How do you guys handle kerfing for custom fluted walnut panels on vanities?

If you're using those thin bendable fluted panels near a 5x5 shower, you absolutely have to seal every square inch, especally the end grain and the back. In an 80 sq ft space, that steam is going everywhere. Most of those bendable products use an MDF or plywood core that swells the second it sees humidity. I've found that back-priming with a shellac-based primer like BIN before installation is the only way to sleep at night. It prevents the substrate from pulling moisture out of the air and popping that walnut veneer right off the kerfs.

Blending the paneling into the medicine cabinets for that continuous look is mostly about how you handle the transitions. Since the walnut veneer is thin, avoid heavy sanding at the joints or you'll burn thru the wood in seconds. I usually use a color-matched wax filler for the tiny gaps where the fluting meets the cabinet carcass. If you're struggling to match the grain, you might need to buy extra sheets from the same veneer lot and re-face the cabinet doors yourself. It’s extra work, but it’s the only way to ensure the flow isn't broken by a diffrent batch. For the finish, stay away from standard poly if you want to avoid that plastic look. I've had the best results with a **conversion varnish** in a dead flat sheen or a high-end **hardwax oil** like Rubio Monocoat with the 2C catalyst. The 2C catalyst is vital for a bathroom becuase it holds up against water spots and humidity much better than the standard oil. It keeps that raw, open-pore texture of the walnut while making it dark and rich enugh to pull in those gold accents and the bird wallpaper. But make sure the ventilation is actually up to the task. Even the best finish won't save thin walnut veneer if the exhaust fan isn't pulling the damp air out fast enough. Those 1940s builds weren't exactly designed for modern steam levels, so double-check the CFM on the fan before you wrap up. It’d be a nightmare to see that custom work start peeling because of a weak motor in an 80 sq ft box.

That shellac tip for the back of the panels is something I never would've thougth of. Does it make it harder to glue the fluted stuff to the wall though? I'm worried about the adhesive not grabbing onto the primer. I’m just getting my feet wet with walnut and the thought of 'burning thru' that thin veneer makes me nervous. Is there a specific grit of sandpaper you use when you're being extra careful, or do you just hand-sand the whole thing to stay safe?

For the glue issue, I ussually stick with a high-tack construction adhesive like PL Premium. Since shellac is a universal sealer, it won't repel the glue if you scuff it with 120-grit first.

Also, watch how those fluted panels hit the floor. Leave a tiny 1/8" gap at the bottom and fill it with color-matched silicone. Water can sit on the tile and wick up the walnut end grain. If that happens, the veneer will delaminate regardless of your finish. It's that standing water that kills custom work faster than steam ever will.