If this is a "damp patch" then PVA will not work because it is soluble ie. it will dissolve in, or on, moisture, creating a slightly more messy situation. I'm not sure what a coating of PVA would be meant to do anyway?
Why not wipe off the "fluffy deposits" with a weak solution of detergent and water, or a drop of bleach and water. Then leave it alone and check it out in say a month's time.
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