Spent the weekend on the basement insulation and learned a lot

I ran into that exact same headache with the electrical runs when I did my basement workshop with Hebel blocks last summer. I thought I'd left enough of a channel for the 14/2 Romex, but those blocks are so unforgiving if there’s even a 1/16th of an inch of tension. I ended up using a small router to notch out the back of the blocks rather than trimming the insulation board, mostly because I was worried about the local inspection. It adds a ton of time to the build, but like you said, it's better than a block kicking out and ruining the whole vertical line. Regarding the wiggle test, I actually switched to using a 24-ounce dead blow hammer after the first couple of courses. I found that if I just relied on a hand shake, I wasn’t always getting the thin-set mortar to squeeze out the sides properly. You really want to see that tiny bead of adhesive pop out so you know there's 100% coverage. My back was absolutely shot by the time I hit the fifth course, so I started using a rolling creeper seat to save my spine while buttering the joints. It’s a grind, but that solid 'thunk' when they finally set up is definitely satisfying.

I acutally avoid the wiggle test once the mortar starts to set. With autoclaved aerated concrete, I've found that if you shake the block after the thin-set has begun to skin over, you are just asking for a bond failure. I prefer using a 3-pound dead-blow mallet and a 4-foot Stabila level to seat everthing in one go. If I have to move a block after sixty seconds, I ussually just pull it off, scrape the bed clean, and apply fresh mortar. It’s more work, but it stops those hairline cracks from showing up under the plaster later on. For the wiring, I stopped trying to sandwich Romex behind the blocks or the rigid foam. It always felt like I was fighting the wall alignment. On my last project, I switched to using a manual wall chaser to cut 1-inch deep grooves directly into the face of the blocks after the mortar had fully cured. It’s messy and creates a ton of dust, but it keeps the blocks perfectly flush against the base and makes the electrical inspection way easier since the inspector can see exactly where the runs are before I patch them with some repair mortar.

I'm finally getting my first shipment of these blocks next Tuesday and I'm so hyped to get started! I’ve been staring at my empty basement for months planning this out.

Quick side question though—did you guys have to use any specific vapor barrier under that fiberglass board? My basement gets pretty humid in the summer, and I'm worried about ground moisture wicking up into the mortar and messing with the bond on that first course.

I had that same moisture concern. I skipped the fancy vapor barriers and just slapped down a heavy-duty dimpled membrane under the board. It creates a nice air gap so the blocks stay bone dry even when the floor gets clammy. Also, for the electrical, I stopped fighting the notches and started using a sacrificial old chisel to just gouge a quick channel right into the concrete floor before setting the first course. It’s way faster than a router and keeps the wires completly out of the way of the mortar bed. Save your back and get a cheap laser level; trying to eye those courses while hunched over is a recipe for a week of Ibuprofen.

The dead blow hammer's the way to go, but don't overdo it or you'll crack the corner of the block before you even realize it. I've found that using a notched trowel on both the floor and the block helps way more than the 'wiggle' anyway. It's like tiling—double buttering makes it so you don't have to fight the level as much. My knees were what relly gave out on me, not my back. If you're doing a big run, get some of those gel pads or you'll be limping for a week.

Update: I finished the wall and it’s solid. I actualy stopped doing the wiggle test after that comment about bond failure and switched to a dead-blow mallet. It felt much more secure. I also took the advice on the dimpled membrane for the moisture zones. everythign is level and those electrical runs are finally tucked away. Thanks for the help, everyone!