I just bought and moved into a house in central Mass that was built in 1960. I bought it from the original owners (who moved to a retirement community) and it was in "original condition" (avocado toilet/sinks/bathtubs, etc). The basement is divided into three areas: the workshop (huge, plain concrete floors) and the finished "gameroom" that was 1/3 painted concrete overlayed with Astroturf and 2/3 original vinyl/linoleum tile glued directly to the concrete. I just spent the day removing all of the carpet (taped down) and tiles (glued) and now have a question: what is this white powder, 'cause I know its not coke!

Before you say, "Well, its efflorescence, of course", let me clarify. There is no white powder on any of the floor of the workshop and RARE patches on the walls of workshop (workshop area is a big "C" around the gameroom). There is no powder on any of the gameroom walls (painted concrete, unpainted in rare areas). There was no powder under the carpet (where the floor had been painted). There was only powder that collected in about half of the grooves in between the tiles(enough to easily scrape up into your hands), but it was not all over the tiled area. Made it very easy to lift up the tiles, whatever it is.

We tested the powder (geeky scientists) and it dissolves easily in water, but does not bubble or foam when undilated vinegar is dripped onto it. After handling it, your hands feel smooth after washing them. I did not taste it. No odor. My spouse thinks its detergent from them mopping the tiles. I think its efflorescence.

The basement does NOT have a sump pump and, per the owners, has never flooded (and I actually believe them). Musty smell, but not too bad (remember, fifty years without a renovation - 60's tile...UGH).

So, here are my questions:

1. Is this efflorescence?
   
2. How should I clean it (other than sweeping)?
   
3. How should I "seal" the bare concrete floor? Paint seemed to do well on one part... Kilz?
   
4. Any recommendations for brands of carpet tiles? (Flor, etc?)

Thanks! And hi to anyone who remembers me from the Ficus and Citrus forums!