hello

we have a second floor condo. we pulled up the carpet and found dusty concrete it appears to be sone kind of sandy dusty floor leveler ontop of concrete slab. The floor is level, but any walking on it creates dust. I tried to shop vac up, then realize it just continues to come up just by walking on it.

questions

we want to install smartcore ultra..because of a specific color and it's in stock

1/ do we need a vapor barrier because we are installing on concrete? I assume no because we are on the second floor and there is no moisture. a sales rep told us there is some gas that comes up from concrete and we still need a vapor barrier?? I think he said boron gas???

2/ because we are worried about noise protruding downwards to the condo owner below, would smartcore ultra (with padding attached to each plank) sufficient? when we pulled up the carpet and walked on the concrete, the owner claim to have noticed.

3/ if we install smartcore ultra, with extra underlayment , something like floor comfort, designed to go under vinyl planks, would this be ok to do? I get mixed opinions from "never do it, to it's perfectly fine from different lowes sales reps.. the manufacture installation instructions and warranty mentions NOTHING ABOUT UNDERLAYMENT... completely absent

4/ we prefer the ultra. but considering installing the entry level smartcore (no padding attached to the planks) and install easygo or floor comfort underneath as a possible better option. we prefer the wider plank ultra though.

lowes employees from multiple stores are either clueless, firm on NO underlayment under ultra, or "we sell 4 different levels of vinlyplank underlayment that goes under any of our products" web searches tell me not to install any underlayment under floors with padding.

I hope someone can clear this up