In my opinion it’s not the foam that’s shrinking it’s the moisture in the wood framing that shrinks or expands. All construction materials come with a high percentage of moisture. This is indeed true fact. That’s why there’s problems with newer homes and mold. Wood is not kiln-dried like in the old days. Adhere your foam with a flexible caulk to it’s base and even spend the extra money to use a higher grade 1 by 4’s for your Framing and you’ll be fine. If the foam floats on its base it will not be affected by the expansion and contraction of what’s going on underneath.
My sections are still all together despite sitting on my basement floor for over 2 years now, in widely varying humidity - rather damp in the summer since there is no insulation or vapor barrier on the walls, dry in winter because it’s naturally dry plus heated. None of the foam has come unglued. None of the frames have warped. And that’s 2 layers of foam glued to one another, and that is glued to 1/4" plywood. 1x4 and 1x3 framing.
Open grid and L-girder evolved to get us away from the “Flatland” look of tabletop railroading. Why would someone want to go back to the tabletop when the open grid/L-girder with cookie cutter sub-roadbed makes everything from scenery to wiring easier and more flexible?
Everything? What if yooou ARE modeling the flatlands? And stacking up scraps of foam with a dab of glue or caulk is pretty quick way to build a base for hills and so forth.
Check Bill Darnaby’s articles, foam makes it super easy to have main and sidings at different levels along with all the ditches - one of his articles shows a hot wire cutter be made that carves the subroadbed as well as the drainage ditches on both sides. Pretty slick.
There are other ways to go up and down that don’t require using a jigsaw to cut patterns out of plywood, and then fit risers in and hope there are enough to not allow things to sag. All is not perfect with cookie cutter or cutting individual pieces of plywood subroadbed - I consider those two different things. To me, cookie cutter is you start with a flat sheet of plywood and you cut around outlines of ares to be raised or lowered, most of it ends up staying connected but with some parts rising higher than others. Cutting out stips of plywood and attaching it to risers I would not call cookie cutter.
All is not perfect in the world of l-girder and open grid, otherwise no one would have even bothered trying foam. Each has advantages and disadvantages. No one method is perfect for everything.
When you look at what’s left of a sheet of plywood after cutting sub-roadbed pieces from it, it looks like a sheet of dough after you’ve cut cookies out of it. Too bad you can’t ball it up, roll it out again and cut more cookies. [:)]
Interesting concept. I thought about that too. Then I thought outside the box. Why buy WS risers if I don’t have to. I love foam. My layout is 100% foam. After I cut out my cookie cutter. It occurred me don’t throw away the rest of the jigsaw puzzle. Put the puzzle pieces back in spaced up with foam ribs at the appropriate levels. So I did. Now I don’t have to carve down far to the lower levels or Build up very high to the upper levels. I have a lightweight wood frame that my foam layout will insert into when I’m ready to do so. My calculations is my 4x8 layout will weigh 40 to 50 pounds when I’m done. It is an N gauge layout. Almost the whole layout is 2% grades maximum. Radius 18 minimum. 16 hidden. Here’s a picture of a portion of it so you can see what I’m talking about.
I’m certainly in the clear then. I only have time to model in the winter. My foam has seen two Winters without track. I measured the 8ft length of the base. It’s only short a sixteenth of an inch I can accept that. I’m led to believe the only place one would have possible problems is a garage layout with extreme temperature swings. My own layout in a conditioned environment is just fine.
There’s two potential shrinkage problems with foam:
One is the shrinkage caused by continued chemical reaction after it is initially formed. I would expect that, if it happens, it would have a diminishing effect over time. Hence the pronouncements about aging for 6 months.
Now, the reaction MAY not be diminishing. Some don’t. Consider zinc pest, and the great sadness that it can generate years after manufacture.
But it does “feel” like the diminishing style of reaction. Anyway, this kind of shrinkage does happen. I have seen the results. Hopefully, doing the six month wait eliminates the problem.
The other is continued and continual shrinkage and expansion caused by temperature variations. It exists, also. I saw it happen with my module, where the widths of cracks in the scenery surface over the foam changed with temperature. The cracks widened when it was hot. And narrowed when it grew cooler. The module was stored in an unconditioned space. I observed it when the temperatures ranged from 50 degrees to 90 degrees.
It seems likely that foam on a layout in a conditioned space would have minimal problems with the above.
