Hey guys. Long-time lurker here, with a question I can't seem to get a good answer to by searching the old posts.

I am installing a floating engineered hardwood (Bruce click/lock natural oak) on a concrete slab, on grade. Calcium chloride moisture test came back at 4.9 lbs. The house was built in 1970, there's no plastic under the slab.

The manufacturer instructions recommend a moisture retardant system if the CC test is above 3.0. They recommend their paint-on product, Armstrong Vaparrest S-135 or a glue down vinyl sheet.

I can't find the Vaparrest anywhere, besides a now-dead link selling it for $300 a gallon. No thanks. Sheet vinyl according to my research went out of style after 2000 or so, due to better paint-on barriers. I'd be happy to go old school if needed, but paint-on or 6-mil plastic seem like they'd be a lot easier on the back and knees.

So my question:

What would you guys recommend for a paint-on barrier if not the Armstrong stuff? Can I just use Redguard or a similar product from the box store?

Or, will I be okay with a 6-mil plastic sheet, then the 3-in-1 pad (which has its own thin moisture barrier), and the floor on top? I saw that recommended somewhere, but am nervous about sandwiching two moisture barriers.

What do you guys recommend?

Quietwalk and six mil works well. As a matter of fact most 2 an 1 underlayments/moisture retarders say six mil if high readings. I prefer sound solutions.