An air-powered wet sander or polisher for stone uses around 500 to 900 l/min at 6 bar, continuously for as long as it runs. For a single polisher, allow an 11 kW 4-in-1 screw compressor such as the K 110, which delivers 1.7 m³/min at 8 bar. For two polishers at the same time, the K 150 and its 2.2 m³/min; from three upwards, the S 220 PM and its 3.6 m³/min.
This article deals with polishing. For carving, engraving and handling, see our page on the compressor for stonemasons.
Why polish stone with an air tool?
Granite, marble and quartz are polished wet: the water cools the diamond pads, carries away the stone slurry and keeps dust down. A hand-held electric machine in the middle of all that water is an obvious safety problem. The air-powered polisher has no electric motor and no cable: the air motor runs in the spray with no electrical risk. The water arrives through a separate hose, at the centre of the backing pad.
It is used for edges and sink cut-outs on worktops, polishing headstones and memorial bases, reworking joints and finishing sculpture pieces. The work consists of going through a sequence of pads, from coarse grit to final polish, which takes time: the polisher often runs for tens of minutes without stopping.
How much air does a wet polisher use?
Values given as a rough guide; the exact consumption is in the machine's manual:
| Machine | Indicative consumption |
|---|---|
| Small wet sander, small backing pad | around 400 to 600 l/min |
| Standard wet polisher for edges and worktops | around 600 to 800 l/min |
| Powerful polisher, large pad, rough grinding | around 800 to 900 l/min |
It is a continuous-use tool. Unlike an impact wrench or a blow gun, you cannot rely on the air receiver to cover the consumption: our configurator counts the polisher at 100%. An under-fed polisher loses speed under load, the pads heat up and every pass takes longer.
What pressure does the polisher need at its inlet?
Most polishers are designed for about 6 bar at the inlet. It is at this pressure that the maker states the speed and consumption. Set the compressor to around 7 to 8 bar to cover the losses through the dryer, the filters and the hose.
An air motor is sensitive to pressure: a 1 bar drop at the inlet costs it a significant share of its power. The usual causes are a hose that is too narrow or too long, a quick coupling with a small bore, or a clogged filter. The pressure drop calculator shows what your line is losing.
The step-by-step calculation
The configurator method: polishers at 100%, blow gun at 50%, then a 25% safety margin and 20% for expansion.
Case 1, one polisher.
- Wet polisher: 700 l/min.
- Blow gun: 150 l/min × 50% = 75 l/min.
- Subtotal: 775 l/min.
- Safety margin: 775 × 1.25 = 969 l/min.
- Expansion margin: 969 × 1.2 = about 1,160 l/min (around 41 CFM).
The K 75 and its 1,100 l/min are too tight. The K 110, 1.7 m³/min at 8 bar, covers this need with a reserve for a carving hammer.
Case 2, a worktop fabrication shop with two polishers.
- Two polishers: 2 × 650 = 1,300 l/min.
- Blow gun: 75 l/min.
- Subtotal: 1,375 l/min.
- With both margins: 1,375 × 1.25 × 1.2 = about 2,060 l/min.
The K 150 delivers 2.2 m³/min at 8 bar: it covers the workshop. With a third polisher, the need exceeds 3 m³/min and the S 220 PM, 3.6 m³/min at 8 bar, takes over. Beyond that, the S series goes up to 132 kW on quote.
Which compressor for how many polishers?
| Polishers at the same time | Need with margins | Recommended model |
|---|---|---|
| 1 | about 850 to 1,450 l/min | K 75 up to 1,100 l/min, otherwise K 110 (1.7 m³/min at 8 bar) |
| 2 | about 2,000 l/min | K 150, 2.2 m³/min at 8 bar |
| 3 standard polishers | about 3,000 to 3,400 l/min | S 220 PM, 3.6 m³/min at 8 bar |
| 4 or more | on study | S series up to 132 kW |
Count the polishers that run at the same time, not the ones hanging on the wall. And do not forget the other stations running during polishing: sandblast engraving, venturi vacuum pads.
Does the air need to be dry if the polisher works with water?
Yes. The irrigation water runs through its own circuit and comes out at the backing pad. The air, on the other hand, passes through the motor: vanes, rotor, bearings. If it carries condensed water, it washes out the lubricant, rusts the internal parts and swells the vanes. The motor loses speed, then seizes.
- A refrigerated dryer at the compressor outlet removes most of the water. It is built into the K series. Our article which air dryer to choose compares the solutions.
- An automatic condensate drain on the air receiver and at the low points of the network. Our article on water in compressed air explains where to put them.
- A water separator at the station, just before the polisher hose, catches whatever condenses in the last length of the network.
Should an air polisher be lubricated?
Most vane motors need a little air tool oil, either a few drops at the inlet each day or through a lubricator at the station. Follow the manual: some motors are designed to run without lubrication.
Do not count on the compressor oil to do this job. Our compressors are lubricated, but the outlet filtration holds back the carried-over oil: the air reaching the station is not a lubricant. Our article on oil in compressed air explains the difference.
The pitfalls of polishing
- The compressor in the wet area. Spray and stone slurry have no business near the compressor. Install it in a dry, ventilated room.
- Condensate mixed with polishing water. It contains oil: collect it separately.
- The air filter. If the room also contains carving or engraving dust, check the intake filter between services. The first service is at 500 hours, then every 1,500 hours.
Enter your polishers and your other tools in the configurator, or send us their manuals with a quote request.
For your trade: Compressor for stonemasons, memorial masons and worktop fabricators.