Well, yesterday officially marked 8 weeks of curing on the bulkhead doubler’s silicone… I was busy, so I didn’t get around to getting my witness lamination cut in half until this afternoon! (55 days of silicone curing)
As you can see, the curing silicone shrunk enough to separate, and/or started trapping gas near the center of the lamination… not what I’d describe as pretty, but definitely not a deal breaker!
Once cut, I was disappointed to be greeted by a familiar vinegar odor, uncured silicone… so, I started probing the core of the lamination to figure out exactly how much of the silicone was still viscous…
It looks like the witness lamination cured right around 1-1/4” - 1-3/8” in from all sides on a 3-1/4” wide silicone swath… so, I’ve got 2-1/2”-2-3/4” distance covered… excellent info for the future, which I’ll refine my measurements on… so far, it looks like I’m getting a mere .5mm/day of cure speed!
This said, I’ve got maybe a 1/2”-3/4” width of uncured silicone in the core of the doubler plate, which I think I can see from how it’s also bubbling at the furthest point from any one edge:
It’s certainly ugly, but is so far from any one edge that I’m not at all concerned about it affecting performance… regardless, I think this lamination could use another 3-5 weeks of curing if I assume .5mm per-day of cure speed…
Thankfully, the overflow box can still go in, as I’ve confirmed that this particular tube of silicone has cured at least 1.25” in from any one point of air exposure… the overflow will only contact the silicone in question at the back pane, with the remainder of the overflow box sitting on top of the doubler!
— this isn’t what I’d describe as an ideal outcome, but it’s somewhat expected when pushing the limits of RTV silicone this far, and won’t affect anything but cosmetics in the long-run… at least I can continue on adding glass to the tank as it finishes it’s immense ~3month doubler cure!
(It also makes me think about different approaches to the front to rear top bracing, which will reduce the silicone slab to <2.5”x2.5” [6in2, over 1ton of shear strength]…)
Edit: I almost forgot, electrical has been moved as planned, 2x 2-gang boxes w/GFCIs on a 20A circuit, plus a GFCI outlet on a separate 20A circuit, all wired in 12g… hopefully, I’ll find some time tomorrow after work to finish waterproofing junction boxes, and re-cladding the wall!