Caulk is used to provide watertight and airtight seals anywhere there's a gap between two different materials (such as tile and drywall). It comes in several varieties, including sanded caulk and unsanded caulk, to suit different applications. Most of the time, you'll want to choose unsanded caulk. The differences between the two will help you decide when to reach for sanded vs. unsanded caulk.
Sanded vs. Unsanded Caulk
As the name implies, sanded caulk has an extra ingredient: sand. Unsanded caulk normally shrinks after application, but the addition of sand prevents this. Therefore, the primary use of sanded caulk is to fill large gaps where shrinking caulk could result in poor adhesion between the caulk and the tile, drywall, wood, stone and so forth. Sanded caulk also may be chosen to match the look of grout.
According to the Grout Specialist, the addition of sand also makes the caulk less flexible and more likely to crack or break. Sanded caulk is less likely to resist mold growth as well, making it a poor choice for use in bathrooms and kitchens as it will have a short lifespan.
On the other hand, unsanded caulk (which can be either silicone, acrylic, latex or a blend thereof) typically remains flexible and mold-resistant and comes in a variety of colors to suit your decor. Its only limitation is the area that it can cover. Larger gaps may need to be covered first by a quarter round or other trim before caulk is applied to the edges.
Sanded Caulk vs. Sanded Grout
If you believe sanded caulk is the best choice for your project, take care when you go to your local hardware store to make a purchase: Caulk isn't the same as grout. Grout also comes in sanded and unsanded varieties, which can make it easy to mistake unsanded grout for unsanded caulk. However, the two materials have different uses.
Grout is more akin to a mortar and is used to not only fill in crevices but also to "glue" materials together. For example, grout is spread on the back of tiles to secure them to the wall or floor and then more grout is spread between the tiles to secure them to each other. Grout dries to a hard, inflexible and somewhat porous consistency, making it inappropriate for use as a caulk.
Although grout is typically sold in a tub, some manufacturers do sell grout tubes that look a lot like caulk tubes. Be aware of the similarities and double-check that the product you purchase says "caulk."
Can You Make Sanded Caulk?
If you want to use sanded caulk but only have unsanded caulk on hand, it's tempting to consider mixing sand in with the caulk before or after application. However, according to Ceramic Tile and Stone Consultants, broadcasting sand over 100 percent silicone caulk will undermine the caulk's performance.
To prevent caulk from sticking out like a sore thumb, a better option would be to choose clear caulk or color-matching caulk in either sanded or unsanded form. According to Your Own Architect, some grout manufacturers also provide caulk already colored to match their grouts to help you achieve a visually appealing transition.