From kadulski@direct.ca Thu Oct 30 18:42:14 1997 Date: Thu, 30 Oct 1997 15:34:08 -0800 From: Richard Kadulski To: greenbuilding-digest@crest.org Subject: Re: GBlist: Wraps discussion [The following text is in the "ISO-8859-1" character set] [Your display is set for the "US-ASCII" character set] [Some characters may be displayed incorrectly] John Salmen wrote: "..... Surfactants are primarily a petroleum based product. A polymer with benzene as a bonding agent. Generally a high VOC product. Surfactants attach (or adsorb) to materials and break the surface tension of either water or oil as it contacts the surface. The molecules are polar in nature being highly solvent to water on one end and resistant on the other (so to speak) Surfactants are used daily in the form of synthetic soaps, cosmetic applications, etc." I believe that the term "surfactant" is a more generic term, for any product that reduces the surfacve tension of water (and presumably other liquids). It does not need to be a petroleum based product - many natural organic compounds can qualify. Regular soap is a surfactant - and it is something you can make yourself from natural compouds (I believe rendered fat is a constituent). "In the case of polyolefin materials the surfactant should allow the transmission of water in only one direction. I am curious as to what is happening in reaction to cedar and redwood - my suspicion is that the oils in those woods being dissolved and possibly blocking any vapour movement from the interior." In this case, oils that leach out of the wood would be the surfactants. "What would allow transmission of moisture from the exterior I cannot guess except to say that surfactants are not very well understood. I'm not very scientifically inclined so I would appreciate if someone more chemically minded can complete the story and solve the mystery." Once the contaminated liquid (i.e. one containing the disolved surfactant) is in contact with the polyolefin material or other building paper, the surface tension that otherwise restrains the water from passing through the material, is reduced, and the water gets through. The intent of the surfactant is to break the surface tension of water molecules. If you look closely at a droplet of clean water, the surface tension between the molecules tends to keep it beaded up. If you place a drop of water on a lightly oiled surface (say an oiled or non-stick frying pan, or newly painted surface) you'll note that the water beads up. But if you put a bit of soap into the water, the tension has been lost, and the water will tend to flow rather than bead up. Surfactants affect all kinds of house wrap products. I've done a simple test with Tyvek, Typar, and regular building paper - try it yourself. All you need is two samples each of the various sheet products you want to test, and a bowl for each. (About 12" x 12" should do). shape each one as a boat and place it over a bowl, so that it will hold a bit of clean water. Step 1 Place an equal amount of water into each "boat" and observe what happens over time. (allow at least 3 or 4 hours for this). [The result will likely be no leakage at all through any of the paper products or housewraps.] Step 2 Take the second sample of each of the papers, and set up over a clean bowl as in step 1. Take a quart jug of clean water and put about 2 or 3 drops of dish detergent and mix to create a "contaminated" water sample. Now take an equal amount of this contaminated liquid and put into each of the "boats" and observe what happens. [you will find that the polyolefin products will let most of the water through in less than an hour, while the heavier asphalt building papers will take a couple of hours] How representative is this test? normal test procedures use clean products and clean water, they don't always simulate what happens in the real world. In the real world water that gets through the siding material (be it wood siding or stucco) will not be pure water, but will have absorbed some of the water soluble compounds that are present in the siding materials. It is these contaminants that change the properties of the clean wood, and create the problems, especially when the siding material is in direct contact with the sheet material - which is why the argument is so strong for rainscreen construction where the siding is kept away by deliberately creating a cavity behind. The only thing needed now, for everyone's comfort level, is for some scientists to document and analize what is happening in these cases. That building papers (all kinds) are failing in some climates has been observed with much pain. The home builders in Nova Scotia are actually pressing the authorities to mandate rainscreen construction details as they have observed extensive deterioration of new structures because of moisture penetration into the walls (behind the building paper - including the high-tech polyolefin wraps). ******************************** Richard Kadulski Architect 208 - 1280 Seymour St. Vancouver BC V6B 3N9 Tel/fax: 604-689-1841 "Climate adapted, energy sensitive, sustainable and healthy design." 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