Clay preparation

Pug Mills: The Pros, the Cons and How to Use One

A pug mill turns a bucket of scrap into ready-to-throw clay in minutes and saves a lot of wrists. It also costs thousands, needs real maintenance, and introduces a contamination problem that a bucket never had. Here is what one actually does, whether a studio should want one, and how to run it without wrecking it.

A pug mill mixes clay and pushes it out as an even log. A de-airing one pulls a vacuum first, so the clay comes out ready to throw. It is expensive, it needs cleaning between clay bodies, and it is unforgiving if you reach into it.

De-airing versus not, and why it matters What it costs to own one Two videos, none of them ours
What it does How to run one Three ways they get wrecked
A studio pug mill extruding a log of prepared clay into a potter's hands
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What a pug mill actually does De-airing versus not The case for one The case against one How to use one Cleaning and maintenance Safety, which is not optional What goes wrong The whole idea, quickly Running one Three ways they get wrecked Questions we get asked Keep going

What one does, whether it is worth it, and how to run it without wrecking it.

The whole idea

A wedging table with a motor

Everything a pug mill does, you can do by hand. It blends clay of different consistencies and it pushes air out. That is wedging.

What it changes is scale and effort. Twenty pounds of lumpy reclaim is fifteen minutes of hard work on a table and about ninety seconds in a machine, and the machine's version is more consistent than yours.

A de-airing model adds something hands cannot do at all: it pulls a vacuum on the clay, removing air far more completely than any amount of slamming.

Start to finish

Running one

How To Operate A Peter Pugger Mixing Pugmill Peter Pugger
  1. Check what was in it last. Wrong clay body still in the barrel is the most common way a batch gets ruined.
  2. Feed clay in at a workable consistency. Too dry and you stall the motor, too wet and it comes out as mud.
  3. Mix first, if it is a mixing model. Let it blend before you pug.
  4. Pull the vacuum, on a de-airing machine, once the load is mixed.
  5. Switch to pug and support the log as it comes out. Do not let it extrude onto the floor.
  6. Cap the nozzle when you are done, or the clay in the barrel dries into a plug.
  7. Hands nowhere near the hopper while it is plugged in, and unplug it before anything comes apart.
If it went wrong

Three ways they get wrecked

Clay left to dry in the barrel

An uncapped nozzle overnight leaves a hard plug that the auger then has to fight. It strains the motor, and clearing it means stripping the machine down.

Something that is not clay went in

A tool, a sponge, a stone, a piece of plaster. Augers are strong enough to keep going and hard enough to be damaged, and the debris ends up in everybody's clay afterward.

The vacuum seal was never cleaned

A single dried flake on the O-ring breaks the seal, so the vacuum stops working and the clay comes out full of air. People blame the machine for weeks before anyone checks the gasket.

The mechanism

What a pug mill actually does

How to use Peter Pugger Pugmill Mia Baker Ten minutes of actual studio use rather than a sales demonstration, including what the clay looks like going in.
  1. An auger pushes clay through a barrel. That is the whole machine. A motor drives a screw, the screw compresses clay along a tube, and the clay comes out of a nozzle as a log.
  2. Compression is what blends it. Forcing clay through a narrowing space mixes wet and dry together, the same way cutting and slamming does, but continuously.
  3. Mixing models blend first, then pug. Paddles knead a batch in a chamber so you can adjust moisture before anything is extruded. That is what lets you take a bucket of varied scrap and get one consistency out.
  4. De-airing models add a vacuum stage. Air is pulled out of the clay before it is compressed into the final log, which hand wedging can only approximate.
  5. What comes out is not automatically ready to throw. A non-de-airing mill gives you blended clay that still needs a quick wedge. A de-airing one gives you clay you can genuinely throw straight off the nozzle, though a short wedge still erases the thin layers an auger leaves in it.
  6. It does not fix bad clay. Too wet in, too wet out. A stone in, a stone out, plus a damaged auger. The machine blends what you give it.
The main buying decision

De-airing versus not

This is the fork that decides the price, the maintenance and whether you still need a wedging table.

Non-de-airing: blends only

Mixes and compresses clay into an even log, and leaves the air in. You still wedge afterward, though far less than you would have. Cheaper, simpler, fewer things to go wrong.

De-airing: blends and removes air

A vacuum pump pulls air out before the final compression. Clay comes out dense and ready to throw, which is the whole appeal. More expensive, and the pump is another thing to maintain.

What de-aired clay feels like

Denser and slightly stiffer than the same clay wedged by hand, and noticeably more consistent. Some potters find it almost too uniform and prefer a short hand wedge anyway.

The case for paying the difference

If wrists or shoulders are the reason you are buying a machine at all, de-airing is the version that actually takes the hard work out of wedging. Non-de-airing reduces it; de-airing cuts it to a short one.

The case against

A vacuum pump is one more thing to look after, because moisture from the clay gets into it. An oil-filled pump needs its oil checked, and changed at once if it goes cloudy; many studio machines use an oil-free pump instead, with its own care in the manual.

Stainless versus aluminum

The other spec that matters. Aluminum internals are fine for stoneware and can discolor white clays over time. Stainless costs more and keeps porcelain genuinely white.

Tips for Using a Peter Pugger Vacuum Deairing Pug Mill in the Pottery or Ceramics Studio! KaransPotsAndGlass Twenty-four minutes of accumulated practical detail, including the maintenance nobody mentions before you buy.
The case for

Why a studio wants one

  1. Reclaim stops being a chore. This is the real reason. A pug mill turns scrap into usable clay fast enough that people actually do it, instead of letting buckets pile up until somebody throws them out.
  2. It saves wrists, shoulders and backs. Wedging is repetitive load, and it is the reason a lot of potters stop or cut back. A machine removes the highest-volume version of that work.
  3. Consistency. Machine-blended clay is more uniform than hand-wedged clay, batch after batch, which matters for anything that has to match.
  4. It makes people more willing to experiment. When a failed pot goes straight back into usable clay within the hour, the cost of trying something drops to almost nothing.
  5. It handles volume nobody would wedge. Hundreds of pounds a week is realistic for a machine and unthinkable by hand.
  6. It pays for itself in clay, eventually. Slowly, and only in a studio generating real volumes of scrap. It is a labor argument first and a money argument second.
The case against

Why a studio might not

  1. The price. A serious studio machine is thousands of dollars, and the de-airing models are the expensive end. That is a lot of bags of clay.
  2. Cross-contamination is a new problem. A bucket cannot mix clay bodies on its own. A pug mill will, every time somebody runs a different clay through without cleaning it, and cleaning means unbolting the barrel.
  3. Cleaning is genuinely a job. Not a wipe down. On most machines it means removing the chamber, pulling the auger and washing everything, which is why studios with one machine often restrict it to a single clay body.
  4. Maintenance is ongoing. Lubricating what the manual says to, looking after the vacuum pump, keeping the seals clean, capping the nozzle. Skip it and you get a machine that quietly stops de-airing.
  5. It is a real injury risk. Augers do not stop for a hand. Among studio machines only the slab roller ranks above a pug mill, and the worst case is severe rather than annoying.
  6. It needs space and power. A footprint, room in front of the nozzle, an outlet it does not share with anything else, and on larger machines a dedicated circuit. Plus noise and vibration, especially with a vacuum pump running.

Who actually needs one

A pug mill solves a labor problem that only exists at volume. A member throwing a few evenings a week does not need one and would not use one enough to justify it. A studio processing everybody's scrap absolutely does.

Operating

How to use one

The machine is simple to run and easy to damage, and nearly all the damage comes from the same few habits.

  1. Find out what ran through it last. If it was a different body, the barrel needs cleaning before yours goes in.
  2. Check the clay going in. No stones, no plaster, no tools, no sponges. Anything hard damages the auger and then ends up in everybody's clay.
  3. Get the consistency roughly right first. A mixing model can adjust moisture, but starting with a bucket of soup means pugging soup.
  4. Load in manageable amounts rather than cramming the hopper. Overloading is how motors stall.
  5. Mix before you pug, on a mixing model, and give it long enough to actually blend.
  6. Wipe the sealing surfaces before closing the lid on a de-airing machine. A single dried flake on the O-ring costs you the vacuum.
  7. Support the log as it extrudes and cut it into workable lengths. A log allowed to extrude unsupported bends, folds and traps air.
  8. Cap the nozzle when you finish, every time. This is the single most important habit on the list.
Keeping it alive

Cleaning and maintenance

  1. Clay can live in the barrel between sessions. On a sealed machine, leaving moist clay inside is not a problem and is often recommended. How long is up to the maker, so check the manual: one says indefinitely, one says to clean it out before a month without use, one says not to leave clay in for long, and porcelain left a few weeks in an aluminum barrel can corrode it. The nozzle has to be capped for any of that to be true.
  2. Cleaning is for cross-contamination, not hygiene. You strip a pug mill down when you are changing clay body, not on a schedule.
  3. That means unbolting the chamber. Barrel off, auger or paddles out, everything washed, then reassembled. It takes real time, which is why studios tend to dedicate a machine to one body.
  4. Wipe the O-rings and sealing rim every time on a de-airing machine. Dried clay on a seal is the most common cause of a vacuum that has quietly stopped working.
  5. Look after the vacuum pump. If it runs on oil and the oil looks cloudy or milky, moisture from the clay has got into it and the oil needs changing right away. Many studio machines use an oil-free pump instead, and its care is in the manual.
  6. Lubricate what the manual says to on the manufacturer’s schedule, with the lubricant it names: some parts want grease, some a few drops of light machine oil, and some gear motors need none for life. This is the maintenance people skip and the reason machines die early.
  7. Watch for air in the output. On a de-airing mill, clay suddenly coming out with bubbles almost always means a clogged filter or a failed seal rather than a broken pump.
Not negotiable

Safety, which is not optional

A pug mill is one of the few pieces of equipment in a pottery studio where the worst outcome is genuinely serious; among the machines, only the slab roller ranks above it. Everything else here is a nuisance by comparison.

  1. Never put a hand in the hopper or the nozzle while it is plugged in. Not to push clay down, not for a second. Use the tool the machine came with.
  2. Unplug it before anything comes apart. Switched off is not the same as unplugged. Keep the plug where you can see it, so nobody plugs it back in, and on a machine wired in without a plug, switch off its breaker or wall disconnect and lock it.
  3. The guards are there for a reason. A machine with a guard removed is not a machine to use.
  4. Tie back anything loose. Sleeves, hair, apron strings, jewelry.
  5. Do not use one you have not been shown on. Not a formality. An auger does not stop.
  6. Know where the stop is before you switch it on, and be able to reach it without moving.
Read this when it misbehaves

What goes wrong

Clay coming out full of air

On a de-airing machine that is a seal or a filter, not the pump. Check the O-rings for dried clay, then the vacuum filter, which clogs with clay dust.

The motor stalls or labors

Clay too stiff, hopper overloaded, or a dried plug in the barrel from an uncapped nozzle. Stop rather than forcing it; a strained motor is an expensive noise.

The log comes out twisted or hollow

Usually clay that is too wet, or a partially blocked nozzle. It can also mean the auger is worn, which is a bigger conversation.

Streaks of the wrong clay

Somebody ran a different body through and did not clean it. The first few pounds out after a change are always contaminated and should be set aside.

Grinding or metallic noises

Something hard in the barrel. Stop immediately and unplug it. Running through it damages the auger and puts fragments into the clay.

White clay coming out grayish

Aluminum internals discoloring a porcelain body over time, or residue from a darker clay. The first is a spec problem, the second is a cleaning problem.

Questions we get asked

The ones that come up at the tables

Do I still need to wedge clay from a pug mill?

From a de-airing machine, barely. It comes out blended and air-free and you can throw it straight off the nozzle, though a short wedge is still worth it: an auger leaves thin layers in the clay, called laminations, that can open into drying or firing cracks later, and wedging erases them. From a non-de-airing machine, yes, though far less than you would have needed otherwise, because the air is still in there.

Can I run different clay bodies through the same machine?

Only if you clean it in between, which means unbolting the chamber and washing the auger. Anything less and the first pounds out carry the previous body. This is why most studios dedicate a machine to one clay.

Why is the clay coming out with air bubbles?

On a de-airing machine that is almost always a broken seal or a clogged vacuum filter rather than a failed pump. Check the O-rings and sealing rim for dried clay first; a single flake is enough to break the vacuum.

Is it bad to leave clay in a pug mill?

On a sealed machine, not between sessions. For longer, check the manual: one maker says moist clay keeps in its sealed machines indefinitely, others set a limit, and porcelain left for weeks can corrode an aluminum barrel. What matters is capping the nozzle, because clay drying in the barrel forms a plug the auger then has to fight.

Is a pug mill worth it for a home studio?

For most people, no. It is thousands of dollars to solve a labor problem that only exists at volume. The exception is if wrist or shoulder pain is limiting how much you can make, in which case a de-airing machine is buying working time rather than convenience.

How dangerous is a pug mill really?

Used properly, it is safe. The worst case is severe, because an auger has enormous torque and does not stop for a hand. Guards on, hands out of the hopper, unplugged before it comes apart, and never operated by somebody who has not been shown.

Stainless steel or aluminum internals?

Aluminum is fine for stoneware and earthenware and costs less. Stainless does not discolor clay, so if you work with porcelain or white bodies and care about them staying white, it is worth the difference.

Can a pug mill mix dry clay from scratch?

Some mixing models can, though it is not what most studio machines are for. Mixing dry powder is also the dustiest job in ceramics, so it needs a respirator and good ventilation regardless of what machine is doing the work.

One last thing

A machine that buys time, not skill

A pug mill does not make anybody a better potter. It does not improve clay beyond what careful wedging achieves, and it will happily blend a bucket of rubbish into an even log of rubbish.

What it buys is time and shoulders. It turns reclaim from a chore that gets postponed into a fifteen-minute job, and it takes the heaviest repetitive work out of a craft where that work is the main reason people stop. Worth understanding whether or not you ever own one, because the machine is only as good as what somebody puts into it.

A pug mill blends clay and extrudes it as a log. De-airing models pull a vacuum so it comes out ready to throw. Expensive, needs real cleaning between clay bodies, and genuinely dangerous if you reach into it.

If you want the full case for and against, the maintenance and the six ways they misbehave, switch to the Comprehensive Version at the top of the page.