Polyurethane vs Lacquer vs Shellac

[RossR]

I am currently finishing my first model, HMS Beagle from Occre.  I had some problems with the polyurethane that I used to finish it.  I opened a new can of Minwax quick dying polyurethane in March and had really good results.  By summer the poly from the same can wouldn't dry.  I expected slower drying due to higher humidity, but no matter how long I waited is stayed tacky.  

 

I would appreciate any insights into why this happened.  

 

Also, I will be starting my next model in a couple months and I am wondering if I should be using a lacquer or shellac instead.  I will be brushing it on, not spraying and would love to hear any thoughts on whether I should stick with poly or switch to something else.

 

Thanks

 

[Jaager]

I have nothing to suggest about why your polyurethane will not polymerize. 

 

I do not think lacquer is an appropriate clear finish for any ship model that is not a toy.  It is out of scale in thickness and is used to build up a thick layer and is usually glossy.  Glossy is not scale appropriate for 1:60.

 

Polyurethane has more who favor it than eschew it here.   I am firmly in the eschew camp.

It is a modern synthetic plastic.  It is great for bar tops and wooden floors. 

I see anything plastic (except for PVA) as being against the spirit of a wooden vessel built before 1860.

A traditional clear finish that is easy to use, allows extensive control, and is compatible with almost everything is shellac.

I can be applied using cloth or a brush.  It has an excellent reverse gear. Ethanol (95%) or isopropanol (100%) (91%?) or Methanol (if you can get it) makes it go away.   I am betting it is not so easy to remove sticky polyU.

 

Premixed shellac comes as "clear" and amber.   Shellac flakes do also, plus there are darker shades - shades that are not dewaxed or slightly dewaxed.   If it is not enough, traditional varnish, poly, lacquer, both types of paint can be used to coat over it.

Edited October 27, 2022 by Jaager

[Dr PR]

I have started experimenting with shellac and I like working with it. I have both a spray can (wasteful) and flakes, both clear and dewaxed.

 

It seals the wood nicely with a mat or satin finish that I like, and it doesn't stink. I have also painted over it with acrylics with good success.

 

One caution about shellac. After it is mixed it has a limited shelf life of only a few months. That is why many modellers get the flakes and mix them in alcohol (95% ethanol, available cheap as a fuel) when needed. Allow a day or two for the flakes to dissolve completely.

 

There are extensive discussions about shellac and how to mix and use it on the Forum.

Edited October 27, 2022 by Dr PR

[RossR]

Thanks for the thoughts on finishes.  I think I will look into Shellac for my next build.  

[Roger Pellett]

Shellac is a traditional ship model finish.  The noted Naval Architect L. Francis Herreshoff has written about the benefits oh shellac and the fact that his father Nathaniel Herreshoff used it to coat his half models; those hanging on the wall of his office in the Herreshoff museum in Bristol R.I. Over 100 years later.

 

Roger

[Bob Cleek]

12 hours ago, Dr PR said:

One caution about shellac. After it is mixed it has a limited shelf life of only a few months. That is why many modellers get the flakes and mix them in alcohol (95% ethanol, available cheap as a fuel) when needed. Allow a day or two for the flakes to dissolve completely.

Everything written about shellac that I've ever read contains the caveat that it has a limited "shelf life." I'm sure at least some of these articles have been written by experts. I've always used Zinsser's "Bullseye" brand pre-mixed "orange" (amber) or "white" (clear) shellac in quart cans. All I know is that I've never perceived any deterioration of the product over the passage of time and, in some instances, it took me several years to consume a quart of the stuff. I've certainly had it thicken a bit due to the evaporation of the alcohol solvent, which is easily resolved by simply adding more alcohol, but I've never seen any of the Zinsser's Bullseye shellac "go bad" sitting on the shelf. As this stuff probably has to set on the shelf in the store for a long time before it's sold, perhaps Zinsser has found some additive that solves the short shelf life problem? I don't know.

 

What i do know is that shellac is one of the handiest materials I know for modeling. It dries very quickly. It's easily thickened by just letting a small amount sit in the open air for the alcohol to evaporate. Thinned shellac is an excellent wood finish that can provide the entire range from matte to high gloss, depending on how thick you wish to apply it. It's also one of the most moisture resistant coatings available. It can be hand-rubbed to a perfect finish ("French polishing") or, applied thin, can serve as an invisible matte sealer beneath any other coating. It can also be used to stiffen rope to form catenaries in rigging and seal rigging knots which can later be easily undone if needed. Thickened shellac is an excellent adhesive. Shellac is archival material that will last for centuries and is easily dissolved and removed with common alcohol. It's also non-toxic (except for the denatured alcohol its dissolved in. Shellac is used in confectionary making to give a gloss to candies such as jelly beans.) And, last but not least, it's readily available in paint and hardware stores and relatively inexpensive.

 

I can't see what's not to like about the stuff. 

Edited October 27, 2022 by Bob Cleek

[DelF]

On 10/27/2022 at 7:19 PM, Bob Cleek said:

I've never perceived any deterioration of the product over the passage of time

I've been using small amounts of pre-mixed shellac out of the same bottle for the last five years and it's still as good as new. 

 

On 10/27/2022 at 7:19 PM, Bob Cleek said:

I can't see what's not to like about the stuff.

Me neither.

 

Derek 

[glbarlow]

I’m quite comfortable with wipe-on Poly and get a chuckle from those that oppose it for what consider the silliest of reasons. I have 20 year old models that look the same as the day after I applied it. straight up Polyurethane I’m sure is a whole different thing I’d imagine.   
 

Never tried shellac. 

Edited October 28, 2022 by glbarlow

[hollowneck]

54 minutes ago, glbarlow said:

I’m quite comfortable with wipe-on Poly and get a chuckle from those that oppose it for what consider the silliest of reasons. 
 

Never tried shellac. 

I only use poly sealers on my models (and base/cases). Fun fact: Shellac is made from the carcasses of beetles(“🎶…Yeah,yeah, yeah”).

[Roger Pellett]

I have built one Dockyard style model, a 1:48 scale model of an 1812 era New York Pilot Boat.  I used classic modeling Woods; English Boxwood, Pear Wood, and Holly.  The model, fitted with stub masts was not rigged.  

 

When I finished the model, I went to a local shop that sold auto body paints.  I had them mix up a quart of clear lacquer.  I sprayed the entire model with a primitive air brush.  

 

The lacquer produced a nice matt finish without noticeable buildup.  44 years later the glass cased model still looks great.  I recently took it out of its case to clean up some dust. The finish looks as good as new.

 

Roger

 

 

[Bob Cleek]

4 hours ago, glbarlow said:

I’m quite comfortable with wipe-on Poly and get a chuckle from those that oppose it for what consider the silliest of reasons. I have 20 year old models that look the same as the day after I applied it. straight up Polyurethane I’m sure is a whole different thing I’d imagine.   
 

Never tried shellac. 

Wipe-on polyurethane is simply full-strength polyurethane thinned down with solvent ("paint thinner"). Solvent is a lot cheaper than the base polyurethane coating, so you are paying a lot of extra money for half the polyurethane canned in a "wipe-on" pre-thinned consistency. It's far higher in VOCs than alcohol, so you've got the toxic fumes and environmental downside to consider and its solvent-required clean up can be somewhat of pain, however small those considerations may be in scale model amounts. (Polymerizing polyurethane produces an amalgam of toxic compounds that can be extremely toxic when released as fumes into the indoor air.)  This "value added for DIY marketing" seems to be a uniquely American phenomenon. I've heard that Minwax doesn't export their "wipe-on" product in Europe because the apparently more sophisticated European market realizes thinning the product yields the same result at lower cost. 

 

That said, polyurethane is a great finish. It is highly abrasion-resistant and impervious to liquids, particularly alcohol, which absolutely makes it the best choice for things like hardwood floors, table and bar tops, and the like. When thinned, It yields a nice finish on any bare wood and can be applied by unskilled finishers by simply wiping it on with a rag.  

 

Shellac is dissolved in alcohol and is easier to clean up without any toxic risks. It doesn't have the abrasion-resistance of polyurethane, and spilling an alcoholic beverage on it will require restoring the finish as the alcohol will dissolve the shellacked finish. However, this characteristic is an advantage in modeling, particularly when shellac is used to stiffen catenaries in rigging line, to secure rigging knots, and as an adhesive. Shellac can be used in a thick suspension as an adhesive and thinned as desired for a variety of finish effects. Obviously, polyurethane's abrasion-resistance and imperviousness to alcohol is unnecessary in modeling applications so shellac's lack thereof is of no moment.

 

About the only reasons I would consider sound for favoring shellac over polyurethane for modeling applications are 1) the uncertainty of polyurethane's long-term archival qualities, although for the relatively short period polyurethane has been around, it's not exhibited any tendency to deteriorate. 2) Shellac and its alcohol solvent is less expensive than wipe-on polyurethane, though not by much. 3) Shellac apparently has a better shelf life than polyurethane coatings and won't start polymerizing upon exposure to air and "go bad in the can." 4) Shellac can be easily removed with alcohol at any time after it "dries" by the alcohol's evaporation. Polyurethane cannot be easily removed with solvent once it polymerizes. Very aggressive strippers or mechanical removal is required once it's "cured."

 

I don't think the any of the reasons for or against both polyurethane finishes and shellac are "silly," they're just a matter of taste. As the saying goes, "Ya gotta dance with the girl ya brought" and it's bad form to judge another guy's date harshly. It's all just a matter of taste.

[Bob Cleek]

4 hours ago, hollowneck said:

Fun fact: Shellac is made from the carcasses of beetles

Actually, shellac is a ground-up resin that is secreted by female lac beetles to build self-protective tubes (sort of like termites) from which they suck the sap from the trees upon which they live. Shellac is collected by scraping the tubes from the trees, then heating them to liquify the shellac, and straining the liquid shellac to remove impurities. Modelers who use shellac can reassure animal rights activists by labeling their models: "No beetles were harmed during the making of this model."  

 

Shellac is also edible! They use it to put a shine on apples and citrus fruit for the supermarkets and to make jelly beans shiny.

 

Edited October 29, 2022 by Bob Cleek

[Dr PR]

Bob,

 

Thanks for the comments about shellac's shelf life. I have wondered if this was just rumor. I have seen other posts from folks who have used containers of shellac that have been around for many years. Like you said, I suspect that solvent evaporation is the most serious problem, and that is easily solved by adding more ethanol.

 

And cheap ethanol is easy to find. It is sold as 95% denatured alcohol fuel for stoves, with 5% methanol to discourage it from being ingested.

[Jaager]

In my hands, the flake form of super blonde shellac has a shelf life.  When it is too old, it does not easily dissolve.  The flakes fuse together and the lot that almost instantly dissolves when new. It will still be a gel at the bottom of the alcohol container after a week,  if you have had the flakes for a few years.  The flakes are sold in plastic bags, which does not exclude oxygen very well.  

 

[Bob Cleek]

2 hours ago, Jaager said:

In my hands, the flake form of super blonde shellac has a shelf life.  When it is too old, it does not easily dissolve.  The flakes fuse together and the lot that almost instantly dissolves when new. It will still be a gel at the bottom of the alcohol container after a week,  if you have had the flakes for a few years.  The flakes are sold in plastic bags, which does not exclude oxygen very well.  

 

Might it be that the flakes absorb some ambient moisture over time and that causes the problems with dissolving completely? Just a guess. 

[Jaager]

2 hours ago, Bob Cleek said:

Might it be that the flakes absorb some ambient moisture over time and that causes the problems with dissolving completely?

It does take on a white color in patches, so it may well be water and not oxygen. 

To speculate, if it is water, then it is a physical mixture instead of chemical reaction.  If so, then if the flakes could be dehydrated, then the flakes would be restored.  I wonder if a low heat oven would drive off the water without degrading the shellac?

[glbarlow]

We’ve done this before, I supplied pricing that clearly demonstrated that the $16 can of Wipe On Poly is cheaper than buying two products, especially given the extra chore of determining the mix ratio.  I’m quite comfortable that WOP is not sold in Europe due to their being more sophisticated, that is also just silly. The silly you reference is the commentary on why WOP is so inferior when in fact it isn’t. 
 

It’s ok to use shellac, if that is your choice. Just because it is your choice is no reason to denigrate any product other than that.

 

i also don’t accept the equally silly comment that WOP is used by the unskilled. In fact just slathering  it on with a rag is not how it’s properly done. Let’s  compare my WOP models against your shellacked ones. 

[Roger Pellett]

I seriously doubt if anyone is going to become financially deprived by buying shellac vs WOP vs lacquer.

 

 I grew up well before we became conscious of environmental hazards of various finishing materials, manmade and otherwise.  My parent’s hobby farm featured a long white board fence and my sister and I were the fence painters, each armed with a bucket of white oil based paint and a large paint brush.  We got as much paint on ourselves as the fence.  I am, therefore, rather insensitive to smelly paints and varnishes in my shop, particularly in the small quantities that we use.

 

WOP, shellac, lacquer- all work.  It’s a matter of personal choice.

 

Roger

[glbarlow]

34 minutes ago, Roger Pellett said:

WOP, shellac, lacquer- all work.  It’s a matter of personal choice.

Exactly!

[Bob Cleek]

7 hours ago, Jaager said:

It does take on a white color in patches, so it may well be water and not oxygen. 

To speculate, if it is water, then it is a physical mixture instead of chemical reaction.  If so, then if the flakes could be dehydrated, then the flakes would be restored.  I wonder if a low heat oven would drive off the water without degrading the shellac?

Hardened shellac supposedly melts around the boiling temperature of water, so care should be exercised in heating it. If it were to melt, though, it need only be ground up to dissolve in alcohol again. 

 

I've no idea if shellac flakes will even absorb moisture, though. Dried shellac is one of the best moisture barriers around, so it wouldn't seem like it would be prone to absorbing moisture. Dunno.  

[Bob Cleek]

7 hours ago, glbarlow said:

It’s ok to use shellac, if that is your choice. Just because it is your choice is no reason to denigrate any product other than that.

 

i also don’t accept the equally silly comment that WOP is used by the unskilled. In fact just slathering  it on with a rag is not how it’s properly done. Let’s  compare my WOP models against your shellacked ones. 

This isn't any sort of contest between polyurethane and shellac. I'm not denigrating any particular finishing option, as I thought I made quite clear in my post.  It was my intent to simply outline the differences between the two. I have no investment the choices anybody makes when finishing a model. As I said, "It's all just a matter of taste." I am sorry that I apparently touched a nerve of some sort. That was neither intended nor expected.

 

[Bob Cleek]

1 hour ago, Roger Pellett said:

I am, therefore, rather insensitive to smelly paints and varnishes in my shop, particularly in the small quantities that we use.

I love the smell of automotive lacquer in the morning. It smells like... like victory!  

[Jaager]

2 hours ago, Bob Cleek said:

I love the smell of automotive lacquer

I appreciate the intended humor. 

I will use this as a gate though.

I very much resist using aerosol anything.  The process turns materials that would not otherwise be available to breathe into particles that gain easy access to our alveoli.  It increases the concentration of volatiles  that are able to get there.

I use lacquer -  the brushing version - to coat my patterns.  It sort of simulates Mylar.  

There are two flavors of lacquer thinner. There is the original and there is "Green".  Both contain a rogues gallery of organics that are better not allowed to float around in our bodies.  From just brushing it, both solvents are fierce to breathe and to the eyes.  Only using it outside works for me. 

The spray version would not only increase the concentration of the solvents in the air, it would allow the actual particles of lacquer itself to be small enough to breathe.   I know - spray booth - and/ or space suit - can remediate most of the effects.  I prefer to not create situations where remediation is necessary if I can avoid it.  

The brushing lacquer is "designed" or "by its nature must"  leave a thick layer - that is the whole point in what I use it for.

 

I know spray lacquer can leave a thin protective barrier - I played a trombone thru age 19.  Lacquer is used to keep the brass shiny and in the hands of teens in travel and outside conditions,  the finish often needs renewal.  But, professionals applied it in "supposedly" ( it was the 60's ) safe conditions.  At home, it fails my cost vs benefit evaluation.

[Bob Cleek]

4 hours ago, Jaager said:

I very much resist using aerosol anything.  The process turns materials that would not otherwise be available to breathe into particles that gain easy access to our alveoli.  It increases the concentration of volatiles  that are able to get there.

My practice is to do any spraying outdoors with a large shop fan to send an airstream away from me. I don't use spray booths because I don't want to concentrate volatile fumes in hoses where they might ignite. 

[RossR]

I have a couple follow up questions about shellac.  I bought some flakes and have been experimenting with it a little with good results.  My question involves when it goes bad after a few months.  Is there any visible sign that it has gone bad?  What happens if I use older shellac?

 

[Bob Cleek]

8 hours ago, RossR said:

I have a couple follow up questions about shellac.  I bought some flakes and have been experimenting with it a little with good results.  My question involves when it goes bad after a few months.  Is there any visible sign that it has gone bad?  What happens if I use older shellac?

 

I buy mine pre-mixed in quart cans, which last for years. I've never had any show any indication of "going bad." Maybe they put some additive in the canned shellac to give it shelf-life. 

 

Shellac will thicken if the alcohol is allowed to evaporate. That's easily fixed by adding a bit more alcohol. I've used a lot of "old" shellac and I've never had any bad results doing so. 

 

Sometimes I suspect that "shellac going bad" is just disinformation spread by the shellac manufacturers to increase sales.  

Edited December 21, 2022 by Bob Cleek

[LyleK1]

I'm also a fan of shellac but to add to the conversation...

I really like using boiled linseed oil too. It easy to apply, fairly fast drying and a satin finish. Plus, I've put acrylics over and under it!

 

[Dr PR]

I have wondered about shellac "going bad." I did find one reasonable explanation - the alcohol solution will absorb water from the atmosphere if left open in high humidity. Apparently the water clouds the solution or something like that, and maybe it spoils the finish.

 

But these are only the "best guess" explanations I have found.

 

However alcohol is hygroscopic and will absorb moisture from the air, becoming diluted with time. Manufacturers recommend using 95% ethanol to dissolve shellac flakes.

 

I have also heard that the flakes will absorb moisture so they should be kept sealed. Manufacturers recommend storing them in a cool place.

 

I have never had a problem with "old" shellac.

[Jaager]

I use super blonde flakes.  A fresh batch dissolves fairly quickly.   Old flakes have a residue (a translucent gel) that never dissolves for me. 

 

Ethanol has a special affinity for water.  It is 95%:5% ethanol to water.  The bond is not covalent,  but it requires much more energy and effort to break than is possible with distillation.  One way is to distill from benzene.  Doing this in a closed atmosphere WILL yield 100% ethanol.  BUT, as soon as it is exposed to our atmosphere, it will pull water vapor in until it becomes 95:5 again.  I have not read anything to indicate that it will continue to pull in water beyond that concentration.  The ethanol will go to its gas phase if left in an open container.

 

[DaveBaxt]

Hi Bob and Derek I have been using sand 7 sealer for my last model with some success but thinking of giving Shellac a go. Is this the sort of thing I am looking for here in the uk

https://andrewscoatings.co.uk/shop/interior-exterior-walls/wall-sealers/zinsser-bullseye-sealcoat/