Getting a Bead on Caulk!
It's not a matter of the wrong caulk improperly applied, it's a matter of the right caulk professionally applied.
By Susan M. Brimo-Cox

Use the right tool for the right job, they say. The same applies to caulk. But how do you know which is the right caulk for the job? Whether you’re using caulk to prevent air, dirt and moisture penetration or to bridge a gap and fill a crack, selecting the right caulk for the job is simply a matching process.

Getting down to basics
Caulks are available in different chemistries. To determine which type of caulk is right for your needs, you must have a clear understanding of what you want the product to do: What is the intended use of the caulk? What stresses will the caulk need to endure? And how long does the caulk need to last? In a nutshell:

The most common acrylic latex caulks are water-based products that offer fair to good elasticity. They are easy to work with, they clean up with soap and water, plus, they have low odor and they’re paintable. Acrylic latex caulks typically can last up to 10 years, whereas, high-performance acrylic caulks can perform for 20-plus years.

RTV (room temperature vulcanization) silicone caulks have excellent adhesion and durability, and they can last more than 50 years. They are good for a variety of surfaces — especially non-porous substrates — however, they typically don’t accept paint. If fumes are an issue, you may want to avoid acetoxy silicone caulks, which have a strong vinegar odor during application and curing, and select a neutral cure silicone, which has low odor.

Some acrylic latex caulks have silicone added. These hybrid ‘siliconized’ acrylic caulks offer the ease of application and clean up you expect from standard acrylic latex caulks, with the silicone contributing extra adhesion and durability. Typically, these products are paintable.

Polyurethane caulks are available in single- and double-component formulas. They provide good adhesion and durability — lasting about 20 years — but they require a solvent for cleanup and can be difficult to gun. Two-component products have a short pot life and must be used within the manufacturer’s recommended window.

Butyl rubber caulks — while they have high moisture resistance — are difficult to apply, require a solvent cleanup and last only 5 to 10 years.

Oil-based caulks have the shortest life — 1 to 5 years. They have the least amount of flexibility and should be painted when used for exterior applications.

Another term you may hear in relation to caulk is “elastomeric.” Technically, all sealants that can withstand significant joint movement can be considered elastomeric; however, the term is also used to describe another family of sealants. “A common sealant technology described as ‘elastomeric’ in recent years is a group of sealants based on the family of Kraton thermoplastic rubber polymers,” explains Larry Brandon, general manager of the Red Devil manufacturing plant in Pryor, Oklahoma. Kraton-based caulks are typically solvent-based, adhere well to a variety of substrates and can be painted.

Bend me, shape me
Price is often the prime driver in product selection, but it’s important to consider value. Generally, you’ll find the lower the price, the lower the performance.

“Adhesion and flexibility are what equate to durability in caulking,” says Dave Fuller, vice president of marketing at DAP Inc. in Baltimore. “Shorter-lived products won’t expand and contract to the degree a 50-year caulk will. Fifty-year caulk can expand and contract plus-or-minus 25 percent in one direction — up to 50 percent total joint movement — without cracking or losing adhesion.” For good results, it’s important to select a caulk at the proper quality level for the job, he advises.

Using the right caulk also can provide extra benefits — giving professional painters a bit of an edge. Some products are formulated to work in lower than normal temperatures; others in moist conditions. “This can be helpful to extend the ‘season’ — especially in Northern markets. Also, acrylic caulks with silicone can increase cure time and help speed up the time involved between caulking and painting,” reports Stephen Sicree, senior chemist at OSI Sealants in Mentor, Ohio.

“The professional painter has various sealants from which to choose in order to facilitate optimum job results. There are the Class A and Class B acrylic sealants, the polyurethanes, the C 834 painter’s caulks, the Kraton-based sealants, as well as the acrylic clear sealants, all of which will provide a level of performance in line with their respective cost and all of which offer paintability,” says Brandon. “Generally, tech service departments are more capable of discussing issues with the professional painter as compared to typical customer services personnel.”

And don’t miss out on the possibilities colored caulks offer. In some applications they eliminate the need to factor in curing time because you paint first. Coming through to fill the gaps and joints with a color-matched caulk afterward can really step-up production.

Ray Heck, marketing manager for construction products for North America at GE Sealants and Adhesives in Huntersville, North Carolina, advises reading the product labels for performance ratings. The American Society for Testing Materials provides test protocols for caulks for flexibility, shrinkage, workability and a variety of other physical characteristics. Heck says the rating codes will be found on the product packaging and you should be looking for ratings ASTM-C 834, ASTM-C 920 and Federal Specification TTS-230.

In a perfect world
Of course, product testing is usually conducted in “the perfect world.” Conditions at the job site may be far different.

Extreme temperatures can affect ease of application, curing and long-term performance. Curing times also can be significantly affected by humidity, the porosity of the surface and bead size. Curing time cannot be over emphasized, especially if the caulk will be painted. Painting too soon can prevent the caulk from curing, which can mean lower performance from both the caulk and the paint. These kinds of variables indicate how important it is to match a product’s attributes with your application.

“Ultimate performance and durability for caulks and sealants is also, to an extent, dependent upon surface condition and preparation,” observes Brandon. “No sealant, regardless of cost or technology will compensate for rotten wood [and other poor conditions].”

Certain caulks are designed for specific substrates. “When choosing a caulk, always refer to [the] packaging for the types of substrates that the product can be used on. Certain formulas may not adhere to some substrates which could produce poor performance. In addition, many sealants contain chemicals that could eat away at the substrate,” Sicree explains.

Avoid three-sided adhesion. “The general rule of thumb is if you have a crack or joint that exceeds one-half-inch by one-half-inch, you should use a foam backer rod,” Fuller says. And be sure you use enough product. “Make sure there is enough caulk to do the job. Most mistakes occur when not enough caulk is applied or too much is removed during tooling.”

What about shrinkage? Shrinkage occurs during curing, as the moisture in water-based and solvent-based caulks evaporate. Remove too much of the caulk bead during tooling and, after shrinkage, you may not have enough material to do the job.

Make sure the surface is clean and free of debris. Beware of mold and mildew on surfaces — don’t just caulk over it. Poor application can result in an improper seal.

If dirt collection is an issue, know that dirt resistance depends on several factors, including speed of cure and the smoothness of the caulk. In addition, some lower quality acrylic latex products contain external plasticizers that promote flexibility, but can make the caulk tacky over time.

Will a coat of paint make caulk last longer? According to the experts, the durability of some water-based caulks may be enhanced with a coat of paint, but with higher-quality caulks, it’s more likely the caulk will outlast the paint.

Making the right match
“Most painting professionals are looking for ease of gunning, ease of cleanup, good retention of color, and flexibility and pliability,” observes Heck.

The type and grade of a caulking product will dictate all its characteristics, from application to lifetime performance. The top two features painters should always look for in caulk are high flexibility and high durability. Tom Rapps, director of marketing at OSI Sealants, also recommends, “Based on their use, [painters] need to be aware of a caulk’s water-resistance, cure time, clean-up procedures, temperature of application [and] substrate compatibilities.”

As Brandon observes, “While none of us can afford to purchase the most expensive alternative when shopping, the old adage that ‘you get what you pay for’ certainly holds true for sealants, as it does for paints, and it should, therefore, be a key consideration.”