Rubber under sole plates

Hi! I'd like to continue the discussion started in this thread about putting foam or rubber under inner-wall sole plates on a single slab. Lilith_envy reports a difference in 1 room which has it compared to 1 that doesn't, and I know that John has recommended it's use as well. From a theoretical point of view, as long as the plasterboard is caulked properly to the floor, then the rubber/foam shouldn't do anything for isolation. It's not decoupling in the true sense, because there's no way that 10mm of rubber is acting as a spring especially with masonry anchors shorting the connection. Would it be providing dampening? Or is it just providing a better seal than caulk alone? Assuming a flat floor where the levelling aspect is removed, is it worth doing? I don't want to follow a cargo cult!

How about using the same material for the top plates to the of the floor joist?

With the amount of pressure from the weight on a wall assembly coupled with the ceiling framing/rock, the caulk will, given a level or at least flat surface, be the better bet. Until these things are tested, it is just best guess.

My plasterboard also didn't touch the slab i used spacers while attaching, that were then removed. Fuller firesound to fill the gaps. Could it be that, because the dyna bolts create such a small contact area compared to slab on timber?

The bolts actually do not make a small connection. The pressure required to secure the bolt will make a harder connection, a flanking connection, thru the timber and directly into the bolt. The attempt to decouple the sole plate is difficult, and this process will not work. That said, with not much information or data on either one or the other it is difficult thing to say this one does this or that one does the other...we have to work on what we can discern as the physical aspects of the building connections and not read too much into any supposed improvement with little to nothing to compare to. As we all can agree, any hard connection is a flanking path.

Lilith, you said in the previous thread that the difference in isolation your report could be down to the different brands of wool you used in the two rooms. What were they? Were they both 100mm thick? Thanks GIles