explain rigid foam on the board

[gandy dancer#1]

HI: I have seen pics of set ups with rigid foam on top of the plywood, explain please why, and advantage, and is the foam paintable istead of having to use say indoor outdoor carpet for grass??  a curious mind wants to know

[darthraven]

I am pretty new at this myself, but one thing that comes to mind is being able to make lakes, rivers, valleys without having to cut your bench work.

[Doneldon]

gd#1-

Yes, the foam is paintable (latex only) and very easy to carve below railhead features like waterways. It's fairly rigid and just right if you frame it and/or put some plywood under it. It's also easy to attach track and scenery to the foam. Just use any foam-safe inexpensive construction adhesive. Many folks use clear caulk; I like Liquid Nails for projects.
                                                    -- D

[rogertra]

I am pretty new at this myself, but one thing that comes to mind is being able to make lakes, rivers, valleys without having to cut your bench work.

Then don't use solid benchwork!

Use open frame benchwork and only put subroadbed where the tracks go.  Elevate ALL your subroadbed on risers so that your scenery can easily be built above and below track level.  Having a large, solid areas under the tracks in only good in yards, where you have multiple yard trackage.

For everywhere else, even at small "stations" and passing track or where spurs leave the main track or sidings,  use open frame benchwork.

[Desertdweller]

With all respects to Roger, I don't think this is a "one size fits all" solution.  Solid plywood benchwork has its uses, especially if you want to be able to change track configurations.

My model railroad is built with sheets of 1/2" plywood, framed by 1x4's.  The framing is screwed to the plywood on edge, with one bracing piece across the middle.  The sheets measure 2'x4' (for an N-scale railroad).

This plywood is covered with two layers of 2" thick blue foam insulation board.  This allows me to cut through one layer to make scenic relief, while retaining a layer still covering the plywood.  2"x4" legs are attached at all corners.  The bottom face of these legs are drilled, with cage nuts and carriage bolts allowing height adjustment.  The legs are braced with furring strips.

My railroad has large yard areas, and models an area that is mostly flood plain.  A length of 1" thick blue foam board, about 10" high, forms a view block on part of the railroad.


If you want secondary track at a lower level than main tracks, use lower ballast beneath the secondary track.  For example, my main tracks are made with EZ-track, and secondary track is flex track with foam
roadbed.

Les

[rogertra]

Dessert.

Agreed, one size doesn't fit all.

My old GER was 12 x 16 feet around the walls with a peninsula.

The only solid sheet of plywood subroadbed was the yard at Granville Junction, which was about ten feet long and two feet wide.  All the yard "bowl" and the industrial tracks were build on a "solid" 3/4 inch sheet of plywood while all the other tracks only had the subroadbed under where the tracks went: -




and from the other direction: -




All the rest of the GER was built using open grid, as seen here in the demolition photo: -

[Jim Banner]

I have used the "conventional" construction Roger speaks of and find it extremely versatile for scenery both below and above track level.  My preference is to use 1" chicken wire tacked/stapled to the sides of roadbed and to its own risers, then cover it with a couple of layers of paper towels, or better, used Bounce sheets dipped in plaster of Paris.  The chicken wire makes it easy to visualize the general shape of the final scenery, rather like a net diagram.  Once the plaster of Paris has set, you have a strong base for the final layer of plaster.  This final layer can be plaster of Paris or Drywall Joint Cement, depending on how you are detailing it.  The only down side of this "Hard Shell" method of making scenery is its weight.  While lots of weight is unimportant  for a permanent layout, it is the last thing you want in a portable one.

Most portable and transportable layouts are limited to flat scenes or minor grades because of volume consideration during transport and storage.  So being able to cut only an inch or two below track level or build up only a few inches above track level is not a problem.  So foam is a great way to go for portables.  But if your dream is a home layout with high mountains and deep valleys, then conventional construction is a better way to go.  As far as strength goes, I find a 1 x 4 fame with 1 x 3 "joists" every 12 inches gives lots of strength for tables up to about 4 feet wide.  With the joists only a foot apart, no plywood is necessary under foam 1-1/2" or thicker, even in large scale.  The exception would be under deep lakes etc. that almost penetrate the foam.  Then pieces of plywood or scrap foam can be glue under the lake to provide extra support.

Access hatches are a snap with foam.  They can be easily cut with a knife, even after the scenery is down if you use soft scenery.  Just make sure you keep the knife angled a bit toward the center of the hatch when cutting down through the foam.  That way, the top of the hatch will be slightly larger than the bottom and will sit in the hole like a cork in a bottle - no extra support is needed.

Keep in mind that the foam we are talking about is Styrofoam or equivalent, usually coloured pink or blue.  White "bead board" that is made of Styrofoam balls pressed together does not have the necessary strength unless you use plywood or similar material to support it.  This added cost usually more than offsets any price savings you might have by buying bead board.  For gluing Styrofoam, I like LePage's PL Premium as it sticks to most model railroading materials including foam, wood and stone.  http://www.lepageproducts.com/ProductDetail.aspx?pid=84   I recently tried PL Premium Advanced but cannot recommend it unless you happen to own a high pressure air operated caulking gun.

Jim     

[gandy dancer#1]

Evening: I appreciate all the replies on this, and it has helped me make some cetter decisions. My workbench if you will, will be laid out in an "L" shape against2 walls. each section measuring 36" inches wide, by 72" long. Made of 5/8 mdf on 2 cafeteria style folding tables. I am thinking of laying approximately 2 inches of foam board on top and going from there. I have been in a quandry trying to decide to lay green carpet orthe fake rolls of grass directly on the board, but have figured out doesnt give me the flexibility of contouring. So thanks guys. by using the foam and being able to paint several brown and tan base colors, then using the shaker gras and foliage ican produce a better look at cheaper cost,bottom line and on budget is it in any  construction have patience with me, i'm learning , and you guys are my "WORLD BOOK ENCYCLOPEDIAS"