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Deleted member 174758
Not sure about new build domestics, but in commercial builds (shops, offices, hotels, bars, etc) using one or two layers of latex to correct discrepancies is very, very common indeed. It is also pretty fast. In general the limit is about 6 to 12mm per coat, but specific latex compounds can be built up to about 25mm in two or three passes.Latex i think they said, by a flooring company who presumably will have done something similar in the past.
The room will need to be emptied of furniture and I'd suggest that you need to take off a couple pieces of skirting where the build-up is going (and refit afterwards) otherwise it might look a bit odd when they are done. Either way it's a heck of a lot less disruption than lifting a large section of floor, sistering the joists to the correct height or packing the floor with timber firrings (they aren't realistically going to reposition the joists) and relaying the floor.