What Makes a Grout "Non-Shrink" — The Engineering Definition
Non-shrink grout is a pre-blended cementitious or polymer material that maintains its volume or exhibits controlled expansion during the plastic and hardening phases of cure. The term "non-shrink" does not mean zero volume change — it means the grout compensates for the natural drying shrinkage of cement paste through internal expansion mechanisms, resulting in net zero or positive volume change at the critical grout-to-substrate interface.
This distinction matters because shrinkage creates gaps between the grout and the equipment base or foundation. Even a 0.1 mm gap eliminates load transfer, causing point loading, vibration amplification, and progressive deterioration of both the grout and the foundation.
ASTM C1107 (Standard Specification for Packaged Dry, Hydraulic-Cement Grout — Nonshrink) defines non-shrink grout by three performance grades based on the expansion mechanism:
| ASTM C1107 Grade | Expansion Phase | Height Change Requirement | Mechanism |
|---|---|---|---|
| Grade A | Pre-hardening (plastic) | 0.0% to +4.0% at 1 day | Gas-generating admixture |
| Grade B | Post-hardening (early) | 0.0% to +0.3% at 1 to 3 days | Expansive cement or oxide |
| Grade C | Combination | Grade A + B requirements | Both mechanisms |
Why Non-Shrink Properties Are Critical for Equipment Bases
When heavy equipment — turbines, compressors, generators, CNC machines — is bolted to a concrete foundation, the grout layer between the baseplate and the foundation serves three functions:
Non-shrink grout ensures all three functions are maintained over the service life. Regular cement mortar shrinks 0.04 to 0.08% during hardening, which on a 600 mm wide baseplate creates a 0.24 to 0.48 mm gap at each edge — enough to eliminate 30 to 50% of the effective bearing area.
Compressive Strength Grades: Matching Grout to Equipment Loads
Not all non-shrink grouts are created equal. The compressive strength must be matched to the bearing pressure from the equipment:
| Application | Required Strength | Recommended Product | Notes |
|---|---|---|---|
| Light equipment (< 500 kg) | 40–50 MPa | Standard non-shrink grout | Most pumps, small compressors |
| Medium equipment (500–5,000 kg) | 50–60 MPa | XQ-GR-NS (Non-Shrink) | CNC machines, medium compressors |
| Heavy equipment (5,000–50,000 kg) | 60–80 MPa | XQ-GR-HS (High-Strength) | Turbines, large generators, presses |
| Precision equipment | 80+ MPa | Epoxy grout (XQ-GZ) | Precision grinding machines, optical equipment |
Flow Properties: Self-Leveling vs. Pourable vs. Packing Consistency
Non-shrink grout is available in three consistency levels, selected based on the gap geometry:
| Consistency | Flow Spread (ASTM C1437) | Gap Thickness | Application Method |
|---|---|---|---|
| Fluid / self-leveling | > 300 mm | 25–150 mm | Pour from one side, flows by gravity |
| Flowable / pourable | 250–300 mm | 20–75 mm | Pour with moderate head pressure |
| Plastic / dry-pack | < 200 mm | 10–50 mm | Ram into place with packing tool |
Our XQ-GR-NS achieves > 300 mm flow spread when mixed at 12 to 14% water content (by weight of dry grout). This self-leveling consistency ensures complete filling of the gap under the baseplate without vibration or rodding.
Critical: Water content matters more than mixing time. Adding too much water increases flow but reduces strength and increases shrinkage. Adding too little water prevents self-leveling and creates voids. Always measure water by weight, not by volume.Cementitious vs Epoxy: When Each Non-Shrink Grout Type Wins
The fundamental decision for equipment base grouting is between cementitious non-shrink grout and epoxy grout. Here is the practical decision framework:
Choose cementitious non-shrink grout when:- Budget is a priority (5 to 8 times cheaper than epoxy)
- Environment is clean (no chemical exposure)
- Temperature range is moderate (above 5 degrees Celsius during placement)
- Fire resistance is required (non-combustible rating A1/A2)
- Gap thickness exceeds 50 mm (epoxy generates excessive heat in thick pours)
- Chemical exposure exists (acids, oils, solvents in food, pharmaceutical, or chemical plants)
- Vibration is severe (epoxy's higher tensile and bond strength resist vibration cracking)
- Zero shrinkage is critical (cementitious is "non-shrink" but not truly "zero-shrink")
- Dynamic loads are dominant (epoxy's fatigue resistance is superior)
- Space is confined (epoxy requires no moist curing)
Standards and Specifications for Non-Shrink Grout
Engineers specifying non-shrink grout should reference these standards:
| Standard | Scope | Key Requirements |
|---|---|---|
| ASTM C1107 | Packaged dry non-shrink grout | Expansion grades A/B/C, compressive strength |
| EN 1504-6 | Anchoring of reinforcing steel bar | Compressive, bond, and creep requirements |
| ACI 351.1R | Grouting between equipment bases and foundations | Placement procedures, testing, inspection |
| GB/T 50448-2015 | Cement-based grouting material (China) | Non-shrink, high-strength, fast-setting grades |
Our cementitious grout products are tested to both ASTM C1107 and GB/T 50448-2015, and our epoxy grout meets ASTM C579 (Standard Test Methods for Compressive Strength of Chemical-Resistant Mortars, Grouts, Monolithic Surfacings, and Polymer Concretes).
Installation Best Practices
From 20 years of technical support for grouting projects, these are the practices that separate successful installations from failures:
Related Guides
- Cementitious Grout vs Epoxy Grout: 20-Property Comparison — Head-to-head comparison with cost data and decision tree.
- Epoxy Grout for Machinery Foundations — When epoxy grout is the right choice for heavy industrial equipment.
- Rebar Epoxy Anchoring in Concrete — Anchor bolt installation before grouting.
- Two-Part Epoxy Adhesive Guide — The epoxy chemistry behind both grout and structural adhesive systems.
- Underwater Concrete Repair Methods — Anti-washout grout for submerged applications.
- View All XINCHOR Grouting Products — Epoxy grout, cementitious non-shrink grout, and underwater grout.
Frequently Asked Questions
What is the difference between non-shrink grout and regular cement mortar?
Non-shrink grout contains expansion-generating admixtures (gas-generating agents and/or expansive cements) that compensate for the natural drying shrinkage of cement paste. Regular cement mortar shrinks 0.04 to 0.08% during hardening. Non-shrink grout maintains 0.0% to +0.3% net volume change per ASTM C1107, ensuring full contact between the grout and the substrate surface. Additionally, non-shrink grout is pre-blended with precise ratios of cement, aggregate, and admixtures for consistent quality, while site-mixed mortar quality varies with each batch.
Can non-shrink grout be used underwater?
Standard non-shrink grout is not suitable for underwater placement — the cement paste washes out in water. Our underwater grout (XQ-GR-UW) contains anti-washout admixtures (cellulose ether) that prevent dispersion, achieving 45 MPa compressive strength even when placed fully submerged. See our underwater concrete repair guide for submerged grouting procedures.
How thick should non-shrink grout be under a baseplate?
Minimum 25 mm for cementitious non-shrink grout (below this, expansion is insufficient and drying shrinkage dominates). Maximum 150 mm in a single pour (above this, heat of hydration can cause thermal cracking — pour in two lifts with 24-hour interval). For gaps of 10 to 25 mm, use epoxy grout or precision leveling compounds instead. The optimal range for most equipment bases is 40 to 80 mm.
What is the shelf life of non-shrink grout?
Our packaged non-shrink grout has a 12-month shelf life when stored in sealed bags in a dry, ventilated warehouse at 5 to 30 degrees Celsius. Moisture exposure is the primary degradation mechanism — even high humidity can cause pre-hydration of the cement and expansion agents, reducing both strength and expansion performance. Always use unopened bags and discard any bags that feel hard or lumpy.
Does non-shrink grout need reinforcement?
For standard equipment bases (gap thickness 25 to 150 mm), no reinforcement is needed — the grout is in compression, and its compressive strength (60 to 80 MPa) far exceeds the bearing load. Reinforcement is only needed for: very thick pours (> 200 mm), applications with significant tensile or shear loads, or when the grout is exposed to thermal cycling that could cause cracking. In these cases, steel fiber reinforcement (0.5 to 1.0% by volume) or welded wire mesh can be added.