On Oct 15, 12:05 pm, wrote:
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.

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...stallation.pdf
Scraps of the Delta-FL can be used to shim up the low spots in the
slab.

R