Using 3/8" plywood with 1/2" rigid foamboard over it on a around the wall layout in N scale (34" table depth) using cookie cutter construction, is this a problem with the flexing, expansion & contraction of the plywood in a non temperature controlled basement?
Temperature varies from 55 to 75 degrees, but humidity has varied from 45 to sometimes close to 100%, but there is a dehumidifier, so high humidity will probably be 75 to 80%.

I was concerned with overall weight of the plywood and thickness of the foamboard when it comes to work with linkage of turnouts. I also have no plans to 'dig down' below the top of the foam for scenery reasons which is why I choose 1/2" over 1".

Hi Bruce,

Welcome to the forum.

What sort of support will the plywood be getting? Dimensional lumber (e.g. 1x4) tend to be less stable than plywood in terms of movement under heat/cold or humid/dry conditions. You might consider going to an open frame (which you will have under the ply anyway) and 2" foam without the plywood. It's a lot lighter, and the foam is completely impervious to temperature or humidity changes. Supported by a frame not more that 24" on centre, it should be plenty strong enough (as long as you do not need to walk on it ). Painting the frame with a couple coats of paint will help prevent dimensional changes due to humiidity.

Hope that helps.


Andrew

I would second Andrew's comment that a layout sits on more than the roadbed and subroadbed. I did an N scale layout on 3/8 inch plywood, and I suppose that's acceptable for N, but you do have other questions -- is the layout sitting on shelf brackets, open grid, L-girder, the tops of bookcases, or what? And while it's popular these days, foam is very noisy and can certainly detract from the effect of sound-equpped locos. It probably depends on where you are in your progress in the hobby, what your expectations and priorities are, and so forth, so there simply isn't a single good answer to the question!

One factor, however, does remain constant. If you allow you're wood to adapt to the ambient temp/humidity of the house, and then seal it completely, you will drastically reduce the problems of expansion and contraction. By "sealing" I mean all four sides or edges of everything, and the open ends of boards as well. Any bare wood is able to react to humidity and swell slightly, which along with temperature changes leads to expansion.

Also avoid laying track across materials with different reactive coefficients.

My layout ( N scale) is 6 foot by 28 inches and is on an open grid of 24 x 28 inches. On top of that I have 1/8 inch peice of paneling ( it was left over from another project) and a minumum (It's a mountain layout) of 1 inch of foam where the trains run, less foam in one spot where a creek flows off the layout. I have central heat but no A/C so the temp runs between 65 in the winter to low 90's in the summer with humidty in the winter around 40% and as high as 85% in the summer. It's been 5 years and no problems so far.

If you're not going below track level with scenery and doing cookie cutter subroadbed, why even bother with the foam? Just go with a heftier plywood.

Depending on how you design your support, your plywood thickness may not be critical. Galen (Ocaliecreek) here at Big Blue, built a small time saver layout and brought it to one of the modular club meetings with a power pack and a Bachmann GE 44 ton switcher and a few freight cars for some of us to play with after one of the meetings. He used 1/8 inch luan ply for a top with no foam, and it was plenty strong enough for HO scale. The secret was that he had cross members supporting the top on 12 inch centers. Depending on what you are building and how you are building it, you might find a thinner ply better for a particular application, or you might want something heavier. You might even find a combination better, with lighter construction for say a lift out section of lift bridge and heavier construction for permanent bench work. The secret is to support it appropriately for the thickness of the top material.

Sorry, notifications were not turned on.

Support risers are around 12" (on average) between risers throughout the entire table. There are a couple of places it is slightly more (narrow elevated sections to the rear of the plan).

radivil Wrote:If you're not going below track level with scenery and doing cookie cutter subroadbed, why even bother with the foam? Just go with a heftier plywood.

I agree: the foam serves no purpose and can actually complicate things when it comes to activating your turnouts, installing roadbed, etc., etc. However, 3/8" plywood, well-supported, should be fine for the layout top.

Wayne

I asked in numerous forums about the preferred table top construction and the majority said foam over plywood.
I was/am concerned about expansion & contraction due to humidity concerns in the basement where the layout room is. It's a little late to change gears.

No need to change gears, Bruce, as you seem to be well on your way. I've noticed a lot of people doing foam over plywood, even though they have a flat table-top layout, with no scenicked areas dug into the foam, and no stacked foam to represent hills or mountains, either. :?
I built my layout on 3/4" plywood, but in most places it's simply cut into strips or arcs of varying radii. I layed it out atop an open grid framework, putting the curves in first, as the layout room is an odd shape. I used the widest curves that would fit, then simply connected them with straight bits. All the pieces were then spliced together, risers added to the underside, then the whole shebang was jacked-up to varying heights and fastened into place. This was a lot more fun than scribbling trackplans, and seems to have worked out fairly well.

Wayne

I underestimated the warpage of the plywood. One piece was so bad I had to use a 'stiffener' (1x2" piece) to flatten it out. I wanted something thin, but I never thought this would be a problem since I used this on a much smaller layout 15 years ago. I beleive it was a combination of leaving the wood out in the garage too long (buying it at the time I bought the wood for the room itself) and the cheap flat paint I used as a sealer (with an apparent high water content).

The piece in question would be what is missing in that 1st attachment on the left side of the photo. It had a real nasty 'bow' to it. So bad, even after days of trying to bend it back in place with numerous gallon cans of paint on top of the piece, it still didn't flatten out. :evil:

Without going too far OT, I don't understand the popularity of 2" and thicker foamboard when it comes to layouts with different heights for the track plan (as in a 2nd level overpass). My example (again using that 1st attachment), how in the world could it be done w/o using cookie cutter construction w/ risers??

videobruce Wrote:I underestimated the warpage of the plywood. ...

Plywood comes it many different qualities. Have a look to the guys that build sailplanes with a plywood skeleton. They buy thin and light plywood as expensive as gold. I am afraid you got a quality not suitable for track base. May be you should go to a good shop and have a talk with a skilled sales person about their plywood qualities and suggested usage.
I did buy ones 3' long wood strips 1/3" * 1/3" at an home improvement center to support my buildings. It was a disaster. The cheep wood strips were everything but straight. I had to buy another set at the double price.

I'm a little late to the party here, however one of the main reasons I re-did my first layout was because I used 3/8 plywood and notice a significant "wavyness" to my trackwork after about several months of use and work put into it. So I pulled it all up and used 3/4 ply for the deck instead. It has proven to be much more stable and have been in place for a few years now.

If you look at this photo showing the risers, spacing is less than 12" on average between the top plates of the risers. I just finished securing all of those and started gluing the foamboard to the ply. I beleive if there is any additional warpage, which I doubt considering it has been in this climate for months, the foamboard on top will mask any of it.
To me, 3/4" is overkill (this is N scale BTW), 1/2" might of been a better choice.

Birch plywood probably would of been the better choice )if 3/8 or 1/2" was available), or that 'stuff' I hate; flakeboard/OSB (at a much cheaper cost). I didn't choose 'finished grade' ply since I wasn't making furniture and no one will see any of it.