# Foam viaduct



## lownote (Jan 3, 2008)

I'm thinking about making a viaduct for large sections of our railway that are elevated. Right now they are just supported on ladder trackbed 

I was thinking of shaping a viaduct out of insulation foamboard, the 2 inch stuff, and the coating it with cement 

Does anyone have any experience with that method?


----------



## Jerry Barnes (Jan 2, 2008)

I used the outdoor type of foam board, about 3/4" thick over a pressure treated frame. Scored it to look like blocks and painted it with house paint and acrylics. Top edge kept getting worn away by my cat and birds, I guess. Did coat the top edge with concrete and it's held up fine since. Might look on my web site and find a pix of it.


----------



## toddalin (Jan 4, 2008)

I have a bridge done exactly as you describe. I made it out of white styrofoam and coated it with hydraulic cement (Dry Lock). This has no aggregate or heavy sand in it (like a milk shake) and you only have a few minutes to work with it so I do small areas at a time. Assemble the foam with "yellow" glue. 

I left mine uncoated, just using the natural grey color, but some areas were very thin and a little of the foam is now exposed. I can simply color this area with a water-based paint (easier), or recoat it (harder). Only use water-based paint/glues on foam or it will melt. 

I also have a building done like this, but was coated with stucco. The stucco on the side that gets watered has deteriorated, so this would not be my suggestion for a wet area.


----------



## lownote (Jan 3, 2008)

Thank you both. 

How did you shape the foam? I'm thinking a hot wire cutter is the way to go, as my wife would not look kindly on millions of small pieces of pink or white or blue foam. No, not kindly at all.


----------



## Jerry Barnes (Jan 2, 2008)

I did it in my shop, in the barn, used a serrated knife. I'm sure the hot wire cutter would be neater. If you use the white foam, make sure you cover it all up real good, sun will mess it up.


----------



## Guest (Sep 17, 2008)

How did you shape the foam?

i use one of these things, that look like small welding irons, used for adorning wood or leather, together with a metallic rule.


----------



## Allegheny (Jan 2, 2008)

The best way to go is using a DC hot wire knife with a variable power supply. The one I have is the following: 

http://hotwirefoamfactory.com/product.php?productid=16192&cat=103&page=1 

When I bought mine years ago, it was around $90. You may want to contact some insulation companies as you might be able to rent or borrow one of them. I doubt that Taylor Rental would have them, but it's probably worth a call. 

On its top setting, it will cut through 6" thick blueboard like it isn't there. While I've never built a viaduct using the stuff, I have cut quite a few panels with it for various reasons. If you get one of these things, it is best to practice with it beforehand. To get accurate straight cuts, I use a template made from 1/4" hardboard with the edge taped with aluminum duct tape. Space the template about an inch above the foam (so the heated blade doesn't contact the aluminum tape) and plunge the blade through. 90% of your practice time will be spent developing the technique to keep the blade perpendicular to the surface of the foam so the edges come out square - the thicker the foam, the more pronounced and noticeable any deviation will be. 

Make sure you do this outside. While there will be no small foam pieces like you'd get with a saw, the smell is not something you want in your living space! Also wear gloves as the blade gets pretty hot (not red hot, but certainly hot enough to blister your skin). I've never seen a fire due to one of these things, but I always keep a small fire extinguisher handy anyway. 

As an aside, another way to cut thick foam is with a serrated blade electric carving knife. You can pick one up at WallyWorld for $10 or so. Not as neat as the hot wire knife, but just as effective. 

Brian


----------



## lownote (Jan 3, 2008)

Thank you all very much, this is very helpful


----------



## Greg Vocks (Jan 2, 2008)

Where I lived in Austria, the buildings were mostly masonry with foam over that, and then a layer of stucco was applied to the foam. Here is a line of products for this type of application: http://www.lahabrastucco.com/exterior_products.htm


----------



## toddalin (Jan 4, 2008)

Posted By lownote on 09/17/2008 1:12 PM
Thank you both. 
How did you shape the foam? I'm thinking a hot wire cutter is the way to go, as my wife would not look kindly on millions of small pieces of pink or white or blue foam. No, not kindly at all.


I simply cut it with a mat knife (box slicer) and shaped it using a rough file. Do it outside as it makes a mess.


----------



## aceinspp (Jan 2, 2008)

When i was up in Canada last month one of the RRs that I visited had several bridges and viaducts made from foam really looked nice and seem to hold up well in in there climate. Later RJD


----------

