My goal for drywall and caulking is to follow a variant of this pattern:
and was vetted by Rod Gervais. I say I'm going a "variant" of it, because I'm only having two layers and I'm not sure that I'm going to do the mudded corner strips (need to find out about that).
But the goal is, indeed, to stagger the pieces in a zig-zag fashion, leaving a 1/4" gap, and filling them in with 3/8" backer rod and a 1/4" bead of 50-year caulk.
FWIW, my drywall layout is also heavily inspired by a
Anyway, as we saw earlier and shall see even more today, getting a consistent 1/4" gap was far too much to ask.
I ordered the caulk well in advance since it's not stocked locally and I wanted to get the best possible price. I ordered OSI SC-175 instead of the typical Silenseal or similar. Why? Well, long discussions on the Soundproofing Master Thread as well as discussions elsewhere on AVS and GearSz all pointed to the fact that the only thing that makes "acoustic caulk" special is the 50-year guarantee. Therefore, if you can find caulk with a reliable 50-year guarantee, then buy the cheapest variant you can find and it'll work just as well as the far more expensive stuff. I ordered mine from Home Depot
at $78 for a 12 pack of 28oz tubes. That comes to 23 cents an ounce, which is even price competitive with typical "all purpose caulk", much less any other acoustic caulk.
The 3/8" backer rod was a sleeping problem, that snuck up on me. I honestly hadn't thought too much about it, compared to the caulk. As it got closer to when I needed to use it, though, I finally calculated how much I'd need... and it's somewhere around 300 linear feet. Hrm. Well, I'll pop in to my local Home Depot and pick up some 100 ft rolls. Or apparently not. Several local big box stores didn't carry 3/8" backer rod at all, much less in the quantities I needed. I started panicking right about then. Yes, I could find resources online where I could buy 3/8" backer rod in bulk, but they all had a week or more shipping time associated with them. I absolutely needed to buy them locally. So I spent some time digging into the Home Depot inventory feature of their website and finally came across a store roughly 10 miles from my house that did have enough.
The next morning, I popped in and grabbed an entire box of packages that each contained 20'. I got lots of curious looks and more than a few questions carrying the entire stuffed box. It definitely cost quite a bit more than the bulk online rod, though, so I was being penalized for not planning this out in advance. Ah well.
I'm not going to have any consistent 1/4" gaps anywhere, since my walls are not truly plumb and the ceiling isn't perfectly flat (since the floor was not). So I split the gaps into two main groups: those between 0"-3/8" and those greater than 3/8". Here's roughly how I do the former.
I first take my 3/8" backer rod and stuff it tightly into the gap:
This compresses quite a bit, so it effectively takes up between 3/8" and 1/2" of the 5/8" drywall thickness. I'm going to measure that next time to see exactly how much. I only use the backer rod if the gap is close to 1/4" or slightly more. If it's 1/8" or less, then I just leave it be and fill it entirely with caulk.
The next step, regardless is filling it with caulk:
I use my finger to smooth it out, and ensure that it completely covers the gap from side to side. It sometimes takes two coats, since I push in caulk as deep as I can and sometimes it doesn't quite fill it.
The end result:
I'd be pretty happy if that was my results all of the time.
But as I've mentioned, since I have uneven floors and non-plumb walls, I occasionally (far too often with the first layer) have gaps that are 1/2" to 3/4". Those are simply too big to easily fill with caulk. I debated getting bigger backer rod, but since it's round, it would just end up filling the depth in addition to the width. I did double up on the 3/8" in a couple of places where it seemed appropriate. But for the most part, if the gap was too big on the first layer, then I just used Great Stuff foam.
Oof.. yeah, that's not generally that recommended in acoustic or theater circles. It's not as dense as acoustic caulk; doesn't have the same lifetime guarantee; is extremely sticky; costs more; and doesn't always cover as completely. But it does do a decent job of air sealing and it expands to fill its own space, for the most part.
So I decided to essentially treat it as either backer rod or as a first layer air sealant. That is, if it didn't completely cover the gap, then it became my backer rod. If it did, then I just touched it up to complete the air sealant capability.
Here's a good example of a filled in gap on the floor. In this case, I switched between "normal" Great Stuff and the "Door and Window" variant in between:
That's what I'm talking about with inconsistent coverage, too. It clearly is filling the gap totally in some cases, but is woefully short in others. It's very very difficult to tell while you're doing it, since so much of foam's coverage is done as it expands, after it's applied. The amount it can expand can be pretty comical, too. Here's on the outside of my theater door. I swear it seemed like a reasonable amount when I applied it:
Anyway, back to the filled in floor gap. I then cut the foam flush using a flush cutting blade on my Multi-Max:
It leaves a pretty flush cut, but you can see how there are still some air holes. Those are likely just a little bit deep, but I do want them covered:
So what I do is go over the foam, no matter what, with caulk. This fills in any inconsistent coverage and also fills in those air holes:
On the Ceiling
I was lucky that most of the gaps on the ceiling were reasonable, but as I described in my previous update, a mis-measurement on one of the ceiling strips left a pretty sizeable gap (3/4"). I figured that since foam is incredibly sticky, that I could just spray it up there like the other gaps and have the same result. Er... nope:
It started sagging immediately and even dropped down to the floor in places. Basically, the weight of the foam counteracted the stickiness and so it simply wouldn't stay up there. I let it dry and then went at it with my flush cutting blade. It did a variable job, ranging from barely okay to really terrible. Here's a section where some chunks of it simply dropped away before they could dry:
Notice how many gaps there are, regardless of the dropped sections. Those are from where the foam sagged. Still, that did act like a relatively decent backer rod and so the amount of caulk that I had to apply was somewhat reasonable (I have low expectations of sagging):
For the first layer of drywall over the outlet boxes, I stuffed the gaps as much as I could with left-over putty; put backer rod where it would fit; and then caulked all around:
Some required more caulk than others, but I didn't mind since it was just the first layer. I'll skip ahead to today, though, and show a photo of the first outlet box cutout I did with my second layer of drywall:
Oof. I have no idea what I'm doing wrong with my measurements on the outlet boxes. I clearly got the sides and bottom spot-on, so why is the top so incredibly off?
More importantly, I'm not sure how to handle that case. What should I use to fill that rather large gap?
For the most part, the caulking is as expected considering my not-as-perfect-as-I'd-prefer base. As of know, I have the ceilings, floors, side corners, and door all caulked for the first layer. The gap on the second layer on the ceiling is also caulked. And finally, as I've been putting up the second layer of the walls, I've been (mostly) caulking that as well.
This mostly brings me up to date. I've been posting a daily update to reflect work that I largely did the week before Labor Day, since I had it off. Some of this was done in the past week, but I don't get a lot of time to work on the theater on week days when I don't take them off.
As such, I'm going to posting one more daily update tomorrow, but it'll be a in-progress update. After that, I'll be back to weekly updates at best.