Boulder Model Railroad Club
Foam Layout Clinic

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Last modified on: Saturday, March 30, 2002 09:42:24 PM

A clinic by Jere Eggleston and Keith MacPhail


Model railroading has been around for the better part of a century. Today, the hobby enjoys perhaps its largest and strongest following, and this trend shows no sign of reversing, at least in the foreseeable future. A glance at the new manufacturers and products contained in the pages of the  hobby's various magazines quickly bears this out.


Perhaps one of the primary explanations for the continued expansion and improvement of model railroading is the willingness of model railroaders to seek out, and incorporate into the hobby, new ideas. new techniques, and new modeling materials. This open minded approach, shared by the vast majority of modelers, has done more than keep interest in the hobby from stagnating, it has continuously pushed it forward from year to year, and decade to decade.


Model railroaders have always embraced new materials and techniques either as replacements. or enhancements, to existing practices. The purpose of this clinic is to take a look at a material, extruded foam building insulation, that falls squarely into the latter category.


The use of extruded foam panels in model railroading goes back about 20 years, but it has only really come into its own in the past 5 years or so. From all indications, extruded foam is destined to become one of the primary layout, and layout module, building materials, as more and more modelers are exposed to its versatility and ease of use.


This clinic will introduce you to the material itself, discuss the use of extruded foam as both a scenery and benchwork material, examine the basic tools and techniques for working with foam, explore carving and finishing foam into fantastic, light weight scenery, and, finally, look at both the pros and cons of foam insulation as a modeling material.  Hopefully, by the end of this presentation, you'll be encouraged to give

foam a try in your next model railroad project!



Let's get started!


What exactly is Extruded Foam Insulation?:


          A solid, panelized construction material used primarily in the building trades to insulate building walls and foundations.


          The material is lightweight, has structural integrity, and is easy to cut, carve, and "form" using basic modeling tools.


          The material is generally available at lumber yards and home centers, and is most commonly found in 2' x 8' and 4' X 8' sheets.


          Panels can most often be found in 1/2", 3/4", I'', I 1/2", and 2" thicknesses.


          Extruded foam insulation is produced by:


            - Dow Chemical (blue foam)

            - Owens-Corning (pink foam)

            - Amoco (green foam)


          Contrary to popular rumor, all share the same characteristics, regardless of color.


What exactly is Extruded foam insulation? (Continued)


          Now that we've defined what extruded foam insulation is, here is a very important note about what it is not:


Foam "bead board", packing styrofoam, floral/art foams, etc. are NOT extruded foams. They are not rigid and do not possess the physical characteristics needed for carving rock- work and forming scenery contours. More  importantly, these foam products lack the structural integrity needed to be used as benchwork!



Basic "Tools of the Trade":


 The following is a list of the tools and materials most often used when working with extruded foam:


          Sharp, straight edged knife with a 6" to 8" blade (ie: kitchen knife, boning knife, etc.)

          Serrated edge knife (ie: steak knife, bread knife)

          Whet stone

          Single edge razor blades

          Hack saw blades (blade only) - 24 and 32 teeth per inch

          Standard carpenters hand saw

          Table saw (optional, but useful if available)

          Stanley "Surform" tool

          "X-acto" knife with chisel blade and #1I blade

          "Hot Wire" cutting tool

          Coarse sand paper

          Hand held wire brush - short bristles

          Drill mounted wire brush (reference the entry for "vacuum cleaner" below)

          Face mask or respirator

          Bamboo "ka-bob" skewers approximately 10" length

          Water base adhesive (Construction adhesive PL300, latex contact cement, rubber cement. etc.)

          Pre-mixed lightweight, non-shrinking, spackling compound

          "Sculptamold" and / or molding plaster

          Latex and / or acrylic paints

          Dry pigment paints

          Assorted paint brushes

          Vacuum Cleaner!! (the bigger, the better especially if you opt to use a drill mounted wire brush!)


Not all of the above listed tools are required to successfully model with foam. As you begin to work with the material, you'll identify those tools with which you are most comfortable. It is also likely that you'll come up with additional tools or materials that meet a specific need. Don't be afraid to experiment.


NOTE OF CAUTION:  If you choose to experiment with any solvent based materials, do so on scrap foam. in a well ventilated area, with extreme caution. Solvents will attack extruded foam, often in a very aggressive manner!



Basics of Working With Foam:




          Use foam as a Scenery Material in conjunction with conventional wooden benchwork.

                      Land forms

                      Carved rock work

                      Basic landforms, with applied plaster rock castings


          Use foam as Basic Benchwork, as well as Scenery Material

                      Remember, the panels have structural integrity

                      Probably best in smaller scales - Z, N, HO

                      Laminated panels, laid flat for around the walls shelves up to 30" wide.

                      Wider applications, use strips on edge (ie: 1"X4") to build an interlocked open grid.  Then laminate flat foam panel "table top" onto top side of grid for layout surface.


          "Hybrid" of foam panels and lightweight framing such as shelf standards and brackets or light dimensional Iumber.

                      Bookshelf or around the walls layout designs

                      Double deck layout designs (especially useful when vertical clearances are an issue).

                      Finish panel fronts with Masonite or wood veneers




Cutting the Foam for Basic Shapes:

          Carpenters hand saw

          Score with sharp knife, and snap (similar to styrene modeling techniques)

          Table saw

          Hack saw blade for curved cuts


Gluing and Laminating:

           Use only water based adhesives

           Apply glue to each panel to be laminated and press together

           If using latex contact cement, follow package instructions

           Use bamboo skewers to secure panels while adhesive dries; or

           Apply weights to panels while adhesive dries; or

           Apply clamps (even out pressure as much as possible) while adhesive dries


IMPORTANT NOTE:  White and Yellow Carpenters glues require air to dry. Extruded foam panels allow very little air to pass through them.  Accordingly, carpenters glue will take a considerably long time to fully set up (possibly up to several months). Once dried, these glues are very effective in bonding the foam, however, if you are in a hurry, you may wish to opt for a latex contact cement. In fact, a latex contact cement, rubber cement applied as a contact cement, or construction adhesive formulated for extruded foam application is recommended for use in laminating this material.



Shaping Scenery Contours:


          Recommend removing panel tongue and groove before gluing

          Laminate panels to the desired thickness for the scenic feature

                      Horizontal (like a layer cake) for rolling scenery

                      Vertical for cliffs and canyons

          For large hills, consider creating "rings" (full or partial) instead of using  solid panels. Stack and glue the rings (diameters decrease as you go up) to create a hollow basic lull shape

                      Even more light weight

                      Less expensive (use the cut out material elsewhere)

                      Great for tunnels - just leave the top layer or two unglued for an access hatch

                      Hollow interior can conceal hidden track

          Use hacksaw blades, wire brush, Stanley Surform tool and coarse sandpaper to "rough in" scenery shapes

                      Hack saw blades and wire brush (especially a drill mounted one) will remove a lot of material fast.

                      Use the Stanley Surform and sandpaper to begin to "finesse" the land contours, cut in water courses, lay in roadways, and shape the track sub-roadbed

          Use spackling compound or Sculptamold to fill in small cracks that may be visible at the joints between layers.


Laying Track on Foam:


          Extruded foam can be used as a sub-roadbed material.

          Chose a material thickness appropriate for the scale you are modeling. It's recommended that a minimum of 3/4" thick material be used regardless of scale.

          Use foam blocks for risers, and glue in place once grades have been established.

          Use " All-Thread" rods with nuts and sheet stock (metal or plastic) cross members to create adjustable risers.

          If creating  embankments, underfill sub-roadbed with chunks of foam, glue, and contour.

          Use bamboo skewers or a length rigid steel wire to "drill" holes for track wire leads through the foam sub-roadbed.

          Alternatively, plywood or other more conventional material can be used for sub-roadbed in conjunction with foam benchwork.

          Track can be glued directly to foam using straight pins to hold it in place while the water based adhesive dries.

          Contour ballast slopes using a Stanley Surform, sand paper, or a hot wire tool.

          Use an X-acto knife with #11 blade to "slice in" track drainage ditches.


Very realistic roadbed profiles are easily achievable with foam.


Track laid directly on foam can be noisy if you are also using the foam as benchwork. It tends to have a "sounding board" effect. If this is a concern, glue a cork, Foamcore, Homasote, or Upsom Board roadbed to your foam sub-roadbed. This additional step will deaden the sound considerably.


"Standard" track ballasting techniques work the same with foam.


Glue (construction adhesive) a I/4'' plywood square to the bottom side of the foam sub-roadbed to serve as a mounting pad for switch machines and other turnout control mechanisms.


IMPORTANT NOTE TO TRACK "HANDLAYERS":  Extruded foam won't hold spikes! If you’re spiking down your rails, you’ll need to use a more conventional roadbed material (such as Homasote or Upsom Board) in conjunction with your foam sub-roadbed. On the other hand, if you use a Pliobond or PC tie technique for fastening your rails, you can use foam, cork, or Foamcore for your roadbed.


NOTE 0F CAUTION:  Extruded foam panels and hot soldering irons do not mix well! Be very careful when soldering on or near foam. If at all possible, solder your lead wires to the base of your track rails at the work bench, and feed them through the lead holes as you lay down the track. If your wire lead hole is a little off, just poke a new one with the skewer or steel wire!



Creating Fast, Lightweight Scenery


Extruded foam is an excellent scenery material

          As a base for applying additional finishes such as rock castings (or a Sculptamold skim coat, though this step is really not required as we'll cover below).


          As a final scenery material in itself. Extruded foam can be carved into very effective rock work, with very little practice and excellent results.


Basic Ground Cover (Earth, Grass, etc.):


          "Water Soluble" scenery techniques work great with foam

          Paint foam with an earth colored latex "primer coat"

          "Classic" zip texturing with powdered paint, plaster, and ground foam for basic cover

          "Modified" zip texturing with thick, liquid acrylic or latex paint and ground foam cover

          Build up layers - ie: "dirt", "grass", "weeds", "shrubs", etc.

          Work in rocks and boulders (real, plaster, or carved foam) as you build up the basic cover


Rock Work:



                      Plaster rock castings will work fine with foam

                      Attach to foam with Sculptamold using tooth picks or bamboo skewers pressed into the foam and cut to length to act as "re-bar" to help secure casting to the foam base.

                      Color with paints or non-solvent washes


          "New Wave":

                      Carve your rocks from the foam itself!

                                  No added weight

                                  Simulate all rock types

                                  Easy to create very effective sedimentary strata

                      Highly realistic results using a few simple tools



Tools, and associated applications, for foam rock carving:


          Hacksaw: Basic shaping

                                  Carve in strata, especially coarse sandstone layers

                                  Texture surfaces

          Single edged razor blade: General carving

                                  Texture surfaces

          X-acto chisel blade: Ledge carving

                                  Carving square cleavage rocks

                                  Carving quarried faces

          Surform tool: Shape / texture surfaces

                                  Soften / blend textures

          Coarse sandpaper: Shape / texture surfaces

                                  Soften / blend textures


Make sure your tools are sharp and Watch Your Fingers!!


Coloring Carved Foam Rocks:


          Don't use solvent based paints or washes (ie: Floquil, Diosol).

          Use acrylic or latex paints.

          Thin down latex paints to flow into carved details.

          You'll need to paint at least a base coat, water based washes don't work on "raw" foam.

          Recommend " Apple Barrel" acrylic craft paints

          Inexpensive (retail price is about 75 cents for a 2oz. bottle)

          Cover well, blend well, and thin well

          Flat finish

          A whole "rainbow" of colors

          Recommend using a paint brush rather than an air brush

          More control - ie: individual rock faces

          Paint on a primer coat using a light, neutral color

          Fill in "blue spots"

          Use a spray bottle with water to blend colors as you paint


Other Scenery Items Carved From Foam:


          Bridge Abutments and Piers

          Concrete and Masonry

          Retaining Walls

          Brick or Stone Building Walls

                      Use a semi-dull X-acto #II blade when scribing bricks or blocks. This is the only time a dull tool should be used with foam!

          Coke Ovens, Kilns, and Brick Stacks

          Mid and Background Trees (both conifers and broad-leaf)

          Hopper Car Loads


Pros and Cons of Modeling With Extruded Foam:


No modeling material or technique is without both pros and cons, and extruded foam is no exception.  Here are a few as we see them:



          Readily available.


          "One Step" benchwork and scenery.

          Extremely versatile.

          Easy to work with.

          Fantastic results with a little practice.

          Compatible with many (not all!) other materials and techniques.

          Pliable, with no "chipping" (white spots).

          "Dry" cleanup.



          Cost (relative).

          Messy - cutting, carving, and forming create statically charged chips.

          Not compatible with solvents and solvent based modeling materials.

          Need to be careful with soldering irons and other hot tools and materials.

          Can be damaged if poked or prodded, especially with tools / hardware.

          "Blue spots" if your  paint job  is less than thorough.

          Won't build into the kind of benchwork you can walk on.



Recommended Readings:


1.       "The Latest on Foam-Board Layout Construction" Bill Darnaby, Model Railroader, March. 1995.  Just what the title suggests.

2.       "Hot Wire Foam Layout Construction" Bill Darnaby, Model Railroader, June, 1994  Basic information on using foam in layout construction. Specific information and techniques for building and using a hot wire tool.

3.       Modeling the Clinchfield RR in N Scale, Kalmbach Publishing "How-to book" reprint of the Clinchfield project layout series which appeared in Model Railroader in 1978 and 1979. Probably the first in-depth coverage of foam modeling to appear in the mainstream hobby publications.

4.       "Foam for Modeling" Sam Powell, Model Railroader, October, 1993 Basic information on using foam to model masonry structures.

5.       How to Build Realistic Model Railroad Scenery, Dave Frary, Kalmbach Publishing. The definitive book on water based scenery.

6.       "Ron Hatch's Midwestern Narrow Gauge" Ron Hatch, Railroad Model Craftsman, Sept, 1994. A 4'x8' HOn3 layout built entirely of foam, benchwork and scenery. Side bar discusses techniques used in building the layout that weighs a total of 70 pounds.

7.       BMRC N Scale Module Specifications,


Even if you’re not ready to build an entire layout out of the stuff, we recommend you give extruded foam a try in your next layout or scenery project. We think you'll find it's an excellent material to work with!


Happy Lightweight Railroading!!

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