Cementitious Grout Glossary

An admixture is a chemical added to a grout mix — almost always pre-blended into the packaged product rather than added on site — to modify its behavior. Cementitious grouts rely heavily on them: water reducers and superplasticizers achieve fluid consistency without raising the water content, expansive agents offset shrinkage, accelerators speed set in cold conditions, retarders extend working time in hot conditions, and corrosion inhibitors protect embedded steel. Because packaged non-shrink grouts are formulated as complete systems, adding site admixtures voids most manufacturer warranties and can defeat the expansion mechanism entirely.

Aggregate is the graded sand that makes up the bulk of a packaged cementitious grout, along with any coarse aggregate added on site. The gradation is engineered to balance flow, strength, and shrinkage: too fine and the grout demands excess water, too coarse and it will not flow through tight clearances. Standard packaged grout aggregate is sized for pours up to roughly 6 inches, above which coarse aggregate is normally added to control heat and shrinkage in the larger mass.

Anchoring is the setting of anchor bolts, threaded rod, dowels, or reinforcing steel into holes or pockets in hardened concrete. Non-shrink cementitious grout is poured or dry-packed into the annular space around the bolt, and once cured it transfers tension and shear from the anchor into the surrounding concrete. Cementitious anchoring is well suited to large-diameter bolts, deep embedments, and high-temperature service where an adhesive anchor would soften, and it requires hole cleanliness and pre-wetting to develop full bond.

ASTM International publishes the test methods and specifications that govern cementitious grout. When a data sheet cites a strength or flow value, the ASTM designation next to it defines how that number was produced, and figures generated under different methods are not comparable. The standards most relevant to cementitious grout are:

A baseplate is the steel plate a piece of equipment or a structural column is mounted to, spreading its load across the concrete foundation below. Cementitious grout fills the gap between the underside of the plate and the foundation, converting an assembly that initially bears on a handful of shims into one that bears across its full footprint. Plate size, clearance, and the presence of stiffeners and internal compartments all determine whether the grout can be placed by gravity flow alone or requires additional head and venting.

Bleeding is the separation of mixing water, which rises to the surface of freshly placed grout as heavier solids settle. Under a baseplate this is a direct failure mechanism: rising water collects against the underside of the steel, and when it eventually evaporates or is absorbed it leaves a void exactly where full contact was required. ASTM C1107 grouts are formulated to bleed zero percent at the consistencies tested. Excess mixing water is the most common cause of bleeding on site.

Bond is the adhesion developed between hardened grout and the surfaces it contacts. Cementitious grout bonds to concrete through the interlocking of hydration products with the pore structure and profile of the substrate, which is why saturated surface dry conditions and an aggressive profile matter so much — a dry substrate pulls mixing water out of the grout at the interface and starves the reaction right where bond is forming. Cementitious grout does not bond meaningfully to steel; it bears against the baseplate rather than adhering to it.

A chamfer is an angled or beveled edge formed at the exposed perimeter of a grout pour, typically 45 degrees. Square edges are vulnerable: a thin feathered corner has little strength, dries faster than the mass behind it, and chips or spalls under traffic and impact. Chamfering the outer edge of the shoulder produces a durable, finishable edge and reduces the exposed surface area from which the grout can lose moisture during curing.

Compressive strength is the crushing load a grout can carry before failure, reported in PSI and measured on 2-inch cubes per ASTM C109. Cementitious non-shrink grouts typically develop 5,000 to 10,000 PSI at 28 days, with high-strength precision products reaching higher. Strength is reported at multiple ages — 1, 3, 7, and 28 days — because early strength governs when equipment can be loaded, while 28-day strength is the design value. Compressive strength falls sharply as mixing water increases, which is why the water range on the bag is a limit rather than a suggestion.

Concrete Surface Profiles are the standardized roughness classifications published by the International Concrete Repair Institute in Guideline 310.2R. CSP 1 through CSP 10 range from a nearly smooth acid-etched finish to heavy scarification, and ICRI produces physical rubber replica coupons so that specifier and contractor can agree on what a given profile means. Structural cementitious grouting generally calls for CSP 5 or greater, achieved by chipping or scarifying to sound concrete with coarse aggregate exposed.

Consistency describes how fluid a mixed grout is, and ASTM C1107 requires that a product meet its performance requirements at whichever consistency is used. The three standard consistencies are plastic (stiff, placed by dry-packing or troweling), flowable (pourable, measured on a flow table per ASTM C1437), and fluid (self-leveling, measured by efflux time through a flow cone per ASTM C939). Consistency is adjusted only within the water range printed on the bag; moving to a fluid consistency by adding water beyond that range produces bleeding, segregation, and lost strength.

Creep is gradual, permanent deformation under sustained load. Cementitious grout creeps less than epoxy under static load at ambient temperature, which is one of its genuine technical advantages and a reason it remains specified for heavily loaded static bases and structural columns. Its creep behavior degrades under elevated temperature and under sustained dynamic loading, which is where epoxy formulations are generally preferred instead.

Cure in cementitious grout is the ongoing hydration of cement, a reaction that requires water and continues for as long as water and unreacted cement remain available. This is fundamentally different from a resin cure: the grout is not drying, it is consuming water chemically. Roughly 70 percent of design strength is typically reached at 7 days and the design value at 28 days, though hydration continues at a diminishing rate long after. Cure rate is heavily temperature-dependent, slowing dramatically as temperatures approach freezing.

A deep pour is a placement exceeding the maximum depth a packaged grout is rated for neat, commonly around 6 inches. Depth causes two problems in cementitious grout: the mass retains hydration heat, raising internal temperature and increasing thermal cracking risk on cool-down, and the greater volume of paste increases total shrinkage. Both are addressed by extending the mix with coarse aggregate, and by placing in lifts where depth is extreme. Confirm the maximum neat pour depth and the specified extension rate on the product data sheet before ordering.

Dimensional stability is a grout’s ability to hold its cast volume and shape over its service life — resisting plastic and drying shrinkage, creep, and thermal movement. For cementitious grout this is a formulated property rather than an inherent one: cement paste shrinks as it hydrates and dries, and non-shrink grouts counteract that with expansive agents. Stability is therefore conditional on correct water content and adequate curing in a way that is not true of resin systems.

Dry packing is the placement of grout at a stiff, low-water plastic consistency by hand — rammed and compacted into place with a rod and hammer rather than poured. Because the mix carries minimal water, dry-packed grout achieves high density and strength with very little shrinkage, and it holds its shape without forms. It is used for anchor bolt pockets, shallow bearing areas, vertical and overhead patching, and edge repair. Consolidation depends entirely on the installer’s effort, so dry packing is not appropriate under baseplates where high effective bearing area must be verified.

Drying shrinkage is volume loss that occurs in hardened grout as excess mixing water — water not consumed by hydration — evaporates over weeks and months. It is proportional to water content, which is the mechanism behind the rule that every extra quart of mixing water costs you strength and stability. Non-shrink grouts offset drying shrinkage with expansion so that net height change stays at or above the original placement height, verified per ASTM C1090.

A dynamic load varies with time — cyclic, vibratory, or impact — rather than remaining constant. Reciprocating compressors, crushers, presses, and high-speed rotating equipment all impose dynamic loads on their foundations. Cementitious grout handles moderate dynamic loading but is more vulnerable than epoxy to fatigue cracking, progressive loss of bearing contact, and anchor bolt loosening under sustained vibration, because it does not bond to the baseplate and has lower tensile and bond capacity to resist the working of the joint.

Effective bearing area is the percentage of a baseplate’s underside in genuine contact with the hardened grout beneath it. It is not the same as the area that was poured — entrapped air, incomplete flow, bleed water collecting under the plate, and shrinkage away from the steel all leave zones that carry no load. A plate at 60 percent EBA concentrates its entire load on 60 percent of the intended footprint, producing localized crushing and alignment drift. Achieving high EBA with cementitious grout depends on fluid consistency, adequate head, continuous placement, and controlling bleed.

Efflorescence is the white, powdery deposit that appears on the surface of cementitious grout when water migrates through the material, dissolves soluble salts, and evaporates at the surface leaving them behind. It is primarily cosmetic and is common on exposed shoulders in damp conditions or where the grout is subject to ongoing moisture movement. Persistent efflorescence usually indicates a water source that should be addressed, since continuous moisture transport through grout is rarely harmless in the long run.

An expansion joint is a deliberate break in a grout pour that lets the mass move with temperature change without accumulating stress. Cementitious grout has a coefficient of thermal expansion close to that of concrete, so it needs joints less urgently than epoxy does, but long continuous pours, exterior installations, and elevated-temperature service still require them. Joints are placed at intervals set by pour length and service conditions, and at stress concentrations such as reentrant corners and abrupt changes in section.

An expansive agent is the admixture that makes a cementitious grout non-shrink by producing a controlled volume increase that offsets cement shrinkage. Different chemistries act at different times, which is the basis of the ASTM C1107 grade classification: some generate gas or expansive reaction products while the grout is still plastic (Grade A), some produce crystalline growth after hardening (Grade B), and some do both (Grade C). Grade selection matters, because a grout that expands only in the plastic state can still lose height afterward if curing is inadequate.

Extending a cementitious grout means adding coarse aggregate — typically 3/8 inch washed, rounded pea gravel — to the packaged mix for deep placements. Extension increases yield, reduces cost, lowers the heat generated in a large mass, and cuts total shrinkage by reducing the proportion of cement paste. It also stiffens the mix and reduces flow, so it is only done above the manufacturer’s stated minimum depth, at the stated rate, with clean saturated surface dry aggregate. Extending a shallow pour to save material will compromise flow and bearing area.

The flow cone is the standard apparatus for measuring fluid grout consistency under ASTM C939. A measured volume of grout is poured into the cone and the efflux time — the seconds required for it to discharge through the orifice — is recorded. Shorter efflux times mean more fluid grout. Manufacturers publish target efflux ranges for their fluid consistency, and field testing with a flow cone is the practical way to confirm that batching is consistent from mixer load to mixer load rather than drifting as crews adjust water by eye.

Formwork is the temporary structure that contains grout until it hardens. Cementitious grout formwork must be liquid-tight at fluid consistency, adequately braced for the hydraulic pressure of a deep pour or charged head box, and treated with form release. It is normally built to leave a grout shoulder outside the baseplate footprint, set high on the pour side to develop head, and kept low or vented on the opposite side so displaced air can escape ahead of the advancing grout.

The foundation is the reinforced concrete mass that supports equipment or structure and transmits load to the soil or supporting frame below. Its mass, reinforcement, anchor bolt layout, and surface condition determine how the completed installation will perform, since grout can only be as good as what it bears on. Concrete should be fully cured before grouting, chipped back to sound material where it is damaged, profiled, and brought to a saturated surface dry condition prior to placement.

Freeze-thaw resistance is the ability to withstand repeated cycles of freezing and thawing while saturated. Water expands as it freezes, and grout with a saturated, permeable pore structure will progressively crack and spall under cycling. Exterior installations, bridge bearing pads, and unheated structures require grout formulated for freeze-thaw exposure, and performance depends on achieving low permeability through proper water content and thorough curing.

A head box is a raised extension of the formwork at the pour point that holds a standing column of grout above the level of the baseplate. That column generates hydraulic head, and the resulting pressure drives grout horizontally beneath the plate to the far edges. Head boxes are standard on any baseplate too wide for gravity flow alone, and keeping the box continuously charged throughout the pour matters as much as building it — letting it run empty allows air to enter the advancing front and leaves voids.

Hydration is the chemical reaction between portland cement and water that produces the calcium silicate hydrate binding the hardened grout together. It is what distinguishes cementitious grout fundamentally from resin systems: the grout gains strength by consuming water, not by losing it. Hydration requires available moisture to continue, generates heat, slows dramatically in cold conditions, and proceeds for months at a diminishing rate. Nearly every rule about cementitious grouting — water limits, wet curing, cold weather precautions — follows from how hydration works.

Laitance is the weak, dusty layer of fine cement particles and water that rises to the surface of concrete as it is placed and finished. It has almost no strength, so grout placed on laitance is bearing on a layer that will fail under load. Removing it completely by chipping, scarifying, or abrasive blasting down to sound concrete with coarse aggregate exposed is a non-negotiable first step in preparing a foundation, and its presence is among the most common causes of grout failure at the interface.

A lift is one placement layer within a multi-layer pour. When total depth exceeds what a product can be placed in at once, the pour is broken into lifts, each allowed to set and gain strength before the next is placed. Lifts limit the heat and shrinkage of any single mass. The surface of each lift must be left rough rather than troweled smooth, cleaned of laitance, and brought to a saturated surface dry condition before the next is placed, or the lift interface becomes a plane of weakness.

A non-shrink grout maintains or slightly exceeds its original placed volume rather than losing height as it hardens, keeping contact with the baseplate above and the foundation below. Under ASTM C1107 the requirement is that height change never falls below the initial placement height at any tested age, verified per ASTM C1090. Cement paste shrinks by nature, so non-shrink performance is achieved through expansive admixtures, and it is conditional: excess mixing water or inadequate curing can produce net shrinkage from a product legitimately labeled non-shrink.

Plastic shrinkage is volume loss occurring while grout is still fresh and has not yet set, driven by surface water evaporating faster than bleed water can replace it. It produces the characteristic short, random surface cracks seen on pours placed in wind, heat, low humidity, or direct sun. It is prevented by controlling the placement environment, minimizing exposed surface area, and covering or fogging the surface immediately after placement — not by adding water to the mix, which makes matters worse.

Portland cement is the hydraulic binder at the core of cementitious grout, manufactured by firing limestone and clay to produce clinker, which is then ground with gypsum. Hydraulic means it sets and hardens by reacting with water and will do so underwater. ASTM C150 defines the standard types, of which Type I general purpose, Type II moderate sulfate resistance, and Type III high early strength are the ones most often encountered in grout formulations. Packaged grouts frequently blend cement with supplementary materials such as fly ash or silica fume to modify strength gain, permeability, and durability.

Precision grade cementitious grout is formulated for applications where equipment must be set and held to tight tolerances — machine tools, presses, structural columns, and heavily loaded static bases. These products emphasize high early and ultimate strength, dependable non-shrink performance across all three consistencies, zero bleeding, and good flow at low water content. Precision grade cementitious grout is appropriate for precise static installations; sustained dynamic loading and chemical exposure generally point toward epoxy instead.

Profile is the texture and roughness of a prepared substrate. Cementitious grout develops bond largely through mechanical interlock, so it needs peaks and valleys to key into — a smooth, power-troweled, or laitance-covered surface will not develop meaningful bond regardless of grout quality. Concrete is profiled by chipping, scarifying, scabbling, or abrasive blasting down to sound material, and the result is classified against the CSP scale.

PSI stands for pounds per square inch, the standard US unit for reporting grout strength. Compressive, tensile, flexural, and bond strengths are all expressed in PSI. The metric equivalent is the megapascal, where 1 MPa is approximately 145 PSI. A PSI figure is only meaningful alongside the test method, the specimen type, the consistency at which the grout was mixed, and the age at test — cementitious grout values in particular are always tied to an age.

Retrofit grouting is the repair or replacement of grout beneath existing equipment or structure, as opposed to grouting a new installation. It is driven by grout that has cracked, crushed, deteriorated, or lost bearing contact, by foundations damaged by vibration or corroded anchor bolts, or by equipment that has drifted out of alignment. The work involves removing failed material, chipping to sound concrete, re-establishing profile, resetting and shimming, pre-soaking the substrate, and placing new grout — usually inside a tight outage window that makes early strength gain a governing selection criterion.

Saturated surface dry describes concrete that has absorbed all the water it can hold but has no free water standing on the surface. It is the required substrate condition for cementitious grouting, and it is achieved by soaking the foundation for a period specified by the manufacturer — often 12 to 24 hours — and then removing all standing water with sponges, vacuum, or compressed air immediately before placement. Dry concrete draws mixing water out of the grout at the interface and starves hydration exactly where bond forms; standing water does the opposite, diluting the grout and creating a weak layer.

Segregation is the separation of a mix into its components — coarse aggregate settling out, paste and water rising. It is caused by excess water, over-mixing, dropping grout from height, over-vibration, or pumping too aggressively. Segregated grout cures with inconsistent strength through its depth and a weak, paste-rich layer directly beneath the baseplate, which is precisely the zone required to carry load. It is prevented by staying within the specified water range, mixing for the specified time, and placing continuously from a single point.

Set time is the transition from plastic to rigid, reported as initial set — when the grout can no longer be worked — and final set, when it has stiffened enough to resist penetration, typically measured by Vicat needle per ASTM C191. Set is not the same as strength gain: a grout can reach final set within a few hours and still require 28 days for design strength. Set times shorten sharply in hot weather and lengthen in cold, and below roughly 40°F hydration slows enough that protection and heating become necessary.

Shims are thin metal plates or wedges placed under a baseplate to establish correct elevation and level before grouting. They carry the load while the grout gains strength and fix the alignment the hardened grout will maintain. Shim packs are set at designated points, the plate is leveled and aligned against them, and grout is placed around them. Whether shims are removed after the grout has cured and their pockets filled, or left in place permanently, is a specification decision — shims left in place create hard points that concentrate load, while removing them requires enough strength gain to take the machine.

The substrate is the surface a grout is placed against — usually the concrete foundation, but also the underside of the baseplate, the surface of a previous lift, or the walls of an anchor bolt pocket. Substrate condition governs performance more than any property of the grout itself. It must be structurally sound, clean, free of laitance, oil, and curing compound, adequately profiled, at a temperature within the application range, and brought to saturated surface dry condition before placement.

Sulfate resistance is the ability to withstand exposure to sulfate-bearing soils, groundwater, or process water without deterioration. Sulfates attack hydrated cement chemistry, forming expansive compounds that crack the grout from within over months or years. Resistance is improved by using Type II or Type V cement, by supplementary cementitious materials such as fly ash or slag, and by achieving low permeability through minimal water content and thorough curing. Wastewater, agricultural, and certain geographic soil conditions make this a governing specification requirement.

A void is an unfilled space within a hardened grout pour, whether from entrapped air, incomplete flow, bleed water that later evaporated, or shrinkage away from the plate. Voids beneath a baseplate reduce effective bearing area directly, concentrating full equipment load onto whatever contact remains. They are prevented by fluid consistency, adequate and continuously maintained head, single-direction placement, air relief holes through the plate, and correct water content. They are located afterward by hammer sounding and corrected where significant by drilling and pressure grouting.

The water-cement ratio is the weight of mixing water relative to the weight of cement in a mix, and it is the single most consequential variable in cementitious grouting. Lower ratios produce higher strength, lower permeability, less bleeding, and less drying shrinkage; higher ratios produce easier flow and worse everything else. Because only a limited amount of water is chemically consumed by hydration, all the rest eventually leaves as bleed or evaporation, taking volume with it. The water range printed on the bag exists to keep this ratio inside acceptable limits, and measuring water by volume rather than eyeballing it is the difference between the published strength and something considerably less.

Wet curing is keeping placed grout continuously moist while it hydrates, and for cementitious grout it is mandatory rather than optional. Hydration consumes water; if exposed surfaces dry out, the reaction stops in that zone and the grout never reaches its strength, while the differential drying causes shrinkage cracking. Exposed shoulders are wet cured with saturated burlap, wet sand, polyethylene sheeting, or a curing compound, typically for a minimum of three to seven days depending on product and conditions. Curing failure is one of the most common reasons a properly specified non-shrink grout underperforms in the field.

Working time is the interval from the moment water contacts the dry blend until the grout must be fully placed. It is a job-site figure rather than a laboratory one, and it contracts sharply in hot weather — a product with 30 minutes at 70°F may give considerably less at 95°F on a sun-heated foundation. Retempering with additional water to restore flow past working time is not an option: it raises the water-cement ratio and destroys strength and non-shrink performance. Plan crew size, mixer capacity, and the placement route before the first bag is opened so that a pour goes down continuously rather than developing a cold joint mid-baseplate.

Yield is the volume of mixed grout produced by one bag or unit, stated in cubic feet and quoted at a specific consistency — yields differ between plastic, flowable, and fluid mixes because water content differs. Estimating means measuring the void, calculating volume, dividing by yield at the consistency you intend to use, and adding a waste allowance for forms, shoulders, and spillage. Yield also increases when a mix is extended with coarse aggregate, so calculate against the extension rate you actually plan to use. Under-ordering is the most expensive planning error in grouting, since a pour that sets before the balance arrives cannot be made monolithic.