Concrete Slab Glue Down Vapor Barrier?

There is a plywood underlayment available that has a built-in vapor barrier. I suspect that is the product the installer has in mind. You will most likely not find this product in a big box store, but will need to go to a "regular" lumber store.

Mark, there should be a vapor barrier under the slab, get a moisture meter and check the moisture content of the concrete. If cured properly and it has a vapor barrier under the slab you should be good to go and glue the engineered wood to the concrete. I had my new home done this way a year ago and have no problems. I'm in Tampa Florida. Muff

You don't need a moisture meter. Take a one foot square piece of polyethyne sheeting and duct tape it to the slab on all four sides. If there is moisture under it after 24 hours, you need a vapor barrier.

I would suggest you do that after a prolonged wet spell.