Base plates are levelled in one of three ways: on levelling nuts threaded onto the anchor rods, on steel shim packs, or on a separate setting plate or grout pad placed to elevation first. In each case the column is set to the right height and plumbed, then the gap under the plate is filled with non-shrink grout so the permanent load bears through the grout. Levelling nuts are the quickest to adjust; shims and setting plates handle heavier columns better.
This guide compares the methods in more detail than our overview of grouting base plates, and covers base plate height, grout holes and posts set on an existing slab. The levelling method and grout space for a real building are set by the engineer and erector, so treat this as an explanation of what you'll see on drawings and on site.
Why base plates need levelling at all
Concrete is never poured perfectly flat or at exactly the right elevation, and a steel plate isn't perfectly flat either. If a column sat directly on the footing, its top would end up wherever the concrete happened to be, and the plate would bear on a few high spots.
So the design leaves a space. Three elevations are set on the drawings:
- Top of concrete on the footing or pedestal.
- Underside of base plate, higher than the concrete by the grout space.
- Top of steel, where the beams land.
Levelling sets the plate at elevation 2 so that the column reaches elevation 3. The grout then fills the space between 1 and 2. Our post on setting steel columns on footings and pedestals explains how those elevations are coordinated with the concrete contractor.
Method 1: levelling nuts
A nut and washer go on each anchor rod below the plate. The nuts are turned to bring the plate to elevation and level, the column is landed on them, and nuts and washers on top clamp it down.
Where it works well:
- Light and medium columns, such as typical building columns and posts with four anchor rods
- Jobs where the erector wants fine adjustment with a wrench rather than adding and removing shims
- Columns that need to be plumbed after landing, since adjusting one nut tilts the plate
What to watch:
- Until the grout is placed, the rods carry the column and any erection loads in compression and bending. They are only as strong as their diameter and the length exposed above the concrete. Heavy columns, or columns left ungrouted for weeks while the frame goes up, may need a different method or the engineer's confirmation.
- The rod projection has to allow for a levelling nut, the plate, a washer and a full top nut with thread to spare. Rods set too low can't take a levelling nut at all.
- The specification says whether levelling nuts stay in and get grouted over, or are backed off after the grout cures. Either way, the permanent load is meant to go through the grout.
Method 2: steel shims
Packs of steel shims of various thicknesses are placed on the concrete at set points under the plate, usually near the corners or close to the anchor rods. The column is landed on the shims and the anchor rod nuts are tightened down.
Where it works well:
- Heavier columns, because the shims carry the load directly into the concrete instead of through the rods
- Plates with rods close together, where there is little room to work under the plate
What to watch:
- Fine adjustment means adding or swapping shims, which is slower than turning a nut.
- Shim packs should be steel, flat and stable. Wood or loose scraps compress or shift.
- Shims normally stay in and are grouted over, so place them where they won't block grout flow from one side to the other.
- Shims should bear on sound concrete, not on a ridge or a broken edge.
Method 3: setting plates and grout pads
For heavier columns, a separate thin steel plate (a setting or levelling plate) can be set to elevation and grouted in before the column arrives. The column's base plate then lands on a flat, level steel surface at the right height, which makes setting quick and accurate.
A variation is a small grout pad cast to elevation under the centre of the plate, with the column set on it and the rest of the space grouted afterwards.
Where it works well:
- Heavy columns that are difficult to adjust once hanging from a crane
- Jobs where the concrete crew or a survey crew can set elevations ahead of the steel
What to watch:
- The setting plate has to be accurate. It becomes the reference, so an error there carries straight into the column.
- It adds a piece to fabricate and an extra trip for whoever sets it.
Levelling methods compared
| Levelling nuts | Steel shims | Setting plate or grout pad | |
|---|---|---|---|
| Adjustment | Fine, with a wrench | Step by step, by shim thickness | Set before the column arrives |
| Erection load path | Through the anchor rods | Through shims to concrete | Through the plate or pad to concrete |
| Typical use | Light and medium columns | Medium and heavy columns | Heavy columns |
| Left in place | Per specification | Usually, grouted over | Yes |
| Main risk | Overloading rods before grout | Shims shifting or blocking grout | Error in the setting plate itself |
Which method to use is shown on the structural drawings, the shop drawings or the erector's procedure. When the drawings are silent, the erector proposes one and the engineer accepts it.
Base plate height, grout holes and plate details
A few details on the plate itself make levelling and grouting work:
- Grout space. The gap from top of concrete to underside of plate is a design number. It has to be big enough to fit the levelling nuts or shims and to fill completely, and within the minimum and maximum thickness on the grout manufacturer's data sheet.
- Oversized rod holes. Base plate holes are made larger than the rods so the column can be positioned even if the rods are slightly off. Large washers or plate washers cover the oversized hole. Our guide to base plate anchor bolts covers hole and rod sizes.
- Grout holes and vent holes. Large plates often have a grout hole near the centre so grout can be placed under the middle, and small vent holes so air can escape. These belong on the shop drawings and are drilled in the shop, not cut with a torch on site.
- Templates. Anchor rods are set with a template that matches the base plate. If the rods are wrong, no levelling method fixes it. See base plate layout and anchor templates.
Base plates on an existing concrete slab
Renovation posts are a different case. A basement post often has a base plate on the existing floor, but a basement slab is not a footing: the Ontario Building Code requires columns to be centred on a footing, so a new post normally gets a pad footing cut into the slab, as explained in our post on basement column rules.
On these smaller posts the same principles apply at a smaller scale:
- The post is cut to measured length from footing to beam, so very little adjustment should be needed.
- Steel shims or a thin bed of non-shrink grout under the plate give full bearing on concrete that isn't perfectly flat.
- The plate is fastened with anchors specified by the designer, with the edge distance and embedment the anchor maker requires.
- The top of the post is fastened to the beam, not wedged in place.
Checks before the grout goes in
Before grouting, the erector or contractor confirms:
- Top of steel and base plate elevation against the drawings
- The column is plumb and braced or connected into the frame
- All anchor rod nuts are snug, with washers in place
- Shims are tight and won't move during grouting
- The concrete under the plate is clean and prepared as the grout maker requires
Erection tolerances are set by CSA S16 and the project specification; the engineer of record and the erector agree on how they are checked. Once those checks pass, the grout can go in.
Base plates and columns made to fit
We fabricate columns with base plates, oversized rod holes, grout holes and cap plates drilled and welded in the shop to your drawings, with in-house shop drawings and CWB certified welding. We supply and install structural steel, including basement beams and posts, across the GTA and Ontario. Send your drawings through our quote form or see our services.
Frequently asked questions
What is the best way to level a base plate?
It depends on the column. Levelling nuts are quick to adjust and common for light and medium columns; steel shim packs or a pre-set setting plate suit heavier columns because they carry erection loads straight into the concrete. The method should be shown on the drawings or erection plan.
Do levelling nuts stay in after grouting?
Usually they are left in place and grouted over, but the project specification decides. Either way, once the grout has cured the column load should pass through the grout, not through the nuts and anchor rods.
Can you use wood or plastic shims under a steel base plate?
Use steel shims unless the engineer specifies otherwise. Wood compresses, shrinks and rots under grout, which can leave the plate with uneven support. Shims that will be grouted in should be placed so they don't block grout flow.
How high should a base plate sit above the concrete?
The underside of the plate sits above the top of concrete by the grout space shown on the structural drawings. That gap has to suit the levelling method and the grout manufacturer's minimum and maximum thickness.
Why do some base plates have a hole in the middle?
Large base plates are often given a grout hole, and sometimes small vent holes, so grout can be placed under the middle of the plate and trapped air can escape. They are drilled in the shop as shown on the shop drawings.
