I have installed Great Northern long planks very similar to the Kahrs that came bowed from the factory. As soon as they were laid and the moisture equalized from top to bottom they laid flat as could be.

Just a quick update.

I contacted the guy who levelled my floor and he reiterated that we were unlikely to get it perfect but that I could try putting a double layer of underlay under the bad sections. Fortunately the worst area was a few planks away from the side wall so it was fairly easy to lift up the planks and slide some more underlay under.

Incidentally I noticed that a couple of the planks that I took up were MUCH more banana-like than when I put them down ie they seem to have BECOME more bowed since being layed. I also noticed that the bottom layer of wood on the planks were quite yellowed - I didn't notice this before. I also notice that some of them seem to have "profiled" a bit to the shape of the floor.

Anyway this bad area is now much better and feels fairly solid, but when I'm sitting on a chair watching people walk over it I can still see varying amounts of deflection practically EVERYWHERE ie over the WHOLE floor. There are SOME areas that are solid and you can see no deflection, but I would say about 50% of the entire floor noticeably deflects by various amounts when you're sitting down watching people walk over it!

I can't believe that the subfloor has been flattened SO badly to cause this and so I am wondering if this is all normal and to be expected.

My floor man did say that people used to apply heavy weights to the floor so it would sink into and conform to any dips that were still present to stop the bounce. Does this work? I was considering getting some 25kg bags of sand that I've got and leaving them on the bad areas for a few days. Would this work or is this just ridiculous?

I've also thought about screwing down through the bouncing sections and into the subfloor to secure them and then covering the holes with appropriate wood filler!? Is this a crazy idea?

Cheers,
Matt

Not so ridiculous, I did that with some bowed long plank engineered bamboo once in a closet. It was all I had left so I had to use them, came back a couple days later and it was flat, still is. I saw the floor the other day and this installed was two years ago.

And whats crazier, this red stained bamboo has no humidification and has no splits, checks.

But back to your problem. Do what ever but do not screw down a floating floor, It will make things worse.