I went with cork

"my question is what to cover

To get the ideal material under both track and non track areas I first cut out 1/4 inch plywood roadbed ( cut to tie width) and glue it down to accept the track. In the non track areas that I might want to carve I then add a layer of thin foam( dollar store foam core works well) or other easy to carve material. If the area doesn't need much over lay I just add a thin layer or fixall, sculptamold, or what ever seems best for the spot. This method doesn't require glueing down large sheets of material and then cutting away a lot of it,  this is more additive than subtractive so easy to work in stages. The photo shows the 1/4 inch plywood roaded bed glued down for my engine terminal area, the non track areas here will get sheet foam to make them into a gravel maintence of way/ parking lot mostly flush with the tracks....DaveB

Cork, Ply

Joe - I thought you had gone with sheet rock, maybe that was on the old layout?  Good to know you're going with cork, and that painting it works.

Dave - pictures of your layout is one of the things that got me thinking about this in fact.  I like your approach, but it requires knowing in advance exactly where the track will go.  I've done the glue down homabed thing in the past and made revisions later and it's doable but not easy.  This time around I want a whole surface of roadbed so I can easily shift the track around to fine tune the operation and appearance until I'm happy with it, then glue the track down, and cut out the stuff wherever the track isn't.

Sheetrock and weight

Yep, old layout. On the new TOMA layout, I'm very interested in keeping things light weight. On the old layout, one 18" wide shelf 12 feet long with plywood and sheetrock, plus the benchwork lumber came out at 250 pounds per the town dump scales. That's 20 lbs per foot! A six foot module would be 120 lbs, the limit of what one guy could lift!

So doing 1/4" ply and cork on the new layout for flat areas. In some cases, I'm just caulking the track straight to the plywood. My goal on the new TOMA 6-foot module sections is no more than 40lbs each.

Foamed PVC...Cellular PVC

http://www.acmeplastics.com/expanded-pvc-foam

https://forum.mrhmag.com/magazine-feedback-was-ezines-891776

I built a turntable pit with this material,.
https://forum.mrhmag.com/post/building-your-own-turntable-12215516

...and my structure for the stone arch bridge
https://forum.mrhmag.com/post/stone-arch-viaduct-bridge-12213517

And JoeF, it is really light weight

...you might get your local sign shop to order you a full size sheet or two at their price and delivery. My shop indicated they would do that for me if I ended up needing more than the scraps I got from them. And you might be able to salvage old signs printed on this material, ,...particularly expired political signs.

try this stuff, it is really versatile

 

Just MHO.

Thank you, DaveB. As for what I did, successfully. I used that Dollar Tree foam board/$1 for 20"x30". Cut it in strips wide enough for track and another strip a bit wider for under that board. Sandwich. All caulked with DAP Alex. All weighted down with the track all at one time. Solid and still going strong. The idea is what DaveB stated. Use the Dollar Tree stuff to cut to size to fit whatever space you need. Easy to cut with scissors or Xacto knife. Easy to adhere in place with the caulk. And can be pried up if necessary. For me, it was the easiest material to work with I know of. No mess. No little foam beads and not as dense as the 2" pink foam. Took paint  really well. Both oil and water based. I did paint both bottom and top, just to seal and take the caulk really well. What made me smile was the cost. Cheap enough to cover a good area. If you wanted the entire layout covered, then go with the cork. But for cutting to size and such, I like my foam poster board. Just trying to be helpful. If you don't like my idea, do what you want. LOL

Foamed PVC

That’s interesting stuff Brian.  Looks like it’s fairly stable temperature wise (~1/16” over 8 feet for a 15 degree change).  The spec sheet has a fairly detailed section on what glues to use for bonding to different materials.  The cost is a bit high, but not outlandishly high given that 3-4 4x8 sheets would do the job for me.

It doesn’t appear to be significantly better than cork though.  Cork gives you more flexibility on glue choice, it’s cheaper, and can be shipped on a roll which increases the odds of getting it undamaged as opposed to 4x8 sheets.

That foamed PVC may be a good material for structures like large warehouses though.

  "I've done the glue down

I guess if I had to do it that way I'd probably go with a fairly high density foam sheet like the purple builder's foam and just glue down all the track. There would be considerable mess made when carving a lot of it away however . Sheet rock would also work if you glued everything to it but it would not be any better than foam for holding nails( the gypsum core cracks when a nail is driven in, just leaving the paper face holding the nail). and would be as messy as foam when carving away the unneeded material. If you are not sure where the tracks will end up I guess you could tack it temporarily down and when you get a configuration you are happy with draw lines around the track and remove it then cut plywood or other suitable roadbed material to fit the lines. Finally glue down the roadbed and re-install the track then fill in the scenic areas as need . More work but maybe easier work? I have a bandsaw so cutting roadbed is painless, if you don't have a good jigsaw it might be harder than carving out all the unwanted areas.....DaveB

planning in XtrkCAD instead of shifting around real track?

It's tempting to put track down, and optimize things on the fly (assuming the track you use can easily be realigned - not necessarily true for e.g. ME flex track), but I would (and am going to) use track planning software to take my time and figure out where the track should go. Then I would (and am going to) put self adhesive camper top seal tape down as the sub-roadbed (cork or AMI or Woodland Scenic roadbed will go on top in non-yard areas). The camper top tape can be lifted up and repositioned if need be, before ballasting of course. 

I am using the relatively stiff ME flex track, so repositioning the track would be very limited anyway once it is all connected.

Also, I'd keep Joe's comment on weight in mind before committing to any substantial amounts of particle board or plywood. 

Ken,Since I can no longer

Ken,

Since I can no longer buy California Roadbed's Homabed product, I had to figure out what I was going to use, as well. I found a product called Flexxbed < https://hobbyinnovations.com/> and sent for a free sample. I have not used it, as construction of the extension I have planned, as not begun. I think it shows great potential. Check out the website listed above. I have no affiliation other than as a possible customer. Glenn

Cork sounding good

I think you are making a case for cork, and not necessarily in sheet form which might make for a lot of waste.

In my limited use of cork I've found I can glue it to the plywood with that flex caulk that came highly recommended, ..then when I wanted to reposition track I could get that cork back up with a nice metal scrapper. And in a few cases I am able to reuse that cork in the new slightly modified position of the track plan.

Cork also lends itself well to ramping / grading. I don't think I would want the mess that might be created by ramp sanding the pvc stuff. And I understand homabed can be quite dusty as well.

BTW, just regular cheap PVC pipe cement does a good job bonding that cellular PVC

Sheet examples

This fellow utilized sheet material like you are asking about
https://forum.mrhmag.com/post/laying-cork-roadbed-12216966

My two ramps for turnout ladders
https://forum.mrhmag.com/post/laying-cork-roadbed-12216966

PVC roadbed

Here are a couple of areas where I am using that PVC material as roadbed

Logging Scene

...and here   https://forum.mrhmag.com/post/logging-locos-logging-track-plan-logging-mill-mainline-pickup-12213119

Cad, weight, flexxbed

Dave - I’ve thought about the approach you suggest of leaving a sheet of 1/4” ply loose on the layout surface, getting the final track positions worked out, then trace, remove everything, and cut to shape and reinstall permanently.  Easy enough to do (I do have a jigsaw).  That is a fallback option if there’s not a good way to try the approach I want to try - glue down the whole sheet permanently, then later after track position is finalized remove the parts in the way of lower scenery as I make progress on scenery.

Glen - If I remember right flexxbed is fairly squishy?  I’m looking for something pretty firm.  And also in sheets, I want to cover the whole layout surface.

Stefan - Totally agree about the cad.  I’ve been using cad (Ashlar Vellum) for layout design for my current plan as well as the previous couple layouts.  Makes it easy to be sure you’ve got easements and everything else accounted for.  But I also know from experience that a plan which seems perfect in cad may run into some unforeseen problem, or a visual adjustment one you get the track in place and start doing some test op sessions.  With homabed and handlaid track the cost of changing positions a little is pretty high, so you tend to live with what you’ve got.  I want the cost of last minute adjustments to be very low so I can tweak positions easily.

Weight is not something I’m concerned with.  The layout is not going to be portable, or modular, it will be permanently attached to the wall.  If I move, it will be demolished and replaced with something designed for whatever the new space is.

Brian - thanks for those links.

Changable Track Plans

I haven't even been using smaller size computer scale dwgs to do my planning, .....but rather FULL scale track plans !!,...and I have had to make numerous 'adjustments/changes' to those plans as I actually lay track .  

I prefer Homasote as sheet

I prefer Homasote as sheet roadbed for large yard area's.  Once it is down and level, I do give it a coat of paint for a base color and to seal it a bit.  No messing around with cork of different thicknesses or ramping up or down.  I can draw centerlines and lay track easily and it holds track nails or ME spikes well.  I find it to be easiest to work with and lay track on.

  "That is a fallback option

Hi Ken, As long as you don't need to nail or screw down any track the purple foam should be strong enough for roadbed and is fairly easy to carve or sand away. I'm not sure what the thinnest purple foam is , I've used 1 inch for carved scenic base. If you have large areas to cover it's kinda expensive but would allow you to get going on the layout design and construction. A cheap alternative would be sheetrock but I'd be worried about it's tendency to crumble into scale talus when disturbed. Certain types of ceiling tile can be used as soft roadbed too but they are not full sheets although there wouldn't be too many seams as they are fairly large panels. There's really no ideal material for both under track and non track areas so everything is going to be a compromise. ....DaveB

High density foam board

Dave, you’re talking about something different from the normal pink/blue foam board insulation you can pick up on home depot?  I can’t find anything useful searching for purple foam board, but I poked around a bit and found there are different densities with different PSI ratings, not sure where to get them though.

Track will be glued down in the long run, double sticky taped down for the test period.  I would like whatever I use to be either firm enough to take a screw, or thin enough so I can use a longer screw into the plywood beneath it.  Mounting caboose ground throws may or may not be something I end up doing (going to try finger flicking for a while before I decide), but I want to keep the option.  Anything 1/4” thick is still thin enough to go with a long screw through to plywood so drywall, strong foam, etc. would be fine at that thickness.

high density

some builders foam has the number 250 printed on it

that is strong enough to go under concrete slabs. The lower number stuff is less dense. Around here we have pink,  and blue but they both have the numbers on them

Tapering the PVC material

Just an update. Yesterday while I was fooling around with my ramp structure for the stone arch viaduct, I discovered that I had sanded a taper into the end that reached ground level. It tapered off OK. I believe this is because it is a homogeneous material,...not a skin-over-core material like most foam boards.

I can post a photo if someones interested?

High density foam board

Apparently the number, at least on Owens Corning Foamular, is the compressive strength, which is in tenths of PSI.  In other words, the 250 can upport a 25 PSI load.  They make at least 150, 250, 400, 600, and 1000.  But the stronger boards get significantly more expensive:  https://insulation.supply/products/.  The 1000 is 5 times the cost of the 250.

  "Dave, you’re talking

Hi Ken,  The purple foam I'm using came from Home Depot. It's 1 inch thick and plenty dense enough for model train use. My track is a combination of hand laid and flextrack so I didn't use the foam under the track but am cutting and carving it for scenic contours. I wouldn't be worried about it's strength under glued down flextrack but I wouldn't use it if nail or screw holding was important. That's why I have the plywood for my roadbed....DaveB

Purple foam

Thanks Dave.  I wonder if it’s a regional thing, I don’t recall seeing purple in the local home depot, just pink and blue.  I’m gluing the track, but I do want to be able to screw some things down.

Cork compressive strength

I was trying to find how the squishyness of cork compares to foam.  I found foam insulation ratings in the link I posted above - typical insulation board compressive strength is 15-25 psi, although you can get 100 psi.

According to  https://www.makeitfrom.com/material-properties/Cork, cork’s compressive strength is 150 psi.

It seems like it might be a better choice than foam - stronger in the way that matters, almost as easy to cut/shape, easier to glue, dust from sawing/sanding doesn’t static cling to everything.