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Help!!!
I’m finishing a musical instrument, made of maple and alder, and I’m having some problems. Just a short history of the finishing process:
– anilyne dye in a waterbase solution stain, wiped on, 2 day of drying
– 1# cut of dewaxed shellac, 2 thin coats sprayed on, 2 days of drying
– waterbase top coat, acrylic gloss finish, sprayed on in thin coats to prevent milky appearance, with hvlp.
– waited 3 hours between 1st and 2nd coat. Fifteen minutes after 2nd coat
was applied noticed some checking of the finish in a slightly heavy spot.
Checked my temp and rh in my shop, according to meter was 70F and 50%.
– after 20 hours, scuffed surface, applied 3rd coat, checking appeared after 15 minutes, also in new spots that were not heavy in coat. In some
spots, checking is very very fine, the lines are .060-.090″ long, almost
invisible in width.
– checked my temp and rh meter, turns out meter may be bad, used different
meter that indicates that original rh may be off by 20%. Used new meter to
humidify shop to 50%, original meter reads 70%. Shoot 4th coat after 24 hours from previous coat, sanded more rigoursly, same checking after 15 minutes.
Very frustrated. Don’t know if the finish is too old, I just bought last
december. Manufacturer does not have an idea, nor does the purchase point.
Maybe finish has too much solvent…my only option may be to sand smooth and recoat with a different waterbase topcoat. Any suggestions????
Replies
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Joe,
While the broken rh meter and age of finish might be an issue, it sounds like the first coat of waterbase top coat didn't dry completely. You mentioned it was sprayed on, could it be that there was one spot where too much finish was applied? If so, the top will "skim" or surface cure, while the stuff underneath hasn't cured/dried and still has some water/solvent trapped in it.
*Is it possible the shellac was old? Did you mix it yourself or buy it in a can? To check the shellac (if you have any left) put a few drops on a piece of glass or metal and let it dry overnight. If it doesn't dry completely (it will be kind of gummy) it is bad. That could be the cause of the checking in the finish. Also, the finish itself could be bad or may have been frozen at some point. Another thing to consider is how clean your spray equipment is. Is it possible another type of finish or solvent came in contact with the waterbased finish?
*Andy,Thanks for the reply.The shellac was fresh, just mixed it from one of the Hock kits. I'lldo the dry test tonite anyway. I called the manuf. of the finish, the finish was made last summer, and my shop doesn't get below 60F. I think I ordered the stuff in December, how would I tell if it froze in shipment?? The manuf is also sending me a small sample of the same finish, I'll apply that to rule out the finish. I think my equipment was pretty clean. I used straight denatured alcohol to clean the gun after the shellac. Should have I followed the alcohol with something else??I've heard of 'cold checking' with nitro lacquer applications, but not with a water base finish. How often have you seen something like this?? My last option before I completely sand down back to bare wood is to try a different waterbase topcoat, and hope the two finishes 'get along'. Any other suggestions??Thanks for your input, I really appreciate it.j
*Bob,Thanks for the reply.I waited 3 hours between the 1st and 2nd coats, to try give that 1st coat a chance to dry completely. The first coat was also very thin,no heavy spots. The 2nd coat was the culprit, and the checking firstappeared at one slightly heavy spot on the piece. In subsequent coats the checking appeared in many different spots, and to varying degrees.I tried exposing the piece to infrared light for a few hours shortlybefore the 4th coat was applied. The infrared light is suppose to dry the film from the inside-out. The manufacturer advised me to expose the piece to the infrared moments after the next coat is applied, to see if the checking is eliminated. Worth a shot, I guess.Once again, thanks for your reply, sorry didn't get back to you sooner. I'm little too busy at work...j
*Joe,Have you used this finishing system in the past? I think the problem may be with topcoating shellac with water-based material. The shellac has virtually no resistance to the water, and is probably softening slightly on application of the water, and possibly absorbing some. It is then a slower drying layer of shellac/acrylic being re-wetted with a coat of faster drying acrylic. The classic way to get crackelure finishes. I'm no chemist, but would stick with a traditional shellac/alkyd varnish or shellac/nitro lacquer combo, or switch to an entirely water-based system of sealer/topcoat.Good luck!
*David, Thanks for the reply.One of the reasons I sealed the stain with the shellac is to prevent the stain from 'bleeding' up into the topcoat and becoming mobile. This was a suggestion by at least two different sellers of finishing products, including the people that make some of the waterbase gel stains, which are great by the way. They recommended a very thin 1# cut of shellac, over the stain.By the way, your statement about shellac not having any resistance to water is not necessarily true. According to what I've read, specifically from Hock(and others, including Chris Minick)dewaxed shellac has pretty good resistance against moisture. Now I'm not sure it applies to topcoats of a waterbase nature, maybe one of the experts can shed some light on the subject. Anyway thanks for the input...j
*You should have no problem with applying water-based finish over shellac, especially a 1# cut that you let dry for two days like you said. In fact, dewaxed shellac is one of the best sealers there is and dries very fast. I have topcoated over a 1# cut within an hour and not had any problems. To answer your question about cold checking, that is a definite possiblility with water-based finishes. These products have a minimum film forming temperature which is usually around 50 degrees. Anything less than that and the finish may not dry properly and may even turn a bluish color. However, that being said, I used to work in a shop with a poorly heated finishing room that got very cold in the winter. I regularly sprayed water-based finishes when the room was only 45-50 degrees and I never had a problem with checking. In fact, I've never had any water-based finish check the way you described. If it's not the shellac and the gun isn't contaminated then I would think that either the finish itself is bad (or froze when it was shipped in December) or you put it on too heavy in a few spots. Without seeing it it is hard to offer a more specific opinion. If I were you I would recreate your finishing procedure on some scrap wood. Make three samples, one with the old finish, one with the new sample the manufacturer is sending and one with a different brand. This may give you an indication what went wrong. Good luck
*Shellac is definitely one of the best sealers available; and that it would be recommended by manufacturers OVER a water-based material (the stain), is no surprise. Shellac has great resistance against water VAPOR; witness the beautiful museum pieces with their French polished shellac that have been around for years. The same for wood floors. Put some wet boots on that floor, however, or a moisture condensing cold drink on the tabletop, and you will quickly see that shellac is permanently miscible; hence the popularity of drink coasters among our parents. It doesn't matter how thin the cut, or how long it dried.I too, use shellac as a sealer over many kinds of stain, but I also use it extensively as a sealer and a toner (orange) over imitation gold leaf, which would otherwise tarnish. Whenever I follow the shellac directly (that is, without a protective coat of varnish or lacquer) with water-based casein paints for "antiquing" purposes, the shellac quickly becomes somewhat cloudy and physically roughened. I don't know that this is what's happening to cause problems with your finish, but I believe it is by far the most likely reason. I agree with Andy that it would make sense to do up some samples, and if you can, I'd try one without the shellac, using a thin coat of your finish material over your stain as a sealer instead. As long as you're spraying, not brushing, it should work fine since once it's dry, nothing else can migrate up OR down through it.I hope you'll let us know if you find the cause and the solution!
*David, thanks for your input on the shellac situation. My next project I'm going to try shooting a waterbase topcoat right over the water base stain. I'm going to try very light mist coats to seal the stain, we'll see how it goes.I did try the infrared lights on the piece directly after spraying and the checking has gone away. Go figure??! The only other thing I'm doing differently is I'm no longer running waterbase solvent thru the gun after each coat. I was running water after the solvent for a minute or so... to purge the solvent.Don't know...Anyway, it looks beautiful, got a few more coats to apply. Thanks to everyone who responded.j
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