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Thread: Covering foam with ... well what?

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    Default Covering foam with ... well what?

    I'm working on a module right now that uses a fairly typical foam-on-plywood construction method. In the past I've used pink foam and coated it with "Foam Seal", a product I bought at a show. It's basically super-thick latex paint, similar to the paint you might use to seal a concrete wall in a basement. It's worked well for me, the modules have held up well.

    For this module I did something different. I've used some of that expanding spray foam (long story, but it worked out well), but I can tell it's a bit "softer". I'm also low on the Foam Seal product. I started asking around at the train show and I found something I found surprising. Some of the guys put plaster over the foam. I would have thought that too fragile for a module, but it seems to be working for them.

    I also have some "Flex Seal", liquid rubber in a can! Aside from the catchy infomercial it would provide a strong layer on top, but I think it would be kind of thick and maybe too flexible over time? Like the ground foam would be more apt to flake off if it expands and contracts.

    Anyway, what do you do to seal/cover foam? Share your secrets!
    --
    Leo Bicknell

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    In the past I've used regular interior flat latex paint. Get a color that matches the dirt in the area that you're modeling, which in the part of NC I model is red clay. The local Home Depot has a sign in their paint department, "We'll match anything." I haven't walked in there with a handful of dirt yet.

    Another possibility is Lou Sassi's Ground Goop:
    1 part (by volume, I'm pretty sure) Celluclay
    1 part fine Vermiculite
    1 part flat laytex paint
    3/4 part Elmer's white glue (not school glue)
    A splash of liquid Lysol

    Mix to oatmeal consistency, adding a little water if needed.
    Tim Rumph
    Modeling the Southern Railway in N-Scale

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    Quote Originally Posted by Tim R View Post
    I've used regular interior flat latex paint.
    - Ditto

    And, have also added white glue on one occasion. - Not on a module. But has held up.
    Steve - Jugtown Modeler..............Don't know enough about railroading yet, but scale modeling is my life..............Web-Folio

    The introduction of so powerful an agent as steam to a carriage on wheels will make a great change in the situation of man. -- Thomas Jefferson, 1802


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    Assuming you've carved the foam, Sculptamold. It won't stick well to the shiny as-dried surface of Great Stuff. Carving with a steak knife leaves a nice rough matrix of sliced open foam cells to work with. I smear the Sculptamold onto the foam with my fingers; you can hear sort of popping noises as the air comes out of the cells. When you do that you get pretty much unbreakable adhesion. Then where I need rock face I add a thick layer for the rock.
    IMG_7180.jpg
    I assume plaster would work the same.

    BTW the small bags of Sculptamold are pretty expensive; if you like it go for the 25 or 50 lb boxes. https://www.dickblick.com/products/amaco-sculptamold/
    Last edited by NtheBasement; 19th Dec 2018 at 08:47 AM. Reason: misspelling

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    I have used my own version of ground goop on my module (over both plywood and expanding foam) and it has held up beautifully, no chips or cracks after a dozen years of shows. I do Celluclay plus joint compound and then tempera paints for color, scoopable kitty litter for texture as needed. It has enough tensile strength and flex to absorb impacts, at least that's my theory. You can add as much or as little water as desired for optimum workability, and you have a good long time to shape it while drying. Only drawback is that it does shrink when drying, leaving cracks to be patched later, so I always leave a little bit of a batch in an airtight container for application later.

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    I also use flat interior latex paint, colored a light tan, so it looks like first. While itís still wet I sprinkle ground foam into it. Once that dries I go over it with a heavier ground cover layer.
    Karl

    CEO of the Skally Line, an Eastern MN Shortline

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    Tannish latex paint over the foam, then ground goop (Sculptamold, tannish latex paint and white glue), then sifted soil, followed by more soils, rocks, ground foams, static grasses or fine dead leaves (dried dead leaves pureed in a blender and sifted). Wet water and dilute matte medium to hold things together.

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    After the suggestions here, and a bit of googling I've decided to try Sculptamold for my current project and tossed a bag in with an amazon present order.

    Always interesting how folks solve the same problem different ways!
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    Leo Bicknell

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    I used ultra lightweight filler mixed with a little acrylic colour.

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    At what point do folks put this layer down? Have I screwed up by putting in roadbed before painting?

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    In order:
    Track installed and working perfectly.
    Foam is carved.
    Buildings sited but not permanently attached.
    Terrain/rock work (this) - after masking the track and ties
    Ballasting
    Fascia
    Foliage (more masking)

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    My order:

    Shape foam.
    Install roadbed.
    Some terrain & rock work.
    Install track & test that it is working perfectly.
    Paint
    Ballast
    Paint + Foliage + Buildings + Trees in whatever order seems the easiest. It varies.
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    Well, it came out both better and worse than expected. The Sculptamould was super easy to mix and apply. It's also clearly quite durable now that it has dried. However I was not able to get it very smooth. I tried using my hands, a putty knife and spritzing with water. I expected to be able to smooth it similar to drywall compound, but no, it left a very rough texture.

    I don't think that's a problem for what I am doing on this module, but will make me re-think how I use it in the future.

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