Interesting.

If it's not too late, what would happen if you just sealed the foamcore with paint? 

Or a sheet of plywood

Seems like a sheet of 1/2” plywood would be simpler and better than a sandwich of brittle plastic and (potentially) squishy foam.

White glue & plastic

Its quite an unconventional choice for benchwork.

White glue really won't be a "permanent" glue on plastic, unless your rough it up to provide something to grip to.

I would be concerned that using a water based glue on one side of the foamboard would cause it to warp and 1/16 plastic isn't going to have rigidity to keep it straight.  I have never tried this, so I have no experience and may be all wet (so to speak).  If you flex plastic on foam with white glue, I would be concerned the white glue would just come off the smooth plastic.

Just as a question, did you consider just a sheet of plywood?  Most big lumber yards will sell a 1/2 sheet of plywood, and will make one cut for free or multiple cuts for a nominal charge.  That would have been cheaper and potentially easier solution.  If you cut a 48x48 piece of plywood 30" wide and then cut the scrap 30" from one end you can cover a 30" x 66" area with an 18" square scrap left over and just two cuts.

If you are going to use foam core and plastic

Like others have said that is a job that white glue may have a lot of trouble with. Also the foam core to an extent. I build a lot of structures with those two materials and the best glues I have found are Super 77 spray and Devcon WeldIt.

Elmer's Foamcore Enhancement Responses

Thanks for the responses.

To answer the questions above. 

1) I am trying to find a way to build without using plywood. Not that foamboard is any better ecologically but even a 1/2 inch plywood is too hard and rigid a surface for what I envision. I am a bit of a contrarian and experimenter trying to find other ways to do things rather than the old tried and true. I am not a carpenter at all and prefer full size materials that I can cut and shape without sawing (model saws on plastic and stripwood are of course allowed.) I did not cut any of the wood in the picture that accompanied my original post. I had it done at a Rockler store which had proper tools and skills for cutting fine grain wood. 

2) I am now thinking about a non-water based spray adhesive like the 3M product above to attach the thin plastic to the foamboard. I realized immediately after the initial post that carpenters glue is a water based product and may weaken the foamboard.  

3) I have enough foam board to laminate two 1/2 inch thick pieces together to build a 1 inch thick baseboard and then cover that with the plastic thin material to create a water resistant (not necessarily waterproof) surface for the first section of the layout (which is essentially one big yard.)

4) For the next layout baseboard section I may try to use 1/2 inch Gatorboard or Sintra.  About 20 years ago there was a board product on the market at 3/16 thick that had a very tough plastic outer layer. Could not find it. For Sintra board I need to find a local source. These are advertising and display materials.

Elmer's Foamcore Enhancement Responses

I realize I did not respond to Jeff's suggestion of just sealing the surface of the Elmer's foamcore with paint. That is not a bad idea. What paint would you suggest?  Wouldn't it have to be a non-water based paint or sealer coat?

I am going to use a small section of Elmer's 3/16 foamcore to test some of these ideas before tackling the larger baseboards.

sealing

I use Krylon or Rustoleum spray paint on the foam board both sides.

"I purchased two sheets of

    30 inches as a long span for 1/2 foam core/thin plastic ro span. I'd divide that space with cross members about 12 inchs apart.  If building with foam sheet for structural strength a 2 inch or 4 inch thick piece is gonna be a lot more rigid than a 1/2 inch thick piece. Not only ultimate strength but stiffness and potential sag has to be considered. ...DaveB

Liquid and foam core

I've had no issue with warping until the latest project. I am modeling an orchard and was using air dry clay for raised rows. The mistake I made was cutting some small holes in the foam core surface for the clay to grab the surface so it wouldn't come off. Common technique under many circumstances when glueing to slick surfaces.

 Cutting to the chase.....I'll never do that again with foam core. Bow.

I was rethinking latex house paint

The stuff is basically liquid rubber sheeting in a can. But if Rick gets good results from Krylon or Rustoleum spray paints (I'd recommend something from the Camouflage line), I won't argue against positive experience.

Test

Test the paint first.  Some paint solvents will dissolve foam.

Jeff

I've also used latex house paint. Works great. If my scenes are going to have open fields I have a tan latex that I use for all my scenery base. I only recently started using camo spray on the modules as I have quite a bit of it and it is quicker........basically I'm lazy.......the spray paint is always handy but the quart of latex I have to find, get out a paint brush, paint, clean up brush etc. Spray I just take outside and blast top and bottom including balsa wood frame....done.

The one module that has a bow in it now was spray painted. Not the paint's fault but a very poor decision by the clown that took the xacto to the top surface to put some "tooth" on it compromising the water barrier.

Latex

dave 1905

Always a good idea but in this instance you are painting the heavy paper facing and not the foam.

Sintra board

Hi Ken,

TAP Plastics has PVC Board which sure sounds like the old Sintra board when you look at it's specs... They have it in grey and white, 1/8" and 1/4". Might be worth a call...

Best of luck,

-Eric

I am a bit of a contrarian

Sounds like you somewhat enjoy looking at alternative methods/materials. I do the same sometimes.

I looked into this 'foamcore' subject quite a bit at one time. The first observation is that there are a LOT of conflicting definitions about this term foamcore. There are all sorts of materials referred to as foamcore.

Many of the cheaper varieties seem to have some sort of paper based facings. These are very sensitive to water-based scenery technics, thus should be avoided.

I would suggest you do some searching and reading on this forum,.... and in particular look up Prof Klyzlr's postings. He has quite a bit of experience with this subject. Look what I just found when I searched "Klyzir foamcore" on this forum site,..
https://www.google.com/search?q=Klyzlr+foamcore+site:model-railroad-hobbyist.com&source=univ&tbm=shop&tbo=u&sa=X&ved=0ahUKEwiVkN6V5_rjAhUFxVkKHavlCXUQsxgIMg&biw=1093&bih=483

Gatorboard and Foamcor are my 2 best choices at this time.
 

Like others have said, plywood for your simply project sounds appealing. Perhaps add a layer of foam insulation onto the top of the plywood and have a carve-able surface, as well as easy to plant trees etc.

NOTE: Foamcor and FomeCor are NO longer at the top of my list

Sandwich Constructed Subroadbed Panels

BTW, here is another discussion where I was looking for alternatives to 3/4" plywood decks/shelves for my round the wall layout plans.
 

Sandwich Constructed Subroadbed Panels, Plywood Sheet Alternative

https://forum.mrhmag.com/post/sandwich-constructed-subroadbed-panels-plywood-sheet-alternative-12207780

Great ideas

Here's what I did. If it helps, good. If it don't, just forget it. LOL

The base is 2" pink foam from Home Depot. It's caulked to metal brackets below. It is painted with regular indoor house paint. Top and edges are tan, bottom is white. View from below is nice, all white. The "roadbed" is two layers of a foam board. Took a 20"x30" roam board, cut it into two sizes of strip, first a little wider than the track and the second a little wider than that. Not pretty. Painted them the same tan. Apparently house paint don't attack plastic foam or the paper on the "foamboard". I sprayed the track with a brown and carefully laid loosely roadbed and track in place. Got it aligned and marked the base. Spread caulk/DAP Alex Plus/again from HD. Placed the first roadbed down, caulked it, next the narrower roadbed, caulked and places track. Weighed them down with cans from the wifes pantry. I did about 6' at a time. All went well. I used some cackle on that end track, but the caulk could work too. I will need to spread something/caulk? on the edges and repaint. Final ballast will come later - after I'm sure the track is reliable. i.e. Play trains on each and every track in every possible way. Fast, slow and act Klutzy to be sure it's good. Ballast is a later thing, as is scenery. In my case, the wiring is on top, to be disguised with scenery. But you could put feeders through the base and also use some bracing below. I did NOT use any nails, screws/except for the brackets into the wall, or wood. Just the plastics. After fascia, it looks good. Hope this is useful information.

Pink Foam Problem is Transportation

The problem with the pink foam solution is transportation. I just don't have a friend anymore with a truck or large SUV to get it from the nearest DIY that sells it about 50 miles away. I am basically an urban dweller.  Then it would need to be cut up as it only comes in 4 ft x 8 ft sheets and I don't have a space to cut a large board of any material.  And I would only need one sheet. 

As to Brian's comments. I did read your earlier thread and it was one of the ideas that started me on this journey. 

I like the idea of foam core

I like the idea of foam core for structures, especially large ones. I wonder about the idea of painting  the foam core and then gluing to the painted surface. I suspect the only bond will be to the paint and that will rely on the bond between the paint and the foam core. It does not sound like the potential for a strong bond exists.

I would suggest a caulking material that is suitable for the materials the foam core is made of and the material that will be attached to the foam core. I suspect a wee bit of time in the glue and caulking aisles of the big box stores might turn up a very easy to use solution.

Another thing that I have always been curious about is why many folks put the supports as far away from each other as possible. L girders at the ends mean the entire span is between them. If on the other hand the L girders are centered on the space 1/4 of the way in from the edges the longest distance from an L girder is 1/4 the width instead of 1/2 of it. It adds to the rigidity of the surface.

I believe one of the folks on the MRH staff came up with a very light and strong layout substructure using 1/8th inch plywood and hot glue for assembly quite a while ago. I always thought this was very innovative and would lend itself to someone with minimal carpentry skills that desired very light weight materials to work with.

Foam transportation is not a problem.

Rob in Texas

Foam core is great for a base but is not as usable for structures....my opinion.

I find that a stable building "pad" and some key vertical partial wall sections utilizing 1/8" to 1/4" sanded plywood to be key to constructing a large structure. Outside surfaces of .040 -.060" styrene laminate quite easily to the plywood inner supports.

 As to gluing and easily building foam core module surfaces it is very easy with minimal tools. Titebond yellow glue, a few little clamps, xacto knife and a little razor saw and you can put together a really strong module surface with foam core top and balsa wood support. 

The following picture is a quick snapshot of the technique in action. 6 modules holding all the structures. All removable for workbench construction and repairs/changes as needed. The green module on the left is turned over to show the very low tech balsa support underneath. The random look to the balsa wood supports is due to it  being installed over an older section of layout that I pulled the top off of to go to the modular approach. The balsa was placed to bear on old benchwork. Trust me....it would be a whole lot easier to do if I had built the benchwork to support these modules in the first place. Live and (hopefully) learn!

These photos show the use of plywood and styrene in the buildings attached to the foam core modules.

Foam Board

I know the problem. I too, was faced with trying to get a 4'x8' board. My local HD would not cut it. The Lowes/which sells the blue stuff would not either. What a bummer. I had to find a friend who could go to HD, buy the board, take it home/or wherever and cut it for me. If that's not feasible, try asking if they/HD or whoever, would let you use the equipment. Sign a disclaimer if necessary so they won't be liable if you hurt yourself. But from what I've heard/read, you can cut it with a sharp knife. The board is 2" and a 1/2" blade should make a pretty deep cut and doesn't this board snap at that cut? If edges are relatively smooth, it's fine. This is just a suggestion and how I would go about it if I hadn't found a friend.

Foam Board Transport

I too was faced with not having the capability of transporting large sheets of foam a while back. I went to the store equipped with a sharp utility knife (blade extends about an inch), a long straightedge, measuring tape and a pencil. In the parking lot I cut the 4x8 sheet of foam using the score and snap method (this was 2" foam). I knew it wouldn't leave a nice clean edge so I "overshot" by an inch and cleaned it up at home with a hot wire tool. Fit everything in a medium sized SUV no problem.

I was going to experiment with GatorBoard but found myself in the midst of a scale change (N to HO), which led me to constructing a shelf layout using Ikea bookshelves and shelf planks cut for me at the local lumber yard.

Either way I can appreciate your desire to seek out alternative methods that do not require power tools etc. After living in a large home with a basement full of tools I am now in a condo.

Rick, I do not think I was

Rick, I do not think I was clear on the type of structures I was thinking of. Clearly those wonderful structures you built would not be suitable for the methods I was thinking of.

I was thinking of large steel mill structures that might be best represented by simple gabled boxes that are very large, more than a foot tall and 4 feet or much more in length. They have little detail on the outside. I have seen some examples of these made from foam core and they looked very good.

As can be seen there is not much to these from a building point of view other than their massive size. Another option I am considering is very thin underlayment plywood such as the 2.7 mm or 2.5 mm stuff that is available now. At less than 20.00 for a 4x8 sheet it is both inexpensive and durable as well as available locally.

Should I desire to I can buy one of those things that makes corrugated sheet goods and cover them with that when I get to it. Many of the structures are similar to this and either red or black in color, some are in very long lengths that would be more than 12 feet long in HO scale.

Nice thing on mill buildings like this is they could accept a long string of cars or three and actually look like they could do something with the contents and turn it into a new product to be shipped out.