Post Plumb and Line Verification Standard
Purpose
A post that's a half inch off plumb at the top of an 8 foot run is invisible standing three feet away and reads as an obviously crooked fence line from the street once four or five posts in a row lean the same fraction of a degree. A post that's individually plumb but sitting an inch off the string line throws every rail cut and every panel gap that follows it down the run, and the error doesn't average out, it compounds post to post. Catching either problem before the post is locked in, whether that's concrete beginning its set, a helical pier passing design torque, or a driven post taking its final blows, is a correction measured in minutes. Catching it after is a correction measured in a jackhammer, a pier pull, or a fence that never quite looks right no matter how good the panels are.
Scope
Covers checking plumb on two faces and line-and-spacing offset for every set post, across all three setting methods this shop uses, concrete, helical pier, and driven post, performed before that post is locked in and before the crew moves to the next post. It does not cover how the post is set; Fence Post Setting Depth and Concrete and Helical Pier Post Installation Technique own their own installation procedures. It does not cover diagnosing a post that's already cured, torqued, or fully driven and is leaning weeks or months later, which the leaning-post troubleshooting guides and the reset-vs-sister decision matrices own.
Roles and responsibilities
| Role | Owns | Hands off |
|---|---|---|
| Technician | Strings the line, checks and corrects every post before it locks in, logs the result | A logged plumb-and-line pass for every post before the crew leaves that post |
| Crew lead | Confirms the string line's own accuracy before checking begins, resolves any post that's out of correction range | A relocate or engineering-review decision for a post that can't be corrected within this standard |
| Shop | Reviews logs for a pattern across jobs, same crew, same setting method, same soil type repeatedly failing | A training or method correction routed to the crew or the setting procedure, not treated as one post's bad luck |
Procedure
String a taut mason's line between the two end or corner posts at a consistent, measured height on both ends, for example a fixed offset down from post tops, confirmed level end to end with a story pole or a laser before any interior post is checked. Acceptance: line taut with no visible sag when plucked, tied at the same measured height within 1/8 inch at both ends. Wrong looks like a line tied at about the same spot by eye at each end, which reads every interior post below it as off-line by a fraction of whatever error the line itself carries, and the error compounds the further a post sits from the reference end. Stop rule: re-tie and re-measure before checking a single post if the line sags under a light pluck or the two ends aren't confirmed level to each other. Hazard: none at this step, it's a layout task.
Check plumb on two adjacent faces of every post with a torpedo or post level, not only the face the crew is standing in front of. Acceptance: level's bubble centered within its lines on both faces, held within 1/4 inch of true over the post's above-grade height. Wrong looks like a post that reads plumb on the face parallel to the fence line, which is the check most people default to, while leaning into or away from the yard on the perpendicular face nobody checked. Stop rule: any post outside tolerance on either face gets corrected now, before the crew moves to the next post; corrections don't get batched for later. Hazard: none new here, ground-level tool use.
Measure each post's offset from the string line at the string's height with a spacer stick or tape, not by eye. Acceptance: measured offset within 1/4 inch of the line at every post, taken with a tool, not glanced at. Wrong looks like a post that appears to touch the line at a glance from a few feet away but was never actually measured, which misses a post that's subtly bowed or twisted along its length and reads fine at the one point the eye happens to check. Stop rule: any post outside line tolerance gets corrected before the crew leaves that post. Hazard: none new.
For a post set in concrete, correct plumb and line by hand within the mix's initial set window, per the manufacturer's stated set time for the specific product used, commonly 20 to 40 minutes for a fast-set mix and several hours for a standard mix, then re-check against steps 2 and 3 and re-set the temporary bracing itself, not just the post. Acceptance: post re-checked and within tolerance on both plumb faces and line offset, bracing re-set and independently re-checked, not assumed to have held through the correction. Wrong looks like adjusting the post but not re-checking its own brace, so the post walks back out of tolerance as the brace's stake shifts under the load of the correction just made. Stop rule: if the mix has already begun its initial set, resists hand pressure, no longer moves under a firm push, do not force it; forcing a partially set post breaks the concrete's bond to the post and produces a post that looks corrected today and works loose within its first season. Pull the post and re-set it instead. Hazard: fresh concrete is caustic to skin on contact; gloves stay on for any hand correction inside wet mix, and rinse skin promptly if contact happens anyway.
For a helical pier post, do not attempt to rotate the shaft to correct plumb once the pier has passed roughly half its design torque, see Helical Pier Post Installation Technique's plumb-correction window; correct instead at the bracket's post-attachment adjustment range. Acceptance: post re-checked against step 2 using the bracket's own adjustment range, within tolerance on both faces. Wrong looks like backing the pier out a partial turn just to true it up, which is exactly the correction the installation standard prohibits, because it loosens the soil engagement the torque reading already certified and makes that reading untrustworthy going forward. Stop rule: if the bracket's adjustment range can't reach tolerance, stop and escalate to the crew lead for a relocate or engineering-review decision rather than forcing the bracket past its designed range. Hazard: if any re-drive is attempted despite the prohibition, the drive head's rotating shaft carries the same hazard as during original installation; confirm the head is fully disengaged and isolated before hands go anywhere near the pier.
For a driven post, correct plumb only within the first few strikes, before the post has taken more than a few inches of set; once seated past that point, correction means pulling the post and restarting at that location, not nudging it while driving continues. Acceptance: plumb confirmed and adjusted by hand within the post's first few inches of penetration; any post pulled for restart is re-driven from a fresh start, not partway resumed. Wrong looks like continuing to drive a post that's visibly leaning on the assumption it'll settle straight, which it doesn't; a driven post's lean compounds with each strike because the post follows the path of least resistance it's already started cutting. Stop rule: a post more than a slight, barely visible lean off plumb after taking more than a few inches of set gets pulled and restarted rather than driven the rest of the way and corrected after. Hazard: the driver's strike zone carries the same crush hazard covered in the daily inspection standard; confirm the guard is back in position before resuming any drive after a pull-and-restart, not left off because the crew is just doing one more.
Log the result for each post, location or post number, plumb pass or fail on each face, line pass or fail, and any correction made, entered before the crew moves on to rails or panels for that run. Acceptance: entry made the same day, tied to a specific post location on the job's post-set record. Wrong looks like a verbal "they're all good" at the end of the run with nothing written down, which leaves no record of which posts needed correction if a lean shows up later and someone's trying to reconstruct whether it was ever actually checked. Stop rule: a run with any uncorrected or unresolved post does not proceed to rail or panel installation until that post's log entry shows a pass or an escalation decision on file.
The record this produces
The post-set log ties a plumb-and-line result to a specific post location, setting method, and date. A crew lead or shop reviewing a season of logs watches for a pattern tied to a setting method or a soil condition, not a single post: a run of helical piers on one job repeatedly needing bracket-range correction points at a lead size undersized for that soil's actual bearing, not at the crew's technique. A log with corrections noted but no re-check result recorded is the gap worth asking about directly.
Worked pass, with a step that failed
An eight post concrete run, corner to corner, string line tied at 6 inches down from post tops and confirmed level end to end.
Posts 1 through 3 check clean: plumb within tolerance on both faces, line offset within 1/4 inch, no correction needed.
Post 4: plumb checks fine on the face-out check parallel to the line, but the perpendicular face reads outside tolerance, leaning slightly into the yard. Fail on the second-face check. Stop rule taken: corrected by hand while the fast-set mix is still within its initial window, roughly 15 minutes into a 20 to 40 minute set, bracing re-set and independently re-checked, post re-verified plumb on both faces before the crew moves on.
Posts 5 through 7 check clean on both plumb faces and line offset.
Post 8: plumb passes on both faces, but the measured line offset comes in outside tolerance, the post sitting slightly proud of the line compared to its neighbors. Corrected by hand within the same set window, re-measured and within tolerance.
Log entry: eight posts, two corrections noted, post 4's second-face plumb and post 8's line offset, both re-checked and passing before the crew proceeded to rail layout.
References
- See related: Fence Post Setting Depth and Concrete, for the setting procedure and cure-time figures this standard's concrete correction window is drawn from.
- See related: Helical Pier Post Installation Technique, for the torque-based correction window this standard's helical-pier step depends on.
- See related: the leaning-post troubleshooting guides and reset-vs-sister decision matrices, for diagnosing a post that's already locked in and leaning after the fact, which this standard does not cover.