My wife and I are installing new flooring, which first involved tearing up what's already there.
First I was horrified by how much dirt was underneath the carpet padding (we have dogs) from ~6y of use.
Then we started tearing up the tongue and groove hardwood under that, which was installed (naildown) in the 1960s, and it too had a ton of dirt underneath it, even in areas with virtually no damage.
Apparently the only way to get a deep clean is to strip down to the subfloor.
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