Measuring Basecoat Thickness
No doubt some of you have been involved with field problems involving leaky EIFS wall assemblies. Please note that I said EIFS wall assemblies, not the EIFS itself. Although the “EIFS” is often blamed as the cause of the leaks, usually it is something at the edge of the EIFS that is actually leaking, like windows, flashings, etc. However, it is possible for an EIFS itself to leak. The often cited reason for the EIFS leaking is the thickness of the basecoat. This article explores how to measure the thicknesses of basecoats so that you can address this claim, if it arises.
There is no doubt that the quality and thickness of an EIFS basecoat affects its waterproofing qualities. A porous basecoat, or one that is super thin, is more likely to let water through it than one that is beefier. However, when the “basecoat thickness” issue rears its head, you need to determine what that thickness is and whether or not it is the source of the problem.
Know the thicknessFirst, it has the finish on its surface. The finish also varies in thickness, and trying to measure both and then subtracting the finish thickness is difficult in terms of accuracy. Also, the finish is not the primary waterproofing part of the EIFS lamina. Thus its contribution to water penetration resistance is minimal.
Second, the basecoat is on the wall. I have yet to find an accurate way of measuring basecoat thickness on the wall; it’s simply an awkward thing to try to do on a job site. Thus samples must be removed. This means making a hole in the EIFS wall, which must then be patched. Assuming that the building owner will permit doing so, the question arises as to how to do the removal process. While it is possible to cut through the lamina and peel off the lamina (without the insulation) in a sheet, this often cracks and otherwise ruins the lamina. Normally, the easy way is to just cut out a chunk of EIFS (including the insulation) back to the substrate. What you now have to work with is a hunk of foam with an EIFS lamina on it. What do you do now?
Taking the right samplesThe first thing is to remove the finish. Finishes soften a bit when wet, so soaking the finish in water, and then scraping off the finish, is one way to proceed. Another is to grind off the finish. Either way, the key is not to damage the basecoat, as measurements of basecoat thickness are performed with a micrometer and are done to an accuracy level of at least 1/100 of an inch.
To remove the insulation, you can cut it away with a hot wire to within 1/32 of an inch, and then hand sand away the remaining insulation to expose the back side of the basecoat. With the piece of basecoat in hand, you can now start measuring it. But the key question is not only how to measure it, but also where.
For example, the thickness of the reinforcing mesh determines the minimum possible thickness of a basecoat. Of course, the mesh should be fully embedded in basecoat adhesive, so the basecoat should be quite a bit thicker than the mesh itself. However, it is normal for the reinforcing mesh in a basecoat to be lapped where the pieces come together. This automatically doubles the minimum possible thickness in the lapped areas. Furthermore, where the edge of the EIFS back wrapped and the mesh is lapped, you automatically have a basecoat that is at least three times the thickness of the mesh.
What does this tell you? First, it makes a difference where you take the samples. It’s very important to precisely document where the samples were removed. This means making a drawing of the building’s elevations and showing the sample removal locations in relation to fixed points, such as the corners of windows. Second, that basecoats can and do vary considerably in thickness. This is completely normal and unavoidable in a handmade, site-installed product like EIFS. Third, it tells you that when taking samples, you need to take a lot of them to be sure that they are representative of what exists throughout a building.
Here’s a typical scenario: Suppose you have a building with EIFS walls that are leaking. During the “why is it leaking?” forensic process, the inspector takes a handful of samples. Based on this small sampling, the conclusion is drawn that the basecoat is thin throughout and that the whole EIFS must be removed. Excuse me, but that’s a stretch. In order to draw such a radical (and expensive) conclusion, you would hope that enough samples are taken so it is clear that removing the whole EIFS is necessary. For example, perhaps only one area is really too thin. Why not just fix the “too thin” area and leave the rest alone?
Once you have the basecoat samples in hand, in addition to measuring their thickness, you can also now easily measure their resistance to water penetration. A number of test methods exist for doing so and some are easy enough to do yourself.
Here’s a do-it-in-your-kitchen method that involves gluing a tube to the outside of a basecoat. The tube could be a piece of 1 1/2-inch PVC pipe a couple of inches long. Glue it using hot melt adhesive. Place the basecoat sample horizontally over a dish and put water into the tube. The deeper the water, the more pressure it exerts on the basecoat. Let the sample sit there for awhile and look at the under side of the basecoat. If water is getting through in a big way it will be dripping, but if water is merely being absorbed, the basecoat will be damp. Neither of these is what you want; the basecoat should remain dry. It should not let water pass through it, nor should it become damp. Clearly, water passing through is bad, but being damp is bad, too. It’s bad because if the water in the basecoat freezes (like during a sudden temperature drop), the expansion of the water can pull apart the basecoat.
Please keep in mind that the above description is hardly an all-encompassing scientific treatise, but it does show the principle. To stand up in court, such tests need to be done under controlled conditions. Frequently, additional measurements are taken, such as the rate of water throughput (if any) and the weight gain of the basecoat. Tests of this basic type are used throughout the world by building code organizations to confirm the waterproofness of the EIFS lamina.
So when someone hassles you about the basecoat’s being too thin and says it’s the cause of all the ills on the building, make sure you make him or her prove the point by requiring an adequate number of samples and measuring them carefully.