Skip to main content

The first time I tried to make a masonry wall with foam, it turned out looking like something you would see on Mr. Rogers Neighborhood Land of Make Believe…anything but realistic. Then I saw a few threads by Tim W (ilovebridges) and tried to copy what I saw. Tim did some amazing work, but unfortunately, he passed away a few years ago.  After some practice, I was able to make masonry that was a bit more realistic.

Here are some things I have made with foam.

Arch Bridge
Bridge Abutments
Retaining Walls - note that the tunnel portals are Scenic Express
Here are the tools I use. Well most of them.

I generally use 1” thick foam. The ¾” thick foam can also be used, but that tends to be a bit warped so it’s sometimes best to cut it to short lengths and glue pieces together as needed. The foam can be cut to size with a hand saw and miter box or power (table, miter or radial arm) saw. To cut a curved archway, I used a razor saw to cut it oversize and then a rasp and sandpaper to bring it to finished size. Cutting and sanding the foam is a mess. The foam “sawdust” particles develop a static charge and stick to everything. It’s best to wear a dust mask. If using a power saw, you should have a good dust removal system. And a shop-vac is a must for cleanup.

Using a power saw (especially a table saw and especially a large piece of foam) can be hazardous to your fingers. If the foam gets even a little out of line, the saw will grab the foam, melt it to the blade, chew up the foam and sometimes send the foam flying across the room. I use an old blade so it doesn’t matter if it gets foam melted to it. The foam has to be held firmly and you need to be very careful to keep the cut in line with the blade, but if it goes bad, it is usually safest to just get your hands away and let the blade chew up the foam or send it flying. If using a table saw, it might be best to first cut the foam a bit oversize with a razor knife and then make the final cut with the saw.

After the piece is cut to size, scribe the horizontal lines. Then use a triangular file to cut the horizontal mortar lines. You need to be careful when cutting the mortar lines as it is easy to make mistakes if you don’t concentrate. But if you do make a mistake, it’s easy to patch with foam putty. If the wall has 90 or 45 degree corners, it’s easier to cut the mortar lines before you glue the pieces together since you can lay each piece flat while cutting (filing). Just make sure the horizontal lines on adjacent pieces line up. Vertical lines can also be scribed and cut at this time (before gluing pieces together). I use a spoon file to cut the vertical mortar lines. You can make the block size whatever you want, but lately, I’ve been making them ½” high X 1-1/2” wide. That’s kind of massive for O gauge (2’X6’), but then the stone blocks I see in real railroad bridges are kind of massive.

To glue pieces together when making corners or when putting together small scraps to make a bigger wall, I use construction adhesive that is foam compatible along with hot melt glue. The hot melt glue bonds in a few seconds and the construction adhesive makes a good permanent bond. Wipe off any excess glue / adhesive before it dries with a piece of scrap foam.

Use foam putty to fix any mistakes and to patch the glue lines for pieces that have been glued together. Before patching glue joints, cut a V in the surface with an Exacto knife. This will ensure there is no glue remaining on the surface and will create a V surface for the putty to adhere. After the foam putty cures, use sandpaper to smooth the surface. Then re-cut mortar lines to remove foam putty as needed. Sandpaper can be used at this point to cut a bevel on the top edges and corners of the wall.

I use a wood rasp to simulate tool marks on the surface of the blocks. I smack the block with the rasp several times and at different angles. A keyhole saw can also be used if you want more pronounced tool marks. On the last few pieces, I made, I used a punch set and pressed lightly to add dates to a few blocks. Before painting, do a test fit and make any needed adjustments.

I use latex paint. First I coat the whole thing with dark gray using a 1” brush. Then I go over it with a small stiff brush to make sure all the mortar lines have paint. You may need to go over it a few times to make sure that no pink is showing. When the initial coat is dry, you can apply other colors (lighter shades of gray, brown, etc.) on some blocks using a small stiff bristle brush. Let that dry overnight and then apply a wash coat (8 parts water to 1 part paint) over the entire surface for weathering. The wash coat also brings out the tool marks. I use the same dark gray color in the wash coat that I use for the initial painting.


Images (11)
  • 2016-08-25-6336
  • 2016-08-25-6337
  • 2016-05-24-5493
  • 2016-08-25-6334
  • 2016-08-25-6320
  • 2016-08-25-6321
  • 2016-08-25-6326
  • 2016-08-25-6329
  • 2016-08-25-6331
  • 2016-08-24-6305
  • 2016-08-20-6263
Last edited by Lehigh74
Original Post

Replies sorted oldest to newest

You can get the pink foam at HD or the green/blue foam at Lowes.  If they don't have a size smaller than 4' X 8', you may need to cut it to fit in your car.  Since it makes a mess, they probably won't cut it for you.  Some sheets come pre-scored, but if not, it is easily scored with a carpenter's square and box cutter razor knife.

Yes.  You can make the portal with one piece of foam.

DON'T use white Styrofoam.  That will ONLY make a mess in my experience.

Last edited by Lehigh74

Very nice write up.  I really like the idea of using the rasp !!  

I have done a fair amount of these carved pink foam block two additional ideas for "texturing" are: 

1.  I roll a wire brush wheel over the foam,  I had an old 6 inch diameter x 1 inch thick wheel.  I put on some leather work gloves and roll it over the foam after scribing the blocks, it makes thousands of tiny pore holes.

2.  I have some pieces of rough broken granite that are really rough and irregular.   I press them into the foam and transfers the edge pattterns into the foam surface.. 

I usually spray a really light coat of rattle can primer, keep the can at least 12 inches away and don't apply too much as the solvent in the paint attacks the foam and increases the texture and opens the pores,  but applied too heavily it will "melt" the foam.   Then I go over it with multipel gray, brown acrylic paint washes and finish with some dry brushing with white or light gray to bring out the highlights. 

All the block walls shown in the photos below are carved from pink foam....  

DSC02858DSC02780 [2)DSC06916


Images (3)
  • DSC02858
  • DSC02780 (2)
  • DSC06916

Bob, thanks for the painting instructions.

Joe, I found styrofoam to be a real pain.

Tim from I love bridges made some real nice retaining walls for us.   His instructions were very much along the line of Bob's work.  For starting to cut your basic panel sizes I share the following:

For basic cuts in sheets of green-purple-pink panels of foam I use a 6" spackle knife which provides a absolutely clean dust free smooth cut.  You can also make diesel engine hand rail stuffers for safe shipping.  

PM of 11.23.09 007PM of 11.23.09 008

Just drag it lightly to make a scribe line then repeatedly retrace the line going deeper each time.  Takes about 4 -5 passes for a 2" thick cut. The angle you hold the handle is very important.  If the foam is crumbling your angle is wrong.  Find the sweet spot and the cuts are perfect.

I cut a lot of 1" & 2" foam and this is my go to method.  I recently had to make some tapered wedges and this method can be used to make feather edge slices.

PM of 11.23.09 010PM of 11.23.09 009

For cutting deck foam edges, place the foam sheet where you want it positioned and slide a spackle knife flat against the face of the platform to create a scribe line then invert the panel and slice away.

PM of 11.23.09 011

A thin Oak fascia caps it nicely.

fitting of backdrop 001




Images (6)
  • PM of 11.23.09 007
  • PM of 11.23.09 008
  • PM of 11.23.09 010
  • PM of 11.23.09 009
  • PM of 11.23.09 011
  • fitting of backdrop 001
Last edited by Tom Tee
Trainlover160 posted:

Bob, can I get this foam at HD? Is it more dense than the white styro? I would like to make something similar to your arch. Can this be done in one piece?


All of the Home Depot's around here have the 1" thick rigid pink foam in 2'x2' squares. I found this to be a nice size for many things around the house. However, I have not yet used this for any train related projects.

And to Lehigh74 (the OP), very nice topic, details and instructions, I'm saving a link to this thread! This also looks like it might be fun and might be just the thing to get me going with some of those 'train related' foam projects that I haven't yet tried! 

Foam makes a great light-weight scenery foundation, too.  Here's a few pic's. of some dioramas I built in the past, using some 1" thick pink foam pieces leftover from a camper repair project.  Although they are N-scale, it could just as easily be O-gauge..............


Above is the very first foam diorama I built, to test out foam scenery.  1" thick pink foam x 10" x 26".  Small hills built and shaped from pink foam and glued on with cheap DAP clear calk.  Cork roadbed and track attached with same.  Painted with flat latex house paint, some "earthy" color that I had.  Then I went to town with ballast, ground foam, ground turf, shrubbery, and trees.  The skyboard was merely a piece of corrugated cardboard painted with some sky blue and white.  I was happy with the result.



And here is the second diorama that followed shortly after.  The only thing I neglected on the first one was digging down into the foam.  So I tried this one, and dug down into the foam to provide a little gully for kicks and grins.  The short bridge was built from basswood and toothpicks.



And here is a little N-scale piece I mocked up to put on a clinic for the HO scale club, to show how easy foam scenery can be.  Nothing more than 1" thick pink foam with 1/8" cork roadbed and a length of track.  The track area and a roadway were left flat, with the balance of the surface worked down a little to provide some rough terrain.


No doubt about it, whether building masonry walls or bridges or mountains or hills or any terrain in general, the pink, green, and blue foams are versatile materials indeed.  They are light weight and easy to shape and carve.  I recommend giving foam a try if you haven't yet, I'm pretty sure you will be pleasantly surprised. 


Images (3)
  • 308
  • 309
  • 310
Last edited by Mixed Freight

I use Hot Wire Foam Factory cutting and scribing tools for cutting and detailing. Below is a corner tunnel I made for a client in California. The tunnel portals are sprayed with Krylon "Make It Stone" black granite. The flecks in the paint give it a texture and, since the propellant in this paint is not petroleum based, it will not react with the foam and damage it.


The entire mountain and rock formations are also made of pink foam.


Images (1)
  • gp_mountain_2
RSJB18 posted:
Tom Tee posted:

Just remember, for residential fire code "all foam is to be covered by at least 1/2" of drywall".  Not that any of us are going to do that, just that foam and fire produces deadly poisonous gas.

Yes- the stuff is highly toxic when burned. Another reason to keep a fire extinguisher near the layout.

Respectfully, this is incorrect. 

This claim (along with the one about the alleged toxicity of acetone) keeps getting repeated over and over again. But in both cases it just ain't so. Pink foam is Extruded Polystyrene, which is a benign, food-safe material. It emits a small-amount of mildly-toxic stuff, but only when burned at extremely high temperatures.  I have documented this in the other "foam" thread:

A lot of common materials ARE toxic. It is important not to cry wolf with the ones that are not.

Any concerns people may have regarding materials used on a layout can be answered doing a search for the MSDS/MDS sheet for the material in question.  I still have thousands of MSDS/MDS sheets in binders from former construction management in locations all over this great nation.  Just don't ask me where each one may be presently.  Too many boxes stored in various locations from each project completed and closed out!  The information needed is constantly updated and can put to rest and questions you have.  The only manufactured product I have ever known to not have a MSDS/MDS sheet is Teflon tape.  And that was from up to the time I retired in 2014.

Jesse   TCA  12-68275

tip for the big box stores who only carry 4x8 sheets.  take a tape measure and use it to scribe a line at say 24 inches.  deepen with knife, then while still on the stack, hit a hard blow to break the thing in two.  Clean and good to go. Sometimes staff will do it for you.

Beyond your basic mtn/stone and wall carving you can get creative making intricate shapes. Using "foam" as a core material, it made constructing the railroad bridge fairly simple. I did attach thin basewood to the sides for extra rigidity. The curved parts of the road bridge were carved out of 2" "foam"; the attaching pilings etc. were made out of wood. Just a thought for inspiration maybe.DSCN0931_LIDSCN0430_LI  


Images (2)
  • DSCN0931_LI
  • DSCN0430_LI
wb47 posted:

tip for the big box stores who only carry 4x8 sheets.  take a tape measure and use it to scribe a line at say 24 inches.  deepen with knife, then while still on the stack, hit a hard blow to break the thing in two.  Clean and good to go. Sometimes staff will do it for you.

I'm assuming you are sharing this information for transport reasons. If not, that's what I get from it and it's good to know. Thanks.



Great first try.   Some suggestions:

1) Try scribing the mortar lines with a non-sharp rounded tool. I really like manicure tools, which you can find at the dollar store.

2) After you lay down the basic color, try lightly dry-brushing a darker color.

3) To add interest, give some of the stones slightly different colors. I do this using a set of broad-tip markers. Do not make the colors uniform or too solid. Be sloppy (but not across mortar lines). Do it before the dry-brushing (or even before the first painting), which will soften the colors and make them more realistic. A common error is to overdue the color differences which to my eye makes the wall look toy-like (not that there is anything wrong with that if it is the look you are going for).

This is a great thread, lots of good information and plenty of tips and tricks.  Great pictures guys, I had tried doing some foam structures in the past using florists blocks, I was making adobe houses and other types of structures for my uncles On30 layout, like a goober, I didn't take any pictures of what I had done.  Thanks for the inspiration and ideas.

Randy,  I don't try to seal the cork for the concrete caps...  I use the basic concrete craft paint colors that I usually mix together...

Bleached Sand,  Khaki, Pewter Gray..... Pretty much use a stamping method and apply blotches of the different colors until I get what I am looking for.

Ron,  I agree,  I have done the XActo Knife,  but I definitely find my carving tool of choice for the mortar joints is a sharp black pencil for the first pass, then I open up the line with a duller wider pencil.... Feels like the graphite/lead acts a sort of a lubricant and doesn't tear out the foam.  

Here's today's project..... Carved and embossed quite a bit of block retaining wall material so that I could paint it all in one batch.  So far I got the gray plastic safe primer done yesterday and just came in from the deck where I have been stamping and mixing and diluting 5 different colors to add some depth. 

There is a photo with the 5 colors I am using for reference.   I squeeze out small amounts on a piece of glass, keep a cup of water/windex handy for thining it and stamp away.... It's great doing in the direct sunlight as it dries faster and keeps from mixing on the wall and becoming one consistent muddy gray color.  

I will have to take some more photos in the layout room ....  The sunlight is washing out the contrast of the different colors.

First 3 photos are after carving and embossing with rough pieces of granite, and the gray primer.  

DSC06983 [2)DSC06983 [3)DSC06984 [3)

Next 2 photos are after 1st coat of stamping and mixing colors for 

DSC06986 [3)DSC06987 [2)

I squeeze out the paints on a piece of glass that I can then pick up small amounts of various colors and stamp away... I purposely am using an really old cheap brush that has uneven worn out bristles as it let's me apply small hints of color rather than large heavy blotches. 

DSC06988 [2)


Images (6)
  • DSC06983 (2)
  • DSC06983 (3)
  • DSC06984 (3)
  • DSC06986 (3)
  • DSC06987 (2)
  • DSC06988 (2)
Last edited by chris a


This is made from wood, cardboard and foam. My son and I built this when he was in 7th grade for a class project. He will be 27 in August! We used a soldering iron to carve the joints, and light mists of spray paint. The rail is made from brass brazing rod. The viaduct is in the work shop on permanent display.


n_a [70)


Images (1)
  • n_a (70)
luvindemtrains posted:

This is some great stuff! I would be interested in creating a stone arch bridge on a curve. I have seen examples of this but would like to see examples of the process to create one.


Determine your height and width requirements, lay them out on a piece of foam and place a circular object such as a plate or a cookie can lid or your layout marks.  Scribe the arc, cut it out slightly oversize with a keyhole saw, coping saw, steak knife or similar.  Then use a wood rasp to remove foam to your scribe line.

luvindemtrains posted:

This is some great stuff! I would be interested in creating a stone arch bridge on a curve. I have seen examples of this but would like to see examples of the process to create one.


Chugman did a great job on a curved bridge using multiple construction materials including foam.



Add Reply


OGR Publishing, Inc., 1310 Eastside Centre Ct, Suite 6, Mountain Home, AR 72653
800-980-OGRR (6477)

Link copied to your clipboard.