I am getting ready to lay pergo (with built-in cushion) on a concrete slab. I am lucky that a moisture test came up completely dry during the wettest time of year so I guess there is a good moisture barrier under the slab. The joint between slab and foundation was filled with a foam pad that I could wring water out of like a damp sponge so I removed it and replaced with backer rod and Sikaflex SL and am very pleased with the results.

The underlayment I plan to use is the pergo moisturbloc plastic. I also have a roll of 30# felt paper to level a couple spots. The floor is extremely level everywhere except along the foundation where the slab has a slight slope up to the foundation. It is 1/8" difference over 8 feet, enough that if I put a plank down here there is a slight but noticeable spring. So I want to roll a few layers of felt paper to build up this area rather than grind down the entire length of foundation.

My question is does the felt paper or plastic go down first? Or does it even matter? Does it matter in terms of the Pergo flooring warranty?

What moisture test was that if I may ask? Your fix with the backer rod and Sikaflex is great but I would still be worried about excessive moisture in the slab....Red Flags!!!. I would absolutely perform a series of F-2170 and CaCl tests unless you already have. What does the Pergo/moisturebloc say about moisture testing?

A 1/8 dif in 8 feet is tolerable but go ahead and throw down some asphaltic felt if you want, on top of the moisturebloc.

That is what I was thinking (felt paper on top of moisturbloc).

I did the plastic sheet test and took RH readings. I know it's not the best but I have read to perform this test first, then if there is any sign of moisture to continue with other tests like CaCl, Wagner RH, etc. The area near the foundation really wasn't as bad as I made it sound. It was damp at the bottom and dry at the top.

The instructions say "When using a calcium chloride moisture test for concrete subfloors, readings greater than 5lbs/1000 sq. ft./24 hrs are unacceptable for installation. When using a moisture meter, readings greater than 4.5% are unacceptable." So I didn't use either of these.

Jake, thats where they will get ya. Do the prescribed tests according to ASTM standards and document, meaning pictures. Can't tell ya how many laminate floors I have seen that failed, even with the manufacturers specified underlayment. Thats why they say to test.

Want to see something really funny? Watch my buddy Jason Spangler from Wagner Electronics do the mat test. LOL Gotta watch to the end.

http://www.youtube.com/watch?v=uAIjz9Io ... e=youtu.be

I've watched that before. What I wanted to see at the end of that video was to now take a Wagner RH reading at both of those locations and see what results you get. Wouldn't they still be drastically different?

Sure they would be different, your comparing apples to oranges and there is no numerical value to a plastic sheet test. I think that was the point of the video.