Engineering, Product Development
Stripping Post-Tension Strand Sheathing: Field Methods, Safety, and a Better Tool
By Mike Moussa, PE — Stripping the plastic sheathing off post-tensioning strand is one of those small jobs that eats time and skin on every PT project. Here’s how it’s done in the field, why it’s harder than it looks, and what we’re building to fix it.
Where This Comes Up
Unbonded post-tensioning tendons are seven-wire steel strand coated in grease and wrapped in an extruded plastic (HDPE) sheath. That sheath does its job beautifully while the strand lives in the slab — it isolates the steel from the concrete so the tendon can move and carry load. But there are moments where you have to get the plastic off:
- At anchorages — the strand has to be bare where it seats in the wedge and anchor casting. Grease and plastic at the wedge line is a recipe for slip.
- Repairs and re-stressing — exposing a length of strand to inspect corrosion, splice, or re-anchor.
- Demolition and strand removal — separating reusable hardware, or prepping for re-tensioning during a renovation.
- Testing and forensic work — pulling clean samples for a lab.
Why It’s Harder Than It Looks
The sheath is tough, it’s bonded to a film of grease, and the surface underneath is a helical bundle of wires — not a smooth cylinder. A few specific problems show up every time:
- The grease fights you. Everything is slick. Knives slide, grips slip, and you end up wearing the corrosion-inhibiting grease.
- The wire wants to bite the blade. Cut too deep with a utility knife and you score the strand — which, on a tendon that’s going to see hundreds of MPa, is exactly what you don’t want. A nick is a stress riser.
- Hands and time. The common field method is a utility knife and patience: a careful longitudinal score, then peel. Multiply that across dozens or hundreds of tendons and it’s hours of slow, repetitive, cut-prone work.
- Inconsistency. Strip length and quality vary worker to worker, which matters at the anchorage.
Field Methods, Ranked
| Method | Pros | Cons |
|---|---|---|
| Utility knife, freehand | No special tools, cheap | Slow, inconsistent, high risk of nicking the wire and cutting yourself |
| Hook-blade / linoleum knife | Hook contains the cut, a bit safer | Still freehand depth, still slow |
| Heat (torch/gun) | Softens HDPE | Open flame near grease, fumes, scorches the strand — generally a bad idea |
| Purpose-built stripper | Fixed cut depth, fast, repeatable, protects the wire | Needs the right tool for the strand size |
The Core Problem: Depth Control
Almost every issue above traces back to one thing — you can’t reliably control cut depth by hand. The fix isn’t a sharper knife; it’s a tool that registers on the strand and limits the blade to the sheath thickness, so it cuts plastic and stops at steel every single time. That’s a mechanical problem with a mechanical answer, and it’s exactly the kind of thing a P.E. shop should solve properly instead of telling crews to “be careful.”
What we’re building. PartSnap is developing a dedicated PT strand sheathing stripper — a handheld tool that sets cut depth to the sheath, grips through the grease, and strips a clean, consistent length without scoring the wire. It’s in active product development with a provisional patent in the works. If you run PT crews and want to weigh in on what the tool needs to do, we want to hear from you.
Safety Reminders Until Then
- Cut-resistant gloves, always. The grease guarantees the blade will slip eventually.
- Score, don’t stab. Shallow longitudinal passes beat one deep cut.
- Inspect the bare strand. Any visible nick or gouge near an anchorage is a flag — document it and check it against your tendon acceptance criteria.
- Skip the torch. Heat near corrosion-inhibiting grease is not worth it.
Post-tensioning is unforgiving work — the loads are enormous and the details matter. If you’ve got a strand-prep, repair, or custom-tooling problem on a PT job, that’s squarely in our wheelhouse.
Bonded vs Unbonded — Know Which You Have
This guide is about unbonded mono-strand systems — greased, plastic-sheathed strand, by far the most common in U.S. building slabs. Bonded systems run multiple strands inside a metal or plastic duct that’s grouted after stressing; there’s no individual plastic sheath to strip, so the problem looks different. Before you reach for a knife, confirm which system you’re working with. On an unbonded tendon you’ll find that slick HDPE jacket and a film of corrosion-inhibiting grease underneath — that’s the one this article addresses.
How Much Time This Really Eats
Do the math on a typical job. Say a crew has 150 tendons to prep at anchorages, and careful freehand stripping runs 3–5 minutes per strand once you factor in scoring, peeling, and cleaning grease off your hands and blade. That’s 7.5 to 12.5 labor-hours of slow, cut-prone work on a single pour — plus the rework whenever a strand gets nicked and has to be inspected or rejected. Cut that to under a minute per strand with a depth-controlled tool and the time savings compound fast across a project. That’s the business case, not just the safety one.
Quick Answers
Does a nick really matter? On a tendon stressed to a high fraction of its capacity, a transverse score is a stress concentrator and a corrosion initiation site. Acceptance criteria vary by spec, but “a little scratch” is not something to wave off near an anchorage.
What about the grease? Leave the corrosion-inhibiting grease intact except where the strand must be bare (the wedge seat). Stripping more sheath than you need exposes more strand to clean and re-protect.