Engineered wood floor in basement

As I am planning to finish my basement, I've decided that an engineered wood floor is what I'd like. I know the concrete floor has to be "pretty level/flat" in order to put a wood floor over top, although I've read vastly different definitions of what that means. Furthermore, the folks at Lowe's and Home Depot are of little help, as they spin completely different stories. I've tried the bowling ball test, and there are a couple spots where it definitely takes off in one direction for a few feet, but mostly it just rolls a few inches here or there. The entire basement is sloped slightly toward the sump pump in the corner, which is fine (I don't really care about levelness as much as flatness), but I still don't know how flat I really need it. The floor definitely isn't wavy by just looking at it, and passing a string and measuring depths shows that it's maybe 6-8 mm deeper in the middle than near the walls (over 30 ft), but is that enough to warrant leveling it with self-leveling concrete mix? I plan to use the Delta-FL underlayment, which I've heard can counteract a small degree of unevenness, but what is the impact if I install the Delta-FL over my concrete floor as-is (even with it being 6-8 mm deeper over the course of 30 ft), then install a floating engineered hardwood floor above that? If it's too out-of-level, will the floor buckle or what? Thanks to anyone who can shed some light on this mysterious question to me.
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On Oct 15, 11:05 am, snipped-for-privacy@gmail.com wrote:

I would be more concerned with moisture, many floors are not designed for high humidity, If you have moisture you will have alot of mold as well, use a moisture meter to test the concrete first, April may be the wettest time, If its to wet you will be removing it in a year or so.
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The Delta stuff the OP mentioned is a plastic underlayment. With taped joints it'd be at least as effective as plastic membrane under the slab (though I'd prefer to stop the moisture below before it came through the slab).
R
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On Oct 15, 12:05 pm, snipped-for-privacy@gmail.com wrote:

You are concerned about how much it is out in a short distance, not how much over the entire length of the basement. Use a six or eight foot straightedge and place one end on a particular spot. Swing the other end around in a circle. Repeat over the rest of the floor. Overlap the circles in the sketchy areas. This will locate the high and low points from that spot. Do something about the bad areas. You are not in self-leveling territory.
The manufacturer wisely included installation instructions for the Delta-FL. http://www.cosella-dorken.com/bvf/ca-en/service/installation_instructions/below_grade/DELTA-FL_Installation.pdf Scraps of the Delta-FL can be used to shim up the low spots in the slab.
R
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Flooring also has a rating which states if it can be used below-grade, like in a basement. . I leveled my basement floor using leveling compound on the big dips in the concrete. I've heard people using roof shingles too under the FL. . After I leveled the floor, I painted it using Drylock just to help keep the moisture down. . The other ideas of using scraps of FL to level are good. I used DryCore panels from HD. It was un-Godly expensive, but the floor came out great.

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On Oct 15, 11:05 am, snipped-for-privacy@gmail.com wrote:

Dont bother leveling, the dips and valleys you described will be no problem at all, in fact the wood will bridge those and make everything look real level. But before you lay it, get some acrylic-based concrete sealer and spread that on heavy with a mop until it soaks in, Behr, etc. sealer. Put a thick plastic vapor barrier over that. HD has thick heavy mil plastic roll I think 100 feet by 20 feet. It will work great as long as it's an engineered flooring made for below grade.
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Thank you RickH for actually providing guidance on the level-ness required. To everyone else who mentioned moisture - I don't have ANY moisture problems so far. The house is 10 yrs old and was equipped when built with the Tuff-N-Dri system for waterproofing, which has a 30 year warranty. Even this past May when my part of NJ got 9 inches of water in 36 hours, and my neighbors basements were flooded with 5" of water, mine was bone-dry. It rained hard the other day and I did the plastic-sheet duct-tape test, it came up dry too. The floor and interior walls are already coated with a BEHR moisture-resistant paint, but I plan to do another coat or two just to be safe, and because there's half a gallon still in the pail. I'm also using the Delta-FL as more of an insurance policy and to soften the floor (plastic dimples HAVE to be softer than concrete), and I'm using engineered hardwood specifically since it's pretty moisture resistant. So I feel I'm pretty well covered on the water/moisture side, which is why my main concern was really the even-ness of the floor. So if anyone has another opinion on if the floor needs to be leveled, or if the wood + underlayment will kind of self-correct, thanks for those opinions/advice.
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On Oct 15, 5:21 pm, snipped-for-privacy@gmail.com wrote:

6 to 8 mm dip spread over 30 feet is actually pretty good for a basement floor.
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