Know Your CMU Foam Insulation

Words: Dan Kamys

Air Barriers

  For more than 30 years, concrete blocks have been insulated by filling the cores with foam-in-place insulation. Many who see the cores of concrete block insulated for the first time, no matter what brand, say it looks like white shaving cream and notice that it begins its initial set in about 30 seconds. Most of these foams are produced by three different components that include a liquid resin, a foaming agent, and air. At the gun, the bubbles created by the foaming agent act as the structure for the foam inside the gun’s chamber. At this point, they are coated with the liquid resin, and then pushed out of the gun into the wall by the air pressure. Once the resin and foaming agent meet, the setting process begins to occur – but not too quickly – allowing the fresh foam to be at a free flowing state. It’s important to note that, if the ratios are off for any of the three components, the foam will come out either too heavy and wet, or too light and fragile. Any good installer should test the quality of the foam before beginning to pump it into the wall, and will have third-party testing to support the product performance claims. The CMU core insulation described above is different from the other types of foam insulation in the market. Two major distinctions exist between CMU foam insulation for the cores and spray-applied, foam-in-place insulation for walls or ceilings. One of these distinctions is that CMU core insulation comes out of the gun/hose pre-expanded, and moves into voids via air pressure from a single point of injection. Spray polyurethane foams are “directed into place” by spraying directly to the surface to be covered, and then chemically expands into voids. The chemical expansion, after it is sprayed, releases heat until it cures. Injected CMU foam does not create heat as it cures. The other big difference is the safety equipment needed by the installer, who is using the product. Injection CMU foam insulation installers do not need to wear fresh-air masks and skin protection suits while installing, since the chemical reactions that create the expansion and curing of the product are completely different. Most well-known suppliers for CMU foam have a non-toxic formulation. CMU foam is specified worldwide for the high-performance and quick installation of the product. Testing Three important performance-supporting, third-party tests should always be reviewed to assure your foam installer truly is meeting specifications required by the architect:
  1. ASTM C518. This is an “absolute method” for determining the R-value per inch of foam. Another ASTM test for R-value under ASTM C177 exists, but this is an “estimate test,” according to ASTM and, in case of dispute, ASTM C518 should be the preferred method.
  2. ASTM E84. This tests the surface-burning characteristic of the foam and can classify them by Class 1, 2, or 3. Class 1 is the best classification here, and this test also has a code-approved UL equal that does not add or take away from the Class 1 rating from ASTM.
  3. ASTM E119. This is the fire test report that will show the hour rating for foam in a specific wall design with or without structural grout. No brand of CMU foam exists in the market place that can make a 2-hour CMU wall a 4-hour CMU wall without the help of structural grout or thicker-than-average CMU face shells. In fact, the grout and/or thicker face shells are the cause of the increased fire rating, not the foam. Be sure to view the specific wall design in the test and all the pages of the third-party testing. Don’t just take sales literature claims as fact.
Proper installation When a foam installer is sub-contracted, the mason and the general contractor should have an idea of proper installation to insure complete fill, and to insure that the masonry is not harmed in any way. The only way foam could affect the look of the masonry is if the ratios are off, and the foam turns into more of a liquid than foam. This liquid, depending on which component is off ratio, could bleed out to leave a sticky, “wet” or stained look on the block. The installer should be inspecting for proper foam consistency in every cell, and noticing immediately if the ratios get off from manufactures specifications. The following steps insure a proper CMU foam fill job has occurred:
  1. The installer does a foam quality test before pumping into the wall.
  2. Holes are drilled in no less than every other cell between horizontal bond beams.
  3. When starting to foam fill, a hole is drilled at the top of the wall at the first few cells to get an average time of complete fill.
  4. Fill the cell until foam begins to come out the following hole, then the hole is plugged temporarily until foam can be seen coming into the third cell.
  5. Move to the third hole, and repeat Step 4, verifying consistent fill time for each cell.
  6. Patch the drilled holes.
Retrofit with foam Retrofitting older homes and buildings with CMU foam insulation is growing as owners want to decrease their energy bills and make the inside environment more comfortable. CMU foam can be injected into preexisting concrete blocks or air space cavities behind veneers. This product also is used for its sound reduction quality. Many older schools have found use in using CMU foam fill around band rooms, mechanical rooms, and even the restrooms. If you are looking for foam to retrofit stud walls, specific retro foams are available in the market for that. It is not recommended by many manufactures to use CMU foam fill for stud wall applications. Become an installer There are opportunities with certain manufactures to become a certified installer. By adding this scope of work to your Division 4 bids and doing the installations yourself, you can increase your profits on each job that has CMU foam fill.
Christopher Liner is national executive director of Polymaster. He can be reached at 800-580-3626 or
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