Is the floor guy at Home Depot who sold me the blue padding to put down under my floating engineered floor correct that this blue padding will also act as a vapor barrior, and nothing else is needed? I was thinking about putting plastic down first.

When you lay the blue padding down, which is aprox 3 or 4ft wide, and you lay the next run along side it, should you tape the 2 pieces together with duct tape?

Sg:

I'm assuming you have a concrete floor this is going on? I would have to think the Home Depot people would know the two in one type pading/underlayment is needed in this situation? If it's a wood subfloor only the padding itself is needed--and yes tape it together. Duct tape works fine but I found it doesn't stick very well.

Yes concrete slab. And also it is the 2 in one pad

Most of that two in one has "peel off type tape" on it so you won't need duct tape.

If you need to tape the 2-in-1 on a splice, or your using just poly/plastic, use clear packing tape.

Technically,2in1 is underlayment and VB in one. The stuff with the peel off tape and the overlap is 3in 1. Yeah,I know,I'm a nitpicker. hoho