There are two principal reasons to apply caulk. You’re either filling gaps before painting to achieve a professional looking paint job, or you’re sealing cracks to prevent air or moisture from penetrating. (There are also caulks for holding back heat and flames, which we’ll touch on with other specialty caulks at the end of this article.)
Types of Caulk
Silicone and Acrylic Caulks
For the majority of household caulking jobs, you’ll use one of two types, either an acrylic latex caulk or a silicone caulk.
Acrylic caulk, also available in what is called siliconized acrylic caulk, is perfect for filling gaps before painting. It also works well around windows or other wall penetrations to stop air leaks inside or out.
Silicone caulk, on the other hand, is better where you absolutely want to prevent any possible water penetration.
You can use acrylic caulk to prevent water penetration, but acrylic caulk is prone to begin shrinking and cracking after a period of time. When the cracks begin to appear, you have to caulk again or risk having water entering where it shouldn’t.
Acrylic caulks may be rated as 25-year, 35-year or 50-year, but in reality, they won’t last nearly that long. Even the best acrylic caulk will begin to show signs of drying and cracking after a few years.
Silicone caulk, sometimes called siliconized rubber caulk, retains a flexible, rubber-like feel for many, many years. It doesn’t dry or crack, and if properly applied in the first place, it maintains a waterproof seal for a very long time.
The advantage of acrylic caulk is that it is easy to apply, smooth out, and clean up for a very fine finished appearance.
Silicone caulk, however, is notorious for being difficult to neatly apply, smooth out, or clean up. Nonetheless, it is usually the caulk of choice around bathtubs and showers. It is usually also preferred around sinks and toilets, though there is an argument for using the less-messy acrylic caulk anywhere a water leak would be easily discovered before causing any hidden water damage.
Silicone caulk is also preferred for exterior applications where undetected water penetration could cause significant damage. Once applied, if applied properly, it should remain sound for at least a decade.
Be aware that silicone caulk is not paintable. The rubbery surface repels paint as well as water. Either choose a color that matches or coordinates with the surface where it’s being applied, or use a clear caulk that lets the existing surface color show through.
Check Out: How to Replace the Caulk Around Your Bathtub
Specialty Caulks
Adhesive Caulk
With many adhesive caulks, adhesion refers to the caulk’s ability to stick to the surface on which it is applied. Some, however, advertise the power to bond materials together similar to a glue. The former is an excellent property for any caulk, while the latter is perhaps overrated. It’s better to use a serious glue where glue is needed and a good caulk where caulk is needed.
For tile or granite countertops and backsplashes, a sanded caulk is recommended for the joint where the countertop meets the backsplash. Although joints in tile are usually sealed with a cement-type grout, that type of grout will crack anywhere there is possible movement or flexing, such as between the countertop and wall. The flexible caulk, on the other hand, will not crack.
Sanded caulk is also used on tile floors where the tile meets a wood threshold for the same reason. The potential flexing of the wood as it’s stepped on can crack any cement grout applied adjacent to it.
Sanded caulk can be obtained wherever the cement-type grout is sold and in matching colors. It’s applied with a caulk gun like any normal caulk and is relatively easy to clean up.
When assembling rain gutters, a butyl rubber caulk is often recommended for sealing joints against leaking. This caulk is so messy to work with, it makes using silicone caulk seem like a picnic. Though silicone caulk could be used as an alternative, butyl rubber adheres well to metal and is even more flexible to help maintain a lasting seal as gutters flex under the weight of water.
Butyl rubber is very sticky so have a small, throwaway putty knife and several disposable rags available when you use it. This caulk is not paintable and can only be cleaned up with a solvent. Also, do not apply it on the outside of the rain gutter because it will be a mess. Apply it only on the inside. Because downspout components slip inside one another, there is no concern for leaking and no need for caulk on downspouts.
Fire Caulk
For a metal or masonry fireplace hearth, several specialty caulks are available for sealing cracks or gaps to keep heat and flames contained inside the firebox. Variations of fire caulk are also available for sealing openings through fire rated walls, such as between your garage and the living area in your home. Consult the manufacturer’s specifications to select the right caulk for your needs.