EIFS was originally developed as a retrofit cladding material for solid substrates like concrete and masonry. EIFS was intended for use on vertical exterior walls, but over the years its use has migrated to all sorts of wall-like applications, some of which work quite well while others simply do not. One of the common marginal uses of EIFS is near or below the ground. This month's column will give you some food for thought for the next time someone wants to use EIFS near or below grade.
First, remember that EIFS is not a waterproofing material, but that it is water shedding. This is why it should not be used for roofs or on large flat surfaces. If it is used on roof-like surfaces, it can absorb water, which in turn can work its ways through the EIFS and start deteriorating the substrate. There's no way to make EIFS totally waterproof; it simply is not glass or metal. But in its use as a vertical cladding, it is plenty waterproof enough to keep the wall dry. (If this logic appears a bit convoluted, consider why shingles are not used on flat roofs, even though they shed water when used as intended on vertical surfaces.) However, it is possible to improve the water penetration resistance of an EIFS by using special basecoat adhesives and surface sealers. These can be quite useful at window sills and on the top edges of foam shapes.
Water resistant or waterproof?
The fact that EIFS is not totally waterproof is important when trying to use it below grade. The continuous presence of water against the EIFS lamina tends, over time, to soften it and reduce its water penetration resistance. In addition, below-grade water may literally be "standing water," in which case pressure is exerted on to the lamina, which increases the likelihood of water penetration. In below-grade applications this can be a problem, since it's not uncommon for people to view EIFS as a below-grade waterproofing and insulation system. Unfortunately, that's not what an EIFS is. So, if you are relying on the EIFS to keep water out of your basement, good luck. The ideal solution would be to use a system designed as a below-grade waterproofing system, not EIFS.There are other problems with bringing EIFS below grade. One is that often there is waterproofing coatings already on the foundation wall. This makes it hard for the EIFS to adhere to the wall. This can lead to delamination problems. Using mechanical fasteners will hold the EIFS to the concrete, except for a little problem: the fastener penetrates the waterproofing.
Termites are a big issue in some parts of North America. Bringing EIFS below grade or near grade is an invitation for them to find some place to burrow through the EIFS to get to the wood framing within the wall. Carefully sealing the bottom edge of the EIFS, combined with using metal trim and keeping the EIFS well above grade, helps dissuade the termites from using the EIFS as a highway to the wood substrate. In fact, in some termite-prone areas, the building code requires holding the EIFS 6 inches or more above grade. There are also chemicals which can be topically applied to the foundation and the lamina that are reported to offend termites, as well of grades of EIFS insulation that are impregnated with chemicals that are repellant to termites. As an interesting side note, in talking with termite experts, they tell me that termites actually don't eat EIFS, but rather burrow through it to get to the wood wall framing.
A near-grade application is clearly one of the places where using a double-layer basecoat makes sense. We all know that there is no lack of things that exist near grade that can bump into the EIFS and damage it. From a practical standpoint, the heavy double basecoat need only go as far up the wall as needed to protect those areas actually at risk; there's no need to do the whole building with a heavy-double mesh basecoat. Hence the use of double basecoats near grade actually does not add much to the cost of the overall EIFS installation.
Six feet under
If you absolutely must take the EIFS below grade, here are some things that can improve your chance for success. First, the soil should be dry. In other words, don't try this in areas with mushy soil; a desert is a better bet. Use a really heavy basecoat; thick basecoats have better water penetration resistance. Make sure the area next to the EIFS and below it is well drained by using a drainable back-fill material and by running drains around the foundation. Putting a waterproof coating over the lamina will help increase its water penetration resistance. In Europe they sometimes place cement board sheets or a sacrificial layer of dense foam insulation up against the EIFS to protect it from crushing. Last, make sure the owner and architect are aware that this is a marginal use for the product, so they don't hassle you later.The same "below grade" issues apply when EIFS is used next to sidewalks, roof decks and other areas when the EIFS goes below the adjacent horizontal surfaces. An example frequently seen is a roof deck that uses loose pavers as the walking surface. If the EIFS goes below the pavers, it may end up sitting in water, and actually wicking the water, thereby leading to its eventual deterioration. Further, in freezing climates, the edge of the EIFS may be lifted by the expansion of water when it freezes. This in turn can shear the EIFS off the wall.
As an architect, I'll be the first to admit that it sure looks nice to have the EIFS simply "die" into the ground. It makes for a clean, simple appearance. But considering the various possible problems that could ensue from below grade, it's usually not worth the risk.
