Pump Skid Grouting: API 686 Epoxy Grout

Why Pump Skid Grouting Determines Long-Term Reliability

A pump baseplate grouted correctly will hold shaft alignment, absorb vibration, and require almost no corrective maintenance for 20–30 years. A pump baseplate grouted incorrectly starts failing from commissioning: soft-foot misalignment, premature bearing failure, mechanical seal leaks, and cracked shafts follow in a predictable cascade that is expensive to diagnose and even more expensive to fix.

The grout under a pump skid serves four functions simultaneously:

Static load transfer — distributes the machine's dead weight uniformly into the concrete foundation mass

Dynamic force transmission — carries cyclic bearing loads from the running machine into the foundation without allowing micro-motion at the baseplate

Vibration damping — the grout column's stiffness and mass damp rotational and impulse forces before they reach the structure

Alignment reference plane — provides the stable, non-settling surface from which chock plates or direct-contact pads hold shaft centerline elevation

All four functions are destroyed by voids. A 2019 machinery reliability study across 127 pump failures in petroleum and chemical plants found inadequate base grouting as the root or contributing cause in 34% of bearing failures and 28% of mechanical seal failures. The investment in correct grouting — typically USD 200–600 in materials per pump — is returned well within the first year of avoided repairs.

API 686 Part 7: What the Standard Actually Requires

API Recommended Practice 686 (Machinery Installation and Installation Design), Part 7 (Section 7), is the primary installation standard for rotating equipment in oil, gas, and chemical process industries. The requirements that directly drive grout selection are:

API 686 Requirement	Practical implication
Minimum compressive strength: 70 MPa (10,000 psi) at 28 days	Eliminates most standard non-shrink cementitious grouts (typically 40–60 MPa); essentially mandates epoxy grout for critical service
Minimum contact area: 50% of baseplate bottom area	Requires a flowable, self-levelling product that fills complex internal rib geometry
No void permitted under any bearing pad or chock plate location	In practice, aim for >80% contact under load-bearing points regardless of the 50% overall minimum
Zero or positive volumetric change at set	Both cementitious and epoxy grouts can meet this; verify per ASTM C827 (cementitious) or equivalent expansion-at-set test
Maximum pour thickness: set by manufacturer (typically 100–150 mm for epoxy)	Foundation designers must provide minimum 50–75 mm clear grout space to allow proper flow
Surface preparation: steel SP-6 (commercial blast), concrete ICRI CSP 5–7	Non-negotiable — inadequate prep is the single most common cause of grout-to-substrate debonding
Pour temperature: 10–35°C for most standard formulas	Cold-climate pours require warm-up tents or winter-grade products; tropical pours require pre-chilled components

Does API 686 mandate epoxy grout? Not by name, but the 70 MPa compressive strength requirement makes non-shrink cementitious grout acceptable only for light-duty pumps under approximately 15 kW on non-critical service. For centrifugal pumps above 75 kW, all API 610 process pumps, and all reciprocating equipment, epoxy grout is the only practical path to compliance.

Epoxy vs Cementitious Grout for Pump Skids

Parameter	Epoxy grout	Non-shrink cementitious
Compressive strength (28-day)	70–100 MPa	40–60 MPa
Bond to steel baseplate	Chemical + mechanical (primer required)	Mechanical only
Bond to prepared concrete	Excellent	Good
Volumetric change at set	Zero to slight positive expansion	Zero to slight positive (gas-release type)
Dynamic load resistance	Excellent — high modulus (E ≈ 5–8 GPa) withstands cyclic loads	Moderate — lower modulus; susceptible to cracking under high-frequency vibration
Single pour thickness limit	100–150 mm (exotherm risk above this)	Up to 300 mm
Maximum continuous service temperature	60°C standard / 120°C high-temp grade	100–150°C
Chemical resistance	Excellent (hydrocarbons, mild acids/alkalis)	Limited (acid attack possible)
Pot life at 25°C	30–60 min — plan the pour carefully	60–120 min
Rework difficulty	High — must chip and re-pour	Moderate — drilled-port pressure injection can top up small voids
Indicative FOB price (Ningbo 2026)	USD 3.20–5.60/kg	USD 0.35–0.70/kg
MOQ	500 kg (≈20 three-component sets)	1,000 kg

Rule of thumb for pump selection:

Centrifugal pumps ≥75 kW or shaft speed ≥3,000 RPM → epoxy grout
Reciprocating pumps and compressors of any size → epoxy grout (API 686 §7.3.4.2)
Small centrifugal pumps <15 kW, <1,500 RPM, non-critical → non-shrink cementitious acceptable if approved by the foundation designer

Centrifugal Pump Foundations: Selection and Procedure

Centrifugal pumps generate relatively smooth radial and axial bearing forces. The dominant loading pattern is 1× running-speed vibration from rotor imbalance, with hydraulic forces at the impeller second. A well-balanced, properly aligned centrifugal pump imposes modest dynamic loads on its foundation — the grout's primary job is to hold the baseplate rigid, not to absorb large cyclic impact forces.

Foundation geometry: For a standard process centrifugal pump, the foundation concrete mass should be 2–3× the machine weight. The grout space under the baseplate is 50–75 mm clear (API 686 recommendation). Baseplates longer than approximately 1,500 mm should include internal fill holes and inspection ports to allow monitoring of grout fill during pour. Soft-foot check: Before starting any grouting work, confirm that all four machine feet are in full contact with the baseplate using a feeler gauge while loosening each hold-down bolt in turn. Any soft-foot gap exceeding 0.05 mm must be corrected with stainless steel shims before grouting — grouting over soft-foot locks the distortion permanently into the machine frame.

The pour sequence for centrifugal pumps is the standard API 686 single-end-fill method described in the step-by-step section below.

Reciprocating Pumps and Compressors: Higher-Impact Loads

Reciprocating machines — plunger pumps, piston compressors, diaphragm pumps — generate fundamentally different forces than centrifugal machines. Each piston stroke reverses bearing load direction, creating impulsive loads at 1× and 2× crankshaft frequency. A single-throw reciprocating plunger pump can generate peak bearing forces 3–5 times the machine's static weight at each stroke reversal. Multi-throw machines reduce the net unbalanced force through phasing, but individual bearing loads remain high.

Factor	Centrifugal pump	Reciprocating pump/compressor
Primary dynamic force character	Rotating imbalance — smooth, sinusoidal	Impulsive — stroke reversal at each half-cycle
Typical dynamic-to-static force ratio	1:1 to 1.5:1	3:1 to 5:1
Foundation mass ratio to machine weight	2–3:1	3–5:1 for large compressors
Recommended grout contact area	50% per API 686	>80% under load-bearing frame members in practice
Grout modulus of elasticity criticality	Moderate	Critical — low modulus allows micro-rocking that causes cracking
Special grouting considerations	Standard single-end pour	Multi-lift pour for large frames; vibration isolator mats sometimes specified for high-speed units

For large reciprocating compressors with skid widths above approximately 3 m, the pour is staged: perimeter grouting first to stop movement and allow inspection, followed by the full internal pour 24 hours later. This prevents the grout head pressure from floating the baseplate during the pour.

Chock Plate Method vs Direct Grouting

Two methods transfer the final load path between baseplate and grout:

Direct grouting: Epoxy or cementitious grout fills the entire space under the baseplate. The machine sits on cured grout. This is simpler, less expensive, and adequate for most centrifugal pump applications where re-alignment access is not a design requirement. Chock plate method: Pre-machined steel chocks (typically 100 mm × 100 mm, 10–25 mm thick) are positioned at each machine foot location and permanently grouted into the foundation. The baseplate is levelled by shimming to the machined chock surfaces; the remaining space is then filled with grout. The chock surfaces provide a precision reference for future re-alignment without regrouting.

Chock plate method	Direct grouting
Alignment precision	±0.01 mm (machined surface)	±0.05 mm practical
Future re-alignment	Easy — re-shim without regrouting	Requires chipping and re-pour
Best for	API 610 process pumps, API 617/619 compressors, all critical service	Standard pumps, lower-criticality applications
Chock grout height (API 686)	Min 25 mm, max 75 mm below chock underside	50–75 mm total grout space
Materials cost	Higher (chocks + grout)	Grout only

When chock plates are used, the grout column height from the concrete surface to the underside of the chock must be within 25–75 mm per API 686. This range controls column stiffness and prevents the mechanical disadvantage of excessively thin (over-stiff) or thick (soft) grout sections.

Step-by-Step Pump Skid Grouting Procedure

Pre-pour checklist:

[ ] Baseplate levelled within 0.05 mm/m in both axes; soft-foot eliminated on all feet
[ ] Concrete surface at ICRI CSP 5–7; completely dry for epoxy grout (SSD for cementitious)
[ ] No oil or grease contamination on concrete or baseplate underside
[ ] Formwork complete, all pipe penetrations and anchor bolt sleeves sealed
[ ] Grout component temperature 15–35°C (critical for working time and final strength)
[ ] Two-coat epoxy primer applied to concrete and baseplate; at correct tack stage

Step 1: Check ambient conditions. Do not pour if surface or ambient temperature is below 10°C or above 35°C. In hot weather (>30°C), chill Part A and Part B overnight and store aggregate in shade to extend pot life. Step 2: Confirm pot life. Mix a small test batch (200 g) and time gel — it should gel in 30–45 min at ambient temperature. Adjust pour crew size and batch size to complete each batch within 70% of measured pot life. Step 3: Mix epoxy components. Pre-mix Part A (resin) + Part B (hardener) for 3 minutes at low speed (≤300 RPM) using a paddle mixer. Add Part C (aggregate) gradually and continue mixing for 2 minutes until homogeneous and lump-free. Never partially add aggregate — mix the full charge each batch. Step 4: Single-end pour. Place all grout from one end of the form. Allow the grout to flow naturally to fill the space — never pour from multiple sides, as this traps air in the centre. Use a straight rod to guide flow around internal ribs and into pockets. Step 5: Fill internal pockets through fill holes. For baseplates with internal frame sections, pour through fill holes using a funnel. When grout appears at the inspection port of the adjacent chamber, that section is full. Move to the next fill hole. Step 6: Consolidate with chain drag. Pull a length of anchor chain back and forth across the top surface of the grout to collapse surface bubbles. Do not use vibrators — vibration causes segregation in aggregate-loaded epoxy grout. Step 7: Top coat and cure monitoring. After initial gel (3–4 hours at 25°C), apply a thin top coat to fill surface voids and achieve a smooth finish above the form line. After minimum 24 hours (standard) or 72 hours (full strength for critical equipment), remove forms. Hammer-sound the cured grout — hollow areas indicate voids and require drilled-port pressure injection. Final-torque hold-down bolts per API 686 sequence and re-check coupling alignment before start-up.

Common Pump Grouting Failures and Root Causes

Failure mode	Root cause	Prevention
Voiding under baseplate	Insufficient grout flow through internal ribs; mix too stiff; poured from multiple sides	Pre-flow test with water; single-end pour; reduce aggregate size for complex geometries
Grout cracking after cure	Exotherm cracking from over-thick single pour in hot weather	Keep each lift ≤100 mm; pre-chill components; shade forms during cure
Grout–steel debonding	Inadequate primer; oil contamination; primer applied at wrong tack stage	Two-coat primer per TDS; blasted clean steel <4°C above dew point; check primer tack before pour
Loss of alignment after start-up	Grout shrinkage (wrong product); soft-foot was not eliminated before pour; foundation cracked under dynamic load	Specify zero-shrink grade; correct all soft-foot before grouting; verify foundation design for dynamic loads
Chemical attack in service	Hydrocarbon or solvent contact with cementitious grout; incorrect epoxy grade	For chemical service: specify chemically resistant epoxy per ASTM C413; apply chemical-resistant top coat

Volume and FOB Cost Estimation

Calculating grout volume:

For a simple flat baseplate: > Volume (litres) = L × W × H × 1,000 × 1.15

Where L = baseplate length (m), W = width (m), H = grout space height (m), and 1.15 covers wastage, topping coat, and anchor bolt pockets. Deduct approximately 25–35% for internal rib and hollow sections typical of fabricated pump base frames.

Example: 1,500 mm × 900 mm baseplate, 75 mm grout space:

Gross volume: 1.5 × 0.9 × 0.075 × 1,000 × 1.15 ≈ 116 litres
Deduct 30% for ribs: ≈ 81 litres net grout required
At 1.34 kg/L (standard three-component epoxy grout): ≈ 109 kg per pump

Indicative FOB pricing (Ningbo, 2026):

Grout type	Grade	28-day strength	FOB price	MOQ
Epoxy grout (3-component)	Standard (service to 60°C)	80–100 MPa	USD 3.20–4.20/kg	500 kg
Epoxy grout (3-component)	High-temperature (to 120°C)	75–90 MPa	USD 4.80–5.60/kg	500 kg
Non-shrink cementitious (dry mix)	High-strength	55–65 MPa	USD 0.45–0.70/kg	1,000 kg
Non-shrink cementitious (dry mix)	Standard	40–55 MPa	USD 0.35–0.50/kg	1,000 kg

A typical order for a 4-pump skid installation (75 kW centrifugals) using epoxy grout: 4 × 109 kg ≈ 436 kg, approximately USD 1,400–1,800 FOB. Compare this to the cost of a single mechanical seal replacement or bearing rework — typically USD 800–2,500 per pump — and the value equation is straightforward.

Sourcing API-Grade Pump Skid Epoxy Grout from China

XINCHOR supplies three-component epoxy grout to EPC contractors and maintenance teams in more than 40 countries, including Saudi Aramco projects, PETRONAS refineries, and PEMEX turnarounds. Our standard epoxy grouting adhesive achieves 85 MPa compressive strength at 28 days (third-party tested per ASTM C579), zero shrinkage at set, and E-modulus of 6.8 GPa — suitable for all API 686 requirements.

We also supply:

High-temperature epoxy grout (service to 120°C, Tg >80°C) for steam turbine and hot pump applications
Low-viscosity injection grout for void-filling under existing baseplates and remedial grouting without full foundation replacement
Non-shrink high-strength cementitious grout (55–65 MPa) for non-critical centrifugal pumps and column base grouting

All products are accompanied by ISO 9001 quality certificates, SGS third-party test reports, and full Safety Data Sheets. Custom formulations for extended pot life (hot-climate pours), winter grades (pour at 5°C), and high-modulus variants for particularly demanding reciprocating compressor applications are available on request from 500 kg.

Tell us your pump model, baseplate dimensions, grout space, service temperature, and site climate and our technical team will recommend the correct grade, calculate your required quantity, and return a FOB quotation within one working day. Request a quote →

Frequently Asked Questions

Q: Does API 686 require epoxy grout, or is non-shrink cementitious grout acceptable? A: API 686 Part 7 specifies performance requirements — 70 MPa compressive strength, zero shrinkage, and minimum 50% contact area — not product types. In practice, standard non-shrink cementitious grouts top out at 55–60 MPa; only premium or ultra-high-strength cementitious formulations reach 70 MPa, and these sacrifice flowability. For all API 610 process pumps and any reciprocating equipment, epoxy grout is the standard approach on refinery and chemical plant projects. Q: How long after grouting can we start the pump? A: API 686 recommends not imposing full dynamic loading until the grout reaches at least 70% of its design compressive strength. For standard three-component epoxy grout at 20°C, this is typically 72 hours from pour. At 30°C ambient, 48 hours is usually sufficient. Use a field Shore D hardness test per the grout manufacturer's TDS to confirm readiness — never rely on elapsed time alone in variable weather. Q: What grout space should I specify in a foundation design? A: API 686 recommends 50–75 mm clear space under the baseplate. Below 50 mm, aggregate may bridge and prevent full fill. Above 100 mm, the grout column becomes softer and may allow baseplate flexure under dynamic load. For chock plate installations, specify 25–75 mm from the concrete surface to the underside of the chock. Q: Can we grout in cold weather (below 10°C)? A: Yes, with active precautions. Heat the concrete foundation surface to at least 10°C and maintain that temperature throughout the pour and the first 24 hours of cure using insulated blankets or a heated enclosure. Pre-warm all grout components (Part A, B, and C) to 15–20°C before use. Standard epoxy grout loses approximately 30% of 28-day strength when cured at 5°C versus 20°C; winter-grade formulations with reactive diluent systems are available for pour temperatures as low as 5°C. Q: What is the difference between pump skid grouting and general machinery baseplate grouting? A: The underlying chemistry and procedures are the same. The distinctions are in load magnitude and foundation design: reciprocating pump foundations must be sized for 3–5× the machine static weight in dynamic forces, compared to 1–1.5× for centrifugal pumps; the grout contact area target under load-bearing frame members is typically 80%+ rather than the 50% minimum; and chock plate installations are more commonly specified for pumps requiring frequent re-alignment access. See our full Epoxy Grout for Machinery Foundations guide for general machinery baseplate procedures.

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*XINCHOR manufactures three-component epoxy grout, non-shrink cementitious grout, and injection grout for rotating equipment foundations, supplied to EPC contractors and maintenance teams in more than 40 countries. Send us your pump baseplate dimensions, service temperature, and site climate and we will return a material recommendation, quantity take-off, and FOB quotation within one working day. Contact XINCHOR — WhatsApp: +86 133 3618 3725 | Email: info@xinchor.com*