I'd say its smooth enough for me...

I've used drywall for our backdrops including corners (using 6mm drywall for corners) and I'm more than happy with the surface smoothness as is. But then that's me, for the ease of installation, overall cost, time and final product I wouldn't use anything else now...

If you haven't already seen it:

https://forum.mrhmag.com/post/jlt-railroad-blog-plasterdrywall-backdrop-12188778

https://forum.mrhmag.com/post/jlt-railway-blog-plasterdrywall-backdrop-12187236

Jas...

UPDATE:  

I've quickly added these photos tonight, this section of the L&T Branch drywall backdrop was given two coats in the last two nights.  Tape & first coat last night (dry over night & day) then light sand back tonight with a final skim coat tonight.  Tomorrow night will be final light sand ready for primer & two coats of final colour...

In total (excluding drying time) the whole process took about 4 hours...

This section is about 3m/10' in length and includes a 90 degree internal corner...

Transition from existing completed backdrop to new section...

Jas...

Ditto what Jas said

Drywall (plasterboard in Oz) is my choice too. For all the reasons Jas stated.

Steve

Welcome back Steve...

Gidday Jas

look forward to catching up. I've still been lurking around here and following your progress and you're still  working way too fast .

Cheers

Painting drywall

I'm a builder and when it comes to painting drywall I recommend "First Coat" primer. I have used lots of primer and this gives the best results.For smooth walls I would use a short nap roller. Usually 3/8" but for backdrops you might consider one of the foam rollers. That may give you an even smoother finish.

Oh BTW, First Coat is sold a Menards.

Yes

I and my brother use drywall for a lot of things. We do some remodeling and end up with end parts and stuff so we incorporate it where ever we can. We also use plaster (Mud) for lots of stuff.

Works for Me

I paint the backdrop around the outside walls of my layout room on the existing drywall.  It works as well as anything.  I paint it the same as with every other wall in the house, with a brush for the corners and a roller everywhere else.  I don't want a perfectly smooth surface, and prefer some texture like an artist's canvas.

Quick Alternative

For the Cornhill & Atherton I tried this..........

The room was already fully drywall lined so I only needed coved corners. I didn't want the hassle of trying to blend the corner cove into the drywall so just applied 3mm MDF (I find it marginaly easier to work with than Masonite) direct to the wall. The MDF is only attached to the corner formers and then glued at the joints. The screws you see at then ends are temporary while the glue dries.

I lose 3mm of space per wall, but it goes up really quickly and easily with the minimum of filler.

Rob

Another method...

I did that exact thing...

I did the same as Bryan and it came out quite well.  I'd do it that way again if I were to start over.