07-28-2013 07:27 AM
While reading other posts the subject of trapping air in finishes came up with shacking vs stirring.
My questions are, is trapping air in finishes not a problem, what method of stirring, mixing is most acceptable and what method is the best for mixing?
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07-28-2013 07:41 AM
For myself, I try not to rush when stirring stain with sediments on the bottom.
It really doesn't take that long to stir and mix all components together.
It's not bad to stir on occasion why applying the stain. The solids do have tendency to slowly fall back to the bottom. Every so often pull the stick out and check it. If solids are still stuck to it, keep going.
If it comes out fairly solids free you are good to go.
If I use brush I try not to rub it hard against can lip because that too can send air into mixture.
But I never shake can for that is nothing but introduction to a lot of mess.
07-28-2013 07:57 AM
There was an article by Bob Flexner I read sometime last year, discussing finishing "myths". One of them was the "stirred not shaken" advice, I think he was specifically referring to varnish. He said it was OK to shake it, the air bubbles would not be in the applied finish. I have to admit a deep respect for Flexner, and I have no reason not to believe what he said, but I still find myself stirring most things before I use them...gloss varnish would be an exception; I usually just start using it as is. I find my brushes put as many air bubbles in varnish as anything, and if I've thinned it carrectly, they level out.
07-28-2013 07:59 AM - edited 07-28-2013 08:02 AM
IMO, stain is no problem shaking as it is a color and can be controlled by how you wipe it on. It either covers or it doesn't. I also don't consider stain as a finish. The clear coat, to me anyway, is the finish and YES ... air bubbles will be a problem. I stir with a stick to alleviate any possibility and as Tony mentioned, stir slowly. Paint can be shook too. If you're spraying, you might wait a bit to load the cup. When mixing I usually use a stick as well. I see the Fred chimed in before I posted, and his advice is sound. If thinned properly there should be no problem, provided you are brushing it on. I use lacquer a LOT and the paint store always asks if I want it shaken, but if I do .... be sure to let it settle for a couple of DAYS before spraying.
07-28-2013 08:21 AM
Russ, thank you for your reply. I haven't any spray equipment other than spray cans and rarely use lacquer. For me there are so many things (when, where, how why and what went so wrong) about lacquer that I do not understand hence the leaving it alone. Most times my final finishes using lacquer have come out with dismal to terrible results. So much doing over again. I have become to believe that cloudy, star fish and concentric rings are the norm for lacquer.
07-28-2013 04:48 PM - edited 07-28-2013 04:50 PM
… are virtually always the result of pilot error or failure to properly thin the finish in the case of varnish (which arguable is also pilot error). You may want to read an earlier thread (actually two threads that should have been one) that deals with this same subject. They are found here and here.
Beyond that, air bubbles in stain are irrelevant if the stain is properly applied; you apply the stain using any technique that is convenient. Then, you wipe off the excess. Air bubbles will not survive the wiping away of the excess stain. I also agree with those who state that stain can be stirred of shook. However, if stain has set long enough for the pigment (an insoluble solid) to settle to the bottom of the can then stirring is to be preferred; shaking will not dislodge the mass of the settled stain from the bottom of the can.
Finally, I have not read the Flexner article reference by Fred; however, I am prone to stick with slow stirring. Yes, air bubbles will rise to the top and pop. But, if the varnish is not properly thinned and is applied too heavily (two common beginner failures) some of them may indeed be trapped in the finish film. Also, if the container has set long enough for the flatting agents to settle to the bottom of the can and clump, shaking will not break them free and get them into suspension as well as stirring. Again, my fear is that the inexperienced finisher will stop shaking far too soon…
07-29-2013 04:37 AM - edited 07-29-2013 04:38 AM
I looked the article by Flexner up if anyone is iterested. It was actually publised in PWW in Aug., 2008 (so much for my memory!). It doesn't seem to be online, so here's some tidbits:
"Myth #3: Never shake the can or you'll introduce bubbles. A corollarry is: never wipe the bristles over thr im of the can because this will also introduce bubbles into the finish.
This is a very old myth that is more "misleading" than myth because it's true but it doesn't matter.
Sure, if you shake the can, bubbles appear in the finish. And if you then brush the finish, bubbles appear in it. But they appear in the brushed finish even if you don't shake the can. This should be the first clue that shaking isn't the critical factor-brushing is."
BTW, the articel is titled "The 7 Myths of Polyurethane". FWIW....
07-29-2013 06:55 AM
… and I agree, especially with this statement:
“Myth #3: Never shake the can or you'll introduce bubbles. A corollary is: never wipe the bristles over the rim of the can because this will also introduce bubbles into the finish. This is a very old myth that is more "misleading" than myth because it's true but it doesn't matter.” (Emphasis added)
My concern is as stated in my previous reply:
“But, if the varnish is not properly thinned and is applied too heavily (two common beginner failures) some of them may indeed be trapped in the finish film. Also, if the container has set long enough for the flatting agents to settle to the bottom of the can and clump, shaking will not break them free and get them into suspension as well as stirring. Again, my fear is that the inexperienced finisher will stop shaking far too soon…”
In other words it may very well matter if the “misleading” truth of the statement is compounded by other errors; in particular a finish that is not properly thinned to improve flow-out and leveling and if said finish is applied too heavily. There is also the issue of properly agitating settled and compacted flatting agents from the bottom of the can and getting them evenly into suspension. The later problem can impact even the most experienced finishers if they don’t at least check by drawing a stir stick over the bottom of the can…