is drilling holes in the places where it is loose the most and either using no nails or expanding foam an option to secure the boards to the wall instead of taking them down??
Foam will push the boards out, no nails not viable over a llarge area.
I've done small areas by cuting holes and packing the proper drywall adhesive in -but not really practical for a room - you'd have holes all over the place, not nice for skimming
Anyone here use the cans of adhesive -would this work?? You'd still have a load of holes.
The problem would be in the future -what will come loose when you put up a shelf or push furniture against it (or in my place when boys decide best place to play football is in the house)
If intent onleaving the boards in situ , use these or similar
http://www.british-gypsum.com/produ...ies/gyproc_fixings/gyproc_nailable_plugs.aspx
quick and easy -drill a hole the right depth and knock them in
and treat the whole area as being in need of fixing ie put the fixings in as recommended ( don't know off hand? 300 - 400 centres? anyone) if you can fix them through dabs you will stop the boards being pulled in -but if there are enough dabs this is not a problem. Your old dabs are now just spacers, as we can't trust them to stick to the board or the wall.
Before you do any of this, do a bit more research - Check if your spread is happy with this.He may need need to bond the wall out to make it straight etc and see if he is happy to proceed before making any decision. He sounds like someone you can trust, he'll be responsible for the job so you should be willing to consider his advice. He's seen the actual job, not me and he'll be doing it !!