Whenever I think of plaster pumps, I think of Paul Bunyon, machine versus man. For centuries, man applied plaster by hand and men cut trees down with an axe. When the chainsaw was invented, the days of cutting trees with an axe quickly disappeared. The chainsaw has, I suppose, an intimate history of evolution. I am not as well versed with chainsaws, but I am with plaster pumps. The minor innovations in plaster pumps over the decades may have gone unnoticed by some, but not by me.


To truly appreciate pumps of today, you have to come from the days when pumping plaster was in its infancy. Plaster pumps have made unbelievable strides from the early days of the original “Two Banger Tommy Gun.” This was the nickname for the first piston style two-cylinder plaster pumps.

Today most piston pumps are the healthier more reliable four-cylinder models. Even the first two-cylinder piston plaster pumps made it possible to deliver high volumes of cement plaster. The plaster would spray with tremendous force out the end of the nozzle. The pressure was so intense that in the first days of pumping cement plaster on tract style homes, the building paper between the open studs would tear when plaster was sprayed. Because of this problem only the brown (second) coat could be pumped and the scratch (first) coat had to be hand applied. The building paper manufacturers answered the need by making a tougher heavier paper and labeling it “Gun Grade Paper.” This new, tougher, paper could handle the additional spray force of the pumped plaster for open stud construction. Pumping plaster took off and never looked back.

Other innovations soon followed to make pumping plastering more cost-efficient, reliable and safer. Some innovations were seemingly minor with big benefits. The pumping unit is the nickname given to the valve and chamber system that controls the flow of plaster. It is a simple but amazing piece of engineering with round balls in a chamber that seat and unseat themselves to ensure the plaster travels in only one direction. Sand in the plaster mix is abrasive and constantly coursing through the chambers wears parts out quickly. The first balls used in the pumping units were made of semi-hard black rubber and would wear out daily. Removing the unit and replacing the rubber balls required a person to stay late or arrive early every day. Tougher, durable nylon balls soon followed and extended the switch out to every couple of days. Then the evolution to hardened steel balls made for longer life and much less maintenance.

Another seemingly minor improvement was the automatic water tank. The first water tanks, named quick-fills, were open boxes mounted over the mixer. They worked like flushing a toilet. A handle, ball cock, flapper and float released a pre-determined amount of water. The flapper seals and the tank fills until the float is raised to shut the valve off. The problem was that while this is perfect for a stationary toilet with a covered tank in your home, the combination of parts vibrating violently and dirty plaster made these tanks susceptible to constant maintenance. Today the tanks are self-contained pressure towers that rarely fail or need service.


Some innovations made pumping plaster a lot safer. Plaster pumps today are very reliable, efficient and not the mechanical dangerous nightmares of their forefathers. Starting the two-cylinder motor in the morning required a heavy steel hand crank. Yes, heavy metal crank, similar to an old Ford Model T. You had to put some muscle into the cranking and then pull the crank away just before the motor kicked in. Failure to pull the crank away would result in the crank handle spinning at an unbelievably high speed and then being flung with velocity. It was potentially dangerous and no one wanted to “crank up the gun.” I had an employee get hit with a flying crank handle that broke his knee. The electric starter solved that problem.

The early days of pumping cement plaster was also an experiment in pumping additives to make the plaster slide easy through the hose. This experimentation made packs in the hose a common occurrence. The packs and the old-style on/off switch made for a bad and dangerous combination. The first plaster pumps used an air line for the on/off switch and not the current electric switch. The air on/off switch had a lack of immediate control by the nozzleman. The air pressure would have to build up before the pump started. That was not a problem. However, it also took a while for the pressure to release before the pump motor would stop, and this was a potential problem. It was eerie to hear the pump screaming wildly with no plaster coming out of the nozzle. You knew at this point there was a pack somewhere in the line. If the hose started to get stiff and hard where you were holding it, you knew the pack was in the nozzle. It was a scary feeling when you switched to release the air pressure to stop the motor, but the machine just kept pumping. This is when you heard the familiar scream from the crew “PACK, PACK” and a mad scramble to safety ensued. The pressure would just keep building in the hose line. Imagine holding a firehose and the pressure just keeps building and building. The pressure could build significantly enough that when the hose blew apart it could lift a 200-pound man off the ground. The nozzleman couldn’t let go and run, because if the nozzle were to blow off, the steel head could fly and injure someone. My personal trick was to wedge the nozzle into a steel scaffold frame to secure it from flying around and pray the motor would shut down quickly. Ah! Good Times.

It must have perplexed the pump manufacturers like Sprayforce and Mayco when they first came out with electric starters and electric controls for the two-cylinder piston pumps. Plasterers rarely had them installed. Why? I believe it was a combination of stubbornness, cheapness, and a macho factor all rolled into one. Thank goodness for the four-cylinder machines. They required electric starters and electric on/off switches.

Today’s piston plaster pumps are the result of years of tinkering and innovations to get it right. They are truly labor savers, safer and more reliable.

Photo courtesy of Sto Corp.


The piston-style pump is still in use today and considered by many to be the workhorse of the plaster and spray-applied fireproofing industry. However, there are new kids in town; the Silos and Hydraulic pumps. These systems are not completely new. However, the Europeans have taken them to a new level. The rotor stator tube pump has been in America for decades, like the models made by Glover and Sprayking, which were always more reliable and safer than the old piston pumps. They also provided a more even spray pattern and were preferred for a dash finish plaster. The drawback was they did not deliver the volume of material the piston pumps could, and the sand in the cement plaster would eat the steel stator tubes when the machines ran at high speeds for prolonged periods of time. The stainless steel stators were pricey to be replacing frequently. However, the rotor and stator pumps are improved and are still every bit a part of today’s plaster and drywall industry.

The silo system has been required in most of Europe for a few decades. Europeans are very recycling conscious. Bags of material and sand piles are severely frowned upon, even in small towns. So, while we were improving the piston pump, they have been doing the same in Europe with the Silo and Auger systems. The old guys must have some stories about the innovations and improvements to this system. Two very popular systems brought from Europe are BMI-Maxit and the STO Technology. What is new are the hydraulic mixers and pumps. These are amazing machines and will certainly be more popular as time goes on.

The first benefit of this system is quality control of the material. The silo contains pre-blended product to exact standards for site-specific work. No guessing on the shovel size of sand or wasted product from damaged bags. The sand is per ASTM standards and the ratios are correct. This takes a huge liability burden off the contractor’s shoulders. Guys on-site cannot be adding products unknown to the contractor and later revealed in a petrography analysis. This is a method used by laboratories to test for impurities, cement paste content, and grade of sand in cement and mortars. These tests are often used in litigation cases. The Silo system eliminates that frustration.

Sand piles and cement bags take up room and tend to be messy. Silo systems first gained popularity in the United States in major inner cities because they were clean and compact. The need to conserve space and provide a clean work area made the extra cost a non-factor. This silo system is growing in popularity throughout the United States and Canada. Plastering is messy, dirty work and anything that can make it a little cleaner and neater is a benefit to the customer and the help.

If you are a traditionalist and think, “I have seen these systems before and they are not for me,” you might want to take another look.


Every once in while I see a specification that forbids the plaster to be applied with a machine. Apparently some architects/designers believe that pumping plaster is in some way inferior to hand-applied; I can testify that is not true. While there are peculiar benefits with each method of application, pumping plaster is not an inferior method. Both hand tool application and pumping are merely a means to move the material toward the wall. Pumping plaster virtually guarantees two things that hand-tool application cannot; intimate contact with plaster, and sufficient amount of cement in the mix.

The intimate contact between coats of plaster will be greater than with hand-tool application. The force needed to move plaster through the hose automatically means the plaster will fill and have sufficient pressure against the surface to which it is being applied. Hand-tool application can be laid on very lightly and has been done in the past. This is the primary reason the “sufficient pressure” words were installed into ASTM C 926 “Application of Cement Plaster”.

The mix will have a sufficient amount of cement. Plaster mixes with high volumes of sand cannot pump.

There will always be hand-tool application and there will certainly be more innovations in plaster pumps. Each method has its place. Architects should consider these “contractors means and methods” and allow them the freedom and flexibility to decide which method is appropriate for that specific project.