When you install a commercial aluminum picket railing, the fundamental structural question is: how does the post transfer load into the building? Two dominant methods exist — post-mount (a.k.a. core-drill or grouted) and base-plate. They look similar from a distance, engineer differently, and cost differently.
Post-mount (core-drilled or embedded)
The vertical post is set into a cored or formed pocket in the concrete, then grouted or expansion-anchored. The post is structurally continuous with the slab.
- Pros: strongest load transfer; cleanest look at the base (no visible base plate); post can be fully hidden in the slab up to top-of-finish.
- Cons: requires coordination with concrete pour or precise core-drilling later; grouting adds a step; not ideal for retrofit onto existing waterproofing membrane.
- Best for: new construction, cast-in-place slabs where the embed can be pre-set, high-load conditions (assembly occupancies, guard-rail loading).
Base-plate (surface-mounted)
The post ends in a horizontal steel plate bolted to the top of the slab with expansion anchors or through-bolts. Cover trim or a decorative shroud usually hides the plate.
- Pros: fast to install; no coring or grouting; forgiving on tolerance; works well over existing waterproofing.
- Cons: visible base plate (unless covered); more sensitive to anchor pull-out; slightly more expensive per post.
- Best for: retrofit projects, projects with tight schedules, applications where the slab already has waterproofing membrane in place.
Post-mount is the structural default — but base-plate is what saves you when the concrete's already poured and the waterproofing's already down.
Structural design notes
- Post-mount: pocket size typically 100–150 mm deep, filled with non-shrink structural grout. Anchor bolts optional depending on load and slab thickness.
- Base-plate: minimum 4 anchors per post, typically 3/8″ or 1/2″ expansion anchors depending on load. Pull-test in-situ before signing off.
- Both: post spacing typically 4′–5′ o.c. for standard picket runs. Longer spans require larger post sections or intermediate stiffening.
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