Plywood vs. Humidity

Discussion in 'Modular Layout Forum' started by riverotter, Jun 20, 2008.

  1. riverotter

    riverotter Midwest Alliance Rail Sys

    I'm trying to decide whether to use 3/4" birch plywood for the "surface" of my next layout which I'm planning to be a "domino"-style modular layout and I am concerned about how well 3/4" birch plywood will hold up against the humidity variations in the Midwest.

    I'm thinking about attaching the plywood to the framework with serrated nails, and paint the plywood a neutral tan or sand color to seal to hopefully at least partially mitigate the warping effect of the humidity changes.

    I can keep the train room at 55 - 60 degrees in Winter and under 80 degrees in Summer, but due to cost considerations, I cannot do any humidity control except what's supplied incidentally by the HVAC system.
    My bottom line question is: will using 3/4" birch plywood work in this scenario?

    I would appreciate any ideas, opinions, questions, comments, etc.
  2. Mountain Man

    Mountain Man Active Member

    It probably will, but thoroughly sealing both surfaces and the edges with something like Thompsons Water Seal wouldn't hurt if you have that much humidity. The average in Colorado is just over 20%, so we don't tend to give it that much thought.

    Just a thought, but have you considered using an alternative to plywood such as MDF, OSB or a sheet of laminate board? These have the advantage to being virtually immune to humidity due to the way they are constructed.
  3. ScratchyAngel

    ScratchyAngel Member

    Why not just foam?
  4. steamhead

    steamhead Active Member

    Will this be in an "uncontrolled" environment..?? No AC/heat..? If so, a good sealer, particularly on the cut edges should work OK. I presume by "Birch plywood" you mean cabinet grade plywood. Plain ol' construction type ply will suffer from heat and humidity.
  5. riverotter

    riverotter Midwest Alliance Rail Sys

    My benchwork is already at 57"; adding another 2" of foam on top of that would be unacceptably high. Besides that, the sides of the foam would have to be painted. I don't mind blue sky; blue subsoil I've never seen in the real world ;-)
  6. Squidbait

    Squidbait Recovering ALCO-holic

    1" foam is stiff enough for benchwork if you support it well enough. As far as painting it, you'd have to paint the plywood too :p But you could carve the foam to bevel down to the outside edge of the domino - let's see you do that with ply!

    I think going with russian ply (I'm assuming that's what you mean by birch? Lots of thin plys?) is overkill. Expensive and heavy. Decent good-one-side plywood should be fine if you're going that route.
  7. riverotter

    riverotter Midwest Alliance Rail Sys

    I can control the temperature within a range of 55-60 in winter to <=80 in summer. I've looked into a humidifier, but at the volume of the train room, the price is prohibitive, not to mention the ongoing cost of power consumption. Do you have a recommendation (re) sealer?
  8. riverotter

    riverotter Midwest Alliance Rail Sys

    I tried 1/2" G1S plywood (probably construction grade :cry:) last summer when I first started this "side project" -- it warped like a canoe, even pulled out some of the screws!
  9. Jim Krause

    Jim Krause Active Member

    3/4 inch plywood is way overkill. Heavy, heavy, heavy, if as you say, you are building modular. How do you folks in the midwest build kitchen cabinets? Do they warp too? As for being concerned about the blue subsurface of foam, it won't be seen if you use a earth tone latex paint over it. It might be best to talk to some local model railroaders and see what they have found that works well. Fascia boards (Masonite) will cover those edges if you use foam.
  10. Mountain Man

    Mountain Man Active Member

    You can buy exterior grade plywood, which is rated for exposure to dampness, but sealer is a whole lot cheaper. Or, you could simply place a sheet of Masonite beneath your foam, which would only add about 1/8" to the layout height, it's cheap and it's stable.

    If you buy too much birch plywood, it might end up being cheaper to just buy a de-humidifier and a thermostat. Even on sale, that stuff ain't cheap! :cool:
  11. riverotter

    riverotter Midwest Alliance Rail Sys

    I've decided to rip out about 85' of fixed, shelf-style benchwork and replace it with hollow core door "modules" to give me more flexibility -- a la "dominoes". A painful and costly decision, but ultimately worth it to me in terms of flexibility.
  12. Jim Krause

    Jim Krause Active Member

    riverotter: I guess I'm confused by the term domino modules. Can you or someone else explain that to me? Are you building a layout that will be transportable? Sorry for the confusion. (I'm easily confused). Jim K.
  13. doctorwayne

    doctorwayne Active Member

    I've used 3/8" sheathing plywood (good no-sides :p) for shelving under my layout, and found it to be strong and stable. My layout room is in an unheated, uncooled basement, although it is well-insulated. Most of the stuff on the shelves has nothing to do with trains, and some is rather heavy. When I get around to building the second level of the layout, I plan on using the same plywood atop 1"x2" framing, perhaps with cork roadbed. Under no circumstances would I use MDF, which has a propensity to sag if you look at it too hard, and I'm not too nuts about OSB, either. Both of these materials, in my opinion, are difficult to work with and neither hold nails or screws well. If you want lightweight, portable sections, I'd go with 1" or 2" foam on a framework of good-quality 1"x2", 16" o/c max, and screwed together, skipping the plywood altogether.

  14. riverotter

    riverotter Midwest Alliance Rail Sys

    Hi Jim,
    David Barrow pioneered the "domino" concept for layout planning. A number of articles by and about him were published in Model Railroader and Model Railroad Planning in the 1990's that contain very detailed information about what dominoes are and how he constructs them. I've used hollow-core doors (80" vs. Barrow's 48" lengths) to construct the free-standing parts of my layout; now it looks like constructing another dozen "HCD Dominoes" is what it's going to take to make me happy with my layout's underpinnings. :rolleyes:
  15. Jim Krause

    Jim Krause Active Member

    riverotter: Thanks for the clarification. Just a different name for something very simple. I like simple. Kinda goes along with my personality. Jim K.
  16. railwaybob

    railwaybob Member

    Whether you use ¾" plywood, 1"x 4" (¾"x 3½"), 1"x 6" (¾"x 5½") fir, or any other material, all surfaces on your wooden frame should have two coats of paint before you install any Styrofoam. It's the unpainted wood that's the cause of most warping.

    The probability of warping increases also with the width of the module and the length. When you start to go over 30" in width, you will get warping. There are, however, ways to minimize the warping, in addition to painting all surfaces. The best way is to add cross-braces about every 2' - 3'. This is simply a 1"x 2" (¾"x 1½") piece of pine that spans the width of the module. It's installed with the 1½" side facing up and next to the Styrofoam so that it also adds support to your Styrofoam, particularly if you are using Styfoam that is less than 1½" thick.

    Another trick to stop warping is how you glue the Styrofoam to the wooden module frame. I use expandable polyurethane glue which expands to fill any cracks and crevices between the Styrofoam and the painted wooden module frame. You then have a "unitized" module, instead of something that comprises two components - the wooden frame and a chunk of Styrofoam.

    Bob M.
  17. Xiong

    Xiong Member

    Given a lot of thought to benchwork. Going modular, weight is a critical consideration -- but so is dimensional stability. Climate control is nonexistent; not only do I have no control at the run session, I must expect extreme conditions during transportation.

    I don't see that any simple set of wood braces under foam will be sufficient. The braces themselves can warp, just as a plywood top. I think any sort of particleboard is out of the question; that stuff is heavy. Nor does it eliminate warping risk; it only minimizes it.

    Why don't I see Masonite mentioned for module tops? Thin, light, strong, not subject to as much warp as plywood although it will require some bracing. At least one side of Masonite, typically, is very smooth, almost polished. Yet it takes paint and glue very well. And Masonite has no resins or chemical fillers; it gives off no weird vapors when heated or burned.

    What about aluminum honeycomb panels? There's the disadvantage that they're electrically conductive but I can think of several strategies to work around that. They have a very high strength/weight ratio. Expensive: A 4' x 8' sheet might cost over $200. But I think a sheet of suitable thickness will not require any bracing at all.

    Aluminum has a medium coefficient of expansion, much more than wood, close to the range of nickel-silver. Wonder if this is a plus. If the module sits in a hot car for a couple hours, perhaps the rails will not pop off the ties.

    Cost may seem to be the deal killer here but I don't see that. Track alone for a module with bought turnouts might run $200; who knows how much more for scenery, not to mention the investment of time. Why put it on scrapwood?
  18. Squidbait

    Squidbait Recovering ALCO-holic

    Because the back side of Masonite is not sealed, is rough, and allows it to soak up moisture. Also, Masonite is brittle, doesn't take screws or spikes worth a darn, and is heavy for its' size.

    You've hit on the big disadvantage - price. But hey, if you want the coolest hi-tech module in the group, go for it.

    Also, I have never worked with it, but I suspect that the aluminum honeycomb isn't as easy to work with as wood. The PITA factor may outweigh (no pun intended) the weight and stability advantages.

    Otherwise, you could just use the materials that other Freemo module builders seem to have had years of success with - plywood and foam. The birch ply they recommend is many thin layers of veneer, unlike regular ply which is a layer of veneer, a layer of particle-board/resin/MDF/gunk. It is extremely strong and quite dimensionally stable.

    Track is probably the most expensive part of what's on top of the module (unless you're using FSM structures ;) ), scenery the cheapest. Why over-engineer and over spend on the project? Who do you think you are? NASA? DARPA? The money you blow on hi-tech fancy benchwork, that while cool, doesn't perform any better than birch ply and foam, could be spent on FSM structures or rolling stock.

    As for time, the time you spend fiddling around trying to make the hi-tech approach work is time you could have spent railroading.

    KISS rule, my friend. But hey, it's your money, your module. :p :D
  19. ScratchyAngel

    ScratchyAngel Member

    I doubt foam and simple bracing would stay in such wide-spread use if they caused major warping and durability problems, but maybe it's more of a problem where you are. You can even get 3" thick foam from Dow if you're worried about sturdiness. If you don't trust finish grade pine or oak for a frame you could always use the birch ply under a slab of thick foam as suggested above. I'd ask the other module builders you're planning on hooking up with what they use and whether they're happy with how it's worked in travel to where you'll be meeting up.
  20. Jim Krause

    Jim Krause Active Member

    Xiong: I can second the cost factor of aluminum honeycomb panels. My career field was in the aerospace industry. Honeycomb panels by definition are hollow and are not meant to have holes drilled or punched in them unless there is some engineering involved to strengthen the area around the hole. Using a regular driil to cut a hole usually results in a big mess of flying honeycomb bits and an irregular shaped hole.

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