Which caulk should I use?
Q:
Recently I went to a home center for a tube of silicone to seal up some cracks in an Adirondack chair I built years ago. (I plan to repaint it.) But I was overwhelmed by the number of products labeled as caulks, sealants, and adhesives, many containing varying degrees of silicone. A store clerk couldn't provide much insight into the differences among these similar products. Can you help?
—Jerry Wise, Boston
A:
It can be confusing, Jerry, so we turned to the experts from DAP, Liquid Nails, and Franklin International, manufacturers of these products, to get answers. We learned that the product categories are defined by two properties: gap-filling ability and adhesion.
* Caulks fill voids, at a cost less than sealants and adhesives. Because they dry to a fairly rigid texture, use caulks on static joints or to fill gaps that won't shrink or swell due to moisture or temperature changes. But caulks can shrink over time and need to be replaced. Caulks usually are latex-based and not intended to adhere things together.
* Sealants, like caulks, fill gaps and create a moisture barrier—but adhere better than caulks and remain more flexible when dry. So sealants work well on joints that move with moisture changes, and adhere better than caulks to materials other than wood, such as glass, ceramic, brick, stone, and metal. Most sealants are silicone-based, but some also use rubber or polyurethane. Sealants provide better adhesion than caulks, but less than true adhesives, and can hold small objects in place where significant bonding strength is not needed.
* Adhesives have one purpose: to bond two materials securely. Primarily used in construction and industry, adhesives have a high bond strength that, depending on the formula, works well with wood, metal, glass, ceramics, and building products, such as drywall, insulation, and flooring. Typically made from latex, rubber, or polymers, such as polyurethane and silicone, adhesives dry rigid; they don't work well at sealing joints or filling voids subject to seasonal movement.
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