The Natural Philosopher wrote:

I levelled mine first, and even so, wish I had levelled it more..

I would honestly recommend you get some levelling compound, and trowel
the while thing as flat as you can..6mm is far too much - 1-2mm over a
meter is better, and no more than 6mm over the whole floor.

Lay battens over the whole room and mark the high pints and draw
circles
round the hollows with a felt tip pen. Then mix up the compound after
PVA/ing the lot, and use battens from the high points to scrape the
compound level, and float smooth it.

Then when set, do it all over again.

THEN when the floor goes down - which is pretty quick - you will be
rewarded by a total lack of flexure.

Thanks very much for that advice.

I am now paying a lot more attention to the levelling before laying the
boards... which are becoming better and better acclimatised as a result
:-)


--
Ian White