With the wide variety of caulk and sealant products available today... many do-it-yourselfers have a difficult time figuring out which one is right for their particular job.
Generally, a sealant is used to prevent air and water from entering an area. For instance around dryer vents. Caulks, on the other hand are generally used to fill a void, for example, where a sink meets the counter. However, it's important to note that today many caulks are also formulated to a provide a watertight, weatherproof seal, and may be a good choice for your project.
The first things you'll need to consider are the following: Will the caulk be used inside the house or outside? What type of surface, or surfaces will be caulked? How much movement or stress will the caulked area undergo? And, do you plan to paint over the caulk?
Once you've answered these four questions, you can begin to narrow down the choices.
If the caulk is to be used inside, for example, along a back splash or around a sink, a latex or acrylic latex caulk is probably the best choice. These products are easy to use, easy to clean up, they have low odor, and are easy to paint. For indoor projects that require a high degree of water resistance and flexibility, an acrylic latex caulk with silicone may be a better choice. These caulks also offer better adhesion and a longer life. If you plan to paint over the caulk, be sure to read the product's package, because some caulks that contain silicone cannot be painted.
If a caulk is to be used in a high-humidity area, a bathroom for example, you should use caulk that is mildew-resistant.
For outdoor projects, for example around window or door frames, siding and vents, a silicone sealant is the best choice. Silicone sealants form a weatherproof seal that remains flexible and won't crack, crumble or dry out. In fact, some silicone sealants feature a lifetime durability guarantee. In addition, silicone sealants withstand greater stress over a wide temperature span and offer better adhesion than outdoor caulks.