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eric himmer
Posted: Sep 28, 2008 09:05 AM
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Foam Shrinkage
Wondering whether water-blown closed-cell foam is more susceptible to shrinkage than a 245/solvent blown closed-cell foam. We and a few competitors have experienced instances of shrinkage using the water-blown foam. We are trying to figure out what factors might be to blame. It appears that the water-blown foam creates a much higher temperature level of exotherm than the 245 we have used and theorize that the added temperature results in increase contraction when cooling. Sometimes the shrinkage sometimes occurs a few days later or up to 3 months after application. The gauges seem to be running fine, filters checked every day, and moisture content of wood under 18% (at least everywhere we check). Please let us know your opinion of this theory and your opinion of water-blown closed-cell foam in terms of performance, workability, long term stability, etc. Thanks. |
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mason
Posted: Sep 28, 2008 09:27 AM
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I have personally observed shrinkage of closed cell foam in both 245 fa blends and pure water blown sysytems. All applications were sprayed in lift thickness greater than 3 inches. There are many factors that can affect the dimensional stability of a given foam formula, type of surfactants, blowing agents, how well the resin can blend with the other ingredients, storage temperature and shelf life. All sprayfoam systems (open and closed cell foam) will expand and shrink depending on the climate and this is measured by a humid aging test. The data is reported in percent change in a linear direction or as a total volume change. The test procedure exposes a sample to 97% humidty or greater at a temperature of 158 degrees F for a period of 14 days. Usually the sample gets larger and the change is reported. ASTM C 1029 provides dimensional stability numbers for closed cell SPF that you can compare your suppliers foam data sheet to. A rule of thumb, higher the density, the better the dimensional stability. In cold environments where freezing temperatures are common for months at a time it is better to go with a minimum density around 2 to 2.2 pcf. follow the manufacturer's recommedation for heat, pressure, mixing, storage and pass thickness. To be safe, the following techniques can minimize the potential for shrinkage. 1. Spray a 1/2 to 3/4 inch "picture frame" lift first. 2. Wait 10 miutes minimum between lifts (or longer if your manufacturer recommends it) 3. Spray in lift thickness of 1 to 2 inches, no greater 4. When spraying mutliple lifts of foam you may have to wait longer between the final lifts of foam. Try to keep the exothermic heat of the foam to less than 250 degrees f. (use a thermometer to determine how hot your foam gets in the center of the pass) If you still have shrinkage after using these techniques, contact your supplier to obtain some help. Be sure to keep track on a daily job log, job site conditions, including temperature, humidity, moisture content of wood, proportioner settings (heat, pressure) any anomalies during spraying, quantity, yield, and keep a few samples to send to a lab for analysis, |
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Circle-D
Posted: Oct 05, 2008 10:49 PM
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With all that said, is the water blown closed cell foams more susceptible to shrinkage than the 245 blown closed cell foams? |
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mason
Posted: Oct 06, 2008 08:00 AM
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It is formula dependent. Period. |
