Also known astodphodrenovationalteration
Mixing a handful to about a kilo of a chosen soil into the flooring raises the energy for a purpose: cowshed, mountain or elephant-stable soil for peace, yellow soil for business, white or yellow soil for homes, and pilgrimage or river soil for temples.
Flooring of the house, factory or temple
Yes, advise removing it: the North is Kuber's place, and keeping filth at the place of wealth is like putting dirt in the mouth, so wealth cannot grow. After any demolition do a Vastu pooja; even a short one is enough, offering 45 small pieces of gud to the 45 devtas or invoking the nine lords with Bho Indra Vastu Dev Vastu Shanti Kuru Kuru and so on for each direction, with Brahma at the centre.
No. Do it at bhoomi poojan or shilanyas, when the first slab is laid, when the main door frame is installed and on griha pravesh; the start of construction and griha pravesh are essential. Also do it after a renovation in which walls are broken, for a marriage, the start of a job or business and the birth of a child, and once a year on a swayam siddh muhurta such as Akha Teej or Gudi Padwa for a year of happiness and peace.