Can You Use Zip Ties for Rebar?

Ties at rebar intersections have one job: keep the bars at the spacing, cover and elevation shown on the drawings until the concrete hardens around them. Once the concrete cures, the bond between concrete and steel does the structural work. The ties are not counted on for strength.

That is why the question comes up so often. If ties are not structural, why not use whatever holds? The answer is that the tie has to survive the hardest part of the job: crews walking on the mat, concrete dropping from a chute or pump hose, screeding and internal vibration. A tie that stretches or snaps during the pour lets bars move, and misplaced bars can reduce cover or change the effective depth of the reinforcement. That does affect the finished structure.

Industry practice reflects this. The Concrete Reinforcing Steel Institute's Manual of Standard Practice is commonly cited for black annealed tie wire of 16.5 gauge or heavier, with coated wire or other acceptable material for epoxy-coated and galvanized bars. Project specifications and local inspectors decide what is acceptable on a given job.

Tie wire has been the default for a long time for practical reasons. Plastic ties have a few genuine advantages, mostly on coated or nonmetallic bars.

Used within their limits, and with permission where permission is needed, nylon ties can be a sensible choice.

• Small, non-structural DIY pours such as garden pads, walkways and shed slabs where no specification or inspection applies.
• Fiberglass or other nonmetallic rebar, where the bar manufacturer lists plastic ties as an acceptable fastener.
• Epoxy-coated bars, where the project specification accepts nonmetallic ties.
• Temporary positioning while a mat is laid out, before it is wire tied.
• Attaching sleeves, conduit, PEX and similar items to a mat, where the trade and project rules allow.

For most structural work, stick with tie wire unless you have written approval to do otherwise.

• Footings, foundation walls, columns, beams, elevated slabs and anything designed by an engineer.
• Any work that will be inspected, unless the inspector or engineer has approved plastic ties in advance.
• Heavy mats, large bar sizes and decks that crews will walk on during the pour.
• Placement with a pump or heavy internal vibration.
• Cold-weather work, where nylon's reduced impact resistance adds risk.

Placement is where plastic ties are tested. Wet concrete is heavy, and it arrives with force. Nylon stretches before it breaks, so a mat tied with zip ties can move more under a worker's boot or a vibrator than one tied with wire. Using chairs and bolsters at the specified spacing matters even more with plastic ties, because the ties should never be carrying the weight of the mat.

Fire is a common concern on forums. Once concrete cures, the ties are encased and are not relied on for anything, so the tie material is not what gives a concrete member its fire resistance. Fire performance of a concrete element comes from its design, including concrete cover over the steel, which the engineer controls. The practical rule is the same for wire and plastic: keep ties and trimmed tails turned inward so they do not intrude into the concrete cover.

Long-term behavior of embedded nylon is another question people ask. Because ties carry no load after the concrete hardens, their condition afterward is generally not a design consideration, but if a project has specific durability requirements, that is a question for the engineer.

Where plastic ties are allowed, a careful installation makes the difference between a mat that holds and one that shifts.

1. 1Confirm that plastic ties are acceptable for the job: check drawings and specifications, and ask the engineer or inspector if the work is permitted.
2. 2Support the mat on chairs, bolsters or dobies at the required spacing and cover. Ties position bars; they should not hold the mat up.
3. 3Use heavy-duty ties, around 120 lb or higher. An 8 inch tie usually reaches around crossing #3 to #5 bars; larger bars or saddle-style wraps may need 12 inch ties. Test-fit a few first.
4. 4Wrap diagonally across each intersection so the tie resists movement in both directions, then pull it tight. A tensioning tool gives consistent, snug ties.
5. 5Keep straps away from sharp bar deformations where possible, and replace any tie that is nicked during installation.
6. 6Trim tails flush and turn heads and tails toward the inside of the mat, away from the concrete cover.
7. 7If the mat will sit in the sun for weeks before the pour, use black UV-stabilized ties.
8. 8Walk the mat before the pour, check for broken or loose ties, and replace them.