Direct Answer
Base plate grouting fills the space between the underside of a steel column base plate and the concrete foundation with a non-shrink cementitious or epoxy grout. It is required because base plates are set on anchor nuts at the correct elevation before the column is plumbed — the grout cavity (typically 1–2") allows final leveling. After plumbing and tightening, grout is injected to transfer column loads uniformly to the concrete.
Full Explanation
Grouting sequence: (1) Anchor bolts are cast in concrete with projecting threads. (2) Leveling nuts are threaded onto anchor bolts and adjusted to the correct elevation. (3) Base plate is set on leveling nuts, with the plate cavity open. (4) Column is set, plumbed, and anchor bolts tightened. (5) Non-shrink grout is mixed to a fluid consistency and poured or pumped into the grout cavity. (6) Grout is cured (typically 24–48 hours before full load). Non-shrink grout (Masterflow 713, Sika Grout 212, or equivalent) is required — shrinkage-type grout creates voids that compromise load transfer.
What This Means for Your Shop
Base plate grouting is typically in the GC's scope, not the fabricator's. However, if you are self-performing erection, grouting becomes your responsibility. Ensure leveling nuts and grout access are designed into the base plate layout — blind plates (no access holes) cannot be grouted.
Common Mistakes
Not providing grout access holes in large base plates. A base plate larger than 18"×18" with no grout holes cannot be fully grouted from one side — trapped air creates voids under the center of the plate.
Recommended Process
For any base plate larger than 12"×12", design grout vent holes (typically 1" diameter) at the center and far corners. Include vent hole requirements on the anchor bolt plan and verify with the grout contractor that their system is compatible with your plate geometry.