Volumetric Mixer Inspection Guide: What to Check Before You Buy

This guide walks through every system to inspect, in order. Bring it with you. Work through it item by item. A visual walk-around cannot tell you one key thing: whether the mixer measures cement, sand, stone, and water the right way. You have to test that directly.

If you have not read our used volumetric mixer buying guide yet, start there. This article goes deeper on the inspection step.

Before Your Volumetric Mixer Inspection

A few ground rules.

System 1: Mixing Auger and Wear Blades

Start here. The auger is the heart of the machine. It blends cement, sand, stone, and water as they move through the mixing chamber. It also takes the most wear of any part on the machine.

Machine off

• Open the mixing chamber. Check for hardened concrete stuck to the auger flighting and housing. Buildup left to harden between jobs speeds up wear and throws off the mix.
• Measure the gap at the auger hub. Look for a gap of 1/8 inch or more. That much wear changes how the machine mixes. Have it fixed before the mixer goes back to work.
• Check the auger housing liner for thin spots or holes. Look closest near the discharge end, where material moves fastest.
• Inspect the auger drive motor or gearbox mount. Look for oil weeping and loose bolts.

Machine running

• Run the auger empty first. Listen for grinding, knocking, or a steady thump. Any of these can mean a bent flight or a worn bearing.
• Feed a small test batch through. Watch the mix come out the discharge chute. It should look even, not streaky or clumped.

System 2: Conveyor System

The conveyor feeds raw material into the mixing chamber. A problem here throws off the mix just as much as a problem with the auger itself.

Machine off

• Check the conveyor chain, belt, and sprockets for wear, stretching, or missing links. The top chain rail should measure at least 5/8 inch thick.
• Inspect the skirtboard rubber along the sides of the belt. Worn or missing skirtboard lets material spill instead of feeding the mix at the right rate.
• Check that the gates that control material flow open and close freely. They should not bind or stick.

Machine running

• Run the conveyor empty. Watch for uneven tracking, slipping, or a belt that wanders side to side.
• Load a small amount of aggregate. It should feed at a steady, even rate, not surge or stall.

System 3: Water and Admixture System

Water and admixture dosing matter just as much to concrete quality as the dry materials. This system is easy to overlook, because problems here do not always show up until a pour fails.

Machine off

• Check the water tank for algae buildup, sediment, or a cloudy tank wall. A tank that sat unused for months often just needs a flush. A heavily fouled tank can mean the pump has been struggling for a while.
• Inspect water lines and fittings for cracking or old repairs.
• Check the admixture tank and lines the same way. Ask what admixtures the seller has been running through it.

Machine running

• Test the water pump. It should hold 80 to 100 psi.
• Run water through the system until it maxes out the flow meter. Then flush the line and clean the strainers. Pro-All’s own maintenance guidance (opens in a new tab) lists this exact check as routine seasonal upkeep. That tells you how often a well-kept mixer should have gone through it.
• Cycle the admix pump through a full dose. It should deliver a steady stream, not a sputter.

System 4: Hydraulic System

The hydraulic system powers the auger drive, conveyor, and discharge chute on most volumetric mixers. A failure here can shut the whole machine down.

Machine off

• Look for oil on the ground under the hydraulic pump, valve bank, and every hose along the frame.
• Check the fluid level and condition through the sight glass or dipstick. Clean fluid is amber to light brown. Dark, milky, or burnt fluid is a problem.
• Rub the fluid between your fingers. Grit or metal particles mean internal wear.
• Check the filter. A filter that is overdue for a change stresses the whole system.

Machine running

• Cycle the auger, conveyor, and discharge chute through their full range. Listen for whining or knocking under load.
• Watch every hose and fitting again once the system is pressurized. New leaks often only show up under real pressure.

System 5: Calibration and Testing Records

This is the single most important system to check. It is the one thing a visual inspection cannot confirm on its own.

A volumetric mixer’s whole job is to measure materials by volume, in exact ratios, on demand. ASTM C685/C685M (opens in a new tab) is the industry specification for concrete made this way. It sets out tests for batching accuracy and mixing uniformity. It also requires checks on yield, unit weight, air content, slump, and temperature to confirm the mix meets spec. A mixer that has drifted out of calibration will not throw a warning light. It will just quietly add too much or too little cement. You will not find out until a pour fails a strength test.

What to ask for

• The date and result of the mixer’s most recent calibration, and how often the seller has had it done. Cemen Tech’s own published maintenance guidance recommends calibration at least once a year, and every quarter if the mixer runs heavy hours.
• Whether the calibration used the actual materials the machine will run going forward. Local aggregate and cement can behave differently than what the seller used.
• Any past yield tests. A yield test pours a measured batch and checks the actual weight and volume against the target. It also checks strength and air content on a sample. This is the clearest proof a machine has been running accurate mixes, not just running.

If you cannot get clean records: Budget for a full recalibration and a fresh yield test before you put the mixer to work. This runs $800 to $2,000, depending on how far out of spec the machine is and whether parts need adjustment or replacement.

System 6: Chassis, Engine, and Undercarriage

What you check here depends on how the mixer is mounted.

Truck-mounted units

• Check the engine, transmission, and brakes the same way you would for any commercial truck. Pull the dipstick for milky or burnt oil. Listen for knocking at idle.
• Confirm current registration, inspection stickers, and that the chassis meets DOT requirements for the state where you plan to run it.
• Ask if the seller has kept up with truck maintenance separately from the mixing system. These are two different machines sharing one frame. Sellers sometimes maintain one well and neglect the other.

Trailer-mounted units

• Check the hitch and coupler for cracking, excess play, or worn safety chains.
• Inspect axles, bearings, and brakes. Confirm the trailer’s rated capacity matches the mixer’s loaded weight.
• Check tire tread and sidewall condition on all positions, including the spare if one is included.

When to Bring a Professional

If you are not comfortable checking the calibration and hydraulic systems yourself, hire a third-party inspector or a technician certified through the manufacturer. This is also worth doing if the machine’s price is high enough to justify it. A professional inspection with a full calibration and yield test runs $800 to $2,000. It can surface what is easy to miss without lab equipment: strength and air testing on a sample batch, hydraulic pressure testing, and an accurate measurement of auger and liner wear. Above $100,000, a professional inspection is worth the cost. The fee is almost always less than the cost of one failed pour on a job.

Red Flags That Should Stop the Deal

Some findings are reasons to walk away unless the price reflects the problem clearly:

Once you are satisfied with what you found, you know what to look for. PayDirt HQ lists mixer trucks for sale, with financing options available (opens in a new tab) through Equify Financial.

If you still need it, our used volumetric mixer buying guide covers sizing, machine history, sourcing, and financing in more depth.