How to Choose the Best Caulk

Enlarge Image Image Gallery These hardy tubes will help you save energy, avoid moisture damage and prevent pest problems. PHOTO: NATHAN HAM PHOTOGRAPHY

Caulk is a home-improvement hero. No matter how skilled the carpentry, there are always small cracks and gaps that need to be sealed around windows, cabinets, doors and sinks. Caulks help insulate, weatherproof and pest-proof your home by sealing those gaps. Caulks also excel in cosmetic repairs. After being painted, caulk-filled gaps and cracks disappear, making cabinets, counters and wood trim seem as if they just grew there.

Picking the best caulk can be the hardest part of any caulking job. Most hardware stores carry dozens of different products, each promising better results than the other. If you use the wrong caulk, the joint will fail long before it should, which means that you'll need to do the job all over again. Although some manufacturers now include helpful job-specific labels, others provide little information or overstate their products' performance. Here's how to pick the right product for whatever job is at hand.

Despite the dizzying selection, caulks are all made from one of four base, or backbone, polymers: latex, silicone, polyurethane or rubber. The base polymer determines specific characteristics, such as what materials it will adhere to, how easily joints can be smoothed, durability and paintability. Most caulks are sold in long tubes, and you apply them using an inexpensive, hand-pumped caulk gun.

Latex Caulk

Also labeled as acrylic caulk, vinyl caulk or sealant, water-based latex products are the easiest to use, the least expensive and handle the widest range of applications. Latex caulks don't contain volatile chemicals, which means you can smooth joints with a wet finger and clean up excess with soap and water. All latex caulks can be painted, or you can also find a wide palette of pretinted caulks.

Latex-based caulks fall into two sub-groups: less expensive acrylics and better-quality “siliconized” latexes. Acrylic latex is fine for sealing areas that won't face major temperature changes or high moisture levels, such as interior windows, doors and trim. Siliconized latex caulks contain a small amount of silanes (a form of silicone) to promote better adhesion. (This is not the same as 100 percent silicone caulk; see below.)

The best siliconized latexes are a good choice for heavy-duty work, such as exterior windows and doors, and caulking seams in kitchens and bathrooms, and to keep moisture out of walls and floors.

Silicone Caulk

Silicone sealants were first used to bond glass panels to skyscrapers — a far more demanding job than most home improvement projects. Because they stay flexible at all temperatures, are completely waterproof, bond well to almost everything and won't support mildew growth, silicones are used around sinks, tubs and shower stalls.