What Are The Different Types of Grout?
In our last newsletter, we referred to two distinct classes of machinery grouts, inorganic and organic. A brief discussion of each type will shed some light on where each should be used.
Inorganic grouts are by far the oldest grouts and are used in a broad range of industrial applications. Sometimes referred to as sand and cement grouts, which are mixed with water, this description does not do justice to the sophisticated properties some modern-day, proprietary brands possess. Plain sand, cement and water mixtures shrink. By the addition of other materials to the formula, however, the natural shrinkage can be offset by various expansive mechanisms. The resulting product will actually expand very slightly, in the range of .03%.
Since a lot of the shrinkage and expansion reactions take place in the plastic stage, before final cure, some expansive formulations can lose part of the net gain against shrinkage when the hydration process moves beyond the plastic stage. There are even proprietary brands that offer double expansive mechanisms, with the second taking over in the later stages of cure.
Certainly such formulations are much more complex than a simple sand and cement mixture. The formulator's goal is to produce a product that, when properly mixed and installed, will provide excellent base plate contact (95 to 100%), good compressive properties (5,000 to 8,000 psi) and the ability to be installed in a range of environments from 50° to 100° F.
Resistance to weathering and to operating or environ- mental fluids is another important property that must be considered in selecting an inorganic grout. The resistance capability of the grout is often the limiting factor to achieving a long, trouble-free life.
In a lot of industrial applications, a good inorganic grout will be stronger and more dense than the underlying concrete foundation. Being less expensive, by perhaps 30% to 50% of what an organic-based epoxy grout costs, inorganic grouts are used quite broadly where operating conditions permit.
The second general class of grouts is called organic because a polymer binder, which is organic, is substituted for the cement binder in an inorganic grout. Organic grouts often contain the same inorganic fillers (sand, silica flour and quartz) found in pure inorganic cement grout formulas.
If inorganic grouts are stronger than concrete and cheaper than organic grouts, why even use an organic grout?
The reason is very simple; the organic grout gives much better chemical resistance which allows it to perform where inorganic grouts can't. Even something as simple as lubricating oil can eventually destroy the physical properties of inorganic grouts.
Organic grouts are also stronger in compressive, shear and tensile strength, so they can perform longer under heavy dynamic loading conditions. There is a place for this more expensive class of grout in machinery grouting, particularly for right angle drive reciprocating compressors, large diesel and gas engines, some turbines and gear boxes, as well as a host of equipment in the steel and paper industries where wet operating conditions are prevalent.
Organic grouts, also called polymer grouts, are usually based on a thermosetting plastic resin system, such as epoxy. Other thermosetting resins, such as polyesters, phenolics and furanes, have been used as well. These materials are used in specialty grouts requiring a particular resistance to strong chemicals beyond the usually good chemical resistance offered by epoxies.
The most common type of organic grouting systems are based on epoxy resins. Because of the popularity of this class of grout, we will deal with the proper use and application of epoxy grouts. These grouts can be summarized as having almost no shrinkage, compressive strengths of 10,000 to 14,000 psi or better, tensile strengths of 2,000 psi or better, and they are essentially impervious to penetration or chemical attack by oils, detergents, water, mild acids and most alkaline solutions. However, with a coefficient of expansion of at least twice that of concrete and steel, care in the design, use and installation of epoxy grouts must be taken. Because of their importance, subsequent newsletters will deal with these issues in detail.
Before long, you may also see what could be called a hybrid class of grout available for some of the applications now being handled by either the inorganic or organic classes of grouts. These materials will be chemically similar to the inorganic grout class but will substitute a polymer solution for the water used in inorganic grouts. This will create a grout with better resistance to chemicals and oils and with less permeability than typical inorganic grouts. Since such products have not yet been fully developed for machinery grouts and have yet to gain wide-spread usage, they are only mentioned in passing.
Typical Physical Properties Comparison
|| Oil Resistance
|| Tensile Strength
| Epoxy Grout
|| 14,000 psi
|| 2,000 psi
| Inorganic Grout
|| 5,000 psi
|| 300 psi
It has been over 63 years since Robt. L. Rowan & Assoc., Inc. developed the first combination of epoxy resins and inert fillers to produce the first epoxy grout. That new class of grouting material has become the standard around the world for the precision grouting of reciprocating and rotating machinery. Manufactured in many countries of the world by several competing companies, its superior properties have allowed the development of better, more sophisticated sub-base assemblies, such as adjustable chocks. Look for more in our next newsletter.