Hello Folks! I am trying to have a contractor glue down 1300 sqft of engineered hardwood (3/4" thickness) to our concrete slab using Mapei Eco 980. The slab has been prepped with a moisture barrier, SLC primer, and the whole area was covered with 1/4" of self-leveler. However, in the direction perpendicular to the way the floor will run, we have variations greater than 3/16" over 10 feet. However, in the direction of the boards, the flatness is mostly within specification.

Multiple contractors have told me that this is fine since the tolerance only really matters along the direction of the floor. However, all the articles/advice/specifications I have read online say that the floor needs to be flat to 3/16" over 10 feet in any direction.

Could some of the experts on here chime in, and let me know if I'm being unreasonable with regard to the spec or if I should insist on it being met. Thanks in advance!

If you have small variations of more than 3/16th of an inch you have a pretty flat floor. Although self leveling compounds get pretty close they are not perfect. After they have been installed the recommendation is that they not be ground. You will have a good base for your new floor. The most important part is wood to glue contact so the wood will be fastened down and hold. All boards are not perfectly flat and may not be perfectly straight so holding them in place by clamping together with straps or weighting areas down is important. If there is a board with a hump in it so only the ends rest on the floor it is possible to back kerf the flooring every inch or so going as deep as the top of the tongue with a circular saw from the underside before installation to make the board limber enough to get good contact without compromising the integrity of the board.