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The distance from the head over which the concrete is actually consolidated.
Take it from the vibrator manufacturer's data for the head diameter and frequency you have, and treat the published figure as an upper bound. A stiff mix, a low slump or congested reinforcement all shorten it, and the working radius in a heavily reinforced wall can be well under the catalogue value for the same head.
How much the circles of action are made to overlap rather than merely touch.
Zero overlap places the insertions so the circles just meet, which leaves the concrete at the meeting point consolidated by the weakest part of both. An overlap is what removes that seam. It also buys tolerance for a crew working fast in the dark with a hose in the way, which is the real condition this number is set for.
The thickness of concrete placed in one pass before the next layer goes on.
Layers want to be shallow enough for the vibrator to reach through into the layer below, and each has to be placed before the one beneath it takes initial set. Deeper layers are tempting when the pour is behind schedule and they are exactly how a cold joint gets built into the middle of a wall.
How far the head is driven into the previous layer to knit the two together.
The head goes down through the fresh layer and on into the one beneath so the two become one element rather than two stacked ones. This is what turns a sequence of layers into a monolithic pour, and it is why the vibrating length of the head, not just the pour depth, decides how deep a layer may be.
Insertion spacing
14.6 in
The geometry is exact for the radius entered, and the radius is the uncertain part. Published figures assume a workable mix and open reinforcement; in congested sections the working radius falls, which tightens the spacing this calculation returns.
- Insertions needed per unit of lift area
- 0.67 points/ft²
- Overlap achieved between adjacent circles of action
- 4.87 in
- Minimum vibrating length to reach the layer below
- 22 in
- Ground consolidated by one insertion
- 1.49 ft²
They open the calculator with your figures already in it
Concrete Poker Vibrator Insertion Spacing Calculator: 14.63 in — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- ACI 309R, Guide for Consolidation of Concrete — consolidation technique is vertical insertion under the head's own weight, a short hold, slow withdrawal, and insertion points spaced so that their radii of action overlap
- Spacing = 2 × radius of action × (1 − overlap fraction); insertion points per unit area = 1 ÷ spacing², for a square insertion grid
- The radius of action is a property of the head and the mix rather than a constant — it is published by the vibrator manufacturer for the head diameter and frequency, and it shortens in a stiff or heavily reinforced mix
Inputs used
- Radius of Action of the Head
- 9.75 in
- Required Overlap of Adjacent Radii (%)
- 25
- Depth of Each Placement Layer
- 16 in
- Penetration into the Layer Below
- 6 in
Intermediate steps
- Insertions needed per unit of lift area
- 0.67 points/ft²
- Overlap achieved between adjacent circles of action
- 4.87 in
- Minimum vibrating length to reach the layer below
- 22 in
- Ground consolidated by one insertion
- 1.49 ft²
Confidence note: The geometry is exact for the radius entered, and the radius is the uncertain part. Published figures assume a workable mix and open reinforcement; in congested sections the working radius falls, which tightens the spacing this calculation returns.
What this calculation does not cover
- Assumes a square insertion grid. A wall is a line of insertions rather than a grid, so use the spacing and ignore the per-area figure there.
- Says nothing about duration. Insertion spacing decides where the poker goes; how long it stays is judged from the surface levelling, bubbles ceasing and a mortar sheen appearing, and over-vibration is as damaging as under-vibration.
- Excludes form-face treatment entirely. Vibrating against formwork or reinforcement puts energy where it is not wanted and can shift bars already tied to tolerance.
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This result is a specification — 14.6 in — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-08-30 · in the site-wide review of 2026-09-06 · v1.0.0
Regulatory standards & verification citations3
- ACI 309R, Guide for Consolidation of Concrete — consolidation technique is vertical insertion under the head's own weight, a short hold, slow withdrawal, and insertion points spaced so that their radii of action overlap
- Spacing = 2 × radius of action × (1 − overlap fraction); insertion points per unit area = 1 ÷ spacing², for a square insertion grid
- The radius of action is a property of the head and the mix rather than a constant — it is published by the vibrator manufacturer for the head diameter and frequency, and it shortens in a stiff or heavily reinforced mix
Which documents these citations point at
Standards referenced: ACI 309R (American Concrete Institute, United States).
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