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| Shellac doesn’t harder? http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10102&t=15034 |
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| Author: | GregE [ Tue Dec 18, 2007 7:27 am ] |
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Hi All: I've been trying to apply a French Polish finish to a guitar, but after about the third session of French Polish the finish doesn't harden. I've left it for months and it will still take a "print" from any surface it is left on. Does anyone have any hints as to what the problem might be. Greg |
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| Author: | Mike Collins [ Tue Dec 18, 2007 7:30 am ] |
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How old was the mix? What did you use as the thinner? Mike |
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| Author: | j.Brown [ Tue Dec 18, 2007 7:30 am ] |
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Sounds like bad shellac. Good test for shellac: Drop a little on a mirror, glass, or a piece of metal. If its not hard by the next day, toss it and get some other stuff. Any other specifics you can give would be helpful for someone to troubleshoot. When it was mixed, what kind it is, where you sourced it, etc. -j. |
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| Author: | Michael Dale Payne [ Tue Dec 18, 2007 7:40 am ] |
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bad shellac!!! Test it on a piece of plate glass at 55-80 degrees f. Place a tear droper on the glass allow to cure over night. If the shellac does not harden the shellac has gone bad. |
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| Author: | GregE [ Tue Dec 18, 2007 7:40 am ] |
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[QUOTE=j.Brown]Sounds like bad shellac. Good test for shellac: Drop a little on a mirror, glass, or a piece of metal. If its not hard by the next day, toss it and get some other stuff. Any other specifics you can give would be helpful for someone to troubleshoot. When it was mixed, what kind it is, where you sourced it, etc. -j.[/QUOTE] Great questions guys: The shellac was an ultra blonde shellac flake dissolved in denatured ethanol (95% ethanol/ 5% isopropanol). I used it immediately after dissolving it (within one week). |
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| Author: | Michael Dale Payne [ Tue Dec 18, 2007 7:42 am ] |
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What is the solvnet you are using? What type of flakes did you use? What cut ratio did you make up. When did you buy the flakes and from who? |
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| Author: | GregE [ Tue Dec 18, 2007 7:46 am ] |
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I was using a 2 lb cut, purchased flakes from Wood Essence Distributing. The actual name of the alcohol was SDAG-9 (specially denatured alcohol from Commercial Alcohols Inc). |
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| Author: | GregE [ Tue Dec 18, 2007 7:51 am ] |
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Is it possible for the actual shellac flake to go bad? I know it can go bad once it is dissolved. |
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| Author: | Michael Dale Payne [ Tue Dec 18, 2007 8:18 am ] |
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Yes old flake can go bad. |
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| Author: | JohnAbercrombie [ Tue Dec 18, 2007 8:20 am ] |
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Greg- I've had good results with the shellac from WoodEssence, but your test on glass will give you the answer about whether the shellac is bad, within 24 hrs. If it is bad shellac, I'm sure Jeff will make it good. If the shellac is OK, there aren't too many possibilities left. Are you using oil when doing your FP? What kind? How much? Have you 'spirited off' the oil? What sort of wood are you applying the shellac over? Did you use pore filler under the FP? What type? Once you get all the details posted, I'm sure the FP experts around here (not me..only FP'd 2 guitars +3 tops so far) will nail down your problem. Cheers John |
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| Author: | GregE [ Tue Dec 18, 2007 8:32 am ] |
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I'm using extra virgin olive oil (very sparingly), which is well before its "best before" date. I'm finishing Indian rosewood. Initially, I put on a spit coat of shellac, then filled the pores with pumice prior to a light sanding and the application of the first session of shellac. I spirit off the oil the following day and then let the guitar sit for about two hours before starting the next session of French Polish. Anything else that would help the diagnosis? Just ask. I really need to nail this down. |
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| Author: | Laurent Brondel [ Tue Dec 18, 2007 9:02 am ] |
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In my experience a shellac that is mixed too thick, and therefore laid on too thick, FP or not, takes forever to harden, but it will harden eventually. A lighter cut cures and hardens much faster, however thinner the finish may be at the end. Also you might want to check if your alcohol hasn't absorbed too much water (if the container is not sealed fairly tight), which is really not good. Hope that helps… |
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| Author: | Michael Dale Payne [ Tue Dec 18, 2007 9:06 am ] |
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I see nothing in your process that would raise an issue. My guess is the shellac went bad either in the mixed state or the flakes were bad to begin with. Tell me; Did the flakes look to be consistent in color and vaugly transparent with little variation in the transparency or did you notice any whitish crystallisation in the flakes like you see on processed chocolate bars when they get old. |
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| Author: | FishtownMike [ Tue Dec 18, 2007 9:11 am ] |
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I believe you should start spirit off the oil at the end of the days sesion not the following day. This might be you problem. The oil sitting till the next day will keep the finish soft. And i don't believe a few hours after you do it the next day is enough time to harden. |
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| Author: | JohnAbercrombie [ Tue Dec 18, 2007 9:17 am ] |
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Greg- BTW, I had a problem with my FP picking up the imprint from a piece of carpet when I foolishly left it on a carpet-covered shelf overnight- but this was during the FP process, not after a few months. I'm sure it would not do that now (5 mos later). It certainly hasn't picked up any imprint from the case it's stored in. I learned to make sure I hung the instrument up after that, during the FP process- as I'm sure you have done. Cheers John |
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| Author: | GregE [ Tue Dec 18, 2007 9:38 am ] |
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[QUOTE=MichaelP]I see nothing in your process that would raise an issue. My guess is the shellac went bad either in the mixed state or the flakes were bad to begin with. Tell me; Did the flakes look to be consistent in color and vaugly transparent with little variation in the transparency or did you notice any whitish crystallisation in the flakes like you see on processed chocolate bars when they get old.[/QUOTE] The flakes I used looked completely consistent with respect to color and transparency (no whitish crystals), they also dissolved easily and completely. I have had other flakes that resisted dissolving and ended up with a good deal of jelly-like shellac left undissolved, but I never used them. |
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| Author: | jhowell [ Tue Dec 18, 2007 10:09 am ] |
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Nine chances out of ten it is the flakes. How old are the flakes and how hae they been stored? A lot of flakes will come in a 1 pound plastic bag that is only stapled. The flakes should be transferred to a air-tight container and stored out of direct sun light -- in the dark prefered. I use some tall kitchen cannisters from wally-world that seal with a rubber gasket for shellac flakes and keep them inside a cupboard. |
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| Author: | Claire [ Tue Dec 18, 2007 10:12 am ] |
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I use a 2 pound cut as my prefered bodying up mix. 2 pound cut should be touch dry in thirty seconds, and usually alot less than that unless you're applying it too liberally. The older the shellac flakes are the longer they take to dissolve. Instead of half an hour to dissolve in 100 ml of alcohol it can take 2 or 3 hours if its over 12 months old in my experience. If it takes longer than that it might be a good idea to toss it out. I think it also depends on the type of shellac flake and how you store it. I decant my flakes into a plstic bag if they aren't already in one, express the air from the bag and store it in a cool dry place. Mix it by weight and not by volume. Cheers, Claire |
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| Author: | Claire [ Tue Dec 18, 2007 10:19 am ] |
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I just read Jim's post. The plastic bags i now store my flakes in is air tight. Jim is right, it has to be air tight, whatever container you put it in. Shellac tends to clump together into a big mass if air and humidity can get to it. Cheers, Claire |
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| Author: | FishtownMike [ Tue Dec 18, 2007 11:01 am ] |
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This might not be a problem as much since it winter. But high humidity in the finishing drying area can be a problem. I have seen some pro's who use french polish hang their guitars in a drying booth thats heated with a lamp. Hows the humidity level in the area you use? |
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| Author: | GregE [ Tue Dec 18, 2007 1:00 pm ] |
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I've just been storing the flakes in the ziplock bag they came in, at room temp in the dark and the humidity is controlled (to around 40%) all year round. The flakes are about 1 year old now, but I've been trying to rectify this problem nearly as long. They worked for the first guitar I finished with them, but this one has been a bear! Although, come to think of it, they did take a long time to dissolve, even though they dissolved completely. |
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| Author: | Kim [ Tue Dec 18, 2007 1:21 pm ] |
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Flakes have a use by date, you can store them in a cool dark place in an air tight container and this will prolong that date but all the time that the flakes themselves are being exposed to moisture in the air, they are being adversely affected. With any exposure, the process of polymerisation IS taking place to some degree dependant upon the storage method employed. At some stage, as the shellac flakes gradually become less soluble in alcohol, they drying properties are also diminished and you will need to eventually throw them out so do not stock up on shellac flakes. Much better to re-order and pay the extra freight rather than fool around with it. That said, older stuff, not too old mind, is OK for coating jigs and benches but is not suitable for use on any project you have invested good time into. Cheers Kim |
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| Author: | FishtownMike [ Tue Dec 18, 2007 1:38 pm ] |
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I year is old. Your probably better off buying in small quantity. If they took a while to disolve they are old. Ziplock bags do absorb moisture and air. They are not trully air and water tight. Your probably best off using a dry mason jar or a plastic container and keeping them in a dry dark closet. Your best bet might be to strip and start again. I know you don't want to hear that but it's probably the best. |
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| Author: | Bruce Dickey [ Tue Dec 18, 2007 3:50 pm ] |
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Okay, I admit it, I've never tried real shellac. Just the Zinnser's stuff. So on my Christmas List (you know the one you make for yourself, 'cause no one asked) is shellac flakes. For sealing what color / grade should I get? TIA Bruce So this thread is once again evidence that some info goes in one ear and out the other. It always boggled my mind that so many of you love this stuff. Well, I'm trying to join the ranks of the convinced.... |
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| Author: | GregE [ Wed Dec 19, 2007 9:34 am ] |
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Thanks for all the help guys! I've just removed the finish for the forth time and I'll fill and start again with some new flakes that I ordered from LMI. Fifth time is the charm, right? Wish me luck! Greg |
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