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News / Past Articles

EIFS Drainage Test

When EIFS with drainage first appeared on the market in the Œ90s, all sorts of ways of providing the drainage capability were initially tried. Some were pretty straightforward and are still used, while others were unusual and quickly fell into disuse. All EIFS with drainage share a few basic design features. This includes some type if weather-resistive barrier over the substrate, as well as some way of creating a drainage cavity. The weather-resistive barrier usually takes the form of a sheet material, such as building paper, or a liquid-applied coating. The cavity can be created by such methods as using thick layers of attachment adhesive to make the EIFS foam stand off of the surface, by using grooved foam, by adding various spacer materials, and so on.

Some of these drainage systems use fewer materials and less labor, and hence are not as costly as others. This caused the competitive spirit to kick in, with each EIFS producer hailing the virtues of their way of doing drainage. This competition also raised the issue as to whether or not some of these systems drained or not. For instance, do barrier EIFS actually drain? Yes, but to what extent.

What the ASTM says

Several years ago, ASTM¹s E6.58 committee on EIF took on the project of developing a test method that determines the extent to which an EIFS with drainage actually drains.

The first question that comes up is, ³What do you mean by Œdrain¹?² Some drainage designs allow rapid draining of water. Some drain slowly. Some also retain water for quite a while but eventually do dry out. For example, if one applies building paper onto a sheathing substrate, and attaches flat EIFS insulation to the substrate using mechanical fasteners, it will drain-well, sort of. This is despite the fact that the foam is directly against the substrate. The question thus becomes one of efficiency and time. The question about the drain-ability of an EIFS then becomes ³how fast?² and ³how much water is left?²

The ASTM drainage test is a system test, that is, it tests the EIFS as part of an EIFS wall mock-up. It does not test individual EIFS components but rather an EIFS mounted on a substrate. The test does not include window openings, which is a whole different type of test. In other words, what we are trying to find out is how the EIFS itself fares regarding draining and not about the limitless number of other wall components that can make up a complete wall system. By the way, ASTM is also working on a wall assembly test for EIFS, which does incorporate openings of various types, so that the effectiveness of flashings, windows and so on, can be evaluated.

The new drainage test uses a 4-foot-wide-by 8-foot-tall panel. The panel uses typical wood or metal studs to make a frame, to which some type of sheathing is applied. The EIFS with drainage is then applied over the sheathing. This cladding system includes a weather resistive barrier, such as building paper, some form of drainage cavity and the EIFS itself.

A horizontal slot is cut through the EIFS near the top of the panel. The slot goes all the way back to the weather resistant barrier that is on top of the substrate. The bottom of the panel is treated in whatever way a real wall would be treated. This could include the use of flashings, or extruded trim with holes punched in it, or simply left open. The point is that the water needs a way to get out. It goes without saying that some method of finishing off the bottom of the EIFS is needed for several reasons.

One is obviously so that it looks reasonable, such as at the head of a windows. Another is so that the water can freely leave the wall and not back up within the wall. Clearly, the usual method of finishing the edge of an EIFS, by back wrapping, will not work, as the wall would fill up with water. Conversely, a wide-open bottom edge would look bad, and would also be an invitation for termites to enter the wall.

During the test, water is sprayed into the cavity via the slot in a controlled manner and is allowed to migrate downward and exit through the bottom into a trough. The rate at which the water collects in the trough is a function of how freely the water moves through the system. The amount of water that is applied into the slot, vs. that which ends up in the trough, is the amount retained in the EIFS test specimen. The test panel is weighed before and after the test to determine how much water remains in the wall.

This test is mostly useful in a laboratory for developing EIFS with drainage products. It could also be used as a regulatory tool, provided someone decided what kinds of numbers are needed in terms of the test results. It is really not well suited for testing in-place EIFS walls, although I suppose it would be possible, although difficult, to stimulate the as-built conditions of a wall in question.

What¹s good?

The bigger question, once a reasonable method for testing drainage has been agreed upon is, ³What is good enough?² The jury is still out on that question. ³Good enough,² in terms of being adequate to serve its function and produce a ³good wall,² depends on the circumstances. The baking heat of a desert building site is different from a perpetually damp place like the Pacific Northwest, where I live. In the former case, a thunderstorm might cause a lot of water to get into the EIFS Œ drainage system due to improperly performing flashings and other wall details, but the relentless heat will quickly dry out whatever happens to be left inside the wall. Also, such downpours are rare and short in duration. In the Northwest case, continuous drizzle would keep an EIFS¹ drainage system wet for extended periods, especially because the dampness of the climate does not promote drying because the air is moist for months on end. This matter of what constitutes adequate performance, in terms of the numbers generated from this test, is a subject worth of additional research. This test method, which was developed by a consensus process with the input of dozens of people, can be used for this type of research.

This test was developed with the assistance of a number of companies in the EIFS business. The test is the result of several approaches to doing such a test. In other words, various ways of applying and collecting the water have been tried. This test has been proven a number of times, and is simple and predictable. The test has proven a number of things, many of which are obvious, but heretofore unproven, such as:

* Bigger drainage cavities drain faster.
* Vertical ribbons of adhesive are effective in creating drainage channels. Conversely, horizontal ribbons do not work well.
* Even mounting the foam directly against the weather resistive barrier does drain to an extent, but some water is retained between the foam and the weather resistive barrier.
* EIFS insulation having vertical grooves on its backside drains well.

It seems to me that what is desirable, in terms of the performance of an EIFS with drainage, is one that drains fast and dries quickly. This hair splitting dialogue about systems that drain marginally is avoiding the real question, namely, having a wall that stays dry all the time. In particular, the idea of fugitive moisture lurking in the drainage systems, and having unknown effects on the wall, is not a smart concept. For instance, consider the effects of moisture on
metal mechanical fastener screws, or that of prolonged moisture on adhesives that hold the foam onto the wall.

Conversely, it¹s not clear to me that drainage is needed at all in certain types of EIFS walls. Take, for instance, prefabricated EIFS panels on commercial buildings that have no openings and are simply one big continuous frame covered with EIFS and sheathing. Adding drainage to these types of EIFS walls is a nightmare, as the prefabricated nature of the construction makes incorporating the drainage difficult. For instance, how do you marry the drainage system within the panel to the flashings at the panels¹ edges? It also raises the question of how the water is supposed to enter the wall in the first place, considering that the EIFS basecoat is bonded to the edge of the panel frame, and not back wrapped.

To my mind, the real key to EIFS is drainage is not the drainage in the field of the wall. Rather, it¹s the proper design and execution of the EIFS at its perimeter. This maxim holds for EIFS with drainage and barrier systems. Carefully designed and installed, it¹s the capability of the wall to capture and immediately route leakage water to the outside that makes the wall work, not routing it into some circuitous drainage system and hoping it relieves itself to the outside somewhere below.

In the end, the real solutions to the pervasive wet wall problems of the construction industry are walls that stay dry because the whole wall works, not because an EIFS happens to have a drainage system. The decades of successful performance of barrier EIFS is a testament to this fact. Drainage is an add-on feature for EIFS, and should not be relied-upon to make up for the inadequacy of the rest of the wall. The sooner the design and contracting community gets this fact into their heads, the sooner there will be a lot less problems with walls of all types. Robert Thomas, president of CMD Associates in Seattle, is a nationally known EIFS consultant and author of the ³EIFS Design Handbook² and the ³EIFS New Construction Inspection Manual.²

Courtesy of Walls & Ceilings


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