Using lasers to create flat floors

Many companies opt to maximize space utilization in their storage areas by installing floor-to-ceiling racking systems separated by very narrow aisles.
By Tom Rohrer September 1, 1999

Many companies opt to maximize space utilization in their storage areas by installing floor-to-ceiling racking systems separated by very narrow aisles. In order to move product to and from this racking arrangement, very narrow aisle (VNA) reach trucks are used.

Some VNA reach trucks travel with the load fully elevated over 40 ft with a side-to-side clearance between the truck mast and racking of only 4 in. A difference of 1/8 in. in floor elevation between a VNA reach truck’s two front wheels set 47-in. apart translates to a static lean of 1 1/4 in. at a height of about 40 ft.

Mast sway when the truck is traveling could triple the static lean and lead to collisions between the mast and racking. In addition to rack damage, floors with poor flatness characteristics can also cause premature failure of truck welds and disrupt wire guidance performance.

A plant engineer faced with collisions between vehicles and racking has no alternative but to reduce the speed of the trucks, which decreases pallet throughput and productivity.

Traditional approaches

Until recently, the solution to improving floor flatness characteristics was either manual grinding or installing a bonded concrete overlay system.

Manual grinding is performed with a rotary machine readily available from construction rental supply firms. This approach utilizes a rotary grinder to remove high spots, as determined by a straightedge placed on the floor. Manual grinding provides an economical solution to floor aisle spot imperfections.

However, with whole aisle or wheel path grinding, the manual method is extremely slow, messy, costly and often leaves the floor concave rather than at a flat plane.

Bonded concrete overlays are the second alternative. The existing floor is cleaned and roughened. A bonding agent is applied between the base concrete and the 3/4-1-in. thick concrete topping, in order to stick the new topping to the old floor. Concrete overlays enhance the structural capacity of a floor slab because the bonded topping becomes composite with the concrete floor to increase load carrying capacity.

Bonded concrete toppings can be placed in narrow strip fashion so that floor flatness tolerances are enhanced far above the original aisle tolerances. Overlays have the added advantage of restoring aisle surfaces to new condition.

Bonded concrete overlay systems run the risk of debonding if surface preparation is not properly performed. Also, any cracks in the base slab eventually reflect into the topping slab.

Since concrete overlays are only placed in aisles, the raised elevation can make utilization of the bottom pallet station problematic. Overlays also require preparation and cure time lasting several days.

Latest approach

Laser grinding is the newest approach to enhance concrete floor flatness. This process improves floor aisle tolerances by grinding just the wheel paths of VNA reach trucks, or the full width of the aisle if the client chooses. A rotating laser positioned at the end of the work area controls the depth of cut. A pair of laser receivers mounted on each grinding head is interfaced with a control box that corrects the depth of cut.

After an aisle is surveyed, both wheel paths are ground to a common profile across the aisle, which eliminates the side-to-side sway of the loaded vehicle as it travels elevated down the path. In order to minimize the amount of concrete removed, the longitudinal plane goes up and down the length of the aisle in lieu of carrying out grinding from the lowest point and making the floor flat to it.

Wheel path grinding could create clearance problems for the truck when deep cuts are required to correct transverse tolerance problems. Floor aisles that have been ground can present problems to an operation that subsequently changes racking location and orientation.

The laser grinding process is clean and dust free. Product can be left in the racks during the grinding operation. The client has the ability to retrieve product either in front or behind the grinding operation as it takes place. Once an aisle has been ground, it can be immediately returned to service.

Improved floor flatness allows operators to safely run the VNA reach trucks at maximum speed. The increase in pallet per hour throughput and reduced truck maintenance costs easily provide a paybackfor the operation in just a few months.

— Edited by Ron Holzhauer, Managing Editor, 630-320-7139,

Key concepts

Very narrow aisle reach trucks require flat floors.

Traditional methods for improving floor flatness are manual grinding and a bonded concrete overlay.

Laser grinding offers several advantages over the more traditional approaches.