Use expanding foam 4 mountains what about texture?

Model Railroader General Discussion (Model Railroader)
1

Hello to all!!

I’ve elected to use expanding foam for my mountains. However, I’m trying to determine how to get a good texture on the surface after I carve out the foam. Plaster cloth? Spackling compound?

I’m also planning on putting some rock molds on the foam, I’m either going to attach them after it dried with liquid nail or just before the foam is dry by simply pressing the molds into it. Any ideas here? [:D]

Thanks!
-Dale

2

Hi, I used expanded foam for mountains. Just about anything sticks to it in the way of spackle/plaster/latex paint if you cut the smooth texture to expose the bubbles. But here’s a procedure for you. Plastic trash bags will not stick to it. So you build a wire frame and cover it with masking tape. You then spray LOW Expansion foam and form and shape it with you hands through the trash bag so it don’t get the popcorn look. When it sets peel off the trashbag and you’ll have a mount that needs little shaping and has area that when painted white will look like snow drifts. I have a 4 foot mount that’s 1/2 inch thick and weighs 10 pounds. But it’s strong. It took 4 cans of low expansion foam and 5 pounds of wire. FRED

3

By "LOW Expansion foam " what exactly do you mean? I’ve thought about using some of that expanding insulation foam they sell in hardware stores. it’s pretty cheap and coems in a handy spray bottle with a tube for fine ly apllying to cracks and such. but not sure if that would actually be good for scenery, i’ll have to test it one oft hese days.

4

The expanding foam comes in three types, printed on the can, low, medium and high. Low will not expand much beyond what you spray out of the can, usually 1 1/2 times what is set down, medium up to 3 time and high will expand 3 to 5 times as much or more and can be very difficult to control.

I’ve thought about trying this for my mountains. You will probably need to shield tunnels and such so the foam doesnt accidentally expand into it and block passage.

If you use a plastic trash bag crumpled up i would expect a “rocky” finish. especially if its left on till it hardens.

5

I wonder if that stuff will stick to aluminum foil or latex rock molds???
Experiment time!!!

6

I posted this in reply to another thread, but it specifically answers this question, so I am re-posting it here:

I use a home-brew papier-mache based on Cell-u-Clay, which is essentially the same thing as newsprint shredded into fine particles. You can even make your own if you don’t mind shredding old papers and ruining a blender. To this, I add a variety of color and texture ingredients, in addition to joint compound; varying the composition can produce vastly different finished textures. In the end, what I have is a much lighter-weight coating, with integral color and texture, which I can mix up in small dixie cups and work at my leisure. When it dries, it maintains some flexibility so you don’t get chipping, and it is far easier to plant trees into (just poke a hole with an awl). The only drawback is that it needs support (it isn’t “hardshell”), but for this I use expanding foam insulation which I can carve readily; other types of foam construction would work fine, also.

For casting rocks, I don’t: the papier-mache mix can be mixed to any consistency, and for cliff faces I just make it solid enough that I can carve it as it is placed. Certainly, it can also be carved once it is dry. By working with small batches and laying them up in horizontal layers, I get a natural-looking stratification, due to inherent differences in color and texture of different batches. And with an admixture of scoopable kitty litter (or any other granular material), I can easily create convincing rough stone surfaces, using just a plastic spoon to apply it.

There may still be a place for old-fashioned castings, though. At the train show last week I saw some ready-made ones for sale, and WOW did they look good. One could easily incorporate such a casting (I am going to try to include real stones harvested from the Appalachians) into a spoon-troweled papier-mache scenic contour.

I did not realize that there are low, medium, and high-expansion foams; I would guess that

7

I used the can foam also. I let it dry them used a razor saw and hobby knife to carve the areas needed. I used Hydrocol to fill gaps and represent rock the rest when covered with ground foam is completely hidden with no need to do anything more to the foam. That’s what I did and am very pleased with the results.

8

I used spray foam also… I just carve and slash w/a steak knife…Smooth out where needed w/ Sculptimold. I save the scraps, Fellet into stackable slices and hot glue them together. No waste . Makes the best stratified rock anywhere. Just slather on the latex earth tones,texture,ground foam ect.

9

I too used expanding foam. What a disaster. The stuff kept on expanding, even after it hardened. Every couple of monthes I would have to carvre it back so the train would clear it. I guess I used the wrong kind. I ended up cutting down my whole mountain and starting over. This time I used cardboard strips and a plaster hardshell.

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That’s probably what he meant by low med and high :slight_smile:

What if I want to make a “rocky” mountain with minimum foilage? Is expanding foam still an answer? Sounds like I can just carve it out, cover it with plaster and paint as desired. What paint should I use? By latex do you mean house paint or will the natural scenics line of earth tones work?

Thanks!
-Dale

11

Any “water based” paints works except maybe art water colors. I use house paint because the local True Value has a paint sale every year where they sale wrong colors, not picked up, alledged defective paints (couple bucks per gallon). If you mix them all together you get mud brown… a good color for mountains or to just seal it. I also use the hobby acrylics like ceramcoat on it. If in doubt test it on a scrap first. I also glue broken ceiling tile to it for stradified rocks. Plaster and spackling stick to it well. Just a word of caution, if you seal the foam by using plastic tape on the form it doesn’t set as foam need moisture from the air to set (experience). Also, if you try and make a big solid mountain it will continue to expand for a long long long time. That’s why I recomended a wire masking tape form, that and it saves foam. I knew a guy who had a car with rusted out back fenders who used foam to seal them. As the foam set it buckeled out the fenders and the car looked worse than before. FRED.