# shellac under poly



## jlmarta (Jul 29, 2012)

Hello. I'm new to this forum and I have a question or three regarding the use of shellac under a poly finish. I'm turning a segmented bowl-cum-ashtray out of walnut, primarily, with a cherry base. The walnut has some sapwood mingled with the darker wood and even when sanded to 400 the wood still seems to be a bit porous. My plan was/is to use shellac as a sanding sealer - maybe more than one coat - and then finish with a satin poly. I want a very smooth finish but I don't think I want a high gloss.

I'm hoping someone with more finishing experience than I have can give me some pointers. I've read some posts that talked of using de-waxed shellac and others that talked of using a water-based poly. I really don't know which way to go and would be grateful for any help with this. Thanks in advance....


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## Steve Neul (Sep 2, 2011)

If it were me I would just seal the wood with the polyurethane. If you just want a sanding sealer, there is a sanding sealer made for polyurethane. The only time I use shellac is to seal pine knots or use the colored shellac to make the finish look old. Often I replace a part of a antique with new wood and the surrounding wood has a finish that is old and yellowed. I will often seal the new wood with amber shellac for the color. Then I normally topcoat the shellac with lacquer as I don't have a local supplier for the de-waxed shellac. You can use standard varnish over shellac however for polyurethane it has to be de-waxed shellac.

What I like to do with finishing turned bowls is leave them attached to the faceplate and sand between coats on the lathe. It makes a lot better finish than you could get otherwise.


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## Fred Hargis (Apr 28, 2012)

The urethane resins in finishes don't play nice with the wax in the shellac, hence the recommendation to only use de-waxed. That applies whether the finish is an oil based varnish or a water borne.


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## jack warner (Oct 15, 2010)

its not recomended to use shellac under any poly's. the shellac will seal the wood and not let the poly bond well.


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## Rick Mosher (Feb 26, 2009)

De-waxed shellac will work fine under poly, however there is also one very important thing to do first. Shellac is a solvent release type coating and each layer of shellac melts into the previous layer like lacquer does. However poly requires a mechanical bond for adhesion so your shellac seal coat MUST be sanded to a 220 grit to assure a good mechanical bond.


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## jlmarta (Jul 29, 2012)

Steve Neul said:


> If it were me I would just seal the wood with the polyurethane. If you just want a sanding sealer, there is a sanding sealer made for polyurethane.....


i think I want the poly because it's supposed to be a tougher finish. This ashtray will be for cigars and no cigar smoker I know props his cigar with the lit end resting on the bottom as many cigarette smokers do, but I still would like to have a tough finish, just in case.

If I use only poly, with multiple coats sanded fine between coats, are you saying I should be able to end up with a glassy-smooth finish without the tiny little dimples from un-filled pores? It sounds like it should work but I'd hate to try it and find out that it didn't.


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## jack warner (Oct 15, 2010)

Rick Mosher said:


> De-waxed shellac will work fine under poly, however there is also one very important thing to do first. Shellac is a solvent release type coating and each layer of shellac melts into the previous layer like lacquer does. However poly requires a mechanical bond for adhesion so your shellac seal coat MUST be sanded to a 220 grit to assure a good mechanical bond.


your key statement is poly need mechanical bond, even de waxed shellac will seal the wood and reduce bonding even if sanded. it serves no purpose using shallac under poly.


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## jlmarta (Jul 29, 2012)

jack warner said:


> your key statement is poly need mechanical bond, even de waxed shellac will seal the wood and reduce bonding even if sanded. it serves no purpose using shallac under poly.


Yeah, I'm beginning to see that. My original idea was to fill the pores with shellac and then finish with poly. 

I think you gentlemen have 'shown me the light' and I now think I'll just use poly. Thanks very much, fellas.


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## Bill White 2 (Jun 23, 2012)

Seems a shame to have that "bowl" finish burned as it will be.:furious:
I use Zinsser de-waxed "Seal Coat" under all my finishes. Never had an adhesion issue, but I don't make ash trays.
Bill


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## jack warner (Oct 15, 2010)

Bill White said:


> Seems a shame to have that "bowl" finish burned as it will be.:furious:
> I use Zinsser de-waxed "Seal Coat" under all my finishes. Never had an adhesion issue, but I don't make ash trays.
> Bill


why?


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## Rick Mosher (Feb 26, 2009)

jack warner said:


> your key statement is poly need mechanical bond, even de waxed shellac will seal the wood and reduce bonding even if sanded. it serves no purpose using shallac under poly.


Even if you seal with poly, unless you are only applying one coat, then you still have to create a mechanical bond between coats because that is the way poly works chemically. It isn't a debate it is science. 

So some people like to use shellac as a sealer because you can use amber, orange, button or many other types of shellac. You can even add alcohol dye stain to color a shellac sealer, as long as you use de-waxed (or remove the wax yourself) and sand properly to create a mechanical bond, you can safely do it. 

I normally like to stay within the same chemical family on my finishes but sometimes you have to push the boundaries and this requires knowing how and why things work. 

If you don't believe me I am perfectly OK with that. :smile:

If you would like to check for yourself and prove me wrong, it is a very simple thing to make a sample and do a simple adhesion test. After the finish has dried, cut 5 slits with a razor blade about 1/8" apart through the finish and parallel. Then make 5 more cuts 1/8" apart perpendicular to those making a tic tac toe board. Get the stickiest tape you can find, I like filament tape, and burnish it down tightly over the cut area with a little flag sticking up. Now rip the tape off and see if your finish is still completely there. If you have 100% adhesion there will be NO missing finish. If there are just a few corners missing you are probably OK. If the whole thing peels off you're screwed. 

This is a good one:









This is a bad one:









If you want to be more scientific order one of these. There are instructions for using it online as well.


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## jack warner (Oct 15, 2010)

mech bond of poly wasnt my pont. my point was there are no benifits to sealing under poly with shellac. there are better ways to color the wood.


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## jlmarta (Jul 29, 2012)

Bill White said:


> Seems a shame to have that "bowl" finish burned as it will be.:furious:
> I use Zinsser de-waxed "Seal Coat" under all my finishes. Never had an adhesion issue, but I don't make ash trays.
> Bill


You could be right about the burning, but I doubt it. No offense, but you don't sound like a cigar smoker. And I don't know about folks who smoke machine-made cigars but there's a certain etiquette/protocol among smokers of handmade cigars. Resting the lit end of a cigar on the bottom of an ashtray causes a cigar to burn crookedly, 'tar-up', and generally louse up the flavor. Instead, you rest the cigar in the 'stirrups' of the ashtray. And you put one out the same way. Grinding one out on the bottom as folks do with cigarettes produces a rather smelly atmosphere. Instead, you just lay it in the stirrup and let it go out on its own.

So, chances of it being burned are very slim but they do exist I'm sure. I appreciate your thought, though. I'm not sure I'd make an ashtray for a cigarette smoker unless it incorporated a glass bowl insert or something similar for that very reason.


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## Steve Neul (Sep 2, 2011)

jlmarta said:


> i think I want the poly because it's supposed to be a tougher finish. This ashtray will be for cigars and no cigar smoker I know props his cigar with the lit end resting on the bottom as many cigarette smokers do, but I still would like to have a tough finish, just in case.
> 
> If I use only poly, with multiple coats sanded fine between coats, are you saying I should be able to end up with a glassy-smooth finish without the tiny little dimples from un-filled pores? It sounds like it should work but I'd hate to try it and find out that it didn't.


 An oil based polyurethane builds in thickness pretty quickly. You should be able to cover most any little dimple with it. If you want it to fill faster you can use a pastewood filler first to fill the grain. I use the pastewood filler with lacquer finishes but they go on water thin and melt into the underlying finish. I think if you put a good coat of polyurethane on the bowl and sand it on the lathe where most of it is sanded off, the next coat or two should do it.


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## jlmarta (Jul 29, 2012)

Steve Neul said:


> An oil based polyurethane builds in thickness pretty quickly. You should be able to cover most any little dimple with it. If you want it to fill faster you can use a pastewood filler first to fill the grain. I use the pastewood filler with lacquer finishes but they go on water thin and melt into the underlying finish. I think if you put a good coat of polyurethane on the bowl and sand it on the lathe where most of it is sanded off, the next coat or two should do it.


I tried some walnut colored paste wood filler on some scrap from this project thinking it would fill the pores but it didn't come close to being the right color. I abandoned that notion. I think I'll try the other half of your suggestion with the poly. That sounds like it has a greater likelihood of producing the finish I want. Thanks very much. Your input is appreciated. Oh, and I'll try to post a WIP photo of this project as soon as I figure out how to post one. Thanks again.....


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## fromtheforty (Jan 15, 2011)

Here is why I use Dewaxed shellac under poly. 

1 - It dries fast and sands well. The first coat of finish always takes longer to dry than any other coat. 

2 - Water vapor does not pass as very easily thru shellac. Less vapor equals less rapid wood movement

3 - I have way less color shift in the finish over time.

4 - Better grain clarity than with stain

5 - less grain raising if I choose to use a water based finish

6 - Easy to color tint without having to wait 8-24 hours for stain to dry (dyes work very well for this as well) 

You may or may not agree with my opinions. I can only give you what I have found from my personal experience.

Geoff


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## jlmarta (Jul 29, 2012)

Another question... The chemical bond was mentioned above. If I were to use, say, a water-based poly, would a second coat 'melt' into the first and produce a good bond? Would water-based poly fill the dimples and eventually build up enough of a coat to produce a glass-smooth finish? I'm not after gloss but I do want smooth.


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## Steve Neul (Sep 2, 2011)

jlmarta said:


> i think I want the poly because it's supposed to be a tougher finish. This ashtray will be for cigars and no cigar smoker I know props his cigar with the lit end resting on the bottom as many cigarette smokers do, but I still would like to have a tough finish, just in case.
> 
> If I use only poly, with multiple coats sanded fine between coats, are you saying I should be able to end up with a glassy-smooth finish without the tiny little dimples from un-filled pores? It sounds like it should work but I'd hate to try it and find out that it didn't.


Think of it this way, at the microscopic level wood is like a bunch of drinking straws. When you put a coat of poly on the wood it runs down into the straws and turns hard. Of course when it dries it shrinks down and leaves a void at the end of the straw. Each time you put a coat on it comes closer to completely filling the straw and eventually it covers the holes and the surface. This is when you get the glass like finish. I know you don't like woodfillers but this is how they work, it's a thick paste that fills the straws in one application so when you put the finish on it builds to a glass like finish faster. Either way will work fine however filling the grain with poly is probably much more durable.


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## jlmarta (Jul 29, 2012)

Steve Neul said:


> Think of it this way, at the microscopic level wood is like a bunch of drinking straws. When you put a coat of poly on the wood it runs down into the straws and turns hard. Of course when it dries it shrinks down and leaves a void at the end of the straw. Each time you put a coat on it comes closer to completely filling the straw and eventually it covers the holes and the surface. This is when you get the glass like finish. I know you don't like woodfillers but this is how they work, it's a thick paste that fills the straws in one application so when you put the finish on it builds to a glass like finish faster. Either way will work fine however filling the grain with poly is probably much more durable.


Now here's an answer that even my stubborn old head can grasp. Thanks very much for that, Steve. Now I feel confident of the way I'll finish this job.


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