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The Use of Polyurethane Foam Technology in Historic Renovation and Remediation Work

Applications

VI.  How are polyurethane foams processed on-site?

Following is a description of the three on-site processing techniques for walls, roofs, and floors utilized in the case studies below:

 A.  Techniques

1.  Injected, poured, blown-in, or foamed-in-place (FIP)

This application technique is known by several names; basically, it involves injecting a relatively slow, pre-expanded foam system into a closed cavity.  The foam reacts, expands again, and solidifies in the cavity within a few minutes.  The process generates pressure, heat, and vapors.  The result is a rigid, bonded product which fills the entire void.  Properly executed, this ensures a thorough fill and complete bonding to the substrates.  This requires a certain installation technique (small lifts and/or bracing), and fastening of the cavity surfaces in applications where pressure from the expanding foam may distort the finishes.  The heat of the chemical reaction (240 degrees) is useful for quality assurance testing using an infrared camera to verify a complete fill free of voids.  This installation approach requires that the area be warm (usually a minimum of 40 degrees F) before, during, and after the processing and curing periods (24 to 48 hours).  The vapors require proper ventilation or personal respiration equipment to be utilized.

Injecting through slots

Injecting through holes

Comments:  Injecting a closed cavity creates little waste, requires less masking than spray applications, and has minimal personal health issues (airborne particles) for the applicator.  A clean, dry surface will maximize adhesion or bonding.

2.  Spray-applied or sprayed-on

This application involves spraying a hot, fast, atomized foam system onto an open surface (like spray painting).  The foam reacts, expands, and solidifies on the surface in seconds.  This process generates heat, airborne particles, and vapors.  The result is a rigid, bonded product which covers the exposed surface in a continuous coating.  The rapid expansion requires a proper installation technique to make the coating as even as possible; however, the finish will never be perfectly “flat”.  For this reason it is typical to spray-apply an “average thickness” which allows for a certain “plus or minus” tolerance.  Alternately, a “minimum thickness” may be specified. The speed and heat of the chemical reaction also requires that the substrate and ambient temperatures be warm before, during, and after the process to prevent thermal shocking of the finished product during the processing and curing periods.  Various chemical formulations have different temperature requirements, and the foam system must be appropriately chosen for the specific project conditions.  Chemical systems are available for applications as severe as the frozen earth project at Boston’s “Big Dig”.  The particles and vapors require proper ventilation or personal respiration equipment to be utilized.  Masking or protecting finishes from over-spray is required as well.

Spraying open walls- Mariposia Museum

Comments:  The spray operation allows the installation to be a specified R-value in a cavity that is too large for injection due to practical considerations.  If over-spray is not an issue, this technique has the highest productivity and usually the lower per-unit cost.

3. Sealant

This application involves dispensing a medium-fast, pre-expanded foam system onto an open surface or into narrow cracks. This process is not atomized as much as a spray system; therefore, the pattern created is “courser”, but can be varied from a caulk-type bead to a broader fan configuration. The foam reacts, expands (low or high-expansion systems are available), and solidifies on or between the substrate surfaces in seconds.  The process generates heat, fewer and larger airborne particles than spray applications, and vapors.  The result is a rigid, bonded, product which covers small areas of exposed surface or expands to fill narrow cracks.  The expansion requires a proper installation technique to fill a crack level with the plane of the surfaces being sealed; however, the finish will never be perfectly “flat”.  Caution and/or bracing may be required in applications involving window jambs where pressure from the expanding foam may distort the trim if precautionary measures are not taken. This technique requires that the area be warm during the processing and curing periods to assure the quality of the finished product.  Sealant is normally processed in small volumes, and while the vapors may still require ventilation, personal respiration equipment typically is not required.  Masking areas which have permanent finishes, and trimming of excess material which expands out of the narrow cavity, may be required.

Air sealing attic skylight well and mechanical systems Air sealing rigid foam board seams

Comments:  Foam sealant is usually used for detail work in small areas; therefore, the equipment output and the related productivity is much lower than with the injection or spray methods.  Truck-mounted and small-scale portable equipment are available for this technique.

B.  Applications

1.  Walls

  1. Injected walls are filled through holes from the side determined by access or job-site conditions.  Typically, 1" holes are drilled 4' O.C. vertically in each bay. Walls with narrow cavities may require a more frequent pattern of holes.  Holes are drilled in the top corners of each bay unless the bay can be “topped off” from above.  This includes staggered studs unless the stagger space is 2" or more. Bays open at the top to attic spaces can be filled without holes, except for bays under window openings.  Walls enclosing large cavities should have a release material on one side of the wall behind the sheathing if the wall needs to be absolutely flat.  This layer prevents the possibility of thermal shock pulling the sheathing material out of plane.  If this material also acts as a vapor retarder, it can serve to protect the framing from moisture.  Fasteners should have a maximum spacing at all sheet edges of 8 to 12 inches, depending on the sheathing thickness and fastener holding capacity.  Temporary bracing would be required for areas with inadequate fastening.

    Closed-cell polyurethane over masonry and relieving angles - Mariposia Museum Closed-cell polyurethane over masonry - Currier Gallery of Art
  2. Sprayed walls are sprayed from the open side, as determined by access or job-site conditions. This includes building the foam out to the required minimum coverage.  No release material is needed unless drainage planes are required in below-grade applications.  The unfilled space in the framing cavity is available for mechanical system retrofits

  3. Sealed rigid foam board wall applications are possible when sequencing, project conditions, or code issues make the use of sheet goods more cost-effective than open spray applications.  This involves filling an intentional gap left around the perimeter of rigid foam panels or board stock which has been cut and fit in each wall bay.  Sealed rigid foam board applications are done from the open side, as determined by access or job site conditions. The rigid foam board stock should be glued, braced, or fastened in place to prevent the foam sealant from lifting the board away from the sheathing on the closed side of the wall.

2.  Flat ceilings and roof slopes

  1. Injected ceilings and roof slopes are filled through holes from the side determined by access or job-site conditions. Injecting from the open top of the bays is generally faster when conditions permit.  Typically, 1" holes are drilled 2' O.C. in each bay. Holes are drilled in the end corners of each bay.  One side of deep ceiling cavities should have a release material to maintain finish flatness.  The rest of the process is as described in the injected walls section, above.

            

Injected roof slopes - Norman Williams Library Spray-applied slopes at the Essex County Courthouse
  1. Sprayed ceilings are sprayed from the open side (above or below), as determined by access or job-site conditions.  Again, working from the top is generally faster. This involves layering the foam out to the required minimum coverage.  No release material is needed.  When done from above, the top can be vented if required.

  2. Sealed rigid foam board ceiling applications are done from the open side, ideally from above, in a manner similar to the sealed walls approach.

3. Floors

  1. Injected floors are filled through holes from the side determined by access or job-site conditions.  Working from the top is generally faster.  Typically, 1" holes are drilled 2' O.C. horizontally in each bay.  Holes are drilled in the end corners of each bay.  One side of deep floor cavities should have a release material to maintain finish flatness.  The rest of the application is similar to the injected walls.

  2. Spraying floors is done from the open side, as determined by access or job-site conditions.  Again, working from the top is generally faster.  This work involves layering the foam out to the required minimum coverage.

    Over and under floor applications - Vermont History Center
  3. Spray-applied foam can be used under slab-on-grade floors when uneven sub-grades prevent the use of rigid foam board stock insulation. A higher density foam system is typically used to reduce permeability, and a vapor retarder can be positioned on the sub-grade before the installation to increase the resistance to long-term water absorption in wet applications.   The sub-grade should be dry, compacted fill or a concrete sub-slab. The finish will not be perfectly flat, but the finish slab thickness can easily accommodate the variation.

  4. Sealed rigid foam board floor applications are done from the open side in a manner similar to the sealed-walls approach.

C. Sequencing

Project sequencing is generally project dependent, but typically follows normal construction practices.  Project sequencing and preparation for the various installation techniques are too numerous and extensive for this discussion. Information is available on line at:

D. Architectural Specifications

Sample architectural specifications (Section 7) are available on line at:

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