The Finish Line: Sealants
March 17, 2011
Because EIFS are a jointless type of wall cladding that can be installed over a huge wall area without joints at all, it’s clear that the only way for water to get behind the EIFS is somewhere at the edge of the EIFS. This penetration is most often at windows, openings and flashings. The proper location, design and sealant type is very important with EIFS. Below are tips about using wet-applied sealants with EIFS.
Reliance on Sealants AloneOnly a cheapskate fool relies on sealants by themselves to keep water out. There needs to be some backup protection. This extra protection can be in the form of flashings or joint designs, or both.
Floor Line JointsOn wood frame buildings using EIFS, a horizontal joint is supposed to be installed at each floor line. This is to accommodate dimensional changes in the lumber that can telegraph through the EIFS and cause cracks. Sometimes these joints are omitted. One way around having an expansion-type sealant joint is to have an overlapping band that doesn’t use sealant at all (shown in the drawing).
Recessed Sealant JointsOne of the easiest ways to get around the task of removing failed sealant from an EIFS joint is to leave the old sealant in place-provided there is some place to put the new sealant. This must be decided when the building is first designed as it can significantly affect the wall’s appearance. The idea is to recess the sealant bead deep in the joint. This makes for a much more visually pronounced joint, but it also keeps the weather away from the sealant which helps it last longer. But if you do recess the sealant bead, the new sealant goes over the old sealant. The outside face of the original sealant needs to be far enough into the joint to allow for both a new backer rod and sealant bead.
Moisture Vs. Finish HardnessEIFS finishes are water-based and harden by drying. When subjected to standing water for extended periods of time, the finish softens slightly. If a sealant is bonded to the finish, the sealant can pull the finish off the basecoat. This is one reason why sealant beads are bonded to the basecoat which is a reinforced, structural material.
If sealant must be attached to the finish-for instance, when replacing existing defective sealant-the finish at the bond-to area can be made stronger and more resistant to water by first brush-applying a clear, hard coating. This seals the finish and can provide a better bond.
Where to Bond toOne of the laws of EIFS is to bond the sealant to the basecoat, not to the finish. The basecoat is strong, while the finish is essentially only a paint. The finish softens when it gets wet, allowing the sealant-when the joint expands-to pull the finish off the basecoat. To make sure the sealant adheres to the basecoat, mask the bond-to area away from the finish area.
Sealant ChemistriesSealants are applied in a semi-liquid, paste-like state that hardens as they dry. This drying can occur in several ways, including evaporation of water, chemical reaction of airborne water and chemical reaction of materials within the sealant itself. It’s important to understand how a sealant works in the curing process. For instance, a sealant that requires airborne moisture to cure will take longer in Arizona than one which cures by evaporation.
Solvents Vs. EPSSome sealants use hydrocarbons as the solvent that keeps the sealant liquid. Some solvents will “eat” EPS foam. Sealant and EIFS producers are aware of this and sealants that do no affect foam are ones that are approved for use with EIFS.
WrappingThe edge of the EIFS, where it stops and gets sealant, must have the basecoat wrapped around the edge. You cannot bond the sealant to raw foam. The sealant will yank the raw foam apart, let water in and result in paperwork from lawyers.
Single Vs. Multi-PartI like single-part, ready-to-use sealants. To me, they eliminate yet one more possible area of problems, like mixing foul-ups. There are one-, two- and three-part sealants. The multi-part sealants have the advantage of changing their color by using a tinted second component. Keep in mind, for large projects even one-part sealants can be provided if the amount of sealant is large enough.
ColorsAn interesting sealant fact: Some architects think a clear sealant will mask the joint. Wrong. It shows up just as much as a colored sealant that is matched to the adjacent wall element. It gets worse: clear sealants allow sunlight in which degrades them.
PaintingSome sealants-especially inexpensive ones-are marketed as being “paintable.” Acrylic sealants are a prime example and EIFS coatings are usually acrylic-based, so the paint will stick. However, some sealant materials, notably silicones, are hydrophobic (they repel water) and adhesion suffers.
I’ve seen designers try to mask the location of sealant joints by applying the EIFS finish over the sealant. This doesn’t work. The joint will still be visible. There is a bigger problem: the sealant is softer and stretchier than the finish, and thus the EIFS finish will develop micro cracks and simply fall off.
ModulusThe “modulus” of sealant is a technical term for how soft and stretchy it is. This matters with EIFS as a soft, stretchy sealant puts less stress on the sealant-to-basecoat bond area. Some sealants get hard as a rock, exacerbating this problem. Premium sealants, especially silicones, remain soft and stretchy over a wide temperature range.
Hardness Vs. TemperatureSealants generally get harder as they get colder, some much more than others. The increased hardness can make the joint movement enough to tear the sealant off the EIFS. For small joints where the sealant is acting like a filler, rather then experiencing a lot of movement, it’s not a big deal. With full expansion joints, such as between EIFS prefabricated panels, a sealant that remains soft and stretchy over a wide temperature range is needed. Sealants that have this quality are often called “low modulus” and silicone sealants have that property.
Width-to-Depth RatiosThe ratio of the width of the joint to the depth of the sealant bead is important. The proper ratio should be a depth that is one-third of the width. Contrary to popular belief, less sealant works better, as it makes the thinner bead more stretchy. A backer rod helps control the depth and shape of the bead and thus improves performance while saving money.
TestingEIFS producers and sealant manufacturers jointly test each other’s products to see which sealants work best. They both publish lists of sealants that they feel work well with different brands of EIFS. It’s important to use these approved sealants, as their use can affect the warranty and performance of the wall system.
Primers Vs. Side-of-JointTo get good adhesion to EIFS, some sealants require a primer. This is brush-applied to the bond-to area before the sealant is put on. Sealant manufacturers and EIFS producers make primers they know will work with their products. Keep in mind that often sealants have one material on one side of the joint and another material on the other side. Thus two different primers may be needed.
Backer RodsBe careful what material you choose for a backer rod. You want a closed cell material, not a sponge-like open material. Open cell backer rods can hold moisture and affect the bond of the sealant to the EIFS.
ToolingTooling refers to seating the wet sealant firmly against the EIFS as the sealant is being installed. After the sealant is applied, pressure is applied to the exposed face. Often this is done with a spoon, spatula or even a finger. This forces the wet sealant into direct contact with the EIFS and greatly strengthens the adhesive. It also makes for a much better-looking joint.
Alternatives to SealantsTo avoid the hassle and expense of removing and replacing old sealant, preformed silicone strips can be bonded to the surface of the EIFS. They come in various widths and colors and are made of soft silicone. They do alter the appearance of the joint to look like a batten.
The thin coatings used in typical North American EIFS are not well suited to using embedded trim as a seal. Trim can be used as trim, but it’s hard to get the “trim” fully seated in the EIFS to the point that it can actually move and do its job. An exception to that rule is large example joints, such as seismic joints between major sections of large buildings. The movement capacity needed is so great that a gigantic and hard to install sealant joint would be needed. A separate mechanical joint, usually made of metal and/or rubber, is normally used in those cases.
LongevityThere are sealants on the market that are guaranteed, by their producers, to last 20 years or more. Given that many commercial buildings in the U.S. are not designed to last for more than a generation before being replaced, this sort of life expectancy is good.
Replacing SealantsIn previous articles in W&C, I have moaned about the hassles of replacing EIFS sealant joints. The longer-lasting sealants are especially good with EIFS due to the thin nature of EIFS coatings. I have seen EIFS on 30-year-old jobs where the sealant is still functioning well, saving the owner a small fortune in maintenance costs for a very small up-charge for a premium sealant when the EIFS is first installed. In contrast, I’ve seen sealant joints on EIFS jobs that have failed in the first few years as a result of trying to get away with using low-grade residential caulking on commercial projects.
My ChoicesMy line of thinking-in terms of being a designer-tends toward simplicity. This is the worn-out “less is more” concept. For sealants, I like one-part products. There’s less of a chance of things going wrong due to some sealant installer that can’t read the mixing instructions for multi-part sealants.
The following brands of sealants are commonly used with EIFS: Dow Corning, Tremco, Sika, Pecora and GE. It’s a good idea to get to know your local rep, as some of these companies provide excellent customer service including tech support and on-site visits. There are many lesser known brands, some of which are simply private labeled versions of major brands.