Choosing rebar tools
The list above is what exists. This is how to decide which of it you actually need, what separates a tool worth keeping from one that ends up at the back of a drawer.
Cover is what protects the steel
Cover is the depth of concrete between the bar and the surface. It is what keeps water and chloride away from the steel, and it is specified for a reason. Too little and the bar corrodes, and corroding steel expands and spalls the concrete off the face.
That is the failure you see on old concrete structures with rust stains and lumps missing. It is almost always inadequate cover rather than bad concrete, and it happens decades later, which is why nobody notices the mistake at the time.
- Cover is specified
- Typically 25 to 50mm depending on exposure. Not a matter of judgement on site.
- Too little means spalling
- Corroding steel expands and pushes the concrete face off. Decades later.
- Use spacers, not guesses
- Plastic or concrete spacers holding the bar at the specified depth throughout.
- Do not lift mesh mid pour
- Pulling mesh up with a hook while pouring is how it ends up with no cover at all.
Lap length transfers the load
Where two bars meet they are not joined, they overlap, and the concrete between them transfers the force from one to the other. That overlap has to be long enough, typically dozens of bar diameters, and it is specified in the design.
A short lap is a hinge. The bars simply slide relative to each other under load and the section behaves as if it were unreinforced at that point. Tying the lap is about holding position during the pour, not about strength.
- Bars lap, they do not join
- The concrete between them transfers the force. That is why length matters.
- Dozens of diameters
- Specified in the design. A short lap is a hinge in the finished section.
- Ties hold position only
- The wire is not structural. It stops the cage moving during the pour.
- Stagger laps
- All laps in one plane creates a weak line. Offset them along the member.
Bending without weakening the bar
Rebar is bent cold around a former of the specified radius. Too tight a radius work hardens and cracks the steel at the bend, and heating it to bend more easily changes its properties and is not permitted in reinforcement.
Rebending a bar that has already been bent, particularly straightening and rebending it, damages it in the same way. If a bar is bent wrong the answer is a new bar rather than a correction.
- Cold, around a former
- The specified radius. Too tight and the outside of the bend cracks.
- Never heat it
- Heating changes the steel's properties and is not permitted in reinforcement.
- Do not rebend
- Straightening and rebending work hardens and weakens the bar. Use a new one.
- Hooks and bends are specified
- The bending schedule states shape and dimensions. It is not freehand.
Tying, and how much is enough
Ties hold the cage in position while concrete is placed and vibrated, which pushes hard in every direction. Every intersection does not need tying, and enough do that nothing can shift, typically alternate intersections in a mat.
Cut the wire ends short and turn them inward, because a wire end sticking out toward the face reduces cover to nothing at that point and gives corrosion a direct route in. It is a small detail with the same consequence as a cover failure.
- Enough that nothing moves
- Vibrating concrete pushes hard. Alternate intersections in a mat is usual.
- Turn wire ends inward
- A wire end toward the face is a corrosion path straight to the steel.
- A tying tool is much faster
- Hundreds of ties by hand costs a wrist. A twister or a battery tier pays for itself.
- Ties are not structural
- They position the steel. Load transfer comes from lap length and concrete.
Handling steel safely
Rebar ends are sharp and protruding vertical bars are an impalement hazard, which is why they get capped. A person falling onto an uncapped starter bar is one of the recognised serious construction injuries.
It is also heavy, awkward and springy. A long bar being carried by one person will hit something, cut wire under tension whips, and walking on a tied mat is how ankles get caught. Gloves throughout, because the ribbing shreds hands.
- Cap protruding bars
- An uncapped vertical starter bar is an impalement hazard. Plastic caps are pennies.
- Cut wire whips
- Tie wire under tension snaps toward your face. Eye protection while cutting it.
- Two people on long bars
- A 6 metre bar carried alone will hit something, usually someone else.
- Gloves always
- The ribbing shreds hands and the cut ends are genuinely sharp.
Frequently asked questions
- What tools do I need to work with rebar?
- A rebar cutter, a bender, tie wire and a tying tool, and spacers to hold the steel at the right cover. For anything more than a few bars, hydraulic or powered cutting and bending saves a great deal of effort and gives more consistent shapes.
- What is rebar cover and why does it matter?
- The depth of concrete between the bar and the surface, typically 25 to 50mm depending on exposure. It keeps water and chloride away from the steel. Too little and the bar corrodes, expands and spalls the concrete face off, which is what rust stained old concrete shows.
- How much should rebar overlap?
- The lap length is specified in the design and is typically dozens of bar diameters, because the bars are not joined: the concrete between them transfers the force. A short lap behaves as a hinge, and the section acts as if unreinforced there.
- Can you weld rebar?
- Only specific weldable grades and only where the design permits it. Welding ordinary reinforcement changes the steel's properties at the weld and creates a weak point. Bars are lapped rather than welded as standard practice for exactly that reason.
- Can you heat rebar to bend it?
- No. Heating changes the steel's mechanical properties and is not permitted in reinforcement. Rebar is bent cold around a former of the specified radius, and a bar bent wrong is replaced rather than straightened and rebent, since rebending work hardens it.
- How do you tie rebar?
- With annealed tie wire twisted at intersections, usually alternate ones in a mat, using a tie twister or a battery powered tying tool. Cut the ends short and turn them inward, because a wire end toward the face gives corrosion a direct path to the steel.
- What are rebar spacers for?
- Holding the steel at the specified cover from the formwork or the ground throughout the pour. Without them the bar rests wherever it lands, ends up with no cover in places, and corrodes there. They are a few pence and they decide whether the structure lasts.
- Why do protruding rebar ends need caps?
- Because an uncapped vertical starter bar is an impalement hazard, and a fall onto one is among the recognised serious construction injuries. Plastic mushroom caps cost pennies, and on any project with protruding steel they are a standard requirement.
