I have seen you quoted as saying that you do not recommend the use of wet spray applied cellulose insulation (WSACI) in the sidewalls of new houses or its use in most circumstances.-Anon 

            That is correct.  I have said it many times and I am even more convinced that WSACI applications may pose an undue risk of mold infestation and subsequent mold exposure to building occupants.

            One may ask what is wet spray-applied cellulose insulation?  Is it the same stuff that I have in my attic?  Is it dangerous?

            Though wet applied and loose-fill insulation (commonly used as attic insulation) are for the most part made using similar materials (ground up newspapers and boric acid/borates), they differ in that the former is blown into attic cavities under dry conditions and the latter is literally soaked with water (with added adhesive) before it is blown into wall cavities.

 (Click to enlarge). Why is there a concern whether it is wet or dry?  As many know cellulose when wet makes a good  medium that a variety of mold species can infest and use for food.  Mold can only grow on cellulose-containing materials if they are wet or have a relatively  high moisture content.  As such, soaking ground up newspaper materials and spraying the mixture into the sidewalls of one’s new house is a pretty dumb idea, right?  On the surface that appears to be the case.  However, cellulose insulation is mixed with boric acid and polyborates that serve as fire retardants and mold inhibitors. Octoborates are commonly used in mold-inhibiting paints, and I have recommended their use for remediating mold-infested attic and crawlspace timbers.

            Cellulose insulation manufacturers and installers maintain that WSACI when applied properly does not pose a mold infestation/exposure risk any greater than the structural materials that it comes into contact with in wall cavities.

            One of the issues associated with the use of WSACI is drying time; that is, how long should it be allowed to dry before the wall is closed up with drywall?  There are no specific guidelines on this.  In theory and in practice a contractor could dry wall up a WSACI insulated wall cavity within 24-48 hours after installation. As such, it could be quite moist for some time thereafter, weeks and even months.

            In part to deal with this potential problem, installers and contractors are strongly advised to not use an internal vapor barrier as is common practice with other types of sidewall insulation.

            As an environmental scientist, the thought of putting wet cellulose, a superb mold growth medium into the sidewalls of a new house is disquieting.  On the other hand borates are excellent mold-inhibiting biocides.  Should one dismiss the former because of the latter?  Should one accept the claims of manufacturers that WSACI is safe because of a reportedly high borate content  that supposedly precludes a mold-infestation problem? 

            Actually in the  methodology (ASTM C1149-02,) used by  manufacturers of WSACI and loose fill insulation, the test is a qualitative one that seeks to determine that mold growth on WSACI will not be any greater than that of wood materials in the walls or drywall on becoming wet.  It is not intended to show that mold will not grow in/on the WSACI. 

            Can WSACI grow mold and if it does, can it be extensive enough to pose an undue exposure risk to those who occupy houses with WSACI?  The answer to both questions I believe is yes. The question then becomes what is the nature of such infestations and how serious may they be? Are there a few houses affected or  many?

            These issues will be addressed in the next two postings with a focus on several case histories.

            Readers in the states of Indiana, Ohio, Michigan, Illinois, or Kentucky who may be experiencing WSACI-related mold problems are welcome to contact the author at 00tjgodish@bsu.edu as he is wishes to identify WSACI homes for possible investigation.