Heavy machinery epoxy grouting: foundation repair and grout design for SAG mills, crushers, compressors and turbines

Why heavy machinery foundations are a grouting problem

Epoxy grout is the usual material for seating heavy machinery — SAG and ball mills, crushers, reciprocating compressors, turbines — on concrete, because it bonds to both steel and concrete, resists oil and cures without the shrinkage of cementitious grout. Whether the installation lasts depends less on the product than on grout design, concrete preparation and the pour.

Under a small centrifugal pump, grout carries a modest load and the vibration of a balanced rotor. Heavy machinery is a different duty. A grinding mill puts a large, permanent load on its sole plates. A reciprocating compressor transmits unbalanced forces at every stroke. A crusher adds shock. A turbine or a compressor frame runs hot, and the grout under it runs warm for years. The grout becomes a structural layer that must stay in full contact with steel and concrete under all of those conditions.

The diagnosis of a failed pump base is covered in our guide to pump foundation and baseplate repair with epoxy grout. This article deals with what comes next on larger machines: how the grout is designed, poured and checked.

Epoxy vs cementitious grout under dynamic loads

Cementitious grout is not wrong: it is cheaper, tolerates deep pours and does not creep like a polymer. Under dynamic, oily, warm machinery, its weaknesses — porosity, lower bond strength, slower strength gain — become the failure mode. For a short definition of the material, see epoxy grout in our glossary.

Two lines in that table are the ones most often skipped. Creep: a polymer grout under a permanent load deforms slowly over time, and more so when warm. For a mill sole plate or a compressor frame, the creep data at the real operating temperature of the grout is a selection criterion, not a footnote. Thermal expansion: epoxy grout moves more with temperature than the concrete it sits on, which is why long pours need expansion joints and careful edge details.

The references: API 686 and ACI 351.1R

Two documents frame most machinery grouting specifications in North America:

• API RP 686, Machinery Installation and Installation Design, the American Petroleum Institute's recommended practice for installing rotating and reciprocating machinery. It covers foundations, mounting plates, grouting, anchor bolts and alignment.
• ACI 351.1R, Report on Grouting between Foundations and Bases for Support of Equipment and Machinery, from ACI Committee 351. It covers both cementitious and epoxy grouts: material properties, design details, preparation, placement and testing.

Neither replaces the machine manufacturer's installation manual. In practice, the OEM manual and the project specification govern, API 686 and ACI 351.1R are the references they are usually written against, and the grout manufacturer's data sheet sets the material limits — temperatures, pour depth, cure time.

Grout design: full bed, chocks, shims and jackscrews

Full-bed grouting. The baseplate, skid or sole plate is supported over its whole underside. It is the normal approach for mills, crushers, motor and gearbox bases, and pump skids.

Discrete chocks. Poured epoxy chocks under the feet of a compressor or engine frame. A different design, with its own load calculation, following the OEM's requirements.

Leveling: jackscrews versus shims left in place. Elevation and level are set before the pour, usually with leveling jackscrews on the baseplate. Common practice, reflected in API 686, is to back the jackscrews off once the grout has cured so the load passes through the grout and not through the screws. Shim packs or wedges left under the plate do the opposite: they become hard points that carry the load, and the grout around them becomes filler. If shims are used to level, the specification should say whether they come out and how the cavity is filled.

The grout does not level anything. Foundation leveling with epoxy grout means the alignment set on the jackscrews is locked in by the grout — including any error. Level and elevation are checked against the OEM tolerance before the forms are closed.

Expansion joints and edges. Long continuous pours — mill sole plates, compressor skids, turbine-generator bases — get expansion joints at the spacing given by the grout manufacturer, sealed with a flexible sealant. Square re-entrant corners are where cracks start: forms use chamfer strips, and the grout shoulder is finished so oil and water drain away from the plate instead of pooling on the grout.

Anchor bolts: sleeves and free length

An anchor bolt holds the machine down by stretching elastically when tensioned. To keep its clamp load under vibration, it needs a free length that can stretch — which is what the sleeve cast around the bolt in the concrete provides.

• Sleeves are not filled with grout. Grout in the sleeve bonds the bolt and shortens its effective length. The sleeve is filled with a non-bonding material as specified, and sealed at the top before the pour.
• The bolt is debonded through the grout layer. It is wrapped or coated so the epoxy cannot grip it.
• Tensioning comes after cure. Bolts are tensioned to the OEM value once the grout has reached the cure stated on the data sheet, then checked again before final alignment.

Preparing the concrete

1. Remove oil-contaminated concrete. Mill, crusher and compressor foundations are often soaked with lubricant. Contaminated concrete is chipped out until the fracture face is clean and sound.
2. Create the profile. Remove laitance and chip to expose coarse aggregate, using light chipping tools rather than heavy breakers, which can crack the layer they are meant to expose.
3. Check soundness. Cracks running through the foundation, delamination or large spalls are a structural repair to address first.
4. Control moisture. The surface must meet the grout manufacturer's moisture requirement; no standing water in pockets or sleeves. New concrete is cured per the project specification before grouting.
5. Prepare the steel. The underside of the baseplate or sole plate is blasted or ground to bare metal and kept clean until the pour.

Forms, head boxes and the pour

Forms are rigid, liquid-tight, lined or waxed so they release, and sealed to the concrete.

• Head box. A head box on the pouring side gives the grout hydraulic pressure to flow under the plate. The grout is placed from one side (or one end) only, so it pushes air out ahead of it; vent holes in the plate let trapped air escape.
• Continuous pour. Once a section is started, it is completed without stopping. A cold joint under a machine is a plane of weakness. Enough full kits, mixers and crew are staged before mixing begins; kits are mixed whole, since splitting them risks ratio errors.
• Pot life. Each batch is placed within its pot life, which shortens as the material warms up.
• No vibrators. Epoxy grout is not vibrated; where it needs help to flow, the manufacturer's placement method applies.
• Temperature. Material, concrete and ambient temperatures must be inside the data sheet's range before the pour and through the cure. Cold grout loses flow and leaves voids; hot grout loses pot life. Measure the concrete, not just the air. For a winter shutdown, the foundation is tented and heated ahead of time — see applying epoxy in cold weather during a winter shutdown.
• Cure. No load, no bolt tensioning and no alignment until the stated cure is reached at the actual temperature.

Checking the job: contact, voids, alignment

• Contact by hammer sounding. After cure, the plate is sounded with a hammer over its whole surface; hollow-sounding areas are marked on a map. The acceptable void extent comes from the project specification or the OEM. Voids are repaired by drilling injection and vent holes and filling with a low-viscosity epoxy suited to injection.
• Bolts and alignment. Jackscrews backed off, anchor bolts tensioned, then soft foot and alignment re-checked — with piping connected on compressors and pumps, to catch pipe strain.
• Records. Temperatures, batch numbers, the sounding map and final alignment readings go into the equipment file.

SAG mill, crusher and compressor shutdowns in Quebec and Ontario mines

At a concentrator, grout work competes for the window with the mill reline, crusher liner change and chute work.

• Removal sets the schedule. Breaking out old grout and oil-soaked concrete takes longer than the pour, and its extent is only known once the work starts. Sounding and inspecting the existing grout before the shutdown reduces surprises.
• Cure sets the restart. The machine cannot be loaded before the grout reaches its stated cure, so temperature control is part of the schedule, not an option. At northern sites in winter, that means tenting, heating and storing the grout components at the temperature the data sheet requires.
• Coordinate the window. Grout repairs fit alongside crusher wear part replacement and chute and hopper wear repair, with the same access and isolation.

FAQ

What is the best epoxy grout for machinery foundations? There is no single best product. Select on: compressive creep at the grout's real operating temperature, flow through the actual gap, minimum and maximum pour depth, chemical resistance to the fluids present, the application temperature range, and the test methods behind the data sheet values.

Can a SAG mill foundation be repaired without removing the mill? Localized repairs — edges, bolt pockets, voids filled by injection — can sometimes be done with the mill in place. Full regrouting of a sole plate requires the load to be taken off the grout, and the method is set with the OEM.

Can new epoxy grout be poured over old grout? No. The old grout is the layer that failed. It is removed down to sound, clean concrete.

Does this apply to reciprocating pump baseplates and pump skids? Yes. Reciprocating pumps load their baseplates with pulsating forces, and pump skid installation with epoxy grout follows the same principles: full contact, sleeved anchor bolts, jackscrews backed off and a verified pour. Pump-specific damage is covered in our guide to centrifugal pump epoxy repair.

In practice

Induscoat carries out machinery foundation repairs — grout and contaminated concrete removal, preparation, epoxy grouting, anchor bolt work and contact verification — as part of its maintenance and rehabilitation service for plants and mines in Quebec and Ontario, alongside pump repair. Photos of the grout line, the machine type and the shutdown window are enough to start: request a quote. Technical data sheets for the Induscoat range are published on the brand site, induscoat.com.