Rebar supports: getting the steel to the right height, and keeping it there

Reinforcing steel only works where it sits. Put a mat of bar at mid depth and it does what the engineer drew. Let the same mat get walked down onto the subgrade during the pour and you have a slab with a rust stain forming under it and no tensile capacity where it was supposed to be. Every support product on our shelf exists to solve that one problem, and the reason there are so many of them is that the right answer changes with the surface underneath.

Start with what you are standing on

On a prepared subgrade with no vapor barrier, plastic sand chairs spread the load and will not punch through. On a vapor barrier, that spreading matters more, because anything with a small footprint becomes a puncture waiting to happen and the barrier is the whole reason you are paying for a barrier. On a hard surface such as a mud slab or an existing deck, a slab bolster or a high chair with a wide base runs continuously and gives the crew something to walk between rather than on.

Dobie bricks are the oldest answer and still a good one for side cover and for spot support on grade. They are concrete, so they are the same material as the pour and they do not float. Where a job needs cover on a vertical face or a beam cage held off the form, a dobie with a tie wire loop is quicker than anything else and does not need a second thought about compatibility.

Continuous or point support

Slab bolsters and high chairs are continuous. They run under the bar in lines and hold a whole mat at a consistent height, which is what you want when the mat is heavy or the crew is going to be moving across it. Individual chairs are point support, which is faster to place on a light mat and easier to adjust. The failure mode is different too: a point support that sinks leaves a local low spot, while a continuous run that sinks takes a whole strip with it.

• Sand chairs, plastic: soft subgrade, wide footprint, no barrier puncture
• Slab bolster: continuous support on a hard surface, consistent height across a mat
• High chairs: taller lifts and upper mats, wide base versions for barriers
• Dobie bricks: side cover, vertical faces, spot support on grade
• Pier spacing sleds, wheels and bolsters: holding cages centered in a drilled pier

Tie it, then check it

Supports hold height. Tie wire holds position. The two are not interchangeable, and a mat that is beautifully supported but loosely tied will still shift under a buggy wheel. Wire bar ties speed up the repetitive work on a flat mat, and loose tie wire is what you want for the odd intersections and for anything that has to be pulled tight by hand.

Before the truck arrives, walk the mat. Look along the steel at eye level rather than down at it. A line of bar at the right height reads as a straight line from the side, and anything that has been stepped on shows up immediately from that angle and is invisible from above. That two minute walk is the difference between a slab that performs and a repair.

Pier and column work

Drilled piers have their own problem, which is centering rather than height. A cage that leans in the hole ends up with no cover on one side and too much on the other. Spacing sleds, wheels and bolsters keep the cage off the shaft wall while it is lowered and while the concrete goes around it. Get the cage centered and the cover takes care of itself.

What we keep on the shelf

We carry the support range rather than one of each, because the right choice depends on the job you are standing on and not on what was in stock. Rebar sand chairs in plastic, rebar wire support, slab bolster and high chairs, dobie bricks, pier spacing sleds, wheels and bolsters, tie wires and wire bar ties are all stocked at 20 NE 30th Street. We do not handle special order items, so what is listed is what you can pick up.

If you are not sure which support suits the subgrade you have, call the counter and describe it. Someone who has sold into the same ground for years will tell you straight, and if a delivery is easier than a trip we can usually get it to you the same day or the next.