How do you handle flat terrain?

[Ed Kapuscinski]

The only think I want to mention is that I would try to sway you away from using just foam as the layouts base.  It needs to be more substantial. Friend of mine build a layout like the one you are planning and he regretted that later.  I worked on it and later operated some trains and it was really flimsy.

I will agree with this.

I tried doing this on a multi-part layout and it just was not reliable enough.
When I build Windsor St it was foam on top of dimensional lumber frames (think NTRAK module style). That worked great.

The issue with a complete lack of a wood structure is that you don't have anything to use to attach things to (like DCC panels) or to use to attach sections together rigidly.

[nickelplate759]

I will agree with this.

I tried doing this on a multi-part layout and it just was not reliable enough.
When I build Windsor St it was foam on top of dimensional lumber frames (think NTRAK module style). That worked great.

The issue with a complete lack of a wood structure is that you don't have anything to use to attach things to (like DCC panels) or to use to attach sections together rigidly.

Good point.  My foam is on top of a wood frame, with strategic reinforcement of aluminum structural shapes for long spans. 
Gluing the foam to the frame made the entire structure a good deal sturdier.

Wires, DCC boards, etc. are all fastened to the wood frame.  Tortoises are screwed to 1/8 plywood plates that are glued to the foam.   The trickiest thing is that invariably the ideal placement of some of the Tortoises is right where a part of the wood frame is in the way.  In one case I actually ran the Tortoise actuating wire vertically through a wood brace.

[Steveruger45]

Good point.  My foam is on top of a wood frame, with strategic reinforcement of aluminum structural shapes for long spans. 
  ....... The trickiest thing is that invariably the ideal placement of some of the Tortoises is right where a part of the wood frame is in the way.  In one case I actually ran the Tortoise actuating wire vertically through a wood brace.

...
Yep, been there and done that too 🤨.  Next time I build I will leave the cross braces out until after the track is down and then put them in glued to the foam and screwed to the side frame.  I too find foam (blue or pink) glued to a wood frame with suitable cross braces is pretty darn solid.  I actually prefer to use plywood strips rather than dimensional lumber though.

[C855B]

The only think I want to mention is that I would try to sway you away from using just foam as the layouts base.  It needs to be more substantial. Friend of mine build a layout like the one you are planning and he regretted that later.  I worked on it and later operated some trains and it was really flimsy.

I'm really not comfortable with the generalizations that all foam is bad. There are pronounced differences in XPS quality. In our use, pink foam (Owens Corning Foamular) is superior to blue foam (Dow), which is better than green-blue foam (Lowes-labeled, and others). Also, 25 psi XPS (Foamular 250) has better structural characteristics than 15 psi XPS. White beaded foam, which I have seen some MRRers use, is a total non-starter. White foam = "What were you thinking?!?"

OK, so some foam paneling is inappropriate as MRR construction base, but not all, you simply have to know what you are using. Bear in mind that the industry manufactures XPS foam as insulation and not as a structural medium, except in the higher grades for use as insulating underlayment under floors, including poured concrete, starting with the 25 psi cited above. So "just any" foam may not be ideal, or even minimally structural.

That said...

My layout is 2" Foamular 250 on riveted steel framing, benchwork panels glued to the frame with foam-compatible construction adhesive. No wood anywhere. In most locations there is no more than 2' between supporting frame members. I am pleased/astounded/elated that this is the most stable foundation I have ever experienced in 50 years of MRR construction. Zero track pops due to expansion, contraction or shrinkage. The 2"/25psi is plenty strong, I could walk on it. But I don't because, yes, it is still foam and just the momentary angled contact would indent the foam.

As to dimensional consistency through the panel, again this is a factor of product quality. Foamular is best in this regard, as well; the blue stuff... well... sucks. The only problem I have observed is occasional thickness variation at the edge, and there is no way to tell if this is due to manufacturing, or shipping and storage. A little lightweight spackle and a few swipes with a sanding block and it's done.

One thing I have found is using the 2" grade is very important. In one area with level changes I used laminations of 1" and 1-1/2" material to create 2", 2-1/2" and 3" thicknesses. That was a slight mistake. 1" + 1" ≠ 2", at least structurally, I get more deflection than I would prefer when I lean on it. It's still dimensionally stable, I just have to be mindful it's going to bend 1/8" or so if I press hard on it.

Executive summary: a high-quality foam makes a difference.

[wm3798]

As for the scenery vs. track work, Yes, there are modest grades everywhere.  Track crossing a culvert or a bridge probably dropped almost imperceptibly to get there.  I've seen plenty of pics where that undulation makes for a really cool picture.

In this view, courtesy of the Borg, you can see the track on the left is in a slight cut in the foreground, then is elevated, then it bends away from the road.  It definitely has some up and down to it, I've followed that line many times.  Meanwhile, the road follows the terrain up and down more completely. 


So it's not hard to trick the eye with the surrounding scenery to make the railroad look a little uppy downy.  But if that's the shot you're looking for, you'll need to have some actual uppy downy...



Lee

[CRL]

I'm really not comfortable with the generalizations that all foam is bad. There are pronounced differences in XPS quality. In our use, pink foam (Owens Corning Foamular) is superior to blue foam (Dow), which is better than green-blue foam (Lowes-labeled, and others). Also, 25 psi XPS (Foamular 250) has better structural characteristics than 15 psi XPS. White beaded foam, which I have seen some MRRers use, is a total non-starter. White foam = "What were you thinking?!?"

OK, so some foam paneling is inappropriate as MRR construction base, but not all, you simply have to know what you are using. Bear in mind that the industry manufactures XPS foam as insulation and not as a structural medium, except in the higher grades for use as insulating underlayment under floors, including poured concrete, starting with the 25 psi cited above. So "just any" foam may not be ideal, or even minimally structural.

That said...

My layout is 2" Foamular 250 on riveted steel framing, benchwork panels glued to the frame with foam-compatible construction adhesive. No wood anywhere. In most locations there is no more than 2' between supporting frame members. I am pleased/astounded/elated that this is the most stable foundation I have ever experienced in 50 years of MRR construction. Zero track pops due to expansion, contraction or shrinkage. The 2"/25psi is plenty strong, I could walk on it. But I don't because, yes, it is still foam and just the momentary angled contact would indent the foam.

As to dimensional consistency through the panel, again this is a factor of product quality. Foamular is best in this regard, as well; the blue stuff... well... sucks. The only problem I have observed is occasional thickness variation at the edge, and there is no way to tell if this is due to manufacturing, or shipping and storage. A little lightweight spackle and a few swipes with a sanding block and it's done.

One thing I have found is using the 2" grade is very important. In one area with level changes I used laminations of 1" and 1-1/2" material to create 2", 2-1/2" and 3" thicknesses. That was a slight mistake. 1" + 1" ≠ 2", at least structurally, I get more deflection than I would prefer when I lean on it. It's still dimensionally stable, I just have to be mindful it's going to bend 1/8" or so if I press hard on it.

Executive summary: a high-quality foam makes a difference.

I’ve built layouts with a wood ladder frame with a plywood top as the structural base, with white styrofoam beadboard on top the plywood, with the track glued directly to the beadboard. Very stable and no problems. I’ve also used the blue foam on top of plywood base with the track glued to the blue foam. I’ve had no problems with this approach either. However, in my experience, the white beadboard is much easier to carve for scenery, so it’s my preference... but NOT without a structural baseboard of plywood, Masonite or a “structural” (blue or pink) foam. If total thickness isn’t an issue, using a structural foam baseboard allows you to use Mr Icepick as a drill for wire drops. But if a thinner total foundation thickness is needed, use plywood.

One issue I’ve had is what glue or adhesive to use when layering foam... water based adhesive takes a LONG time to dry if more than a couple of inches from the “edge” exposed to the air. I think there are some foam compatible contact type spray adhesives I intend to investigate. Hot glue also works, but sets up very fast on “low heat” setting, or may melt the foam on a “high heat” setting. It’s good for small pieces, but not for bigger pieces.

[wm3798]

Sure, you can carve the white beadboard stuff, but you better have the vac handy.  Those little staticky devils get everywhere.  I much prefer extruded foam. more rigid, less crumbly, much easier clean up.
Lee

[davefoxx]

I will agree with this.

I tried doing this on a multi-part layout and it just was not reliable enough.
When I build Windsor St it was foam on top of dimensional lumber frames (think NTRAK module style). That worked great.

The issue with a complete lack of a wood structure is that you don't have anything to use to attach things to (like DCC panels) or to use to attach sections together rigidly.

I've got 2" foam over 1/4" lauan over 1" x 2" framing over L-girders.  That plywood does make it strong enough to lean on, and I have, as evidenced by the elbow dents in the scenery.    That plywood also, as Ed pointed out, gives me structure to mount under-table switch machines.

DFF

[Dave V]

[CRL]

Sure, you can carve the white beadboard stuff, but you better have the vac handy.  Those little staticky devils get everywhere.  I much prefer extruded foam. more rigid, less crumbly, much easier clean up.
Lee

In my experience, you need a vac with both types of foam. Both the white beadboard and the blue or pink foam produce the same amount of foam waste/dust. The beadboard just carves so much faster & easier using a small wire brush that it seems you’re producing more waste. You have to use a sure form plane or rasp to carve the blue/pink foams, and that dust is just as bad as the beadboard... it just takes so much longer.

In order to look good, you still need to cover the styrofoam with some type of goop to form ground cover.

[wm3798]

I use my band saw to cut the main shapes out of 2" foam... granted, not everyone has a band saw... or a workshop that's separate from the living areas.  But for fine trim work, I use a sharp serrated filet knife.  Cuts through the blue foam like butter, and hardly leaves a scrap.

I also like 2" blue foam because my customers who are builders always seem to have a lot of big scraps in their dumpsters...
48" panels, 32" deep crawl spaces...  do the math!  16" makes a nice shelf layout!

Lee

[Ed Kapuscinski]

I used to be a fan of the 2" stuff but I've recently changed my mind and prefer the 1". That's because it's a lot easier to stack and get plateaus at different elevations AND it's easier to carve. It's a lot easier to do gentle slopes through two sheets of one inch (individually) than one sheet of 2".

[eja]

Anyone besides me old enough to remember the must have Christmas gift a long time ago - the GE Electric Carving knife. A two bladed instrument that was OK for its designed purpose (carving the bird I suppose) , but also wonderful for carving foam of any kind. 

Clean cutting and very little of the flinging  excess.


Probably available at your local thrift shop .....

[peteski]

Anyone besides me old enough to remember the must have Christmas gift a long time ago - the GE Electric Carving knife. A two bladed instrument that was OK for its designed purpose (carving the bird I suppose) , but also wonderful for carving foam of any kind. 

Clean cutting and very little of the flinging  excess.


Probably available at your local thrift shop .....

Electric knives are still being made.   If you look hard enough, you might even find a cordless electric version (but I think all of those are vintage).

[CRL]

Yes, I rough cut foam with a knife, but it leaves an unrealistic flat shape. For final shaping I use small painters wire brushes. These work wonderfully on white beadboard foam because the wire brush will break open the beads and leave a fuzzy surface that is perfect for accepting the Celluclay & Latex Paint goop I use for ground cover base texture. If you leave unbroken beads on the surface, you’ll get little white boulders peaking through your ground cover. Dust with dirt or ground foam while it’s still wet, then spray with wet water solution until the paint color starts leaching through the zip texture cover. The Celluclay will accept “soft” detail like dirt contours, but if you want hard detail like rock ledges, use a plaster product like Sculptamold or rock molds.

I’ve seen some very nice eroded rock detail accomplished by carving blue or pink foam and some precise application of solvents to erode the foam, finished with color washes, but the finished surface is easily damaged & gouged. The Celluclay/Latex Paint surface is very tough & remains flexible if the zip texture layer remains thin. Overall, I’ve been underwhelmed carving blue/pink foams.