I’m building my third layout. The surface is foam. The first two were plywood and I glued the cork to the plywood with good adheasion. Unfortunatuly the plywood warped and messed up the trackage.
This time I’m using 1 -1/2" foam over 1/2" plywood.
The question is should I paint the foam before gluing the cork down? On the plywood layout I glued the cork to the plywood. I never got a chance to paint the area around the trachage before it warped.
Will I have any problems painting the foam then gluing the cork and track to the paint? Or should I glue the track to the foam then paint around the sub roadbed and track?
If you have had a problem with the plywood warping, you should seal it before you attach the foam. A good coat on both sides should keep it from warping. After gluing the foam on you can glue your cork on (cheap latex caulk works fine for both jobs). If you are going to do any major carving or stacking of foam, I’d suggest you do that before attaching your track. Probably doing the base coat of paint before laying track would save worry about getting paint on the track. I would suggest you paint the cork your ballast color at least in the areas of your switches, this makes it so you don’t have to use as much ballast around them, which can be a problem. Before you do a lot of scenery work though, get your track down (latex caulk works here too) and run your trains, run your trains, run your trains. to make sure your trackwork is not going to be a problem. When you go to ballast, I have seen it recommended that you do a few feet at a time to make sure the ballasting does not upset your track or electrical work. By doing short sections you do not have to tear up a lot of track to find where your problem is.
I would advise painting the foam first. Paint it an earth colour (depending on the region you’re modelling) to avoid having to look at pink or blue landscape until you get around to finishing your scenery. It also makes any bald spots in your scenery less obvious later on. I don’t know what kind of glue you plan to use but it should stick to a painted surface. I use a very thin layer of caulk to attach attach the cork roadbed to my painted foam and it sticks very well. I had to remove some track one time and some foam came up with it. Cowman’s advice to paint all wood surfaces is good advice. My layout is built of 2 foot wide “dominos”–a 1X4 box frame with cross members in the longer ones, 3/8" plywood on top and foam on top of the plywood. All the wood surfaces got a coat of primer and a coat of paint. I painted the underside of the box white to make it easier to see the wires etc. when working underneath and it gives me a surface to write on with a felt pen to identify the wires going up to the track etc.
As my railroad is outside, I seal everything, all sides, with an elastomeric paint before fabricating and assembly. I also paint the extruded foam. Before installing any benchwork, I seal the exposed cuts.
If you’ve had plywood warp, you really have to address that first. Sealing it is a good idea, I guess, but you might want to consider framing your new layout. A 1x4 frame should do it. If the 1/2" ply decides to warp, the foam won’t stop it. If a framed piece of plywood warps, then you’re in pretty scary territory…
Some people laughed at me when I used treated lumber and plywood for my benchwork for my current layout. I did it for the very reason that you discovered. Previously I had used untreated wood and due to the humidity here by the lake it warped, plywood and benchwork both. I suggest you glue down your cork first then paint. If you paint first you could have a condition where the paint doesn’t adhere as well as you’d want it to and the glue could cause it to pull loose from the foam. Been there and done that.