Procedures & Tolerances
The tolerances listed here are achieved using skilled tradesmen following standard industry workmanship practices. Due to variations in fabrication equipment and stock availability, these tolerances may not be achievable, or in some cases, closer tolerances may be achievable. Therefore, for any particular project, you and your contractor may agree to tolerances that are more or less stringent than those listed here. Such agreements should be documented in writing. Unless otherwise agreed, the tolerances listed here are acceptable guidelines.
The tolerances in this section pertain to large stone panel-type countertops only. Tolerances for stone tile countertops are listed below, in Adhesives and Joint Fillers.
Lippage.
In the stone industry, the term “lippage” refers to the unevenness of the finished surfaces of two adjacent stone units. Due to the relatively tight seams used in countertop installations, even minor amounts of lippage are noticeable. Lippage may be unavoidable due to permanent warp in the Page 6 © 2008 Marble Institute of America slab stock. There should be no detectable lippage at the front or rear edge of the countertop. Maximum allowable lippage at the centre of the countertop is 1/32″ (0.8mm).
Slab Thickness.
The thickness of the stone slabs used in a given project shall not vary by more than 1/8″ (3 mm) between the thickest and thinnest slabs.
Exposed edges of adjacent stone slabs must be matched in thickness and properly installed so that neither the top nor bottom surface exceeds lippage tolerances.
Joints at Materials Transition.
Visible joints between stone and other materials (e.g., cabinetry, gypsum wall board) shall be 1/8″, with a tolerance of ±1/16″ (±1.5mm), and filled with a soft, elastic material. Exceptions to this would be the joint between a full height backsplash and the underside of the upper cabinets, which is to be a nominal ¼” with a tolerance of ±1/8″ (±3 mm). Concealed joints between the stone and other construction materials (e.g., stone-to-wall joint underneath the backsplash) shall be sized to ensure a minimum of 1/8″ (3 mm) of cover.
Slab Flatness and Levelness.
Individual stone slabs are to be flat within 1/16″ (1.5mm) when measured with a 4′-0″ (1.2 m) straight edge. Finished countertop surfaces including multiple stones are to be both flat and level to 1/8″ (3 mm) across 10′- 0″ (3 m).
Seam Filler Materials.
Seams in the stone countertop are usually filled to the level of the top surface. The most common filler materials are polyester resin, epoxy resin, elastomeric sealant, and grout. Elastomeric sealants can be made from silicon, polyurethane, or acrylic bases.