Underlayment over old, dry concrete and under engineered vinyl planks

[Oakmanii]

I did a 48 hr moisture test and the concrete is dry (40 years old, but partly below ground level.)
I have 5.5 mm engineered vinyl planks.
I also have some leftover 3 mm and 4 mm felt underlayment with a vapor barrier attached.

I read I should use a vapor barrier over concrete, but the underlayment's attached vapor barrier is on the TOP side of the felt underlayment.
So do I first lay down a plastic vapor barrier of 6 mil, then the felt underlayment with the vapor barrier on TOP and then the planks?

Or can I turn the underlayment upside down and have the attached plastic vapor barrier on the bottom, with the felt on top, with the planks on top of that?

 

[Nick]

 

[Ernesto]

Are you sure you have the correct underlayment for LVT and not for laminate? LVT requires a different one if you need it. Some LVT manufacturers say not to use one or it's optional. If the LVT has an attached cushion already, then just use six mil plastic.

 

[Oakmanii]

My LVT doesnt have a pad, and the underlayment I have was for laminate. I have seen at Amazon that some have used a 3 mm foam underlayment, which many reported as spongy, but I thought the felt would be less compressable and less spongy, just a bit concerned about moisture over time, I guess coming up from the ground, even though I did the plastic square taped over the concrete for 48 hours and it was fine.

 

[Ernesto]

The underlayment for laminate is to soft and thick for LVT and could cause mechanical failure of the locking mechanism, plus void any warranty. What does the installation guidelines say? If not on or in the box look online. Many times the only requirement is six mil.
I just had it out with Mannington about this. They claim you don't even need six mil with their product over concrete, it has an attached cushion on it, but most every other manufacturer says to put down six mil. They are idiots! I put down six mil anyway. There's a thread in here with me venting about it. lol

 

[Ernesto]

Oh BTW, no manufacturer accepts the plastic sheet method anymore.

 

[highup]

I think Core tec makes a version of their product with and without an underlayment.
One has a built in cork back and the other doesn't. I would assume an underlayment could be used on the version tha doesn't come with it. That said, I'd ask the manufacturer of your particular product if an underlayment could be used. If that underlayment you have is approved, I'd install it as it's supposed to be, and not flip it upside down.

 

[highup]

Oh BTW, no manufacturer accepts the plastic sheet method anymore.

what do they recommend now? Are you speaking LVT or all floating products?

 

[Ernesto]

what do they recommend now? Are you speaking LVT or all floating products?

For moisture testing High. ASTM D4263 Here's my all time favorite video of it being done by Jason @ Wagner meters. Actually I did perform a couple on a job just for shits an giggles about a month ago.

 

[Nick]