I'll shortly be laying a floating floor of solid hardwood onto an
existing concrete floor. The boards are oak, 18mm thick, 150mm wide, T&G
in random lengths, and they will be laid over a combined DPM-foam
underlay. The intention is to glue the boards.

By all normal standards it's a very good concrete floor - dry, and
perfectly smooth and level for walking on. However, a long straight-edge
reveals some very gentle ripples in height, maybe 6mm maximum variation
over 1 metre.

Will this be tolerable? I don't have a feel for how well the boards will
follow the contours of the floor - especially in open areas where they
won't be weighted down by furniture, but will be walked on.

There may be some limited areas that would benefit from self-levelling
compound, but there doesn't seem much point in covering the whole floor,
since that would probably introduce more ripples than it solves.

Obviously this is all to avoid the nightmare scenario of a floor that
has been glued into a solid sheet... and then sags or creaks underfoot.

Any advice based on practical experience would be very welcome.

--
Ian White