Trip Posted December 16, 2013 Report Share Posted December 16, 2013 ==>You get alligatoring with old shellac When I think of alligatoring, I'm thinking of a broad patch, not a single line... Something like the photo below... It's just I've never seen a single line of alligatoring being down to just old shellac -- but I've seen it plenty of times with old shellac combined with some contamination... Note: old shellac has adhesion problems and makes it far more prone to even the slightest contamination... ==>Silicone is no issue for shellac Well, in the most literal sense, you're right... Granted, the issue it not the silicone itself... The issue is spot contamination causing a differential surface tension resulting in differential adhesion... Over time, the shellac can crack, but not always... It could crack within a day or many years later... but in all probability, it will crack at some point... Note: one way to cure alligatoring is to add silicone to the mix (a very tiny amount) -- when I worked at a finishing shop, that's what we did... It imparts a consistent surface tension to the entire project resulting in consistent adhesion... We had a dedicated gun to avoid contaminating the spray gear... Also note, many of the shellac additives are actually silicone-based... Which is why they carry warnings about top-coating... Quote Link to comment Share on other sites More sharing options...
AceHoleInOne Posted December 16, 2013 Report Share Posted December 16, 2013 Could be all of the things above. Shellac should always be put down in thin coats and allowed to dry. Built up multiple thin coats. When you get heavy handed with shellac and pile it on, such things can go wrong even orange peel. Always use fresh finish, especially shellac. If this were me. I would chemical strip everything down. Then wash your wood good with 50/50 denatured alcohol and water. If finish contamination is the issue, it will/could/maybe happen again and you will have a re do it again. Why not do it once and call it a day! -Ace- Quote Link to comment Share on other sites More sharing options...
dwacker Posted December 16, 2013 Report Share Posted December 16, 2013 ==>You get alligatoring with old shellac When I think of alligatoring, I'm thinking of a broad patch, not a single line... Something like the photo below... It's just I've never seen a single of alligatoring like that being down to just old shellac -- but I've seen it plenty of time with old shellac combined with some contamination... Note: old shellac has adhesion problems and makes it far more prone to even the slightest contamination... ==>Silicone is no issue for shellac Well, in the most literal sense, you're right... Granted, the issue it not the silicone itself... The issue is spot contamination causing a differential surface tension resulting in differential adhesion... Over time, the shellac can crack, but not always... It could crack within a day or many years later... but in all probability, it will crack at some point... Note: one way to cure alligatoring is to add silicone to the mix (a very tiny amount) -- when I worked at a finishing shop, that's what we did... It imparts a consistent surface tension to the entire project resulting in consistent adhesion... We had a dedicated gun to avoid contaminating the spray gear... Also note, many of the shellac additives are actually silicone-based... Which is why they carry warnings about top-coating... The photo is alligatoring which is very common with old shellac sprayed properly for lack of a better word. Silicone and shellac are almost made for each other. We used silicone based bed lube on our high speed moulders decades ago. All the moulding had to be coated with shellac prior to being shot with tinted lacquer. Obviously that isn't done anymore but shellac blocks the silicone permanantly with no long term side affects. This was done in commercial manufacturing for many years after the the transition from shellac to lacquer to stave off retooling. We used this process at the plant until 1980. Quote Link to comment Share on other sites More sharing options...
AceHoleInOne Posted December 16, 2013 Report Share Posted December 16, 2013 I think the term "alligator" is spoken to address old dried out finishes that have cracked/checked and been on old furniture for a very long time? -Ace- Quote Link to comment Share on other sites More sharing options...
dwacker Posted December 16, 2013 Report Share Posted December 16, 2013 I think the term "alligator" is spoken to address old dried out finishes that have cracked/checked and been on old furniture for a very long time? -Ace- Alligatoring in this conversation is from out date shellac drying to slow. The bottom coat doesn't fully dry but appears to dry to the touch, You spray on another coat. The top coat is exposed to the air and the bottom is sealed in. The top coat hardens and as the bottom coat shrinks and hardens over time it creates the crackle finish. Much in the same way you would create a crackle finish on purpose. Why we use the glass plate test. Quote Link to comment Share on other sites More sharing options...
Trip Posted December 16, 2013 Report Share Posted December 16, 2013 ==> out date shellac drying to slow. The bottom coat doesn't fully dry but appears to dry to the touch Yea, forgot about that one... In a perfect world, I'd mix for every project... It's best practice, but my shop is not a perfect world... In my imperfect shop, I date my mixes... As they age, I allow more cure time between coats... I absolutely toss the mix after 6 months... Assuming it makes it to six months, which doesn't happen all that often... BTW: I'm using Jeff Jewitt's shellac additive on decorative pieces... It does improve flow-out and leveling... It also appears to improve the depth of the finish, but that's probably wishful thinking and self-justification of the purchase -- it's mostly a silicone-based additive: http://www.homesteadfinishingproducts.com/htdocs/shellac3.htm Quote Link to comment Share on other sites More sharing options...
AceHoleInOne Posted December 16, 2013 Report Share Posted December 16, 2013 The glass test is to see how long and how hard it takes shellac to dry, yes? Didn't know you could glass test for fish-eyes that way? If you apply old shellac over old shellac it drys at the same rate so how does it crack? Just saying. Old shellac is still good it just dries slower and not as hard and more moisture sensitive (water rings). In most cases, we desire instant dry from good shellac. So we have no finishing issues with fast or slow dry rates with other finishes in the schedule. -Ace- Quote Link to comment Share on other sites More sharing options...
dwacker Posted December 16, 2013 Report Share Posted December 16, 2013 The glass test is to see how long and how hard it takes shellac to dry, yes? Didn't know you could glass test for fish-eyes that way? If you apply old shellac over old shellac it drys at the same rate so how does it crack? Just saying. Old shellac is still good it just dries slower and not as hard and more moisture sensitive (water rings). In most cases, we desire instant dry from good shellac. So we have no finishing issues with fast or slow dry rates with other finishes in the schedule. -Ace- No old shellac does not cure very fast it will skin over and appear dry to the touch. The top coat will cure only because it is exposed to the open air. This causes the crackle. Not anything new been happening for hundreds of years. You dont glass test for fish eye you glass test for drying times. Shellac will fish eye if sprayed to thick and is past it shelf life giving the same appearance as you would get with contamination with other finishes like poly or lacquer. Thats why you use glass, so that you can be certain that it dried all the way through not just the surface. Old shellac is not good the longer it goes past its date and the older it gets the better the chances that it will never harden at all making it worthless as a finish. If you use outdated shellac under finishes like lacquer the lacquer will fail. Quote Link to comment Share on other sites More sharing options...
AceHoleInOne Posted December 16, 2013 Report Share Posted December 16, 2013 No old shellac does not cure very fast it will skin over and appear dry to the touch. The top coat will cure only because it is exposed to the open air. This causes the crackle. Not anything new been happening for hundreds of years. You dont glass test for fish eye you glass test for drying times. Shellac will fish eye if sprayed to thick and is past it shelf life giving the same appearance as you would get with contamination with other finishes like poly or lacquer. Thats why you use glass, so that you can be certain that it dried all the way through not just the surface. Old shellac is not good the longer it goes past its date and the older it gets the better the chances that it will never harden at all making it worthless as a finish. If you use outdated shellac under finishes like lacquer the lacquer will fail. Shellac over shellac can crackle in light coats if its old and past its date and newly applied. This is interesting to me. Here is some interesting reading about shellac from the "BIG MAN" http://www.michaeldresdner.com/2009/02/how-and-why-does-shellac-go-bad/ He talks about how you can use old shellac, that Its a perfectly good finish, just not as durable as fresh. So a picture frame or something not requiring a lot of protection such as a table top. Shellac away! -Ace- Quote Link to comment Share on other sites More sharing options...
chopnhack Posted December 17, 2013 Author Report Share Posted December 17, 2013 Well that explains why it happened to me - I put on too many coats too quickly. I usually put on two passes, but this time I put on four so that I could break for lunch.... Here are some pictures of what the inside of the perfectly cleaned cup looked like after the bad shellac. I don't know why there is spotting all over the inside, but the "bad" shellac, even though it was old, passed the glass test. Hard and brittle, even more so that the new batch - go figure. This is the bottom panel of a blanket chest. I sanded down the board to try and level out the spots as best as I could. I really don't have much more time to spend on this, its a charity build for school. That is not to say I don't want it to look great, but I have never had to deal with this problem before so I just tried to be expedient about it. Some flaws are ok ;-) this is going in front of a group of parents, not woodworkers! Here is the same panel after it was refinished, this panel has not been sanded, this is straight off of the gun. Quote Link to comment Share on other sites More sharing options...
AceHoleInOne Posted December 17, 2013 Report Share Posted December 17, 2013 You have a nice project going! Chop....for grins and giggles. I took a little shellac and some mineral spirits and mixed. Guess what? It pulled back...like oil and water do. Are you sure you cleaned the gun properly? You didn't get caught in the heat of the moment and oops...final clean with mineral spirits? You didn't thin by accident with mineral spirits? I read you wash out with DNA? Did your dry the cup out? Was the cup still full when you were done spraying or sorta empty? -Ace- Quote Link to comment Share on other sites More sharing options...
chopnhack Posted December 17, 2013 Author Report Share Posted December 17, 2013 Chop....for grins and giggles. I took a little shellac and some mineral spirits and mixed. Guess what? It pulled back...like oil and water do. Are you sure you cleaned the gun properly? You didn't get caught in the heat of the moment and oops...final clean with mineral spirits? You didn't thin by accident with mineral spirits? I read you wash out with DNA? Was the cup still full when you were done spraying or sorta empty? -Ace- Thanks for the efforts Ace! I used mineral spirits to clean out the gun one night because I had a bunch of old paint that I wanted to nuke. I left it overnight sealed, next morning, I was able to easily take out the paint with a rag, this was then washed out twice with DNA, first wash was a scrub and wash with a gun cleaning kit with all the little brushes. All parts of the gun were broken down and cleaned. A new needle set and cap were installed for the shellac spraying. Rinsed out the first DNA wash with acetone followed by another DNA wash which was sprayed through the gun. I opened the cup up dumped out the few drops that were left and poured in the new shellac. The first run of shellac with the new batch went without problems. Then I mixed 1/2 cup of old amber shellac with 1/2 cup of the new shellac - this was the mix that gave me trouble. Good thinking Ace and this would probably be the case, but the first batch went off without a hitch. I think PB nailed it with the shellac being sprayed too heavy and it being an older batch, date stamp says its from June of 2012. Does anyone know why DNA stains concrete? I would think that the alcohol would just evaporate leaving the surface clean, but I have noticed several darker colored stains from when I have dumped out those last few drops when cleaning my cup and not thinking about it! Quote Link to comment Share on other sites More sharing options...
AceHoleInOne Posted December 17, 2013 Report Share Posted December 17, 2013 Thought MS by the look of the pickup tube and cap. Alright, good luck. Show some pics when it's finished. -Ace- Quote Link to comment Share on other sites More sharing options...
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