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Community and Q&A

Sulphates in cellulose insulation

gf2011 | Posted in General Questions on

I’m within a few weeks of dense packing the walls of the house I’m building with cellulose.

The installer uses cellulose with a “blend of non-corrosive borate and sulphate fire retardant additives.”

Should I have any concerns about the sulphates? I’m waiting to hear back from the manufacturer about which sulphates are used.

Any other things to look for (or avoid), with respect to cellulose, would be much appreciated.

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  1. Expert Member
    Dana Dorsett | | #1

    The only concern with sulfated fire retardents is what happens when the insulation gets wet, at which point it both stinks, and is highly corrosive to metals (particularly copper, but iron too) , corroding ing plumbing & bare wiring (and sometimes nails & screws) that it may be in contact with. In wall assemblies, if the window flashing is lapped correctly &/or you have decent roof overhangs, the risk is pretty low- maybe a gia-normous roof leak or a plumbing leak could wet it sufficiently to become a problem, but if your wall stackup is decent it's pretty unlikely.

    The worst sulfated cellulose story I've heard of was an antique church in Maine built with clapboards nailed directly to the framing, where the nails rusted out and the building had to be condemned. The fact that it didn't have a proper weather resistant barrier and no air-gaps / capillary breaks between the clapboard & insulation means that even with borate fire retardents the building still would have failed, but it might have taken a decade rather than just two years. With sheathing between the studs & clapboards it would probably still be standing, even with the sulfated fire retardents.

    It's not a big upcharge to insist on "borate only, sulfate free" material. Almost all "stabilized formula" cellulose used for damp sprayed installation is sulfate-free, and works just fine when dry-blown.

    Sulfated fire retardents in insulation materials is explicitly banned in some countries (Australia comes to mind), but SFAIK it's legal everywhere in north America.

    A cheap test for the presence of sulfates in cellulose is to drop a pellet of Drano (sodium hydroxide) into a coffee cup of water, and stir in a heaping tablespoon of the insulation. With your nose 18-24" above the cup you'll know within seconds if you have a sulfated product.

  2. gf2011 | | #2

    Thanks for the very helpful answer Dana.

  3. mackstann | | #3

    From what I recall, all borate cellulose (with no sulfate) is only about 10% more expensive. I would specify it. One less thing to worry about.

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