How much of this is silica? Does it become respirable when sanded?

Thank you for posting your inquiry. This product is comprised of about ~30% (by weight) of silica sand. While the Grain Fitness Number (AFG) for the sand used in manufacturing this product is 59 per American Foundry Society, the smallest grain size in this sand passed through a U.S. mesh size of 200 (about 2%) with no grain passing mesh size 270 and smaller. This means smallest particle size in this sand would be about 74 um. Since the U.S. mesh size of 200 corresponds to 74 um. While some particles with a diameter of 10 um or less can get deep in the long, grains with a diameter of about 4 um are considered respirable. Therefore, the likelihood of this product producing respirable size particles is unlikely. Additionally, being a paste and in a wet form as packaged this product does not form any dust, respirable or not and the likelihood of one having to sand this product when dried is extremely low. Nonetheless, we recommend the use of an appropriate dust mask, should one decide to sand the product. Should you have additional questions or require further assistance, please feel free to contact DAP Technical Customer Service at 888-327-8477.