Hi Javier! It's been a while!
Whats the updated consensus regarding the best (if any) way to float a floor. specifically on a 6th floor (concrete floor).
There's three ways, basically, and which one you choose depends on budget, and also on how much you need to isolate.
The "cheap" way is to build the floor as a drum riser: Lay OC-703 (or equivalent: Volcan, the makers of Volcanita, makes good stuff here in Chile) across the entire floor, then build a deck of plywood, OSB, or MDF on top of that, at least a couple of inches thick (several layers of wood, screwed together, preferably with Green Glue in between), taking care that the edges of the wood do not touch the walls: leave a gap of a few mm. Fill that gap with flexible caulk.
That works, sort of, but mostly for impact noise, not so much for airborne noise, and you can't build walls on top of that: It's just the floor that is floated, with the inner-leaf walls around it.
Number two is similar, but using concrete instead of the layers of wood. Same idea: lay OC-703 over the floor, put thick plastic on top of that turned up at the edges and sealed, put wire mesh on top of that, then pour concrete, about 7 to 10cm, also taking care to leave a gap around the edges. To do that, put a thin wood shim between the wall and the turned-up edges of the plastic, and after the concrete has hardened, pull out those shims.
This has much more mass than the wooden deck, but still is not truly floated. And you might be able to build walls on top of that, if the concrete is thick enough and the loads are properly calculated.
Number three is the complete floated floor. Very similar to number 2, except that you embed isolated floor jacks in the concrete, and after it has hardened you jack up the floor several cm, to create a larger air space under it. The floor jacks are proper isolation mounts (Mason Industries makes good ones), with internal springs and(or rubber pads, to correctly float the floor. You can build walls on this, no problem, so the entire room is floated.
Of course, considering where you and I live, you will need seismic snubbbers al around that, and you'll need a structural engineer who specializes in seismic structures to check your calculations and sign off the paperwork, to keep the inspectors and the government happy... .)
But regarding the floor, Should I try adding more mass to the existing concrete floor?
That won't help much: you are on the 6th floor, so flanking and impact noise are going to be a big problem. Adding mass to the floor without floating it, wont do much. Doubling the mass (doubling the thickness of the existing slab) would only get you a maximum of 6dB extra, and very likely it won't even get you that much. If you need a lot of isolation, or you need to isolate impact noise, then the only real way to do it is by decoupling the floor in once of the ways I mentioned above. The best way to do it, is the third way, with proper isolation mounts that jack up the new inner-leaf floor slab after it is cured. The jacks look like this:
mason-floating-floor-isolation-jacks.jpg
mason-floating-floor-isolation-springs.jpg
Not worth even trying?
Definitely worth trying! For sure! Provided that there's a really good budget to do it... this is not cheap...
Take a look at the Mason Industries website: they have some useful information there. Look for the document "BULLETIN ACS-102-3": it guides you through the entire process. IR-802 also has some info that might be useful.
- Stuart -