene mix in roughly equal parts on top.

flairwoodworks's picture

(post #112468, reply #1 of 23)

You're going to run into adhesion problems if your shellac contains any wax. Dewaxed shellac is a great sealer.

Chris @ www.flairwoodworks.com
and www.flairwoodwork.spaces.live.com)


 - Success is not the key to happiness.  Happiness is the key to success.  If you love what you are doing, you will be successful. - Albert Schweitzer

Chris @ www.flairwoodworks.com
and http://flairwoodworks.wordpress.com

 - Success is not the key to happiness.  Happiness is the key to success.  If you love what you are doing, you will be successful. - Albert Schweitzer

YesMaam27577's picture

(post #112468, reply #2 of 23)

So long as the shellac is dewaxed, the poly should stick to it for a few hundred years or so. And I doubt that the oil -- once polymerized -- will give up and sooner.

I won't be laughing at the lies when I'm gone,
And I can't question how or when or why when I'm gone;
I can't live proud enough to die when I'm gone,
So I guess I'll have to do it while I'm here. (Phil Ochs)

. . I can't live proud enough to die when I'm gone, So I guess I'll have to do it while I'm here. (Phil Ochs)
SteveSchoene's picture

(post #112468, reply #3 of 23)

You are going to run into problems regardless of whether the shellac contains wax or not.  Shellac seals the wood.  Oi//varnish mixes must penetrate the wood.  Any oil/varnish mix that doesnt' penetrate should be thoroughly wiped off.  If not, any film remaining on the surface will be excessively soft, wear badly, collect dirt, and otherwise be a nuisance.  If there is a reason to do so, you can use a thinned varnish over shellac, though varnish containing polyurethane will need to be applied only over dewaxed shellac.   

Test your finish on scrap, FIRST, or risk having to scrap your finish.

BurrDodd's picture

(post #112468, reply #4 of 23)

Thanks very much for the feedback.

As far as I know the shellac flakes I use don't have any wax added. Do natural flakes have wax? It certainly looks as if the test batch of finish is holding well. I guess only time will tell.

Steve, I'm (tentatively and subject to correction) somewhat doubtful about the penetration of oil-varnish-thinner going very far into wood. Why wouldn't shellac or varnish go just as far? Does penetration depend on viscosity? I seem to remember reading somewhere that the idea of a finish penetrating into wood was somewhat of a myth. These are genuine questions/doubts. Anyway, I certainly do wipe off excess varnish-oil mix. And the oil-varnish finish is much smoother and quicker drying that on bare wood, and the result looks and feels like an oil-varnish one.

Reason I decided to try shellac under oil-varnish was that just oil varnish was producing varied results across the surface and drying slowly even though thinned. 4 to 5 coats still left some spots where oil-varnish had not produced a smooth surface. My main worry now is that the bond between shellac and oil-varnish is not strong enough.

Rich14's picture

(post #112468, reply #6 of 23)

Burr,

You're right that an oil finish (either alone or part of an oil/varnish) does not penetrate into wood as much as the description "an IN the wood finish rather than an ON the wood finish" seems to imply.

The penetration depends on the wood, and while it is actually quite small (microscopic), it's more than happens with "film" finishes such as shellac, lacquer or varnish. Solvent from film finishes may penetrate (then evaporate), but the solids don't.

I don't think that oils provide any protection as a finish worth thinking about. The protection afforded by an oil/varnish mixture is all in the varnish. But whether one argues about oil as a finish or just a wood colorant/figure enhancer, for it to have any protective properties at all, it has to polymerize within the very superficial wood fiber depth that it can achieve. It does no good just sitting on top of a barrier.

Shellac adheres tenaciously to the wood fibers below its film layer and as long as it's intact, it offers much more protection than polymerized oil can. And even a thin layer of shellac seals the wood enough to prevent most if not all oil applied to its surface from getting into the wood. So any oil in an oil/varnish top coat, not wiped "dry," does little other than form a polymerized residue that has no use at all, and actually becomes a nuisance for all the reasons Steve explained.

If you need the extra protection of a varnish film over shellac, and you want to use a wipe-on technique as is done with an oil/varnish, it's best to use a wiping varnish, not an oil varnish. You can build a wiping varnish film however much you want, from a very delicate, thin, one-wipe application or many thicker ones. But if you use an oil/varnish, over any other film finish, you have to wipe it so completely "dry" to avoid the residual, useless oil that you remove all the varnish.

In fact, wiping on many "coats" of an oil/varnish really doesn't accomplish much for the above reasons and if the object is to build any kind of protection, it's probably best to follow the first 1 or 2 oil/varnish applications simply with wiping varnish. That way, the wood gets the color and figure development that the oil imparts and then some extra varnish is built over top of that.

Rich

SteveSchoene's picture

(post #112468, reply #7 of 23)

Rich has given a very good explanation. 


It sounds perhaps that you might be looking for the wrong thing from an oil/varnish finish.  It's only purpose is to wet down the wood to reveal the wood grain and color.  It's not supposed to provide a film on the surface.  Other than color the wood is expected to look like it has no finish at all.  The only protection the oil/varnish look is expected to supply is to give you a little more time to wipe up water spills before the water discolors the wood. 


The amount of thinnner has very little effect on drying time. The "drying" of an oil, oil/varnish mix, or varnish consists of a chemical polymerization process including an oxidation with the air.  The only way thinner speeds drying is that it facilitates applying a thin coating that gives the molecules more contact with air.  Otherwise it just evaporates and then the real curing can begin. 


As Rich said, if you want the protection and look of a film, then one way is to use a wiping varnish.  You can make any varnish thin enough for easy wiping by adding thinner.  The amount isn't critical, though equal parts varnish and thinner are often recommended.  The film will build a little faster if you don't add quite so much thinner. 

Test your finish on scrap, FIRST, or risk having to scrap your finish.

HowardAcheson's picture

(post #112468, reply #8 of 23)

>>> As far as I know the shellac flakes I use don't have any wax added. Do natural flakes have wax?

I'm not sure this point got answered. Shellac contains wax in its natural state. To get dewaxed shellac, natural shellac is treated to get rid of its natural wax. The downside of shellac that contains its natural wax is low adhesion finishes like poly varnish and waterborne finishes do not adhere well to a shellac that contains its natural wax.

Dewaxed shellac is harder and more water vapor resistant than natural shellac.

Howie.........
Howie.........
BurrDodd's picture

(post #112468, reply #9 of 23)

Many thanks for all the information - much appreciated. I've learned a lot.

If anyone has the patience, three more questions:

1. What is happening with a Maloof finish of initial coats of oil-varnish-thinner and then final coats of oil-wax? Is it initially getting some oil a little bit into the wood and then just building varnish, i.e. does the setting of the varnish in the first oil-varnish coat preclude the oil in subsequent coats doing any good at all since it is applied over a hard sealer coat of varnish and then wiped off?

(A second coat of oil-varnish-thinner is probably a good idea in case any spots were missed in the first coat. These followed by one or two wiping varnish coats.)

And is the beeswax-linseed oil final polishing coat simply a waxing exercise or does the oil-wax mixture have properties that wax alone doesn't? The idea that this final coat penetrates INTO the the surface seems an impossibility if the set varnish is impenetrable. Sounds as if the rubbing of several coats of oil-wax is simply a polishing exercise that is perhaps likely to remove the oil.

2. If oil on bare wood is is a "colorant/figure enhancer", why not just apply oil, wait a bit, wipe off excess and then apply thinned varnish?

3. Is there any particular advantage in wiping on vs. flooding and wiping off? I find wiping on a thin coat more tedious than using a brush to apply a liberal coat and then wiping off.

Could we come up with a simple set of conclusions, a kind of very short Bible of descriptions/prescriptions concerning oil, shellac, varnish, lacquer, wax to demystify this whole finishing business - finish the finishing debate? (Not likely, but worth a try?)

SteveSchoene's picture

(post #112468, reply #10 of 23)

1.  If the first coat has completely sealed the wood surface, it subsequent coats will just be entirely wiped off.  The oil/varnish probably needs a couple of coats just to get the full and even effect without missing areas. 


The oil/wax is a polishing exercise, but it won't really remove the oil/varnish, since it will have cured in the wood.  The thinner in the oil/wax isn't a solvent for the cured or oil/varnish mix.  It is a solvent for wax.  The finish on the Maloof pieces I've seen is very nice, but not noticably unique.  But the chair I had a chance to sit in was extremely comfortable and felt "right."


2.  What you mention might work but there is a risk that applying varnish over the as yet uncured oil will cut off enough air to the oil that it delays it's cure.  The possible result is the oil underneath stays uncured for much longer than one would expect.  It's much safer to let each coat cure before applying the next.  There are circumstances where you don't have to do this, but if in doubt let it cure. 


3.  With oil/varnish flooding on gets greater penetration because the surfaces remain really wet longer.  Since only the bit that penetrates does any good with oil/varnish it's best to encourage it by the flooding, then wiping. 


But, using varnish is different.  There the object is different.  It is to build a film of multiple coats of varnish that provides the protection and desired appearance.  That means the coat is not to wipe off all the varnish, but to spread it smoothly and evenly, though still quite thinnly. 


A very strong recommendation for folks wishing to demystify finishing to to get a copy of Understanding Wood Finishing, by Bob Flexner.  It is more than a book of recipes, but gives a bit more background in that allows making sense of the process.  Jeff Jewitt's Complete Illustrated Guide to Finishing, which is a Taunton publication is also excellent. 


 


 

Test your finish on scrap, FIRST, or risk having to scrap your finish.

flairwoodworks's picture

(post #112468, reply #5 of 23)

Uh-oh. Steve, you have me worried now. On a past project, I sealed with a coat of shellac, then sanded it back and finished with an oil/varnish blend. That was about a year ago and I haven't heard about any problems yet. I'm not certain how far I sanded back - whether it was back to bare wood save for what filled the pores or just levelled.

Edit: Sealing with shellac did seem to reduce the blotching.

Chris @ www.flairwoodworks.com
and www.flairwoodwork.spaces.live.com)

 - Success is not the key to happiness.  Happiness is the key to success.  If you love what you are doing, you will be successful. - Albert Schweitzer


Edited 9/12/2009 1:11 am by flairwoodworks

Chris @ www.flairwoodworks.com
and http://flairwoodworks.wordpress.com

 - Success is not the key to happiness.  Happiness is the key to success.  If you love what you are doing, you will be successful. - Albert Schweitzer

CStanford's picture

(post #112468, reply #11 of 23)

Pick a film finish and stick with it.  Shellac is a finish in its own right and so is varnish.


There's no need coat one with the other.  Figure out which one is appropriate for the project and proceed. 


Shellac doesn't need 'protection' other than perhaps for a little wax, nor does it need to be used as a bar top finish. 


Use your common sense and quit making things harder than they need to be.


Edited 9/13/2009 8:32 am ET by CStanford

SteveSchoene's picture

(post #112468, reply #12 of 23)

CSTanford makes a good point.  There are times to be "fancy", but not as a matter of course.  There should be a specific reason to mix finish materials in a finishing schedule. 


Dewaxed shellac is billed as a universal sealer, but that doesn't mean sealer is needed very often.  Shellac itself is one of the most long lived finishes available.  It doesn't turn yellow over time, it deteriorates more slowly than almost any other finish.  It is a bit more brittle than varnish, which means it can scratch more readily, but it is easier to repair.  It is about the best at slowing transfer of water vapor, and is quite water resistant.  Yes, you can get white rings but you have to work at it.  No, you can't place cassarole dishes direct from the oven on it.  Mostly you can't clean it with alkalai cleaning products.  Ammonia is just one.  Basically all you need to do is exercise basic care and it will live longer than you will. 


Oil based varnish needs less care, but probably won't last as long as shellac before it needs a full scale refinishing.  It's harder to rub out. 


But if you want varnish, there is no reason to routinely start with a shellac undercoat.  Varnish is compatible with most stains after they cure, and with water and alcohol soluble dyes.  No barrier coat is needed.  Except in the high tech realm of certain pro finishes, every film top coat is it's own best sealer. 


If you have a watersoluble dye and want an waterborne acyrlic top coat you may want a barrier coat of shellac.  If you have an oily wood that prevents oil based varnish from curing or a waterborne finish from adhering, you may need a shellac barrier coat. 

Test your finish on scrap, FIRST, or risk having to scrap your finish.

Tony Z's picture

(post #112468, reply #16 of 23)

Steve,


One of the most pleasing finishes I've used is 3 coats of garnet shellac on bare cherry.  To gain a bit more protection on table tops I'm considering wiping a coat or two of satin poly.  Opinions?


Incidentally to others reading this thread and curious about shellac, I've been using a two pound cut (brushes very easily), with a brush made specifically for finished such as shellac.  If I remember correctly the brush came fro LV, was a natural bristly with the ends tapered.  Local borgs had nothing specifically tagged for this use, but I'm sure a good look-see at the bristles could find you one.  The right cut of shellac and brush make this a very nice finish to put on.


T.Z.

Gretchen's picture

(post #112468, reply #17 of 23)

Your "poly" might not adhere to the shellac unless it is dewaxed. Of course, there is a wonderful alternative to "poly" varnish, which would be NON-poly varnish, which would adhere to your shellac, waxed or dewaxed. AND look better.

Gretchen

Gretchen

Tony Z's picture

(post #112468, reply #18 of 23)

The shellac is "de-waxed" (Hock).  Can you explain the "non-poly varnish" a bit?


Thanks!


T.Z.


 

SteveSchoene's picture

(post #112468, reply #19 of 23)

There are plenty of varnishes on the market that contain no polyurethane.  You just won't find them in the borg.  Examples include varnishes based around phenolic resin (bakelite) such as Waterlox Original/Sealer, Gloss, and Satin also Behlen Rockhard; and, alkyd based varnishes such as Cabot Varnish (8000 series) and Pratt & Lambert 38.   


These traditional resin varnishes, compared to single part poly varnish, tend to cure harder, making them easier to rub out, to have greater clarity, making it easier to avoid a plastic look, and have better adhesion properties, making them easier to repair, and avoiding the necessity of using dewaxed shellac under them if shellac is used. 


None of these are natural resins.  Natural resins used to make varnish include amber, copal, and rosin.  They are still available as artist mediums and violin finishing.  Not much call for amber varnish for furniture finishing.  One source offers it for sale at $60.00 for 30 milliliters (a little over 1 fluid ounce). 


Edited 9/14/2009 10:47 am ET by SteveSchoene


Edited 9/14/2009 9:58 pm ET by SteveSchoene

Test your finish on scrap, FIRST, or risk having to scrap your finish.

Tony Z's picture

(post #112468, reply #20 of 23)

Thanks Steve!


I will definitely try one of the suggestions and I have no "heartburn" at all for not using poly.  The reason for topcoating the shellac was to get a bit more protection as we tend to entertain a lot, and many of the guests tend to over indulge a bit!


T.Z.

BurrDodd's picture

(post #112468, reply #21 of 23)

Have found out on the net that:

1. You can dewax shellac very easily - http://www.inthewoodshop.org/finish/dewax.shtml also - http://books.google.com.au/books?id=xSmgN9myx8cC&pg=PA63lpg=PA63&dq=shellac+dewaxing&source=bl&ots=J9zeV1albA&sig=rXYJYlGO4wt3khPhJcHMFhdFnf8&hl=enei=LK2uSsPGJ5TI6gPa-eDwBw&sa=Xoi=book_result&ct=result&resnum=4#v=onepage&q=shellac%20dewaxing&f=false

BUT YOU DON'T HAVE TO -

2. Poly varnish and water based clears generally stick well over waxy shellac -
http://www.josephfusco.org/Articles/shellac_test/dewaxed_shellac.html

Joseph Fusco (website just above) stuck Duct Tape down on a poly over waxy shellac finish, pressed it down hard, let it sit for 10 minutes and pulled it off. There was no visible residue on the tape. Also, he has generally been using poly over waxy shellac and has never had a finish failure.

Joseph used poly varnish, not oil-varnish. Time will tell if my oil-varnish over waxy shellac develops problems. I suspect not, but I also guess that duct tape could peel off some oil-varnish (especially some oil) no matter what was below the oil-varnish because I think even cured linseed or tung remains comparatively speaking a bit soft.

SteveSchoene's picture

(post #112468, reply #22 of 23)

A more standard adhesion test would involve cross hatched films of finish, with tape of specified properties.  But, that's not the real issue.  First, since it is so easy to obtain and use dewaxed shellac why mess with guessing that it will all work out.  Just play it safe and use the dewaxed.  Sure if dewaxed cost three times as much as shellac that still had wax, or if application was significantly harder then you might want to say "good enough", but since neither of those things is true you don't need to find excuses to try to get away with the less than best practice.   Also, realize that the tests are very static, and test at a specified time a finish that has had a limited amount of curing time.  But the real issue is longer term durability.  It's very hard to know whether the wear and tear you see after 10 years is normal, or based on bad adhesion. 


I've only seen really bad adhesion a couple of time, in this case with $200 per gallon bottom paint, which sloughed off the bottom of my sail boat with great abandon--it only required a plastic scraper to remove it entirely, in order to put on the replacement paint provided free by the manufacturer.  You can be experiencing adhesion problems long before you start seeing the finish peeling off in sheets.   


But, really when you get down too it, adhesion isn't an interesting question for an oil/varnish mixture over shellac.  You don't want the oil/varnish mix to adhere to a film of shellac.  Why, because as a film itself the oil/varnish mix is way to soft to make a good finish.  You mostly have to hope than none of it stuck where there was any shellac.  Because if the film remains on the surface it will be gummy, attract dirt, and generally become obnoxious.   


Edited 9/14/2009 10:03 pm ET by SteveSchoene

Test your finish on scrap, FIRST, or risk having to scrap your finish.

BurrDodd's picture

(post #112468, reply #23 of 23)

Here in South Australia dewaxed shellac can only be had at absurd prices for small quantities. Easy enough to dewax a cheap mix of flakes and ethanol. See http://www.inthewoodshop.org/finish/dewax.shtml. But I'd still like to see what happens to my test pieces with oil-varnish over waxy shellac. So far they are not gummy at all and just as hard as oil-varnish on bare wood.

I've been using VOT, i.e. varnish-oil-"thinner" (turps, mineral spirit or naphthalene) for years in mixes varying from roughly 1:1:1 to 2:1:3. Have never had a gummy finish. It always goes hard. Has a very slight linseed smell for a few months until (I guess) the oil completely cures. (Don't like the smell of tung.) It has been extremely durable on table tops probably because the varnish sets. It takes more building than a pure shellac or varnish finish, but varnish alone is too prone to dust nibs for my conditions and VOT is fixable by just applying another coat or spot fix and rubbing it out a bit.

I agree it's not as hard as just varnish, but for me its other qualities compensate. I did some scratch tests in inconspicuous places on a varnish surface and a VOT one - medium pressure with the prongs of a staple puller for paper staples. The results were similar. Scratching the varnish was more "scratchy" than scratching the VOT surface which was more "pillowy".

If I were building wooden kitchen bench tops, I guess I'd go for a two pot mix of epoxy or whatever. But for ordinary furniture VOT seems to work for me and shellac for inside cabinets, drawers, etc. Also, shellac for bookcases because there's no possibility of oil getting onto books. Shellac sets so fast and is so easy to sand or steel wool that dust is not a problem.

Rich14's picture

(post #112468, reply #13 of 23)

Burr,

While I basically agree with CStanford's post, there is at least one good reason for using shellac under a final finish of varnish. Shades of shellac darker than ultra blond impart their characteristic color to wood due to the natural dye in shellac. Many finishers rely on achieving exactly the coloring they want with a particular wood by the use of a particular grade of shellac.

Of course such finishers probably also use shellac as the only finish on such projects, but varnish could be applied over such shellac "coloring" if a varnish final finish is what is wanted.

(As an historical note, shellac was originally used not as a wood finish at all, but for its inherent dye which was extracted for coloring fabrics and other goods. The shellac resin solids were discarded as a waste by-product. Financial empires were built on that industry. Then aniline dyes were invented - about 200 years ago I believe - I may be a few years off - and being far superior in their range of color, intensity and ease of use, devastated the shellac-based dye industry. Shellac then came into use as a wood finish and a as coating for many other products, including foods and pharmaceuticals)

Varnish finishes other than water-borne variety also impart color to wood, usually an amber hue. Water-borne varnishes usually add no color at all.

If my final finish is going to be varnish, I simply start with varnish as the first "sealing" coat. I use a dilute mix of 50% solvent and 50% percent varnish out of the can. But some people like to use a thin coat of shellac as a "sanding sealer" to raise the last bit of wood fuzz before the last "finish sanding." There's no "one way" to do anything, what's really important is to gain understanding of the various processes and to use them knowledgeably to achieve an end that is pleasing to the craftsman (for all the reasons he/she is doing the work), based soundly on the properties of the materials and (usually) efficient.

Have fun.

(Steve, I must have been typing as you posted)

Rich


Edited 9/13/2009 10:22 am ET by Rich14

BurrDodd's picture

(post #112468, reply #14 of 23)

Thanks for the continuing feedback.

STEVE - Re your 2nd point: I should have said that an initial coat of oil would have to cure. Wasn't making myself very clear. Thanks for the recommendation of Bob Flexner's book; I'll get it.

CSTANFORD - I agree entirely with your feelings/advice. I usually use either shellac or oil-varnish. What caused me to start this thread was a recalcitrant table top made of "Northern Spotted Gum" (maybe eucalyptus citriodora) which was taking forever to absorb oil-varnish at all evenly. It finally did, but I wondered about sealing first since I have more Spotted Gum. So I tried shellac under oil-varnish on test pieces of Spotted Gum and Pinus radiata, which worked fine. But I had doubts about the longevity of shellac under oil-varnish.

Steve had a somewhat similar problem and also used shellac under oil-varnish. We both used shellac that was not dewaxed, which both of us have learned is a no-no. So far, however, our finishes are holding. Whatever the chemistry, time will tell.

RICH14 - Thanks for the knowledgeable summary and particularly the historical bit. Also, it should have been obvious to me that a first sealing coat of thinned varnish was the way to go. But am habituated to shellac and it's quick, so I thought I'd try it.

Rich14's picture

(post #112468, reply #15 of 23)

"am habituated to shellac and it's quick"

Burr,

I completely agree. Usually it's easiest to stay with one just one finish, but there's NOTHING that says that's some kind of rule. If using shellac is something one has become familiar with, why not start with that? Whatever works well within the properties of the materials.

Rich