I noticed that many layouts in Model Railroader show Homasote on top of 1/2" plywood for the base. I can see using the Homasote but the 1/2" plywood seems like overkill. What would be the disadvantages of using a thinner plywood base, such as 3/8" ?
I used 3/8 on my first layout... worked fine. I guess it somewhat depends on the weight of the scenery, structures, trains, etc, but that also depends on your benchwork under the plywood. Cheers
Depends on what type of benchwork you are building. Flat tabletop? Cookie cutter? Open Grid? You can use 3/8" for your sub base, but you'll have to put in more supports. The thinner the plywood, the more it will sag between supports over time. If you are building a tabletop layout with the proper framework, then 3/8" is just fine. Cookie cutter or open grid will need alot of supports or a thicker sub base. Some people even say that 1/2" is too thin, and use 3/4". -Mike
You could even use 1/4" luan or masonite safely, especially if you cover it with 1" of extruded foam. As stated above, it requires closer centres between supports below it. I used 5/8" GIS plywood for my first layout, and it was overkill by a long shot. Even so, my supports below it were 30" apart. I did have the 1" foam as a layout surface for senicking. If you want only 3/8" ply, your supports below it should be about 10-14" apart.
You might want to think of it a little bit like framing a floor. If someone were to build a floor without beams holding it up, the thickness of the material would be a lot greater. With periodic supports (e.g., 16" O.C. floor beams) you can use much thinner material. The analogy may not work very well for anyone who doesn't have much construction experience. Basically, you can use beefy materials, like 3/4 in. plywood, or you can use thinner materials and then use more intermediate supports such as "beams" or L-girders or T-girders or what have you. Of course, to use lighter materials you'll have to use more engineering. I am using lightweight materials but employing gussets in the corners and deep-but-light blue foam with some intermediate supports, putting a bit of 1/4" luan underneath my mainline tracks attached directly to the ends of the module and supported atop the blue foam, which is in turn supported by some "beams" that span in the short direction. Where I see people get into trouble on light-weight modules or benchwork is when they neglect to design stiffness into all three spatial dimensions, and when they put too much faith into, say, unsupported thin materials. Of course, in my work I see people screw up buildings in similar ways. Adam
Nice topic for an inexperience builder. One of my pieces is 5' long by 3' at one end, narrowing down to 2' at the other end. The 3/8 plywood has a frame of 2 x 4 all round. I intent to lay 1 1/2" blue foam on top of the plywood. So if I am understanding you guy’s right, I probably should run a 2 x 4 down the center of this piece, to give the middle part of the plywood support for this piece. Right? Steve
It couldn't hurt is probably the best answer we could give you. For the time and expense, it is cheap insurance against a "D'Oh!!!" But, seriously, if you securely glue the ply and the 1.5" foam together, they really ought to be quite stiff. But maybe you could stiffen the outer frame more by having some cross members...just a thought. BTW, I would consider 2X4 outer framing to be overly robust. If you block the inner corners and provide cross-bracing, 1X3 or 1X4 should be more than enough to frame your foam/ply inner panel. Just my opinion...if you have the material and wish to use it, sure, by all means.
I used 1/8" luan "door skin" from HomeDepot for my upper track and I glued some 3/4x3/4" sticks around in some strategic spots as stiffeners. I was trying to minimize the weight and it worked well. My 18 month grandson actually climbed up unto it and the only damage was to some plastic structures and some gouges in foam The other advantage was I that I was able to form it into a ramp down to the lower level. I will defiantly use it again on my next layout.
I think the old MR guru, Lynn Wescott is the one who preached about having heavy table / frame work. But then, I think ol Lynn used to walk on his. I have been using 3/8 inch plywood for my sub-roadbed on an open grid frame for over 30 years. On top of that I glue down strips of 1/8 inch foam-mounting board that I get from an art supply store. I hand lay wood ties and rail on top of the foam-board. My horizontal 'joists' are 1 X 4s that I have ripped in half, (now about 1.75" thick) placed about 24 inches apart and have an "L-girder" support about every 4 feet, with braced gussets supporting 2X2" legs. Some places where the track crosses the benchwork at an angle, there is as much as 33" between risers. One place in particular has been exposed that way for over 20 years. When I read the posts of this thread, I was curious. I placed a 4 foot level on top of the rails and was surprised to see that over the past 20 years the roadbed had sagged only about 1/64th of an inch. And to be honest with you, I don't know if that's the way I built it. Where scenery will be heavy on those long spans between risers, I would rip a 1/2" wide strip of plywood, then glue and clamp it with the grain up/down to the center / bottom of the roadbed for support. This works very well as you can also follow the curvature of the roadbed; and, it is an inexpensive way to add a good, solid support. It's true though, I can't walk on my layout. But, I really don't want to anyway. :thumbs_up:
People tend to overbuild because they just don't know any better. I see it all the time. My neighbor built a Christmas display out of 3/4" plywood and 4x4s. He could not even pick it up to move it outside after it was all done and over. I admit I used 3/4" plywood in my Christmas display but that was only because I didn't have frame only some blocks to set it on. I had the advantage of destroying a lot of different things and I saw how strong wood can be when assembled properly. As far as the plywood goes, the nail factor may have something to do with it, but if you use glue and have an adequate frame, than thickness doesn't mater much. As far as heavy scenery goes, unless you are using concrete and solid steel structures, I just can't imagine "heavy".
