We are Hebei Leeter Import and Export Co., Ltd, a wire, mesh, anchor and rebar support manufacturer working out of Dingzhou, Hebei since 2006. We ship supports to jobsites across North America and Europe, so we field these questions daily from estimators, precasters and rebar placers. This guide lays out how each support behaves, the practical height ranges, and a clear way to match the support to the mat.
What is the core difference between point and continuous support?
The whole decision starts here. Point support means a device sits under one bar or one crossing and transfers that load to the subgrade or formwork at a single footprint. Continuous support means a device runs along the bars, spreading load across a line rather than a dot. That single distinction drives spacing, stability, and how the mat behaves before the pour.
Point supports include rebar chairs, individual high chairs, and bolster-style singles. They are quick to place and easy to reposition, but each one only holds where it stands, so you need enough of them to stop the bar sagging between supports. Continuous supports, like slab bolsters and continuous high chairs, come in standard lengths, usually 5 feet, and lock a full run of bars to one consistent height in a single motion.
In our experience, crews reach for continuous runners when they want speed and a dead-flat mat on soft or uneven subgrade. They reach for point chairs when the layout is irregular, the pour is small, or they need to fine-tune cover in tight spots. Neither is "better." They answer different questions on the deck.
What does a bar chair do and when should you use it?
A bar chair is the workhorse of point support. It cradles a single bar, or the crossing of two bars, and holds it at a fixed cover from the form face. Heights typically start around 3/4 inch and step up through 1, 1-1/2, 2 and 3 inches for slab-on-grade and thin decks. You place them on a grid so each bar is held often enough to resist foot traffic and the weight of wet concrete.
We make bar chairs in plastic, wire, and epoxy-coated wire. Plastic chairs suit slab-on-grade and general commercial work; they are cheap, corrosion-free, and forgiving on membranes. Wire chairs carry more load per unit and hold up under heavy walking loads. For architectural or corrosion-sensitive faces, buyers ask for plastic-tipped or epoxy-coated legs so nothing rusts and telegraphs to the surface.
Use bar chairs when the mat sits low and you need clean, adjustable cover at points. They shine on driveways, footings, small slabs, and any layout where a continuous runner would be overkill. The trade-off is labor: more pieces to set and tie. On a large flat pour, that piece count adds up fast, which is exactly where bolsters earn their keep.
What is a slab bolster and why choose it for the bottom mat?
A slab bolster is a continuous wire runner built to carry the bottom mat of a slab. It has a repeating triangular truss with feet that spread load along the whole length, so the mat stays flat even on gravel or vapor barrier where a single chair leg might punch through. Standard height range runs from 3/4 inch up to about 3-1/2 inches, matched to your bottom cover.
Bolsters place fast. You lay a runner perpendicular to the bottom bars, drop the bars into the truss, and one length holds a dozen or more bars at once. That is why precast plants and large flatwork crews prefer them: fewer placement moves, a more uniform bottom cover, and better stability before the pour. For extra bearing on soft subgrade, we add a bottom plate, and that version is a slab bolster upper when it sits on top of a lower mat.
Compared with point chairs, a bolster resists tipping because its footprint is a line, not a dot. That matters when workers walk the mat. Where a lone chair can rock or sink, a runner bridges the soft spots. If you are weighing bar chair vs slab bolster for a wide, flat bottom mat on grade, the bolster usually wins on speed and consistency.
What is a high chair and a continuous high chair?
High chairs solve the top mat. When a slab has two mats, the upper layer must sit at a defined height above the deck, and standard chairs cannot reach. High chairs bridge that gap with tall legs, typically from 2 inches up to 15 inches, so the top steel lands at the right depth for negative moment or crack control. Above roughly 15 inches, most crews switch to fabricated bar supports or upstands.
There are two forms. Individual high chairs are point supports with tall legs, good for spot placement and irregular layouts. Continuous high chairs are runners, again usually 5 feet long, that hold a full line of top bars at one height in a single set. On elevated decks and mat foundations, the continuous version keeps the top mat dead flat and speeds the crew, much like a bolster does for the bottom.
We offer both in plain wire, epoxy-coated wire, and with plastic-tipped legs where the leg meets the form to protect the finished soffit. For rod chairs and heavier top-mat runs, the continuous high chair with a runner wire under the legs adds rigidity so tall supports do not splay under load. Tall legs want extra care: the higher the chair, the more it can rack sideways if you skimp on spacing.
How do you select the right support by mat position?
Start with the mat. Bottom mat on grade favors slab bolsters for speed and flat cover; bottom mat in a small or irregular pour favors bar chairs. Top mat almost always calls for high chairs, continuous where the deck is wide and flat, individual where the layout twists. Once mat position sets the family, pick height from your required cover, then pick material from exposure and finish.
Here is the quick comparison we walk buyers through.
| Support | Support type | Typical height range | Best for |
|---|---|---|---|
| Bar chair | Point | 3/4" - 3" | Bottom mat, small or irregular slabs, spot cover |
| Slab bolster | Continuous | 3/4" - 3-1/2" | Bottom mat on wide, flat pours and precast |
| Individual high chair | Point | 2" - 15" | Top mat in irregular or spot layouts |
| Continuous high chair | Continuous | 2" - 15" | Top mat on wide, flat decks and mats |
Two more factors decide close calls. First, subgrade: soft ground and vapor barriers push you toward continuous runners or plated feet that spread load. Second, finish and exposure: exposed soffits, marine work, and de-icing salt environments push you toward epoxy-coated or plastic-tipped legs so nothing corrodes at the form face. Match those, tie into spec, and you have picked well.
Contractors sometimes ask which single product covers the most jobs. There is no universal answer, and any supplier who says otherwise is guessing. A parking deck, a precast panel, and a footing want different supports. That is why we stock the full family rather than pushing one line, and why we ask about mat position before we quote.
How does spacing change between these supports?
Spacing follows the support type and the bar it carries. Point chairs need a tighter grid because each one only holds at its footprint; heavier bars and longer spans want closer spacing so the steel does not sag between supports. Continuous runners can sit farther apart along their length because the truss itself bridges short gaps, though the runners still repeat on a set module across the mat.
As a rough field guide, many crews run bottom bolsters and top continuous chairs on a module near 4 to 5 feet across the bars, then verify against the project drawings and the placing spec. Point chairs on the bottom often fall on a tighter grid so no bar spans too far unsupported. Always defer to the engineer of record and the referenced support classes, since load, bar size, and traffic all shift the numbers. When in doubt, add supports rather than chase the minimum.
Frequently asked questions
Is a slab bolster stronger than a bar chair?
A slab bolster does not have a higher per-point rating so much as a better footprint. Its continuous truss spreads load along a line, so it resists tipping and sinking better than a single chair on soft ground. For the same bottom mat, that usually means a flatter, more stable result with fewer placement moves.
What is the maximum height for a high chair?
Individual and continuous high chairs commonly run up to about 15 inches. Above that, most crews and specs move to fabricated bar supports, upstands, or engineered assemblies, because very tall wire legs can rack sideways under load. If your top mat sits higher than 15 inches, ask us and we will detail a suitable fabricated support.
Can I use bar chairs for the top mat?
You can, but only where the required height falls within a standard chair range and the layout is small or irregular. For most two-mat slabs the top steel sits too high for ordinary chairs, so individual or continuous high chairs are the correct choice. Matching leg height to your top cover is what keeps the mat at the right depth.
Do I need epoxy-coated or plastic-tipped supports?
It depends on exposure and finish. For interior slabs on grade, plain wire or plastic supports are fine. For exposed soffits, marine structures, bridge decks, and any de-icing salt environment, epoxy-coated wire or plastic-tipped legs prevent corrosion at the form face. We supply all three so you can match the support to the durability spec.
How do I decide between point and continuous support?
Judge by mat width, subgrade, and speed. Wide, flat mats on soft or barrier-covered subgrade favor continuous bolsters and high chairs for stability and fast placement. Small, irregular, or heavily obstructed layouts favor point chairs you can set and adjust one by one. Mat position and pour size settle most cases quickly.
Talk to us before you order
Picking the right rebar support is easier when someone has shipped these to your kind of job before. Tell us the mat position, cover, bar sizes, subgrade, and exposure, and we will recommend the support, height, and coating that fit your spec and budget. Request a quote and we will size the full package for you.
