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GFRG Processing FAQs 

Why you can't effectively use your GFRC machines to spray your GFRG materials

RimCraft's patented process allows you to retard the Gypsum to give you longer working time

while providing you a controllable set time by injecting the Accelerator at the gun.

Q: What is the Accelerator/Retarder process and how does it work?

A: The accelerator typically is Aluminum Sulfate. It is used to give the operator control of the gypsum slurry set time. Gypsum slurry has a natural set time (Pot Life) when mixed with H2O. The average pot life is 30-45 minutes before the gypsum slurry begins to harden. This time is insufficient for mechanically processing the gypsum slurry because the entire system would need to be flushed to prevent the slurry from hardening in the spray system.

Q. How does RimCraft overcome this issue?

A: Through our Patented Process that gives you longer working time while also being able to control your set time.

There are Gypsum retardants available for purchase, that change the natural setting time of the Gypsum slurry from 30 minutes to over 4 hours. This allows the operator to continue spraying for up to 4 hours before flushing the system.

The Gypsum slurry is pumped from the plastic slurry tank to the RimCraft Gypsum Spray Gun. When the slurry passes through the Stainless Steel Spray Nozzle the Atomizing Air is injected to burst the slurry into small droplets, creating a spray pattern. The Aluminum Sulfate Accelerator is metered into the atomizing air and then injected into the Gypsum slurry as it exits the spray nozzle. The slurry set time can be adjusted from 5 - 30 minutes, dramatically decreasing mold turn-over time.

Q: Is the accelerator easy to adjust?

A: Yes! Simply turn one knob.

Q: Do I have to use the Gypsum Retardant?

A: It is HIGHLY RECOMMENDED, unless you are using a gypsum slurry that provides a pot life greater than 1.5 hours. RimCraft offers for purchase, the proper Gypsum retardant for this application called NoGo.

Q: How is the RimCraft Gypsum Spray Equipment Designed, Engineered, and Constructed for gypsum processing?

A: The gypsum slurry and the accelerator are abrasive and corrosive materials that require compatible fluid passages made from Stainless Steel and certain plastics. RimCraft does not use conventional plumbing fittings that are made of steel for these reasons.

Q: Why use a Peristaltic Hose Pump instead of a Piston, Diaphragm or Rotor/Stator Pump?

A: RimCraft uses a peristaltic hose pump for it's ability to pump abrasive and corrosive materials. The slurry passages are engineered in such a way as to provide total residual-free cleanouts. Rotor/Stator Pump create too much friction which causes premature curing of Gypsum.


RimCraft Gypsum Spray System peristaltic pumps are:

* Sealless  Dry-Running  Self-Priming to 27'

* Abrasion Resistant  Reversible Rotation

* Metering Accuracy to ±1% 

* Integral Conventional Gear Drives 

Q: How does a peristaltic hose pump work?

A: Peristaltic pumps work using the process of peristalsis to pump products through a hose the same way that blood and oxygen are pumped around the body.

* The hose sits around a rotor which, when turning, compresses a segment of the hose almost flat.
* This compression is released as the rotor moves around the hose with the hose reinforcements causing it to spring back to its round shape,  thus creating a partial vacuum refilling the hose.
* This compression creates a seal and, as the rotor turns, any product on the discharge side of the rotor is propelled forward and displaced from the pump. 

* Combining this suction and discharge action results in a self-priming positive displacement pump.


Q: How is the RimCraft Gypsum Spray System different from other marketed gypsum equipment?

A: Most of the other equipment on the market that is being presented as Gypsum processing equipment is lacking in technology.


These systems are usually designed for other applications and are being modified to process a Gypsum slurry. They typically work for the first few batches, then it becomes a high maintenance and troublesome piece of equipment.


RimCraft researched the environments that the Gypsum Spray Systems had to operate in when we started to design our system. The system would be in water prone areas at all times, must require little to no maintenance and flush quickly and easily with no disassembly of components. All components must be laid out for easy inspection and access. The system must be USER FRIENDLY! With all of this in mind, RimCraft set out to engineer a TRUE GYPSUM PROCESSING SYSTEM!

RimCraft tested several pumps before designing its own current model, the RimSpray 1 1/4" Peristaltic Hose Pump.

* The entire system can be flushed with less than 8 gallons of water and in less than 10 minutes.

* The RimCraft Gypsum Spray Gun is modular in design. The spray nozzle is CNC Machined from Stainless Steel to provide long life.          (Competitor's are typically machined from a soft aluminum material.)

* The pneumatic and electric components are protected from the elements by a watertight fiberglass control box enclosure.

* All fittings, clamps, fluid passageways are engineered and manufactured from Stainless Steel and certain plastics for corrosion resistance.

* The Accelerator Injection System is engineered to provide a accurate delivery of the hardener.

* The system is powered by a 2 hp (1.5 kw) AC Motor set up for the customer's power requirements.

* RimCraft uses Direct Drive Gear Boxes and Motors to power the peristaltic pump. (Others use a chain drive to power their pumps which is prone to rust and slurry build-up, causing it to pop off. The chain is usually located in a position that makes it almost impossible to lubricate and is a maintenance nightmare when the chain pops off.)

* All electrical components on the RimCraft Gypsum Spray System are sealed from water and can be washed down.

* All fasteners (including the nuts and bolts) are Stainless Steel to resist corrosion.

Q: Can the RimCraft Gypsum Spray System spray Gypsum slurries that have aggregate mixed in them, such as sand?

A: Yes, all of RimCraft Gypsum Spray Systems can spray Gypsum slurries with sand. However the Max G Gypsum Spray System is better suited for this application, due to the stronger pump hose and larger pump size. It is recommended to use a polymer modifier. The polymer keeps the sand in suspension. Consult your gypsum sale representative for more information.

Q: Does RimCraft offer training and setup?

A: YES, when required! When a customer purchases a RimCraft Gypsum Spray System we want them to get a fast return on their investment so we can set up training at our facility with your machine. 


Q: Does RimCraft build custom Gypsum Processing Systems?

A: Yes. RimCraft has produced Gypsum Systems that were completely PLC controlled and built in mixer. Various chassis configurations and boom lengths. Please see our Custom Equipment Page to view pictures of these system. We will build to suit YOUR NEEDS!

Q: Is there somewhere I can find out about pricing?

A: Yes. Please see OUR PRICING PAGE for some information. However, since we will build to suit your needs, please fill out our CONTACT FORM so we understand what those needs are!

Peristaltic Hose Pump
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