Speaking of blown in.....does any one out there have any knowledge about rodents moving in and nesting in cellulose with borates? Any one ever take apart an old job and find critters in borate cellulose?..........terry- The Practical House

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Can't say that I have, can't say that I haven't for certain - but with 100's of diffrent types of borates and not all of them are designed for pests...

borates are used predominately as a pesticide for termites, bugs, ants, stuff like that it will kill them if they ingest it. As boric acid It is used as a fire retardant in cellulose. the cellulose blow I used last has about  20% borates in it.

My question is not; is not- will kill mice or rats, because there is no reason for them to be eating it, but...... would/does it act as an irritant to their eyes and lungs and that factor keeps them from setting up shop in it.

I also know there different proportions of borates mixed in with cellulose as well as other compounds to act as fire retardant, which makes the answer to my question a little more complex, but the question remains does any one actually know- not theory, or I think, or I believe, but know, or have examples of how rodents will not nest in borate treated cellulose?

BTW- There are not 100s of diff types of borates. Borates originate from the element Boron which is pulled out of the ground in diff compounds- a few if I recall.

In the 7 years i spent crawling in attics on a daily basis, an attic with cellulose has never had evidence of rodents and I live in Minnesota where critters will do anything to stay warm!

Thanks Chad, this is just the kind of testimony I was looking for. After posting this question on several web sites, I have gotten theory and probabilities but never actual case studies. How about wall assemblies- ever seen rodents in cellulose there? Any one else have any cellulose/rodent war stories?


In cellulose - yes, as for borate treated as I said I can't be positive (hard to know exactly what was installed).

Basically if the air sealing work is done, chases closed, and the HO keeps up with regular cleaning, maintenance & humidity levels one shouldn't have an issue with any product used there, especially one with borates

Terry, I have never seen it. I took apart a house with a badly leaking roof, the wing wall that was uninsulated had a 6' tall bees nest with 1000's of bees, the next bay over was dense-packed cellulose and had 0 bees.


In New England, I've never opened up a fiberglass-insulated wall that didn't have evidence of mice infestation, but have seen no evidence of mice in cellulose (which is all I've used for the past 20 years for new construction). If I have to use batts on a renovation project, I prefer borate-treated recycled cotton blue jean batts (though they're awfully hard to cut).

I've talked this issue over with the technical manager for National Fiber, New England's largest cellulose manufacturer (CelPak), and he's not sure whether it's the borates that irritate rodents or just the dessicating quality of the cellulose. But he agrees that mice and cellulose just don't mix.


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