The pump is fine. The ground under it is not.
A pump that will not hold alignment usually has nothing wrong with its bearings: the baseplate is moving on its foundation. Every alignment done on a moving baseplate is temporary. Every bearing replaced because of the resulting vibration is money spent on the wrong component.
The foundation system has three layers: the concrete block, the grout between the block and the baseplate, and the baseplate itself with its anchor bolts. Failure can start in any of them, and the symptoms overlap — which is why the diagnosis has to be done on the foundation, not deduced from the pump.
Recognizing a foundation failure
| What you observe | What it usually means |
|---|---|
| Alignment drifts within weeks of being set | Baseplate no longer rigidly bonded to the grout, or grout debonded from concrete |
| Cracked or crumbling grout at the baseplate edge | Grout shrinkage, oil or chemical attack, or freeze-thaw where water reached it |
| Oil-soaked, dark grout | Cementitious grout that has absorbed lubricant; it has lost strength and will keep degrading |
| "Soft foot" that reappears after shimming | The baseplate is distorted or the grout no longer supports it uniformly |
| Vibration that changes with load or temperature | Loss of stiffness in the mounting — the foundation is acting as a spring |
| Anchor bolts that will not hold torque | Bolt pocket grout failed, or concrete cracked around the bolt |
A straightforward test: with the pump running, place a dial indicator between the baseplate and the concrete at several points. Relative movement means the grout bond is gone. If the baseplate moves relative to the concrete, no amount of alignment will last.
What grout is for — and why cementitious grout fails under pumps
Grout has one job: transfer load from the baseplate to the concrete over the full contact area, with no voids, and keep doing so under vibration, thermal cycling and whatever leaks onto it.
Cementitious grout does this well for static equipment. Under rotating machinery it has three weaknesses. It shrinks slightly as it cures, which can leave it in contact with the baseplate at the edges only. It is porous, so oil and process fluids soak in and attack it. And it has low tensile and bond strength, so under cyclic loading the bond to the baseplate and to the concrete fatigues.
Epoxy grout answers each point: negligible shrinkage, near-zero porosity, and bond strengths that let it act as a structural link rather than a filler. That is why API 686, the Recommended Practice for machinery installation, treats epoxy grout as the normal choice under rotating equipment in process plants. It is not that cementitious grout is wrong — it is that the duty under a pump is one it was not designed for.
The repair decision
Not every foundation failure calls for the same repair. The choice depends on which layer failed and how far the damage went.
The grout failed, the concrete is sound. Chip out the old grout completely, clean and roughen the concrete to expose sound aggregate, prepare the underside of the baseplate to bare metal, and re-grout with epoxy. This is the most common repair and the one that restores the installation to better than original.
The concrete cracked locally — around anchor bolts, at an edge. Remove the damaged concrete back to sound material, re-pour with an epoxy or polymer-modified repair mortar bonded to the old, then grout. The anchor bolt pockets are often the real problem here; they can be rebuilt with epoxy grout after the bolts are checked.
The concrete block has lost integrity — through-cracks, spalling over large areas, chemical attack from long-term leaks. This is a civil repair: partial or full re-pour, with the machine removed. Epoxy grout will not fix a foundation that is itself moving.
The baseplate is distorted. Grouting a warped baseplate locks the distortion in. The baseplate has to be checked for flatness and either corrected or replaced before grouting; otherwise soft foot will return no matter how good the grout.
Doing the epoxy grout repair properly
The material is the easy part. The failures seen in the field come from preparation and pour, not from the product.
- Concrete preparation. Remove laitance and all old grout; chip to expose aggregate; the surface must be dry and free of oil. Oil-contaminated concrete is the first cause of epoxy grout debonding — where oil has soaked in, the contaminated layer has to be removed, not cleaned.
- Baseplate preparation. Underside blasted or ground to bare metal; a primed or painted underside will not bond. Vent holes in the baseplate so the grout can fill without trapping air.
- Forming. Forms sealed and, for epoxy, released with a compatible agent; head boxes to give the grout hydraulic pressure to flow under the plate.
- Temperature. Epoxy grouts have a working window for both the material and the substrate; in a Canadian plant in winter, the foundation may need to be tented and heated for a day before the pour. Pouring cold produces voids and slow, incomplete cure.
- Pour and cure. Continuous pour from one side to push air out ahead of the grout; no vibration; cure to the manufacturer's schedule before torquing anchor bolts and aligning.
- Verify. Tap-test or ultrasonic check for voids under the plate; check anchor bolt torque; final alignment only once the grout has reached its stated cure.
Frequently asked questions
Can epoxy grout be poured over old cementitious grout? No. The old grout is the layer that failed; leaving any of it in place carries the failure into the new installation. It has to be removed to the concrete.
How long is the pump out of service? Typically several days: removal of the old grout and preparation take longer than the pour itself, and the cure before alignment is set by the product and the temperature. A repair planned inside a shutdown window is the normal case.
Does the pump have to be lifted off? For a full re-grout, yes — the baseplate underside must be prepared. For localized repairs at anchor bolt pockets, it can sometimes stay in place, with the machine supported independently.
What about the anchor bolts? They are checked for corrosion, thread damage and pull-out; bolt pockets are cleaned and re-grouted. Anchor bolts are the most frequently ignored part of a foundation repair and one of the most common reasons it fails again.
Is epoxy grout resistant to the fluids that leak onto it? It resists most lubricants, hydrocarbons and mild chemicals far better than cementitious grout. Aggressive acids or solvents are checked against the manufacturer's resistance data before selection.
In practice
A foundation repair done once, properly, ends a cycle of alignments and bearing changes that can run for years. Induscoat carries out pump foundation and baseplate repairs — old grout removal, concrete preparation, epoxy grouting, anchor bolt rebuild — as part of its maintenance and rehabilitation service for plants in Quebec and Ontario, alongside pump repair without welding. To assess a foundation, a photo of the grout line and the alignment history are enough to start: request a quote. Technical data sheets for the Induscoat range are published on the brand site, induscoat.com.
Hicham M, P Eng, PMP
Engineer and project manager (PMP) at Induscoat. Over 16 years of experience in industrial coatings, composite repairs and wear protection on mining, energy and petrochemical sites in Canada and internationally.