Damaged Shellac Finish

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aushbaush

Well-known member
I have a mahogany table top which was finished about four months ago with about 20 coats of thin rubbed-out shellac.  About three weeks after finishing I put a lamp and a small statue on the table top.  I have discovered that both items have left "etched" surface marks in the finish.  On the bottom of the small statue I had placed small stick-on felt pads so that the item would not mar the finish. But it is as if the pads have somewhat dissolved the finish, to the point of green felt fuzz sticking in the remaining finish.  The lamp, about 25 years old, already had a felt bottom.  It has not "dissolved" the finish but has left several "felt-like" impressions in the finish.

It appears that I did not let the finish cure long enough before placing objects on the shellac surface.  How long should one wait?  And also, it may be that the sticky felt pads have some sort of "emission" from the adhesive which leaches through the felt and into the shellac?  Is this possible?

Fortunately with some work the shellac should be repairable.  I would welcome hints or references about how to "spot" repair without refinishing the entire table top.

Thanks, Dale
 
Dale, I'm interested in this subject as I recently had similar damage to a French polished sideboard. I blamed it on the Seedlac I used and the considerable wax content. To repair the surface I switched to a de-waxed blonde over the existing Seedlac. Not sure yet whether this is an adequate fix.

Tim
 
Dale, I am far from an expert finisher but seeing as how your not getting much of a response I will give you my thoughts. First I,m not sure what you actually did. Did you brush on 20 coats of shellac and then rub it out with pumice or did you brush on one coat then sand it before you added another coat 20 times also what cut was the shellac. The amount of build would be very different with the different approaches. In my experience shellac works best when it is keep thin and 20 coats sounds excessive to me no matter how you did it, unless you were french polishing or padding with very thin polish. For me shellac normally cures in much less than 3 weeks but I've never used 20 brushed coats, in fact I always pad or polish shellac. In regards to Tim's repair, it is usually not a good idea to put a hard finish layer over a softer finish layer because it may alligator eventually. To repair a shellac surface I would level it carefully by scraping with a razor blade and then french polish the area in need of repair but you need to get it cured first. If it will not cure wash it off with alcohol and start over. Put some shellac on a scrap board and put your statue on it to see if it was  the felt but I doubt that it was.
 
Dale, I have had this happen to me a couple times in the past, now a long time ago. The shellac I mixed was fresh, and it had "dried" for 2 or 3 weeks. It became clear that while it was dry, it had not fully cured. I now allow at least a month for a multi-coated (brushed or french polish) shellac finish to cure before I allow or advise placing something on it. If the climate is hot and humid, this could be longer. Also, if even a cured finish gets very hot such as being in the sun or in a shipping box the shellac may soften and whatever is pressed against it may stick or imprint. I guess this is one of it's drawbacks, nothing is perfect.
To repair I would could carefully sand the etching smooth with very fine paper, 1,000 grit or higher. Then pad more shellac on to polish it back up, or you may be able to get away with just polishing with a very fine polish. Behlen makes a product for just this problem. It is called Deluxing Compound. It is a paste wax that has extremely fine polishing compound in it. It polishes and wax's at the same time. It cuts the harsh gloss of new shellac and leaves a warm sheen and it feels silky to the touch. Also, it doesn't fingerprint. I use on just about everything. It goes a long way and I have had a pint can for years. I believe Woodcraft stores carry it. Good luck! 
 
The shellac was fresh, super-blonde dewaxed, 20 thin coats with small brush (like Don Williams advises) for some, and pads in the final stages, all sanded between every three coats.  I may have a sun heating problem as the table does get some low angle sun in very late afternoon.  I am going to place one of the "felted" objects back on the table in another spot to see if the impression occurs again.  I have to repair anyway, so I might as well test if the shellac is cured now after more than four months. 

Thanks for the info and repair recommendations.  Just a little more elbow grease.

I have to solve this issue of the shellac because if one can't use the furniture I will either have to choose another finish, another hobby, or perhaps another wife.

Dale
 
Hi All
  Dale, I think I can save you some time with testing the felt pads.The adhesive used on some felt pads do off gas enough to react to the off gassing of the shellac. You can get some cool reactions with melmac and lacquer also.Shellac can be soft if you apply too many coats without proper set time,or by using dated mix. The press marks can also be caused by heat. Antique dealers often get packing marks [blankets melted to surface] when they move from show to show in the hot summer.
I like to tell people to take it easy setting things on top for at lest 30 days for new finishes and 2 weeks for spot repairs. Over time heat will less of a problem but the felt pads will.  Kids and felt pads are good for business.  I also think some of the problem is the way you apply the shellac, if your using 20 thin coats,its  difficult to know when to apply the next coat. % of Water in the alcohol will make a difference as will weather when applying.Try French Polishing,after you "master" that try some French Patching,  this will give you total control of the color through the entire finishing process.
  Don't give up on Shellac,it's one of two finishes that can easily be repaired.

  Both Tom and John have workable repairs, it takes me about 30 min to 1 1/2 hrs [if felt or cloth is embedded] to repair.
  Good Luck    Randy
 
Dale - Not all shellac flakes are created equal.  Specifically, if the shellac has been exposed to high warehouse temerpatures and humidities while in the flake form, the material may not dissolve well (or fast) in alcohol, and also may not harden well once applied to a substrate.

This was the case for just about all stocks of shellac a couple of years ago - I'm not sure of the details, but apparently one of the main distributors of shellac flakes had some issues with storage that resulted in material that simply wouldn't harden properly.  I unfortunately experienced this first-hand, with several different purchases from several reputable outlets having the same issue.  I eventually had to toss 3 1-pound packages from these purchases into the trash.

Fortunately, at least one retailer (TFWW) recognized the problem and pushed the issue back up the supply chain.  I purchased a pound of de-waxed blonde from Joel about a year ago, and this material is amazing. It sets up extremely hard, and there is virtually no residue on the bottom of the jar.

So - it may not be you, it may be your shellac.  In response to your specific question, I usually allow 72 hours for the finished surface to harden and off-gas before putting it into use.
 
Thanks for all the great and knowledgable replies.  I believe that David has the answer that best fits my data.  I did an experiment overnight where I simply reset the same objects on the table in a slightly different position, and new marks appeared, in one case after only an hour.  The room is warm (85 deg f) but not hot, and no sun for the test period.  My shellac is simply not hard, even after four months.  I am lead to believe that the shellac must have been "damaged" even before I purchased it, even though it seemed to dissolve reasonably and left no residue in the jar.  The shellac was Tiger Flakes brand from Woodcraft.  So I will have to remove all the shellac from the top (I will leave the other parts alone) and start over.  I certainly now am gun shy and will have to do some major experimentation to ensure I have a solid solution betore I go through several weeks work to refinish the top.

I suppose my application technique could have been at fault, although I used methods described to me by Don Williams and several other extremely experienced SAPFM members.  Several thin coats in one day, dry 24 hours, lightly sand, then more.  I did use several methods to rub out the finish when application was complete, including Behlen Wool Lube with steel wool, and wet/dry sandpaper with water.  None of these "solvents" were on the surface for more than a few minutes.  I also polished with Rottenstone and parafin oil.  All of this was done in the wintertime with a very dry workshop.  If these techniques are questionable then I'll have to try french polishing, but even that will fail to harden if the shellac is fundamentally damaged from the start.

 
I know there has been talk the last year or so about "old" shellac flakes not dissolving and or hardening and that they should be thrown out. Last year, after these comments started circulating on the web, I attended  a workshop Don William's held at the Dakota County Tech school of Finishing and I specifically asked him if shellac flakes get old and should be discarded. He said as long as they dissolve, they are good. I believe him, as he has the chemistry as well as the working background to back up his comments. I personally am using stock that I have had for 5 or more years, and I know of others who do also, without any problems. Also, I have amalgamated many shellac finishes that were over 100 years old, to remove crazing. These finishes harden up again perfectly. I just hate to see folks throwing out perfectly good product.  Perhaps Randy can comment on this, I think he uses more shellac than the rest of us. 
 
John - I think the issue here wasn't so much the age of the shellac flakes as it was exposure over a number of months to very high temperatures and very high humidity (perhaps 120 degrees and 80% + R.H.).  I've personally done this (by accident, of course).  I stored a pound of shellac flakes in my finished attic room, and it gets quite hot and humid there in the summer.  When I pulled some of this material to use on a project in the fall (after a summer's storage in the attic), it would not set up properly.  This same material worked well when I purchased it in the spring.

From a chemistry perspective, it makes some sense that the presence of water as humidity and high temperatures would have a deleterious effect on shellac, as the chemical strucure of its main constiuent resembles a polyester that could be hydrolyzed under conditions of heat, humidity and exposure to oxygen.

In any event, I decided that a sealed mason jar, kept under the kitchen counter (where's it's cool year-round) with a dessicant and oxygen scavenger would better meet my needs.  So far, no bad experiences when stored this way.
 
Hi All 
  John  -- Being a follower of Don,s magic my self, I tend to go with, if it dissolves use it group. I found a bag of dewaxed orange flakes packed away in a road case I haven't used in about 15 years. I thought no way it could be any good, so I mixed some up. [That's just the kind of stuff I do around here]. It dissolved and mixed fine.

On the other hand, dkeller is on the right track. Heat and humidity can take-out a bag of shellac in 3 months , or less.  Many years ago, when I followed dealers to shows, I had a bag of shellac in the van for a 3 month trip. The van was parked in a sun filled lot for what still seemed like forever. Temps had to hit 120 f  every day. After the trip, I broke a chunk off, hit it with a hammer a few times and started to dissolve it. Well, I kept the goo about 4 months trying to come-up with some thing to dissolve it. For those of you that may be thinking, [what was I thinking?], remember ,[ that's just the kind of stuff I do around here]. When the shellac clumps together it called [blocking. ]  Not all blocked shellac is bad, try it before discarding.
  Here's a little tip, for those of you that French Patch, and can remember Star Chem. Co.,  Graining liquid and Wilpro, The portion a shellac that does dissolve can be pored off, and with a little tweaking, will substitute pretty good.
  Oh ya, I like to store the flakes in the frig, next  to the beer.
Do Good Work      Randy
 
A note about storage of shellac in a refrigerator -

All chemical reactions take place more slowly at lower temperatures, and in this case, a chemical reaction is what you don't want - oxidation/hydrolysis of the polyesters in shellac.  The other ingredients in this chemical reaction are moisture and oxygen, so minimizing those will also slow down the degredation over time.

The important thing to realize about a refrigerator is that when opened often (such as a household food refrigerator), the atmosphere inside the refrigerator will have a very high relative humidity.  As the refrigerator stays closed, the refrigeration coils will gradually remove the water from the air and the relative humdity will drop.

The other aspect of storage in general is that plastic - any plastic, whether a plastic bag, screw-top bottle, or snap-close "tupperware" type containers will allow both moisture and oxygen to diffuse through the walls of the container.  On the other hand, glass and metal has an effectively zero oxygen and water vapor transmission rate.  So if you want to minimize degredation of the shellac by avoiding moisture and oxygen uptake, you will want to store it in an impermeable container.  Common examples include mason jars with metal lids, and empty metal paint cans bought at the home improvement store.

To further reduce the oxygen and water vapor in the internal atmosphere of the container, you can add a dessicant and an oxygen scavenger.  There are several easy ways to obtain these:  for dessicant, you can purchase -sealed- dessicant packages at some pharmacies, and on-line.  You can also use rice - place the rice in the oven at about 200 degrees F for about half an hour.  Then place it in a sealed metal cookie tin or glass jar and let it cool.  Once cool, it's an effective moisture absorber.

For an oxygen scavenger, you can use one of the "pocket hand warmers" such as the Hot Hands brand.  These are basically iron filings mixed with keiselghur (a clay-like substance, which is just filler).  The iron filings oxidize and take up oxygen (i.e., they rust), and as a by-product produce heat.  However, when placed in a sealed oxygen-impermeable container, they use up the oxygen relatively quickly, and then the reaction stops, so the container never gets all that hot.  A substitute, if you choose, are fresh iron or steel filings, but these must be swept up after a filing session very quickly and put into the closed container.
 
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