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Hi All,

A clay stumper question for you.

My brother works for a ceramic tile company, and recently called me with a clay question that has him (and now me) completely stumped.

They roll out slabs of commercial clay fresh from the bags to make their tiles. Fresh out of the bag, the clay is perfect. When they cut out the squares from the slab, the edge scraps (still soft and pliable) get pugged using a de-airing pug mill. The ONLY thing they add to the soft scraps is a bit of water. 

The pugged clay is now always completely short and breaks apart when they try to run it through the slab roller. The only way they can stop this, is by adding "too much" water, which makes the clay sticky and hard to use for their production purposes.

I asked him a ton of questions, trying to figure out the problem, but can't find the obvious answer. 

My brother has been working for the company for 4 years, using the exact same process, and this problem is brand new.

They are using the same clay body they've always used.

They buy their clay in multiple ton  loads, and are using clay from the same shipment that originally they had no problem with.

The clay has not been frozen and then thawed. 

As mentioned above, nothing other than a small amount of water is added to the clay when it's pugged.

Does anyone out there have any idea what could be causing this problem? I'm stumped.

Thanks in Advance for any info you might have.

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I have been thinking about this a lot lately, since I don't throw, only hand build, but realize the same shortness throwers experience with reclaim, and blame on a lack of fines due to throwing wet taking off fines.

How can I experience the same shortness?

That theory is falling off for me, and adds to my belief that it is microsopics alone. Bacterias and Fungi.

Even exposed to the air for a short while, or x amount of time in a bag then exposed to chlorinated water, can be what kills/changes them.

Time changes everything, including the numbers of these microgrowths. 

The population of good bacteria in the clay could have reached a critical point where it all dies again, or becomes so numerous that it has the opposite effect. There is a good balance to everything!

I am a believer then, in the aging game.

Get that stank back.

The Good Book says clay is good when it smells like the bowels of the Earth. When my reclaim smells like this, it is never short.

I keep it funky in wet towels in a closed cooler.

Perhaps their production should account for these times, and allow for a longer wet storage of this clay before use.

Let time work.

I reckon of you start adding concoctions, like is usually suggested, tiles won't be the same, and time may work against you.

 

Sorce

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I noticed the exact same problem with my reclaim clay.  I called Laguna and asked their clay "expert" about it.  Their reply was that the commercial pug mill they use has so much more powerful vacuum that my Peter Pugger.  I don't know if I fully buy their explanation, but I don't have a better one.  The working solution I'm using is to pug wet and age.  Very nice clay that way.   I think Sorce may be on to it.  By the time I get around to a session with the pug mill, the scrap has been sitting in bags wet for quite a while.  Sometimes even a touch of green.  It's definitely not short coming out of the pugmill now, but it's really soft and needs to age to be ready to use.

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The clay once rolled  thgen cut off and ever so slighly dried then wetted and pugged has not aged. Its the aging process-they could add a splash or vinegar with that water or not but that clay needs some time to get right. They need a rotation so they are always using the aged pugged clay.

That story that Laguna said about the strength of the vacuum holds zero weight for me. By the way they better use a larger vacuum as I have seen the size of those machines and the output size is the pug size so it needs to be a lot larger suck to make that happen.That has zero do with the ageing process.

Laguna has a New clay guy (Evan) the older guy -Jon Pacinni retired as I have talked to him lately after retirement as I have know him for a long time.

I wonder which one told him that story. This guy may have worked for Disney before this job.

This is where Bacterias and Fungi are our friends

I have found using fresh pugged slab scraps its always short unless you age it.

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I think it has more to do with saturation than bacteria or fungi.  As you say, the clay is fine if it's "wet", or aged, both allow time for even wetting.   I don't have a pugmill, but when I recycle clay I don't have to age it to use it.  I just slake it (complete hydration) and then dry it on a slab until it's nearly the moisture level I want.  

I think it may make some sense about the stronger vacuum, placing the freshly mixed clay under a STRONG vacuum will not just remove the air, but it will cause any dry spots to hydrate as well.  That said, I think they probably use a filter press, and in that case they are wet mixing anyway so that point may just be moot, or redundant steps to maintain plasticity.

I have a box of porcelain manufactured a month ago when I bought it, and one that is a year old, I cannot tell the difference when throwing.  I always heard of aging my clay but noticed that when I buy clay it's usually manufactured within the last 30 days, and a lot of times in that same week.  But I know my clay is filter pressed, I have seen the giant filter press machine, and apparently that is not standard procedure anymore?

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Interesting thoughts here. To rule in or out the microbes or vacuum theory I'ld try taking the scrap, misting it lightly with water then hand wedge it and see how plastic it is. If it's plastic then it would point to the vacuum being the issue. I can't see how the microbes would decrease in the pugger unless it was being pugged for so long that the clay gets hot enough to kill off the microbes. Doubt it would get hot enough though.

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25 minutes ago, Min said:

Interesting thoughts here. To rule in or out the microbes or vacuum theory I'ld try taking the scrap, misting it lightly with water then hand wedge it and see how plastic it is. If it's plastic then it would point to the vacuum being the issue. I can't see how the microbes would decrease in the pugger unless it was being pugged for so long that the clay gets hot enough to kill off the microbes. Doubt it would get hot enough though.

Or taking a fresh bag of clay and running it through the pugmill.  I've not tried this, but I suspect if it was hand building firm and not throwing soft, it would come out short(er).

The process SBSOSO is talking about dries the clay significantly by the time it gets back into the pugmill.  It's an interesting question why they were able to get away with immediate use after pugging scrap and now they can't. 

Lots of ins, lots of outs and lots of what have yous.

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4 minutes ago, CactusPots said:

Or taking a fresh bag of clay and running it through the pugmill.  I've not tried this, but I suspect if it was hand building firm and not throwing soft, it would come out short(er).

Plenty of people do this instead of wedging, I think that's how @Mark C.starts his day?

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22 minutes ago, Mark C. said:

That story that Laguna said about the strength of the vacuum holds zero weight for me. By the way they better use a larger vacuum as I have seen the size of those machines and the output size is the pug size so it needs to be a lot larger suck to make that happen.That has zero do with the ageing process.

There is a difference between the vacuum power of the commercial machines and the studio machines, but it's not about the size of the pug. Large commercial puggers don't vacuum the air out of the solid 8" block, it cuts it into pellets as the clay enters the vacuum chamber so the air can more easily be removed. An upper auger moves the clay into the vacuum chamber, it's cut into pellets and falls to the bottom of the chamber, where a second auger moves it out and extrudes it into the block. If anything I'd say the larger commercial vacuum is needed because the clay is moved through the system a whole lot faster than a studio pugger. But there's a limit to how fast clay can be pugged because a worker has to bag the blocks as the clay comes out, and you can't bag anywhere near as fast as the machine can pug, so the de-airing is very, very good. I do believe that the commercial puggers do a much better job of de-airing the clay.

In terms of the relationship between clay particles and water, pugging has the effect of near instant aging. It removes the air between clay particles, so all the particles are coated with water and hold together well. Aging further enhances the process with the growth of organic material, but a freshly mixed batch of clay right out of the mixer is very useable. When I worked for A.R.T. clay I regularly used clay that was fresh out of the pugger, with no problems. There was a big difference between that clay and the stuff I mixed in grad school, which required further aging of at least a couple of weeks after mixing and pugging a batch, even when using reclaim in the mix.

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43 minutes ago, neilestrick said:

Large commercial puggers don't vacuum the air out of the solid 8" block, it cuts it into pellets as the clay enters the vacuum chamber so the air can more easily be removed. An upper auger moves the clay into the vacuum chamber, it's cut into pellets and falls to the bottom of the chamber, where a second auger moves it out and extrudes it into the block.

Same principle behind the Bailey machines, after the mixing chamber the clay goes through screens which extrude spaghetti like extrusions which are de-aired then clay goes along to the final auger to be extruded. Different method than the Peter Puggers which de-air the mass of clay in the chamber.

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Sbsoso- welcome to the forum.

You did not State clay body type: but I will go with porcelain. When doing production: not a bad idea to keep 25lbs from the previous lot to compare to the new lot if problems arise. No problems before, and now problems means the first stop is to check with supplier if others have reported issues. Like potters, clay manufacturers shop for low prices: which sometimes creates issues. You have a plasticity issue which you can only resolve by adding water. Adding water does not increase plasticity; just moves the body closer to its liquid limits. Adding water will also increase drying issues such as warping. Your plasticity issue is caused by one of two things: the % of plasticizer has been lowered, or the plasticizer (ball clay) has lower plasticity properties. The second is Nep Sy being used as a body flux. Nep Sy has 14% soluble salts that can migrate: which can cause rapid dehydration of water. Sodium is hydrophobic- fancy word for- not fond of water. Again adding water compounds the problem by allowing further migration of soluble salts. 

As others stated: de-airing pugmill has zero influence. All a de-airing pluggers does is remove the air between clay particles which speeds up the transfer of negative particle charges. De-airing has zero influence of the actual chemistry of the material.

Tom

 

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On 1/2/2021 at 5:52 AM, Sbsoso said:

using the exact same process, and this problem is brand new.

They are using the same clay body they've always used.

Go back to the supplier.  If processes haven't changed, must be source materials.

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@Sbsoso When I was the tech at A.R.T. clay, I had to work with customers having problems with clay bodies and glazes. They described their processes to me but often left out a small detail that turned out to be the cause of the problem, because they didn't think that little detail could be the problem. So please describe, in detail, the process by which they make the tiles, including every little thing they do- any dry materials or resists added during the process, types of materials the clay touches (canvas, etc) and maybe we can find some little thing that's causing the problem.

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O.k.... I just got a call from my brother.

He has figured out and solved the problem, and the answer was nothing I would have ever come up with. He kept thinking the problem had to have something to do with the pugmill--- and I kept telling him that didn't make any sense. Well, he adjusted the speed of the augers and the clay is now coming out perfectly again.

I don't know how or why, but there ya have it.

Thanks again to all of you for taking the time to respond.

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27 minutes ago, Sbsoso said:

Well, he adjusted the speed of the augers and the clay is now coming out perfectly again.

Slower speed, better mixing, less bypass, likely more uniform moisture content. Wonder if he even has to mix longer. Hmm, might be a cool lesson here as aging would tend to even out the moisture content as well. Maybe we really don’t need to hope for foul smelling clay?  Maybe I can take that warning sign down that says no bad mold spores allowed! Just some food for thought.

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On 1/6/2021 at 6:57 PM, Bill Kielb said:

Slower speed, better mixing, less bypass, likely more uniform moisture content. Wonder if he even has to mix longer. Hmm, might be a cool lesson here as aging would tend to even out the moisture content as well. Maybe we really don’t need to hope for foul smelling clay?  Maybe I can take that warning sign down that says no bad mold spores allowed! Just some food for thought.

What kind of pugmill has speed adjustment?

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