Would 1" foam over 5/8" ply compress with the weight of trains?

[BroadwayLion]

In HO scale, no, not a chance. If you plan to run a real train over it... SQUISH!

[gregc]

putting some type of roadbed will not only raise the rail above the surrounding terrain, which is more prototypical, but also provide something stiffer than the foam.

[Santa Fe all the way!]

OK, Thanks, that makes me feel a lot better about using it.

[tomikawaTT]

If you routinely run 1:12 scale cars fully loaded with real iron ore your roadbed might deteriorate with time.  A derailment would do it serious hurt - just like the real material under a 1:1 track if a derailment occurs.

In the more usual modeling scales the models don't have the mass to cause damage to foam supported from below or thick enough not to sag.  Since my heaviest train (2 locomotives, 20 cars) doesn't weigh 15 pounds, it could be supported on one square inch of foam without causing distortion.  one square inch equals about 7/8 inches of flex track, and my train is seven feet long...

Chuck (Modeling Central Japan in September, 1964)

[kasskaboose]

I have 2" foam on an open layout, so I would'd think that even with 1" foam it would compress.  The locomotive isn't that heavy.  Even with scenery and structures, the weight per inch is probably much less than foam. 

Using the pink or blue foam is perfect.  I would suggest the 2" variety because that gives you more freedom for making valleys and hillls.

[mbinsewi]

The typical rigid styroam board (blue or pink) you get at a lumber yard is rated by psi and density in cubic foot. You'll typicaly see the number 150 or 250 next to the brand name.  The 150 is 15 psi and 1.3 pcf density, and the 250 is 25 psi and 1.55 pcf density.  I have a mixture of 150 and 250, pink and blue.  Most was salvaged and unused from construction sites I have worked on.

Both types are used under concrete slabs for insulation, and easily take the weight of men working, getting the slab ready, installing rebar, etc., and pouring of the concrete.

You won't have any problems with your trains "sinking" into the foam.

Mike.

EDIT:  Even if you use the real cheap white "expanded bead" foam, like the foam used in cheap coolers, and drinking cups, you won't have any problems.

[Anonymous]

A BLI PRR M1a w/o tender weighs 15 ounces, which equals roughly 425g in my metric world. Assuming an even weight distribution over the length of the loco, this would make a weight of about 61g per axle or a tad over 30g or a notch over an ounce per wheel.

That´s not enough to let the loco sink into the foam or compress the foam.

[bearman]

I have 1" foam over 1/2" plywood and have noticed no problems. I am, however, running 4 axle diesels, not steam locomotives.

[hon30critter]

Santa Fe:

I'm pretty certain that the foam will not compress with the weight of a locomotive on it, even over time. The reason is that the locomotive's weight is distributed over a much larger area than the tip of your finger. Think of it this way - why does a snowmobile not sink into the snow when a person getting off of one does? The reason is that the snowmobile's weight per square inch is much less than a human's. A better example is a military tank. They weigh many tons but they don't sink into sand or even snow much.

Also, if it was a problem your fellow modellers would have given up on foam a long time ago.

Dave

[Santa Fe all the way!]

Would 1" foam compress/distort over time? You can, with the tip of your finger, compress foam, so how would it do, over time with ho steam engines running over it? Could you track start to get out of level? I've always used cork over plywood, so foam is new to me.