Latex Acrylics

Acrylics have been the rising stars of the caulk market during the last decade. Just as acrylic paints are now matching or beating the performance of the best oil-based paints (and winning over skeptics along the way), acrylic caulks are starting to move in where previously only silicones or polyurethanes dared to go. Choosing a bedding caulk for installing door and window units is a no-brainer — you grab a tube of a reasonable quality latex caulk and have at it. Likewise for any interior trim and painting caulking — nothing beats the workability of a latex formulation. Latexes tool with a finger and clean up with water; plus they’re nontoxic and produce little odor, making them ideal for indoor work. They stick well to a variety of materials and can be painted.

High-quality latex acrylics win the prize for user friendliness, and claim to meet the same performance standards as some silicones and polyurethanes. But are they up to heavier-duty work — a tile shower or exposed outdoor caulking? The answer is yes, as long as you choose the product carefully and give it some protection as it cures.

Flexible chemistry.

Older-generation latex caulks have less flexibility — +/-7.5% movement capability. The new high-performance acrylics are formulated with a high percentage of plasticizers, so many are capable of +/-25% movement. This doesn’t come close to the ability of silicones and polyurethanes, some of which can withstand 100% elongation and 50% compression (+100%/-50% movement), but it’s adequate for most residential demands. The plasticizers in these new-generation acrylics are nonvolatile — that is, they don’t evaporate as the caulk ages, so the caulk remains flexible indefinitely. Top-performing acrylics also have good UV resistance and aren’t susceptible to adhesion loss from water. So why not toss all those messy silicones and urethanes and move over to acrylics? There are a couple of reasons. For one thing, acrylics are much slower to firm up as they cure than urethanes or silicones, leaving them more vulnerable to the weather. Much of the ASTM testing is done after the caulks have been able to cure for days or even weeks. But on a remodel, an exterior caulk bead goes into service from the moment it’s tooled. To test how these softer acrylics would handle a surprise rainstorm, I ran beads for six different acrylic caulks on a piece of painted sheet metal, along with sample beads of silicone, polyurethane, and Kraton-based products. I let all the beads cure for an hour outside at 70°F, then hit them with spray from a garden hose for five minutes. Of the six acrylics, all were deformed by the spray; in two cases the bond lines were smeared and weakened, and in one case the caulk partially dissolved and ran down. The other three types of caulk were virtually unaffected. This was no white-smocked, scientific test by any means, but it supported my suspicions that compared with other types of caulk, these soft acrylics might require special care to be able to cure properly in exterior joints where movement is anticipated. (For light caulking of nonmoving joints before painting, however, acrylics are fine as long as the weather is cooperating.) Acrylic caulks also have to be protected from freezing in the package and can’t be applied below 40°F. However, once they’re in place and cured, many remain flexible at very low temperatures. DAP’s Formula 230, for instance, has a service temperature range from -30°F to 180°F. With care, I would also use a top-of-the-line acrylic to caulk the expansion joints in a tiled shower — another fairly severe environment. Allowed to cure properly, these caulks are up to the task. Tile guru Michael Byrne swears by Color Caulk’s Pro Line Class A — an acrylic caulk that meets C 920 and comes in specially mixed colors, and sanded if desired, to match most commercially available grouts. Always use a caulk with mildewcide for kitchen and bath work. Because of their water content, latex acrylics will shrink as they cure — up to as much as 30% by volume. For a tight waterseal, you may have to go back and add more caulk. What does siliconized mean? In choosing a high-performance acrylic, don’t be misled by the term "siliconized." All caulks are "siliconized," which refers to the addition of small amounts of adhesion promoters called silanes (a form of silicone). Early on, the term was a marketing ploy that let latexes piggyback on the reputation of silicone. Nowadays, with 100% acrylics coming into their own, the term is just as likely to be used on a medium- or even low-quality latex caulk. Because there are so many grades of latexes (including polyvinyl acetates, vinyl acrylics, and 100% acrylics), you will have to choose carefully to find a top performer. Look for an acrylic with the ASTM C 920 Class 25 designation, which indicates

+/-25% movement capability. Don’t confuse this with the marketing claim of "25% total movement," which indicates +/-12.5% movement.

Kratons, or Block Copolymers

Kratons are the new kid on the caulk block. These are typically the "super-clear" caulks — products such as Sashco’s Lexel, Geocel’s Pro Flex, and OSI’s Quad. The strength of these caulks is their versatility. They stick to just about everything (they’ll melt rigid foam, however), and can be applied to damp substrates and in temperatures down to 10°F or lower. And there’s no doubt about their clarity, if it’s a clear caulk you need. (I hate to take sides in the caulk wars, but I found Quad to be the clearest of all.) These caulks skin very quickly, but can typically be wet-tooled with soapy water.

New solvent-based "block copolymer" synthetic rubbers are the backbone of these caulks. The products are known for good performance and versatility, but the fumes can be strong and persistent.

For me, the biggest drawback to the Kraton products is their heavy solvent odor. Despite some marketing claims to the contrary, these are not caulks to be used indoors — unless you’ve got at least a week for ventilation before occupancy. One tech support person told me that sensitive individuals can smell the solvents for months. A second drawback is shrinkage: After the solvents flash off, the bead is as much as 35% smaller. The caulk will meld to itself, however, so if shrinkage is a problem you can add more sealant. Kratons can be painted, and they’re easy to color — a fact that OSI has used to advantage in its Quad line, which is available in more than 100 colors to match standard shades of vinyl and aluminum siding. I could probably live without Kraton products if I had never heard of them, but I might keep a tube of Geocel’s Pro Flex in the truck, for one reason: It claims to stick to oily surfaces — a unique claim in the caulk market, as far as I know. This could come in handy if you have to get caulk to stick to a concrete foundation that has traces of form release oil on it. I’m not ready to bet the ranch that it will work, but it’s worth a try.

Get Your Hands Sticky

So who can you believe when it comes to caulk claims? Ultimately, you have to get your hands on the product and try it, then go back and see how it performs over time. Your own house may be your best test site. If you’ve got a question about how a caulk will work in a given application, call tech support by all means, but don’t ignore your own field test with the actual substrate materials; it’s the only way you can be sure.

Caulk Manufacturers

Bostik 211 Boston St. Middleton, MA 01949 800/726-7845	Macklanburg-Duncan 4041 N. Santa Fe Oklahoma City, OK 73118 800/654-0007
Chemrex 889 Valley Park Dr. Shakopee, MN 55379 800/828-0253	Mameco Intl. 4475 E. 175th St. Cleveland, OH 44128 800/321-6412
Color Caulk 723 W. Mill St. San Bernardino, CA 92410 800/552-6225	OSI Sealants Inc. 7405 Production Dr. Mentor, OH 44060 800/321-3578
DAP 855 N. Third St. Tipp City, OH 45371 800/543-3840	Red Devil 2400 Vauxhall Rd. Union, NJ 07083-1933 800/423-3845
Dow Corning Midland, MI 48686 800/248-2481	Sashco Sealants 10300 E. 107th Pl. Brighton, CO 80601 800/767-5656
Franklin Intl. 2020 Bruck St. Columbus, OH 43207 614/443-0241	Sika Corp. 4800 Blue Pkwy. Kansas City, MO 64130 800/548-0496
GE Silicones 260 Hudson River Rd. Waterford, NY 12188 800/255-8886	TACC Intl. Air Station Industrial Park Rockland, MA 02370 800/503-6991
Geocel Corp. P.O. Box 398 Elkhart, IN 46515 800/348-7615	Top Industrial Inc. 16149 Leadwell St. Van Nuys, CA 91406 800/473-1617
Gibson-Homans 1755 Enterprise Pkwy. Twinsburg, OH 44087 800/433-7293	Tremco 3735 Green Rd. Beachwood, OH 44122 800/321-7906
Gloucester Co. 235 Cottage St. Franklin, MA 02038 800/343-4963	UGL P.O.Box 70 Scranton, PA 18501 800/845-5227
Macco Adhesives 925 Euclid Ave. Cleveland, OH 44115 800/634-0015	White Lightning 770 Tipton Indust. Dr. Lawrenceville, GA 30045 800/869-4483

It's getting harder to find a good, old-fashioned "caulk" on the store shelves anymore — seems they've all gone off and become "sealants." The term sealant implies higher performance — a material that not only sticks well to a variety of substrates but that withstands the weather and is flexible enough to stretch and compress with building movement without losing adhesion or tearing. Silicones and urethanes are invariably called sealants. Among the latex brands, the terminology is mixed: Lower-performing compounds are ore likely to be called caulks (for example, "painter's caulk"), while 100% acrylic products moght be dubbed either a caulk or a sealant. Dap's 230m acrylic is labelad an "advanced latex sealant" while M-D's Maxx 5000 is touted as "an advanced professional sealant" and our best acrylic caulk. This inflationary language is more than just marketing hype — it has to do with terminology adopted by the ASTM (American Society for Testing and Materials) C-24 committee, the standard writer for the sealant industry. ASTM C-834 is the "Standard Specification for Latex Sealants," a minimun standard for older generation caulks; ASTM C-920 is the much more rigorous "Standard Specification for Elastomeric Joint Sealants." Caulk code: ASTM C-834 is the standard for latex caulks; ASTM C-920 is the spec for sealants for moving joints. TT-S-00230C is a federal standard similar to, and being replaced by, C-920. If a caulk meets the requirements of either (or both) of these standards, the manufacturer is likely to use the name "sealant" on the label. The C-920 standard was originally created for polysulfides, polyurethanes, and silicones — rugged sealants that met the demands of high-rise curtain wall construction. To pass C-920, caulk samples on glass, aluminum, and concrete are exposed to a battery of tests, including being heated in ovens, frozen, immersed  in water for a week, and out through numerous cycles of compression and elongation, without showing adhesive or cohesive failure. As acrylics have improved, they are also proving able to meet this standard —  almost. Don Jackson is JLC’s managing editor.