Latex grout bag is made from reinforced canvas and is puncture and tear resistant. We attach a nipple from a Wilton brand cake icing bag and use these to apply thinset for tiny detail work, such as cementing in small artifacts in found-object mosaic. The bag is large, about 22 inches long, so it's also great for larger grouting jobs where you need to apply grout in different areas in controlled amounts, such as the tops of mosaic walls near the ceiling. In either example, the bag makes it easier to keep the grouting process neater and cleaner.  We have written some thinset instructions which specifically address how to use thinset for detailed mosaic artwork.