Replies

1. 
   Kevin | Aug 22, 2003 06:05am | #1

   It sounds like there is some type of solvent or something similiar which is attacking the cat. lacquer from the underside of the finish. Exactly what... I couldn't hazard a guess. Call the manufactorer of the cat. lacquer and ask to speak to someone familiar with the chemistry of the product you are using. That person should know enough about the chemistry of the cat. lacquer to be able to offer some plausible causes for the failure.

   Regards,

   Kevin

1. 
   srenovo | Aug 23, 2003 10:59pm | #6

   Dear Kevin

   Thanks,

   srenovo

2. 
   Tao | Aug 23, 2003 07:21pm | #2

   Your problem is both the shellac and the thickness of your film.  You didn't say whether it was dewaxed or not, or what type of lacuer you were using (pre-cat, post-cat, what brand, how reduced, etc.), but you did two things that just don't work with most catalyzed finishes.

   I haven't used a catalyzed lacquer yet that doesn't have a limit of five or six mils for maximum dry coat thickness.  How soon you reach that thickness depends on wet mil thickness per coat, solids content of the finish, and how much you reduce it, but one or two seal coats and a couple of top coats is about the limit in most cases.  Fifteen coats is not only completely unnecessary, but is a pretty good guarantee of film failure, which usually shows up in the form of checking or crazing.

   Second, while shellac is a very good barrier coat in many cases, most high performance finishes do not adhere to it well.  Catalysed finishes can be self sealing, or they can use a catalyzed sealer, or you can often get away with a vinyl sealer with many catalyzed finishes.  I use a vinyl sealer under post-cats when I do specialty finishes with glazes.  

   I don't want to rag on you, specifically, but this is a good place to mention that it pays to read the literature when you try a new finish.  At least 80% of the finish problems I run into are due to improper application, wrong thinners, and incompatibility between one coat and another, almost all of which is covered by the product literature.  Professional finishes are not nearly as forgiving as those sold on the regular consumer market, and while a lot of pros have their own little tricks and variations, it is still safest to follow product instructions.  End of lecture.

   You can get a super deep, mirror like finish with regular NC lacquer, French polish(shellac), CAB lacquer (I think - - haven't tried to polish it myself), catalyzed urethane, and polyester.  The historically correct finish for a Herman Miller table is probably plain old NC lacquer. 

   If the table were mine, I would strip and start over, but you may have a hard time using store bought stripper.  You might have to use a stripper formulated for catalyzed finishes, and that brings a new set of problems with safety and darkening the wood, since most such strippers are fairly caustic.

   Michael R

1. 
   Kevin | Aug 23, 2003 09:33pm | #3

   You make a great point about the shellac sealer. I use Sherwin Williams products (on wood at least) for the most part and every one of their catalyzed finishes is called out to either be self-sealing or to be used over a vinyl (preferably catalyzed) sealer. AWI (Architectural Woodworking Institute), who set industry-wide standards to even out the bidding field, also calls out either self-sealing or vinyl sealer for use under catalyzed wood finishes.

   Like you, I use vinyl sealer a lot. Interestingly enough... vinyl sealers are just as good a barrier coat between dissimiliar finishes/surfaces as shellac is, as far as I've ever been able to determine. Jeff Jewitt mentions this attribute for vinyl sealers too, for those who want the say-so of a known authority on wood finishes.

   Good call on the sealer issue! That hadn't really occurred to me as I read his post.

   As for the dry film build... that caught my attention too. Correct me if I'm wrong here but, isn't that more an issue with the film's advertized properties such as abrasion/chip resistance etc.? Particularly given the way srenovo says he built up the finish in multiple thin layers, I'm inclined to think that each layer was properly cured out and therefore the dry film build shouldn't have failed the way that it did on this one panel. If he'd complained about it chipping or scratching easily, then I would have focused in on his excessive dry film build, since overly thick dry films are famous for chipping and otherwise marring very easily due to brittleness issues associated with the film's known properties at those thicknesses. But, it doesn't seem to be the source of his problem here IMHO. Or am I missing something here?

   Regards,

   Kevin

1. 
   srenovo | Aug 23, 2003 10:44pm | #5

   Dear Kevin,

   The finish was allowed to dry out between coats but not to the point of complete catalysis (if that is a word) as you have said -- because the lacquer doesn't completely cure for several days to more than a week.   I do believe that all of the layers "melted together."  I am contacting Chemcraft to see what they have to say.    Sanding is out as this is only veneer on a solid wood core.  Since the flaking is all the way through to the substate and I can get large flakes I'll try "miking" a few with my 1" in  0.0001 micrometer just for the fun of it.  I know that there is a proper tool for determining finish thickness but I do not have one.

   Any thoughts on removing this finish from just one side on the panel without damage the finish on the other side as this is a two sided panel?

   srenovo

1. 
   Kevin | Aug 24, 2003 12:13am | #7

   Hmmm... There is a fairly significant difference between catalyzed (usually referred to as "post-catalyzed") lacquer and pre-cat. lacquer. Pre-cat. lacquer usually isn't used as a self-sealing finish, for one thing... at least according to AWI. My earlier response was predicated on the assumption that you were spraying post-catalyzed lacquer (aka conversion varnish). I'm not chemist by any means... but, I'd be a lot less concerned with adhesion/compatibility issues between pre-cat. lacquer and shellac, personally. Although I will confess that I don't and never have used shellac as a sealer coat under any lacquer type. I prefer vinyl sealer or nitro sealer, personally.

   Given your description here, I'm inclined to believe that each coat of lacquer was sufficiently dry before the next coat was put on, and that trapped solvents isn't the problem here. Depending on the length of time between the first coat and the last coat, I would agree that each suceeding coat most likely did melt into the one before because that's just what pre-cat. lacquer does. I spray quite a bit of it, myself.

   Now... I've talked to the lab guys at Sherwin Williams about the refinish window for pre-cat and they tell me there isn't one. But... I do have one experience with pre-cat wrinkling upon being recoated with more pre-cat.... and I'm still not completely sure why. It is a known issue with post-cat. lacquers and varnishes that there is a so-called recoat window where the existing finish will react and wrinkle or lift upon being recoated. Post-cat finishes have to either be recoated before said "recoat window" or afterwards to avoid running into this known problem. As I understand it, this is a chemistry issue involving the catalyst where the catalyst will attack the existing catalyzed finish if recoated at the wrong time.

   As I say... I've been told by the "experts" that this isn't an issue with Pre-cat. lacquer. Yet... I have ran into it once. And my sole experience with pre-cat lacquer lifting was such that it only did it in some places and not others. To this day, with the "experts" being stumped by it... I don't know myself exactly why it did it.

   Anyway, it may be that this is what's happened to your finish. I doubt it, though. That kind of failure should occur within minutes, not after a couple days. It's hard to say without being able to look at the failed finish. If it is what has happened to your finish... I would say that the fix would be to use less coats and/or try to apply all of the coats within a shorter time frame. The one time that I had a problem (actually it was my experienced helper who had the problem), it was a case of a heavy coat of pre-cat being applied the day after the piece had already been finished with pre-cat. If you are reducing your pre-cat with lacquer thinner, try reducing it with MEK instead. MEK will evaporate much quicker and not get trapped... thus allowing you to apply the next coat sooner. If you're doing thin enough coats (and it sounds like that's exactly what you've been doing), blushing should not be a problem.

   As for how to strip the failed finish... That depends. If you applied the veneer yourself and you used contact adhesive to stick it with, it's much dicier to strip. If you purchased it already veneered or veneered it yourself using one of the common wood glues... I would suggest using MEK to soften the finish and then scrap it off with a putty knife or spatula, and then using more MEK or Lacquer Thinner with a synthetic steel wool pad (like 3M's red abrasive pad) to remove the remaining finish... wiping the dissolved finish off with a clean absorbant cloth as you go. It would have to be done very carefully to avoid damaging the other surfaces, though. The solvents would attack contact adhesive and probably cause the veneer to bubble... which is why I say it'd be dicier. It can still be done, though. Usually the bubbled veneer can be re-flattened after the worst of the solvents have flashed off by rubbing it back down with a block of hardwood or something like that. But... it's definitely a more difficult task to pull off, no doubt about that.

   Regards,

   Kevin

   Edited 8/23/2003 5:18:09 PM ET by Kevin

1. 
   srenovo | Aug 24, 2003 12:38am | #8

   Kevin,

   Thanks, I hope to hear from Chemcraft on Monday.  I will try MEK as both a stripper for the solvent for the refinish.  I will also give vinyl sealer a go.  I talked with the guy that I got the table from and before he brought it to me he did have someone start to refinish the table.  The person only got as far as removing the finish from one panel.  That panel had water damage to the finish and it is possible that it was contaminated with other things as it was thought to be just an "old table" only good for a "plant stand."  It is possible that the side that is giving me fits is the side that was "water damage as well as who know's what."

   Best,

   srenovo

2. 
   Kevin | Aug 24, 2003 01:03am | #9

   I talked with the guy that I got the table from and before he brought it to me he did have someone start to refinish the table.  The person only got as far as removing the finish from one panel. 

   Ah... now this is interesting! There may well be a connection here. He may have used one of the commercial paint strippers that contain parafin wax. If that's the case and some of it is still inside the panel you're having problems with... that could explain things. The solvents in your finish may well be dissolving into the parafin wax and then slowly evaporating.... much slower than you would want. Or it could be something similiar where something in the residual stripper is the source of your problem with this one panel. If that's the case then you shouldn't need to worry that any of the other panels will fail eventually since they weren't stripped. That's good news because now you don't have to worry about anything other than this one problem panel.

   When you get in contact with Chemcraft, mention the stripped panel. That should help them to help you diagnose the problem as well as custom tailor a fix that will work.

   There's another fairly recent thread here on the Finishing board where a guy was having problems with something attacking his nitro finish (that's basically what pre-cat lacquer is except it has an added acid catalyst) which was sprayed over shellac sealer. In his case the failure was strictly in the lacquer and the shellac wasn't being harmed at all. We also suspect, though we can't confirm it, that something waxy in the wood was the source of his problem too. If that's similiar to what you're experiencing... I would suggest that the easiest solution would be to strip that one panel and just use shellac to refinish it from beginning to end. Whatever is inside the panel will still be there. But, it would be effectively neutralized by the substituted finish which is unaffected by it. The shellac's obviously not as durable as pre-cat. lacquer. But... at least it shouldn't fail like the pre-cat. has been doing.

   Actually... now that I think about it... I dont' *think* parafin wax is alcohol soluable and it's certainly not water soluable. That may well be why neither water-based nor alcohol-based shellac are adversely affected. If you're using alcohol-soluable shellac and whatever is under there is also attacking your shellac coat, try switching to one of the water-based shellacs. I believe Goldhiller was using SealCoat brand shellac... if that helps.

   Regards,

   Kevin

3. 
   dondownunder | Aug 24, 2003 07:18am | #10

   srenovo,

   I very much concur with the previous posters. What I would add is that a collegue of mine had a delamination failure when using pre-cat over shellac so it may pay to be a little cautious.

   Don

   Edited 8/24/2003 12:40:10 AM ET by Dondownunder

2. 
   srenovo | Aug 23, 2003 09:54pm | #4

   The shellac is dewaxed super blond.  I desolved the flakes myself and after three days I decanted just to be sure.  The lacquer is precatalyzed.  The brand is Opticleer 900 made by Chemcraft.  The counter boys at my local professional finishing store had no literature so shame on me for not contacting the manufacture.  What makes this so difficult to fathom is four panels and six sides are visible as the table is used in it various configurations.  Only one of the six sides will not hold finish.  But I do get the idea that I have too much material on one side.  Since they were all sprayed with the same schedule do you think the other surfaces are about to fail?.    Also I have done this side over twice.   Before doing it a third time I will check with the manufacturer.  Finally since, new materials offer advantages over nitrocellulose finish and since I feel more like a preservationist than a restorer I like the fact that I can have better liquid resistance.  The piece will be used daily if I can get the finish to hold.

3. 
   Tao | Aug 24, 2003 07:50pm | #11

   I've used Opticlear a lot, and it's a very good precat, easy to spray and very durable. It's definitely designed to be self-sealing, and 5 mil dry film thickness is definitely the advertised limit.  It works fine over vinyl sealer, too, but not shellac. Regarding recoat windows, I really like to do all my lacquering in one day, usually 3 coats maximim, to get as much burn in as possible, but I sand between coats with 220 anyway.

   As I mentioned before, when I have seen precats fail because of too thick a film build, it usually takes the form of checking or crazing.  In this case, however, it might be delaminating instead of checking because of poor adhesion combined with excessive film build.

   It would be interesting to know just where the finish is separating -- at the shellac / lacquer interface, or at the wood.

   As far as the other panels go, I'd do and adhesion test on a couple of them in an inconspicuous place that can be easily touched up.  One very easy test is to drag a nickel (smooth edge) across the finish with varying amounts of pressure.  If the finish separates or comes off in flakes, you have an adhesion problem.  A more formal way is to cut an 1/8" grid through the finish with a very sharp knife, put tape on the grid, and pull it off.  Count the squares that come up.  If it's more than a very few, you have a problem.  If it passes the adhesion test, you might want to leave it alone until and unless it starts to check, which should show up within a year.  Marginal is just that -- marginal.  Might hold up, and might not.

   It seems pretty clear that the one panel has been treated diferently at one point in its life, and wax from stripper COULD be a problem, but when I have refinished with Opticlear, I usually get hot spots from wax residue where I didn't rinse well enough, and they go away after a couple of days.  I've sprayed a couple of hundred gallons of Opticlear, and never had any other problems with it.  I can't fault your preparation.  When I refinish cabinets and trim on site,  I usually strip twice with paste stripper, wipe down thoroughly, wash with TSP and wipe dry immediately, then rinse with clear water and wipe dry immediately.  Cleaning with solvent can't hurt and could help providing the solvents were clean.

   Opticlear is hard to strip.  It has very good chemical resistance.  The fact that you have a shellac undercoat might be a blessing here, because if the stripper can get under the lacquer, the shellac dissolves easily.  My first try would be to score the surface with coarse sandpaper and apply a methylene chloride and methanol stripper (read the ingredients label) and hope the stripper will penetrate to the shellac.  Be patient, and let the stripper do the work.

   I've redone a lot of table tops where the whole table didn't need to be stripped.  I just mask off the bottom carefully with lacquer tape (light green) and masking paper, and that generally works fine.  I use a paste stripper in the top, and hand strip.

   As for measuring dry film build, I only do this with a new finishing schedule, but an easy way is to stick a piece of aluminum foil down to a piece of scrap right next to the piece I'm working on, and make sure it gets the exact same treatment as my workpiece.  After a week, I pull up the foil, measure the total thickness, subtract the thickness of the foil, anthe result is dry film thickness.

   Michael R

1. 
   Kevin | Aug 24, 2003 08:50pm | #12

   It seems pretty clear that the one panel has been treated diferently at one point in its life, and wax from stripper COULD be a problem, but when I have refinished with Opticlear, I usually get hot spots from wax residue where I didn't rinse well enough, and they go away after a couple of days. 

   My experience has been the same. Ditto for all of the various nitro, acrylic or CAB based lacquer formulations. They all respond the same way to surface wax deposits in my experience. The reason I suspect wax here is that if it's underneath the surface far enough, it won't cause a visually noticable hot spot but will still be trapping solvents. Those solvents could, theoretically, prevent the underside of the finish from curing out and be the source of the overall finish failing even after the surface is apparently cured out - which is the case here since he was able to work the apparently cured surface before it ended up failing. This is all theoretical, of course. But, with his description of the failed panel having bubbled or blistered... it seems to me that something gassing off underneath the surface is what's causing the failure. So, from that I just try to backtrack and think of what could be down there gassing off. It could well be something other than wax, though.

   Like you, I'd very much be interested in knowing whether the failure includes the shellac or not. That would be a helpful thing to know in narrowing down the possible causes.

   I would like to throw in here that I've seen CAB lacquer respond to certain adhesives much the same way that it does to wax deposits. A number of years ago I was doing a job for Nike that involved putting a clearcoat on some structural wood beams made of something very much like OSB (oriented Strand Board) in that it was composed of a bunch of wood pieces all glued together in some sort of a press. Anyway... there were shiny hot spots all over the thing a number of hours after the rest of the finish had cured out. It took another day or so before everything was cured out and looked the same. Whatever was used in the manufactoring of the beam to glue it all together was a substance that the solvents clearly infiltrated and had a hard time flashing back out of.

   Regards,

   Kevin

1. 
   Tao | Aug 24, 2003 10:04pm | #13

   Kevin, I think we forgot about the shellac.  It is, after all, a very good barrier coat.  Even though catalyzed finishes don't adhere well to it, I would think that it would pretty well keep any wax residue away from the precat.  On top of that, a wash down with alcohol, mineral spirits, and laquer thinner, as well as a water wash, should result in a pretty clean surface, especially when sealed over with shellac.

   It would be really helpful to know what layer was failing......

1. 
   Kevin | Aug 24, 2003 11:02pm | #14

   I definitely agree that shellac is an excellent barrier coat and that it would effectively separate the wax from the pre-cat. The problem isn't the wax itself... it's the solvents that get trapped in the wax and then gas off slowly due to the inherent capacity of wax to hold solvents for a long time. That is the very reason why parrafin wax is used in stripping compounds. It skins over and holds the solvents and hydrochoride (or whatever that chemical is) against whatever is being stripped so that they can do their work of attacking the finish to be stripped. Shellac's well known barrier qualities don't do any good if it is permiable by the solvents so that they pass thru it.

   If you find that other thread that I alluded to earlier, you'll see that in that case something was definitely gassing off underneath the shellac, passing thru it without harming the shellac at all, and attacking the nitro lacquer above the shellac. The shellac was unharmed and still well adhered to the wood underneath. That tells me that shellac's barrier coat qualities don't extend to preventing certain solvents from passing thru it.

   As you say, though... it would be helpful to know whether the shellac is failing in this case or not.

   The potential problem with washing wax residue off with a solvent that will readily dissolve wax is that some of the wax, having been converted into a liquid, can soak further into the wood and thereby not be removed at all. This is a known issue with automotive paints, where wax is a greater problem than it typically is with wood. Everything I've read or been told on automotive surface prep says to degrease with a wax and grease remover (a refined Naptha is the preferred solvent for this) before abrading the surface so that the dissolved wax or grease can't be driven further into the metal substate and pose a problem. If the metal surface is sanded first and then a wax and grease remover is used, some of the wax/grease can and often will be driven into the freshly abraded surface and not be removed by the degreasing step. Obviously metal that hasn't been abraded leaves precious few places for wax or grease to hide where they can't be removed. Since wood is chock full of pores where wax and grease can soak into, this remains a potential problem with most solvent-based finishes for the same reasons that wax and grease pose a problem for solvent-based automotive paints.

   That said... I've stripped a number of items with the parrafix wax containing strippers and never ran into a problem like the one in this thread. But, I've also never used shellac as a barrier coat or sealer. So... it seems to me that the shellac is the substance that deserves closer examination in relation to possible causes for the lacquer failure in this case.

   Regards,

   Kevin

4. 
   mistikdragon64 | Jun 05, 2011 05:55pm | #15

   contaminating finish

   ok to start what type of detergent did you use?stripping and then two or three solvent baths, in laquer thinner is best/ detergent of most kinds are a sterate and will contaminate. second , mineral spirits shouldnt be applied to raw wood, its an oil base product and will repel a solvent base or water base finish.

1. 
   SteveSchoene | Jun 05, 2011 10:11pm | #16

   You are asking about posts that were made years ago, and where it is doubtful if the original participants are still hanging around to answer. 

   Mineral spirits is regularly and successfully used on bare wood under all kinds of finishes.  All but the lowest grade products will evaporate so completely that no harm to a subsequent finish could occur once it has evaporated. Since it is hard to know the quality of mineral spirits, I tend to use VM&P Naphtha which is a slightly lighter petroleum fraction.   For that matter, some petroleum distillates are often used as thinners in lacquer thinner.  Any residual oily portion of mineral spirits won't repell a finish with lacquer solvent, it will just be dissolved into the lacquer thinner with negligible affect.