Background: Workplace exposure to respirable crystalline silica (RCS) can cause silicosis, a progressive lung disease marked by scarring and thickening of the lung tissue. Quartz is the most common form of crystalline silica. Crystalline silica is found in several materials, such as brick, block, mortar and concrete. Construction and manufacturing tasks that cut, break, grind, abrade, or drill those materials have been associated with overexposure to dust containing RCS. Stone countertop products can contain >90% crystalline silica and working with this material during stone countertop fabrication and installation has been shown to cause excessive RCS exposures. NIOSH scientists are conducting a study to develop engineering control recommendations for RCS during stone countertop fabrication and installation tasks. The site visits described in this report are part of that study. Assessment: NIOSH scientists conducted three site visits to evaluate the effectiveness of three wetting methods in reducing occupational exposure to RCS for the grinding task at a stone countertop fabrication shop. The evaluated wetting methods included a water spray from a nozzle on a grinder, a center-feed feature that is built into a grinder, and a combination of water spray and a sheet-wetting method. During the field evaluation, the NIOSH scientist collected personal breathing zone (PBZ) air samples to assess the short-term task-based time weighted average (TWA) exposures to respirable dust and RCS for a worker who performed the grinding task using one of the three wetting methods in the final grinding and polishing area of the site. Additionally, two area samples were collected each day during the first site visit to assess the TWA background respirable dust and RCS concentrations in this area. The NIOSH scientists recorded detailed field notes about the work process to understand conditions leading to measured dust and RCS exposures. PBZ samples from the first site visit were taken only during active grinding to allow for direct comparison of the two wetting methods (water spray and center-feed) on worker exposure. The following two site visits focused on the evaluation of the wetting method of combining water spray and sheet-wetting, with the PBZ samples taken continuously while working in the final grinding and polishing area. Results: The short-term task-based respirable dust and RCS exposures were 354.3 +/- 60.7 and 190.4 +/- 105.4 µg/m3 when using water spray, and they were 354.9 +/- 149.6 and 195.3 +/- 168.4 µg/m3 when using center-feed. Area samples from the two sampling locations have RCS concentrations of 50.1 +/- 29.0 and 44.5 +/- 12.6 µg/m3, respectively. The respirable dust in the area samples have concentrations of 161.2 +/- 82.5 and 182.3 +/- 28.5 µg/m3 at the two locations. When using the wetting method of combining water spray and sheet-wetting, the short-term task-based exposure was 33.2 +/- 11.4 µg/m3 and 123.4 +/- 27.5 µg/m3 for RCS and respirable dust, respectively. Due to the difference on the sampling strategies used, the exposure data with the wetting method of combining water spray and sheet-wetting is not directly comparable to those with the other two wetting methods evaluated in this study. However, compared to the exposure data from a previous study when only water spray was used as the wetting method for grinding, the exposures to respirable dust (P = 0.026) and RCS (P = 0.002) are both significantly reduced with the addition of sheet-wetting. The average RCS exposure with the addition of sheet-wetting was only 27.5% of the level reported when only water spray was used. Conclusions and Recommendations: Although the short-term PBZ exposures or concentrations from area samples for RCS are not to be directly compared with the Permissible Exposure Limit (PEL) by Occupational Safety and Health Administration (OSHA) and NIOSH Recommended Exposure Limit (REL) of 50 µg/m3, the background RCS concentrations observed in the final grinding and polishing area of the site suggest that workers in this area are likely to be overexposed to RCS without additional control measures. Both wetting methods of water spray and center-feed performed equally poor in terms of wetting the grinding spot and reducing the worker's RCS exposure during grinding, despite having very different water flowrates. The significantly reduced respirable dust and RCS exposures by adding the sheet wetting is evidence that this wetting method helps wet the active grinding area effectively, thus successfully suppressing the dust formation. With this new wetting method of combining water spray and sheet-wetting, the TWA RCS exposure for grinding can now be reduced to levels below the OSHA PEL and NIOSH REL of 50 µg/m3. With some improvements, sheet-wetting could become a promising and practical engineering control solution for reducing RCS exposures during grinding. Additional field surveys will be needed to further validate that this engineering control solution can reduce the workers RCS exposure consistently below the OSHA PEL during stone countertop grinding and polishing. In the absence of sufficient dust controls, respirators should continue to be used to reduce exposures, and the employer should ensure that the company respiratory protection program follows OSHA standards.