Just as there are tolerances for concrete construction, there also are tolerances for concrete removal. Four years ago the St. Petersburg, Fla.-based Concrete Sawing and Drilling Association (CSDA) formally adopted the International Association of Concrete Drillers and Sawers' (IACDS) Tolerance Standard.
The CSDA is one of the associations that joined with related organizations from around the world to create IACDS in 1995, and then worked together with IACDS members to determine useful tolerances applicable to this type of work. Originally developed in 2002, the IACDS standard was updated in 2006 and provides information on the dimensional accuracy that can reasonably be expected from professionals performing various types of work.
Although no formal link exists between that standard and ACI documents, the complementary data it includes is designed to help “create trust, clarity, and certainty between planners, contractors, and building owners” where some form of concrete cutting is involved.
Tolerances are presented in tables organized by the particular type of work involved, which includes core drilling; diamond cutting of ceilings and walls; diamond cutting of floors, with one set of tolerances for rail-mounted equipment and a slightly different set for wheel-driven saws; wire sawing, in both horizontal and vertical structures; crushing; and bursting.
Depending on their applicability, as many as eight different measurements are addressed for those six sawing and drilling activities. For example, core drilling and diamond cutting include tolerances for alignment accuracy and for hitting the target depth, whereas wire sawing, crushing, and bursting do not. All include tolerances for some form of directional accuracy, for vertical and horizontal levelness, and for “surface roughing,” which is explained to be the flatness of the drilled or cut surface. Finally, a tolerance is given for hole diameter deviations in core drilling, and width of cut deviations for wire sawing and diamond cutting.
Issues relating to the scale of the work are accounted for as well. In the case of core drilling, the specific tolerances depend on whether the core diameter is between 11.8 inches and 39.4 inches or less than 11.8 inches. (Those cutoff points make a little more sense when one considers the metric equivalents, which are from 301 mm to 1000 mm and less than 301 mm. The standard includes both units.) Some tolerances also vary based on the dimension of the structure. Tolerances for surface roughing and deviations in diameter are somewhat tighter where the structural dimension is less than 39.4 inches, for example.
For diamond cutting, the applicable tolerances depend on the floor, ceiling, or wall thickness. For floors, the threshold is 3.9 inches (100 mm) and ranges up to 19.7 inches (500 mm). For ceilings and walls, certain tolerances apply for thicknesses less than 11.8 inches (300 mm) and others apply if the thickness is between 11.8 inches and 19.7 inches (500 mm).
To put this in perspective, consider what a you can expect to end up with when you hire a professional to core a 12-inch-diameter hole vertically through a 4-inch slab, assuming that mounted equipment rather than handheld is used to do the work. The hole's location should be within 0.5 inch of where it was specified, which comes from adding 2.5% of the diameter to the +/- 0.2-inch alignment tolerance. The vertical nonalignment between the top and bottom edges of the hole should be less than or equal to 0.23 inch, and any roughening of the hole surface should be less than or equal to 0.6 inches. Finally, the hole diameter should be no less than 11.4 inches and no more than 12.6 inches.
Another interesting example is where a ceiling is being cut with a rail-mounted diamond saw. First of all, these tolerances are only valid when the cut is being made from above. Assuming a ceiling thickness of 4 inches, one can expect the cut to be vertical to within +/- 0.14 inch. The surface roughening should be less than 0.2 inch and the width of the cut should be within 10% of the target value. Also, the cut should be within 0.4-inch of the target line.
So we see that although cutting concrete is not as easy as cutting butter with a hot knife, it is accomplished routinely within predictable limits of accuracy.
The standard “Tolerances and Limits for Construction Drilling and Sawing” is available as a free PDF at www.csda.org.