This is a question for a pro who installed many floors. But pros usually would tell you to follow the manual. My guess would be the glue is used because thin flooring has more chance of cupping. As such, if it was my floor and suspecting that the panels have higher chance of cupping, I would over engineer and go to 6" spacing for glue, or trowel and glue the entire surface. This is because manual spacing may also contain the manufacturer's worry that some people may not buy the flooring if more gluing (therefore more annoying) is recommended. Doing things this way, also voids the warranty. This is long time ago. I used bruce 5/8" thick and about that wide edge glue floating floor. Finish layer nearly 1/8 thick. Over time, I could see that the flooring was not absolutely flat. This wasn't from feel. Just how the light reflected off the surfaces. The panels were plywood, not mdf layer. I also thought maybe they were slightly cupped from the beginning.
Not sure if glue would solve that problem. But that is also my amateur's opinion. Not using such foam layer, I don't think you'd lose much sound insulation. The panels are tightly nailed anyway. Only sensible recommendation I saw was using actual thick rubber sound sheet and I think it was a floating floor.
Not sure if glue would solve that problem. But that is also my amateur's opinion. Not using such foam layer, I don't think you'd lose much sound insulation. The panels are tightly nailed anyway. Only sensible recommendation I saw was using actual thick rubber sound sheet and I think it was a floating floor.
