The Finish Line: Unusual Substrates
The vast majority of EIFS is applied over a handful of substrates, namely, concrete, cinder block, brick, gypsum-based sheathings, various mineral boards, OSB and plywood. Once in a while, and especially on retrofit applications, the substrate is some odd material that is difficult to fasten to. There is almost always a way to work with unusual substrates and get the EIFS properly attached. This month’s column will give a number of approaches to dealing with specific situations.
PaintAdhering to paint is risky, as EIFS attachment adhesives will stick to certain types of paints and not to others. One sure fire way to get good attachment is to use mechanical fasteners, but the cost, reduced holding power (compared to adhesives), and the inability to adjust the flatness of the outside surface can point to using adhesives. But how? You can often remove the paint by sandblasting or water blasting, but in some cases this is impractical, such as on a hospital retrofit where patients and staff are in the building all the time.
It’s common, when attempting to bond to existing paint, to do a test patch of the EIFS adhesive to see how good the bond is. Be careful. The normal practice is to simply prepare the adhesive (one may want to try several types) and apply a “blob” of it to various parts of the building. Let it cure, and then take a chisel to it to see how well bonded it really is. If the surface needs to be cleaned to get good adhesion, make sure to do that as part of the test and when doing the job. When attaching the foam over paint, examine the surface carefully:
• What may appear to be the same paint on all sides of the building may actually be different types of paint of the same color, some which may bond and some which may not.
• If it is an old building, there may be multiple layers of paint, some of which are well bonded to one another, while others may not be. The layers of paint are like the links of a chain, and the weakest link determines the strength of the whole chain of paint layers.
• The degree to which the paint has weathered on any particular wall may depend on its location in regards to the sun. In the northern hemisphere, south and west walls tend to get the most sunlight, which can cause chalking of the surface, which inhibits bonding.
• With each painted surface that you want to bond directly to, at the very least, clean the surface thoroughly. This is an essential step.
The preferred process is to remove the paint or mechanically attach the foam. I’ve seen numerous attempts to bond to painted surfaces, and despite doing lots of adhesion tests, the adhesives fail. A really wild true example was the entire elevation of a tilt-up concrete, windowless warehouse–several hundred feet long and three stories high. The entire elevation came off in one gigantic piece of EIFS, and was lying on the ground intact, next to the original painted wall.
Metal LathOne of the best ways to get a good bond on a wide range of unusual substrates is to fasten metal lath to its surface. The EIFS adhesive keys into the lath, and also bonds somewhat to the substrate wall itself. This gives a very strong attachment, and can also provide a bit of drainage capability behind the foam layer. The lath is attached using screws, shot fasteners, or nails.
In Europe they have an interesting way of mounting lath to masonry or concrete. They use a power tool that shoots short pieces of wire (about the diameter of a pencil lead and a few inches long) directly into the concrete; no hole-drilling is needed. These wires protrude out of the wall a few inches, and are spaced roughly six to eight inches on center. The lath is impaled on the wires, and the wire is bent over and cinches to the lath in place. It’s a slick system.
Clapboard SidingIt’s not unusual to use EIFS to give an old wood building a modern facelift and to achieve better energy efficiency. A common residential siding is wood clapboard. Sheathing can be placed directly on the wood (it rides on the ridges of the boards) and nailed or screwed into the clapboard. One can also stretch lightweight, flat galvanized expanded metal lath over the clapboard, and staple or nail the lath to the thick end of the boards.
Fluted BlockThis type of block usually has flutes that are a couple of inches on center. It’s an easy matter to apply the attachment adhesive to the flutes, and then stick the foam board directly to the adhesive.
StuccoIf the stucco is smooth and unpainted, one can usually bond directly to it, but there should be a test patch first. Sometimes stucco’s texture is too rough, or has many layers of paint. In that case, mechanically attaching metal lath is a more positive approach. Stucco is structural enough that such a technique is reliable.
Foundation WallsNear grade, waterproofing sometimes gets applied up and onto areas that are supposed to be covered with EIFS. Thus, sometimes the EIFS is applied to raw concrete at foundations, but also over waterproofing because the waterproofing is already in place by the time an EIFS contractor starts his work. The EIFS adhesive will not bond properly to the waterproofing, so rather than trying to remove the coating, it’s easier to mechanically fasten the lower courses of foam boards and leave the waterproofing as is.
Curved WallsTo allow the foam to follow the curved substrate, sometimes small slices, called kerf cuts, are made in the back of the foam to allow the foam to be warped. Mechanical fasteners are used too, to clamp the warped foam down while the adhesive sets. To avoid the work of making millions of kerf cuts, I’ve also seen multiple thin layers of foam warped and built-up in thickness, rather than kerf-cutting a single thick piece.
MetalEIFS adhesives do not adhere well to metal. Adhesives also do not adhere well to various paints used on sheet metal and extrusions. If the metal is in the form of curtainwall or windows with multiple window panes and frames, sheathing can be attached directly into the metal framing, providing a continuous substrate. This is somewhat like boarding up your windows for a hurricane. Similarly, metal lath, as described above, can be stretched across the frame, and attached with screws.
If the metal is sheet metal, such as corrugated siding used on industrial buildings, the profile of the metal determines what method can be used. For example:
• If the corrugations are closely spaced, metal lath can be screwed into the sheet metal at the high points, or sheathing can be placed over the sheet metal and screwed into the sheet metal.
• If the flutes or seams are widely spaced, there may be problems with the lath or sheathing flexing too much. An example would be a standing seam roof with wide sheet metal panels. A subframe of Z-shaped girts or hat shapes can be fastened across the high points, and then sheathing is attached to the subframe, as shown in the illustration accompanying this column.
• When covering corrugated siding, it’s a good idea to check the deflection of the metal. Some of these lightweight walls are quite flexible, so much so that the EIFS could be overflexed by the wind, resulting in cracking.
Glass BlockEIFS can be attached to glass block by anchoring metal lath into the block’s mortar joints and applying the EIFS over the lath with an adhesive. Another solution is to use a bulk caulking gun and run strips of adhesive all over the mortar joints, then press the foam into the wet adhesive.
The Finish LineThere’s almost always some way to get the foam layer attached to virtually any kind of wall. Sometimes it requires some creativity. This is where the EIFS producers come into play. Give them a call. They see countless ways of using their products, and by asking, you may be given some information about some unusual method of attachment, that has been used for years but is not widely-known.
The most robust attachment system I’ve ever seen was a prefab panel system. The frame was 6-inches deep, 12-gauge brake-formed steel at 12 inches on center, which was dip-galvanized after welding (like a boat trailer). Urethane structural adhesive and screws with washers were used to attach 3/4-inch cement board sheathing to the substrate. Metal lath was screwed through the sheathing into the studs, and the EIFS foam was attached with a structural adhesive (not a normal EIFS type adhesive). The base coat was reinforced with Kevlar instead of fiberglass. Needless to say, this was EIFS on steroids. We proof tested a mockup of this “Schwarzenegger Wall” to over 300 pounds per square foot wind pressure, and it didn’t even creak. This mega panel was for a high-rise office in a typhoon area, and the owner was known for his paranoia regarding wind storms.