8.2 Setting Baseplates and Soleplates: Leveling, Anchoring, and Grouting

Why grout exists

A rotating machine bolted to a baseplate that is bolted to concrete has to become one structure. The grout is what makes that happen. It does three jobs:

1. Transfers the machine's static and dynamic load into the foundation over the full area of the baseplate, rather than through a handful of shims.
2. Damps vibration by adding mass and stiffness under the machine.
3. Holds the alignment achieved at installation, by preventing the baseplate from flexing or shifting.

A poorly grouted baseplate is the root cause behind an enormous number of "chronic misalignment" machines. No amount of alignment work fixes a base that moves.

Preparing the foundation

• Chip the concrete to remove the weak, laitance-rich top layer until sound aggregate is exposed. Typically 1 to 2 inches is removed. Chipping is done with hand chisels or light chipping hammers; heavy demolition hammers fracture the concrete below.
• Clean thoroughly. Remove all dust, oil, and loose material. Oil-soaked concrete must be cut out — grout will not bond to it.
• Check the anchor bolts: correct pattern, correct projection, threads protected and undamaged, and sleeves packed with a compressible material so grout cannot enter and lock the bolt.
• Verify top-of-concrete elevation against the foundation drawing, allowing for the planned grout thickness.

Setting and leveling

Baseplates are set on leveling jackscrews, shims and wedges, or a combination. The procedure:

1. Lower the baseplate over the anchor bolts, keeping it free to move.
2. Bring it to the correct elevation and position against the layout lines established in Chapter 4.
3. Level the machined mounting surfaces — not the top of the baseplate skirt — with a precision level. The target is on the order of 0.002 inch per foot, and the mounting pads for the driver and the driven machine must be coplanar within a similar tolerance.
4. Check level in both directions, and check the diagonals for twist. A baseplate can be level along each axis and still be wound like a propeller.
5. Snug the anchor bolts only lightly. Tightening them before grouting pulls the baseplate down onto the jackscrews and distorts it.

Do not attempt to correct a warped or damaged baseplate with the anchor bolts. If the pads are not coplanar, they are machined coplanar, in place if necessary.

Grouting

Epoxy grout is the standard for rotating equipment in process plants, especially where oil exposure or vibration is a concern.

Placement practice:

• Build forms tight and sealed, with a head box on one side so grout can be poured from one point at a sufficient head to push air ahead of it.
• Pour from one side only, letting the grout flow across and out the other side. Pouring from both ends traps air in the middle, and an air void under a machine pad defeats the entire purpose.
• Vent holes in the baseplate let trapped air escape; grout holes let it be placed. Both are required on any baseplate large enough to trap air.
• Do not vibrate epoxy grout the way concrete is vibrated; it entrains air. Chain-drag or strap it into place per the manufacturer.
• Observe the temperature window. Epoxy grout has a minimum and maximum placement temperature and a pot life that shortens sharply as temperature rises.
• Chamfer the exposed edges of the cured grout at about 45 degrees to prevent edge chipping and stress cracking.

After the grout cures

1. Back off or remove the jackscrews. If they are left bearing, the machine load sits on four small points instead of the grout, and the baseplate will flex. Screws that are left in place must be backed clear and the holes sealed.
2. Torque the anchor bolts to the specified value in a crisscross pattern.
3. Re-check level on the mounting pads. Any change indicates the grout was not supporting the baseplate uniformly.
4. Sound the grout with a hammer across the whole area. A hollow ring means a void, which must be pressure injected with epoxy.
5. Record elevations, level readings, grout type and batch, cure conditions, and final anchor bolt torque.

Soleplates

A soleplate is a flat machined plate grouted into the foundation, with the machine feet bolted directly to it rather than to a fabricated baseplate. Soleplates are used under large machines, under individually mounted bearing pedestals, and where field machining of a single flat surface is easier than fabricating a full base. The setting, leveling, and grouting principles are identical; the tolerance on flatness and coplanarity is usually tighter, because the soleplate is the mounting surface.