Thoughts on pre-fitting trim vs waiting for the drywall finish?

I've learned the hard way to stay away til the rockers are completely finished and the primer is dry. When you're dealing with those tight bay alcoves, especially with Marvin or Andersen units, the mud buildup in the corners can be a nightmare. I’ve seen drywallers slap on an extra 1/4 inch of compound that completely changes the plane of the wall. If I pre-fit my casing against the studs, I ussually end up fighting those humps and spending twice as much time with a block plane or a power sander just to get the miters to close up. I keep my Kapex and the CT-26 vac on-site for the dust, but there’s no protecting prepped wood from the fine white powder the finishers leave behind. Waiting until the walls are primed gives me a stable surface for my layout lines. I use a Bosch laser to check for plumb across those five windows and scribe my stools to the actual finished surface. It feels slower at first, but it saves me from the frustration of seeing a perfect shop-fit joint get ruined by a wonky wall.

I actually prefer the opposite approach because if the framing is out of whack, no amount of scribing after the primer is dry is going to save those miters on a radius. I’ve started making it a point to get on-site while the rockers are still hanging. If I see a window buck that isn't plumb or a header that's sagging 1/8 of an inch, I can still convince the super to have it shimmed. Once that 5/8" rock is up and taped, you're stuck with whatever wave the finishers left you. On those complex bays, I like to pre-assemble my window stools and aprons in the shop using Festool dominoes or pocket screws based on the actual rough openings. If I wait for the mud, I’m fighting the build-up in the corners which usually throws my angles off by a degree or two. I’ll take the risk of a little dust over the frustration of trying to scribe a 12-foot piece of poplar against a wall that looks like a topographical map. I just keep a vacuum hooked up to my miter saw and throw some plastic over the finished pieces.

This is all so cool to read! I'm just starting out with my first real miter saw and I'm obsessed with how crisp those joints look. Seeing you guys talk about drywall mud vs framing is making me realize how much I have to learn. Quick question though for the pros here: when you're doing these big window setups, what kind of work boots are you wearing to stay comfortable on those hard subfloors all day? My sneakers are killing me!

Listen to the guys telling you to wait for the mud to dry. I spent forty years chasing my tail trying to 'beat the rockers' and all I got for it was extra work. Back before these fancy lasers, we’d use a straightedge and a plumb bob to see how much the studs were bowing, but at the end of the day, you're trimming to the wall, not the wood. If you're worried about those radiuses, skip the pre-fit and learn to make a proper template out of 1/4 inch luan. It’s the only way to get a tight fit against a wonky plaster or drywall job without losing your mind.

If you're worried about the drywall dust trashing your prep work while you wait for the painters, just wrap your stock in Trimaco Floor_Paper. I've found that waiting for the primer is the only way to go, but you need a solid surface to mark on. I use a Tajima GS-16BW chalk line for all my layout becuase the line is ultra-thin and doesn't bleed into the finish. It gives me that surgical precision for scribing against those bay windows without the mess of a standard thick line.

You're overthinking the 'early' vs 'late' thing and forgetting the real bottleneck: jamb extensions. On those tight bay alcoves with Andersen 400 Series casements, the factory jambs are almost never flush with the finished rock. I wait for primer, then I grab my Graco FinishPro II 395 to seal the back of my custom poplar extensions before they hit the wall. It stops the wood from sucking up moisture from the fresh mud. Also, if you aren't using a Collins Miter Clamp for those radius joints, you’re making it way harder than it needs to be. Those springs keep the tension exactly where you need it while the Titebond III sets up on a wonky wall.