Levelling for wood Laminate over conrete & Marley tiles

[Chris198801]

I live in a high0rise ex-council flat. It has concrete floors wih Marley tiles.
The living room floor has under-floor heating, and access panels can be lifted to access the inner workings.
This heating system is not in use and never will be again.
The panels do not fit exactly flush with the floor - in parts rising 4.6mm above.
Also, to the left and the right of the panels, the floor has gradual dips spanning maybe 3 feet on one side and 1 foot on the other.
Having fitted a third of the wood laminate flooring the springiness from going in to the dip, then up onto the panels then into "air" on the other side is too much to ignore.

Couple of questions:

1. This is oak surfaced, with cheap wood backing, 10mm in total (called BISHORN, from B&Q). Along the lengths it's the kind where you insert the long side of one board into the previous one at 30% then tap it in and it sits down. You then hit it hard lengthwise into the adjacent board in the line to close a tongue and groove joint. My question - if I lift whole rows (4m) of connected boards (I need to lift 3 rows, I think) will they re-seat well? Or will the sealing tongues be too loose?

2. Can I apply levelling compound to the dips either side of the panels to remove the "ski jump effect" with two "lakes" of compound and then put everything back in place?

3. Can I just say to hell with it, lay it as-is, fit scotias to hold down the "flying end" and whistle nonchalantely?

Sikafloor say they won't advise on this as they have not tested on Marley tiles. Other options I've considered are putting 6mm ply sheets on the low spots under the underlay to minimize the problem, or grinding off the high spots on the floor access panels.

Any thoughts are very welcome.

Thanks
Chris

 

[blup]

Underlay.

Blup

 

[Chris198801]

Do you think that was a useful contribution, Blup? As I mentioned, I'm using underlay.

 

[magicmushroom666]

I've lifted and refitted boards just fine that were still new, ie only put down the same week.

Can you just double up the underlay in the dips to bring everything up to the hightest points? I'd not be happy with large voids underneath, that hollow sound and feeling isn't nice on laminate.

 

[oldbutnotdead]

Sand (yes loose sand) can work quite well combined with underlay (the green felt tiles are good for smoothing out dips).
The non-flush access panels- bet they were originally flush and there's dirt and rubbish holding them proud.

 

[Chris198801]

magicmushroom - thanks for your comments. I'll lift the boards then. Doubling up on underlay has a great speed and simplicity to it but I don't know if it would be a durable fix though. It's Diall green expanded foam. I guess the load is spread over a wider area via the boards. I'll have to bit the bullet soon and make a choice without great confidence in whatever I do, as living round a half-laminated floor isn't convenient. Have you doubled-up on underlay like this before? Thanks again.