I just did a foam core backdrop and used mat board to cove the corners. You can use drywall compound if you use the powdered type that you mix like plaster. Mix it so its not soaking wet. It's called "Easy Sand" and comes in different drying times... IE: "easy sand 20" starts to dry in twenty minute.

Notice the clips at the top at the joints in the first and last picture... those were 3d printed and keep the boards aligned at the joints. You can buy edging for foam core boards online if you don't have a 3d printer.

The foam core slips into wood brackets screwed to the rear of the layout and can be lifted out with one hand.

Foam core can be purchased in 4x8 sheets at art stores like Plaza Art.

Edit... The drywall compound in the pictures below had not been sanded, they were the first coat.

I just went through the same questions for my new layout, and for what it's worth, I landed on YorkShield rolled white vinyl flashing.  It comes in 50' lengths for anywhere from $45-$56 and feels and looks just like 0.020" sheet styrene.  See my post at https://model-railroad-hobbyist.com/node/40784?page=9#comment-460996 for more info.

I found the 18" width at several sites, with Walmart.com being the cheapest, and I just recently learned of a source for 24" x 50' as well.  I'm waiting on that order to arrive to confirm that it's what I'm after before I recommend it, but it sounds promising.

If you cant get a full 4x8 sheet of masonite to your home, the big box stores usually sell it in 2x4 pcs. A little more work as you would have more joints to mud and finish and a little bit of a price premium, but the pcs will fit in a car.

My plans have been to buy 4x8 sheets and have them cut to 2x8, and install them that way.  I'm hoping and guessing 2' high will be sufficient for two sided back drops.  Of course they will need to be supported at the buttom so I'm guessing they will really be about 21 or 22 inches of actual back drop rising above the track level since it will have to be attached to something at the bottom.

"My plans have been to buy 4x8 sheets and have them cut to 2x8, and install them that way. I'm hoping and guessing 2' high will be sufficient for two sided back drops."

   Hi Jim,  All my backdrops are 2 foot tall. They seem to be fine for height. I guess it depends on your layout height and viewing distance but I rarely think about the backdrops when running trains.. ....DaveB

So, one problem I have with foam core boards is that the paper is coated with WAX which causes it to not hold paints, glue, plaster as well as it might otherwise. this is particularly true of cheap dollar store foam core. 

I have not tried this specifically, but my current thinking on my small shelf layout is to use foamcore as the structure for it's rigidity, but glue paper roll paper over the top to provide a better painting surface and hide the seams. Vinyl contact paper as someone else suggested could also work well. 

"one problem I have with foam core boards is that the paper is coated with WAX which causes it to not hold paints, glue, plaster as well as it might otherwise. this is particularly true of cheap dollar store foam core."

 

 

       The paper face peels off easily from the foam core that I get at the local dollar store , so it can be finished any way one wants. I find it handy for roads, parking lots, or anywhere I might need a large flat expanse.........DaveB

Ok, I have managed to install the foam boards on half of the layout with seems and I am quite happy with them knowing they are a 'canvas' for holding the vinyl roll I plan to use. They cover the unsightly years of tennents patched up holes and the hanging wires from the lights I currently have (another post in the near future). So here is the result of the first half of the layout. See what you think so far...

The 'window' on top at the left is blocked out because of previous leaking. Good to know. It looks out on a alleyway anyway, if I was above ground I think there's sufficient backdrop for a cut-away to let the light in.

@kregan rounded corners... Thanks for your detail and info. I have yet to 'graduate' to 3-D printing. But I also have to keep the corner real-estate for my 'Northern Silicates' industry's silo's. The corner, as it happens, is a great location for them! Not planned as the Silos were already situated there. 

@IAISfan - Joe thank you for that suggestion Re: Rolled vinyl flashing. Inded the answer for me! Thank you. A Walmart is just the other side of CP 'Lambton Yard' here. In fact, it's right across from the Yard office where they park the engines! Right now a lot of BNSF have been rolling through on CP some even have been parker there! So great suggestion killing two birds railfanning whilst getting supplies! The Vinyl sheet roll is exactly what I need thank you for this. And i've always loved your work.

@ricksutton, @manofkountry - There are 3 big box supply shops including Home Depot and Rona (Lowes) just the other side of the tracks here! Problem is cutting to size. There are differing heights to the ceiling including a cuttaway for the Duct work. 

@YoHo - I currently have no problem with sticking images to the coating on foam boards from the Dollar store with 'Gorilla' double sided sticky tape. I'm in the basment, so I don't anticipate a problem in the heated days of Summer. Maybe 3 floors up in the last location I called the 'Hell Hole'. ;)  But the stuck on images are just for now and your suggestion is the exact same as I posted. The foam boards being a cheap 'canvas' for the vinyl roll as suggested by Joe. So you guys are on the same page! And @DaveB, you're right, even if the board rips a bit not bother as it will be covered.  Thanks. 

Here's a couple stuck on temporary street to backdrop images i'm experimenting with 'Gorilla' double sided sticky tape. OK for now in my opinion. 

@UglyK5 - always handy with suggestions.. shelving, backdrops, now lighting next...wait for it. ;) Thank you!

Thank you all for your suggestions.

Brad. 

This is the middle and the original 6 Feet part of the layout. The Foam Board was tricky to cut away to clear the Ceiling Duct work.

........painted backdrop and photo backdrop. I cut the sky out of the photo backdrop and mounted the rest on foam board up against the painted Masonite. I’ve been fooling with painting the clouds but I’m so so on the result. Sometimes I think it’s not too bad and other times I think they suck!’  Go figure........

Peter