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a thick shellac finish is supposed to do that alligator skin thing but how thick does it have to be before it will happen? how long does it take for it to happen? tried searching but haven't been able to get anything substantial. thick is a relative term when not defined, which is how it is often found when search info about shellac. no real definite answer on the time line either, most reference antiques showing the alligator/cracking finishes.
Two to three applications of a 2# cut of shellac should be all that's necessary. Four to five applications can lead to problems. "Alligatoring" can begin to occur within a year or so. But, there are lots of factors that can affect the time.
so how thick is 2-3 applications of 2# cut? application method used will effect the final thickness. i guess what i'm asking for is a number.
Hi David, thickness can be determined by volume of solids applied, if your applying a 2 lb. cut of shellac then you have a 20% solids content since shellac bulks up at 10% per pound. a 5 lb. cut would be 50% solids for example. To know how thick your coating application is, you need a wet mil gauge that will indicate how heavy each application you apply happens to be.Quote:
Originally Posted by David Hawxhurst
For example - if you apply a 5 mil [5 thousandths .005 " ] wet coat of 2 lb. shellac to the surface, after the solvent has evaporated you will have a 1 mil - .001" thick film of shellac left as a coating. If no sanding is done on the first coat - and you applied further coats, then each coat would give the same if you apply it uniformly such as spraying. With sanding, there will be less thickness, but that will vary of course with individual means and time spent and coarseness of abrasive. to actually find out what the overall final thickness of a dry coating is you need to measure the surface or substrate your applying it to first with either a micrometer or digital calipers, other instrument and then again after all your coats have been applied and are through dry after 30 days.
Alligatoring is not a common occurrence as it was long ago, though it can or may happen. those antiques that have such were not done with pure unadulterated lac, they had varying amounts of rosin in them back then which helped lead to the phenomena more so and much quicker than modern lacs which do not have such. What you'll find with present bleached dewaxed shellacs is that it is rarely the case if freshly dissolved and applied and the finished pieces kept in a controlled indoor atmosphere, which were not available back a hundred or more years ago ok? Even if it does happen, it's no big deal to re-knit it back together with alcohol if you don't wait till it gets to the point of being so obvious that it looks like what you see on antiques. This is of course if shellac is used by itself and not just as a first coat under other finishes applied over it, Then ease of repair is a totally different story!!
I'm becoming increasingly aware of the importance of "freshly dissolved" shellac applied in a "controlled low humidity enviroment"
There are other side benefits to Joel, one usually not discussed on forums such as this is the bulking factor i mentioned, for example - if you dissolve 1 lb. of lac in 1 gallon of alcohol you bulk the over-all mass by 10%, giving you 140.8 oz of material. [128+12.8]. when instead you buy canned shellac, you do not get the extra 12.8 oz. Of course you will still have 128 oz. of 1 lb. shellac, but if you were to let it dry out till solvent free [hard] and weigh it, you would find it's weight to be only 14.4 oz. This allows the manufacturer [unintentionally] to gain profits when you consider that in the instance they sell a 2 lb cut shellac for example, a 20% bulk up, that every 6th 1 gallon can is pure profit on the lac portion of the material. In other words they gain the cost of 2 lbs. of lac as profit!! Might not seem like much when talking small amounts but when dealing with thousands of gallons - different story!Quote:
Originally Posted by Joel Wesseling
You or others on the other-hand when mixing your own, gain use of that extra shellac that is not present in a purchased can form, so if your using more than 5 gallons of 2 lb. cut a year, your the one who benefits in the extra free sixth can [2 lbs. of shellac] not them, in otherwords you get all that your paying for! :)
right now with the current weather the dna from the shellac evaporates so fast i not sure i can get a accurate wet mil reading. so generally how thick can i make a stand alone shellac finish? i'm using on a walnut picture frame. using a 2# cut of garnet for the finish. will be sanding some to level out the finish. have no idea how thick the finish will end up at because i didn't measure the frame with no finish first so, no baseline to start from.
I hate shellac.....really I do...
David,
You're trying to over think this.
IMH -Experience with shellac - trying to over think the application is a sure way to invite trouble.
A "thin coat" is one that, when brushed on or sprayed on, doesn't run or sag on a vertical surface or pool up on a horizontal surface.
IIRC, it also depends on the rate of spread doesn't it?Quote:
For example - if you apply a 5 mil [5 thousandths .005 " ] wet coat of 2 lb. shellac to the surface, after the solvent has evaporated you will have a 1 mil - .001" thick film of shellac left as a coating.
That's the way I'm used to dealing with wet/dry film thickness - to determine how far those 5 mils wet will go and still give 1 mil dry.
Opps - never mind. I didn't read far enough. I see you got that covered.(no pun intended ;))
well its done. many thin coats and some sanding. i guess i could sand it some more and put a couple more thin (hate this term) coats on and have it perfectly smooth, but the wife says leave it as is because you can still sort of see some grain and its wood thats how it supposed to look. i'm guessing that it was applied "thin" as it didn't pool or run. i really don't like this term thin it doesn't really define anything as there is no reference. credits cards are thin, paper is thin, photo paper is thin and yet when compare to each other a cc would be thick, photo paper a little less and the paper would be the thinnest. i guess this is just more of rant than anything because its always stated thin but never defined. oh well if it alligators i just fix it later.
You make a good point David, but thinness in this case has to do with the amount of solids the coating has, like lacquer and acrylics also, In other words, If you normally brush on a 5 mil coat in the same manner, be it 1,2,3,4,5 lb. shellac or not, when dry, it will give you a pretty consistent build. Yes, the build will vary, but only by the solids content in the solved shellac. If a 1 lb. cut applied 5 mil thick gives you one mil when you flow a coat on - the a two lb, applied the same way, will give you 2 mils and so forth. Another method for home use determination would be to use the average business card [5 mil] - and take a piece of glass and apply your normal coats your using to the glass until you reach the thickness of the business card - 2-3-4-5 coats or whatever, your hand is pretty sensitive when judging thickness when two thicknesses are butted up against each other to compare, besides, i don't find it critical enough to worry if your a mil or two more or less anyway, lac is very forgiving. Though if used as a first coat only under other finishes i would advise only to use 1 coat of no more than 1 lb cut ok?Quote:
Originally Posted by David Hawxhurst
Re: alligatoring...
Chances are if it hasn't done it now, it won't later...
With old alligatored, crazed and/or cracked shellaced pieces, who knows what all else they were subjected to over the years.
I know it bugs you - but - "thin" is the only way to say it.
Since dry film thickness is used for performance reasons only, it's not something that applies to shellac - therefore it has no relevance.
Thick or thin, shellac performs the same.
One or even a dozen mils one way or the other is a meaningless figure.
It will affect the appearance, but, not the performance.
The reccommended dry film thickness of a coating is the minimum thickness the coating can be applied and still deliver maximum performance.
If two coats of 2# cut look good, then a third coat or even a fourth coat will do nothing to add to the performance or protection it affords.
BTW- Sheldon did actually give you the "number".
2# cut is 20% solids by volume.
It will go one 5 mills thick wet, at a rate of 500 sq ft per gallon (some sources say 600) and deliver 1 mill dry.
However - while you're fiddling around with a wet film gauge checking, the shellac is going to be setting up and making it all the more difficult to get a smooth lap free finish.
Well...... you dont have to check it on the piece[s] your doing with a wet mil guage, just brush your normally applied coat on a hard surface like glass or metal or laminate, have your wet mil guage and paper ready and push the guage into the coating right after applying then push lightly with the guage on a piece of yellow paper on a pad and see where your at ok? then you can be pretty sure if applied in like manner cosistently, that you'll get the same ball park readings.
Rich - i don't understand what you mean by lac is not considered to be a performance coating?
i'm spraying the lac on and it looks good now so i not going to add anymore at this point. i will let it cure a few day then buff it down to a stain or semi-gloss as the natural gloss is a little much for us on this particular picture frame. i do realize sheldon put out some numbers and i will keep those in mind when doing lac work.
rich,
am i to understand that alligatoring happens rather quickly? i only been working on the finishing of the frame a couple days. its not showing any alligatoring yet.
i choose to only use lac for the frame because its going to hanging on a wall. i don't think i need a super durable finish like pre cat lacquer or anything like that after all it just hanging there looking pretty.
Only that there isn't a dry film thickness requirement for shellac as there is for other products.Quote:
Rich - i don't understand what you mean by lac is not considered to be a performance coating?
Varnishs, lacquers, acrylics, enamels, paints in general,,,all coatings w/the sole exception of shellac have a required minimum dry film thickness to achieve the published performance specs of the product.
Additional film thickness isn't required for the shellac to be able to resist abrasion, UV and/or chemicals.(performance reasons)
Additional film thickness may be aplied for cosmetic reasons - "depth" of finish.
[QUOTE][rich,
am i to understand that alligatoring happens rather quickly?/QUOTE]
It's been my experience that it happens within the first couple of days - most frequently in the first couple of hours - or - shows up decades later.
If it's decades later, as is the case with the old pieces where it's often seen, then it's anybody's guess what has also been done to that piece.
Someone may have, for example & this could very possibly apply in your case - cleaned the piece with Windex or another cleaner with ammonia.
Ammonia is the true solvent for shellac.
Not to put words in your mouth or anything, but, your first reaction to an alligatored finish on the picture frame, if it was cleaned with an ammonia cleaner that damaged it, would probably be to blame it on a "too thick" finish.
Shellac has a hundred and one different ways it can bite you in the butt.
(Did I mention - I hate shellac?)
Wet/dry film thickness is a low priorty concern when shellac has so many other ways to bite you.
In my past career, I probably had to remove as much shellac to settle customer complaints as any three people combined have applied.
Sanding and wiping w/alcohol a shellac job that went South in the 90 plus degrees and 86 plus % RH of an Ohio August day - in a garage with no ventalation - for three days straight - stands out in my mind as an experience I could have done without...
Toss in one very angry and vocal customer - constantly telling me how upset she was with the salesman and the company in general was just icing on the cake..
Shellac is the most unpredictable finish there is.
I've seen fresh shellac not dry on one part of a door, and dry fine everywhere else.
I've also seen 30 plus year old shellac, stored in an unlined metal can, dry perfectly fine.
As I said above - you're making this too difficult by over thinking it.
Thin coat, look at finish. Is it even? Fine, you're done. If not, another thin coat and recheck for an even finish.
What is thin? No runs or sags on a vertical surface and no pooling on a horizontal surface.
Dewaxed only..it lessens the chances of problems to some degree..
IMHO - you're fine w/the frame where you're at with it.
"Brown bag" it and maybe give it a coat of paste wax and if it looks good, call it done.
Then be careful to not use Windex on the glass..
Its good to know about the thickness.. Better undestanding of it all
My experience with seeing the alligatoring is when the shellac is older and put on thick like for grain filling.. Its shows up quickly as well
Fresh and controlled enviroment and it dosent seem to happen... Put some old and fresh on today and one coat of old and looks not to smooth and very slow to harden..
Joel