Sub road bed

Just started to build a new layout and was wondering if anyone has used OSB ( 3/8" ) for sub road bed rather than plywood of the same thickness. The road bed will be supported every 12"

Thanks for your response

Jim R.

 

Jim, I have seen it used, The only bad thing I have heard about using it is that it is very moisture sensitive. A little to much humidity or moisture and it will warp like crazy. Also when it dries out again it tends to fall apart!!

 

I have used it for storage cabinets in my basement. It absorbs a lot of moisture and falls apart when dry. And I sealed it.

 

People have tried sealing OSB with shellac, and even polyurethane, but nothing seems to work successfully for long.

Unless you live where it never rains, or where you will never have a water pipe break, you would be better off to use Marine Grade plywood, or even solid lumber.

 

I think a lot of you are thinking of MDF which is very moisture hungry and will fall apart if it gets damp.

OSB is different, in fact it is replacing plywood in house construction and now used by a lot of RV manufacturers in the construction of the roof and floors.

 

I am thinking of Oriented Strand Board. Chips of wood ( like from a chipper) glued together in a common orientation. And yes common in house construction to replace more expensive and stronger plywood. That's why they cover it with Tyvek right away.

I don't know what MDF is. Is like MDO (sign board) which is a course saw dust glued and pressed to gether. The 'O' stand for a plastic over lay or coating on a least one surface. That is good sound stuff. After all they make high way signs out of it.

My two cents.

 

Hi:
The stuff we all identify as swelling amazingly when wet is particle board. It is sawdust held together with glue. It used to be used a lot in furniture, and countertops. It has very little span capability. MDF is medium density fiberboard. This is a finer grained product than particle board and is more dimensionally stable. Folks are using it a lot for furniture when a veneer or laminate surface is applied. High Density Fiberboard is also showing up as a paintable molding. The MDF has very little "span strength. OSB, oriented strand board, is a structural panel that is replacing plywood in many applications. I looks like wood chips glued together. using a 7/16-inch panel you can space supports 24-inches apart and walk on it if the edges are properly supported.

All of these are "interior" products. They are not designed to be used where they will be subjected to moisture. The OSB can "sorta" handle being exposed to the elements during construction since the edges are sealed, but then, ya gotta cut it somewhere, sometime.

MDO, Medium Density Overlay, is plywood with a paper/phenolic resin wearing/finish layer. The field will weather fairly well if it is painted but you have to protect the edges as they will allow moisture into the plywood substrait.

Me, i still like plywood or rigid insulation for a road bed/table top. Depends on whether you're gonna look at it or walk on it.

Regards,
Ted

 

I think that when you consider the cost of baseboard materials relative to the value of the models you are going to put on top, it isn't worth risking it with low grade stuff. For manufacturers of furniture a couple of dollars a board makes a difference; you may save the cost of a few freight cars, but then it may turn sour later on.

For the sub-bed I use 9mm (3/8") exterior grade ply (UK, not sure what US equivalent would be). This is pretty water resistant, but not immersion proof.

My layout is made up of 2'X4' modules. Each module base has a 2 1/2" x 3/4" frame round the edge with the ply screwed and glued on top, so my spacing is basically 24" (though there is no centre cross member, so it's 4' that way ). This saves me the cost and work of having (eg) 12" spacing to support a lesser material and almost eliminates problems of underside switch motors, etc, being foul of a support.

I top this with 1/2" wood fibre board for sound deadening and so I can chew out depressions in the 'ground'.

I'll certainly be considering foam panels for my next layout, but I'm not certain about that as fixing switch motors will be trickier (and I tend to have a lot of them )

 

Mike, If you put a piece of 3/16 plywood under your foam you will have something to mount the switch machines to without adding alot of height!!

 

There are two differences between interior and exterior plywood. The first is that the exterior plywood uses a glue that is more water resistant (and more expensive) than the glue used in interior plywood. Unless your layout will be subject to rain or regular water leaks, this is not a factor.

The other difference is that exterior plywood is treated with chemicals to prevent rot and mildew. This makes the sawdust created when cutting highly toxic. It is not needed for interior applications unless you are building in a high humidity location, or directly in contact with damp concrete foundations.

Exterior grade plywood is overkill for indoor layouts, especially if the layout room is air conditioned. In addition, since it is made for exterior use, the surfaces are typically poor quality, making for a rough surface to work with.

For plywood, I would only work with "paint grade" (something new at my local hardware store), birch veneer plywood, lauan, or AC interior plywood. All of these are relatively expensive.

Particle board is sawdust glued together. It has poor spanning strength and swells when wet (like when bonding ballast). A poor choice for subroadbed.

MDF is much denser and stronger than particle board. It is less prone to swelling when wet. Ballasting using the bonded ballast method produces no evidence of swelling. It is very smooth and easy to work with. Its biggest disadvantage is that you must predrill all screws to avoid splitting or mounding. Self-tapping drywall screws will not countersink themselves flush due to the density of the product. It is about 50% heavier than plywood, but about half the cost.

MDF is my choice for both layout decks and subroadbed, and for numerous projects in my shop.

 

PeterZ; I can't speak for US ply products, but in the UK we have shuttering ply, which is pretty rough (used for making concrete molds and general building site work). It sounds equivalent to what you describe as exterior.

What I have found as 'exterior' grade over here has a quite smooth finish - the odd crater where a knot has popped out, but certainly smooth otherwise. Usually costs about 30% more than interior grade at the DIY store, but I get it from a timber merchants where it is cheaper than the interior stuff from the store. (Before someone asks; the merchants don't stock interior grade - it's not worth it for them )

Interesting point about chemicals. I doubt if that applies to the UK products or there would be health warnings all over (there is some paranoia about such things these days and the regs are pretty tough), but I will do some research on that, ... cough ... splutter .

 

Things to keep in mind when building the sub roadbed and main support structure:

1. When building for mobility, worry about weight, and build a layout that can tolerate some flex, as lighter layouts WILL felx. Heaveir foam is popular for this, but I'd personally have the heebie jeebies doing it.

2. When building a stationary layout, build for strength. You want no flexing of the layout, especially if you have changes in elevation, mountains, or trestles. Trestles canot handle any flexing of the layout at all. Go to heavier plywood or OSB and don't span very far. When the main structure is completed seal it all with paint or varnish. Anything to slow the flow of water into or out of the wood.

If you're building a stantionary layout, use standard building materials for your area as much as possible. You'll have good availability and plenty of people that know what you're workng with.

I'm about 3 months away from starting my dream layout - once I finish our basement of course. It'll be an around-the room layout with two continuous running lines, a switchyard, and passenger terminal.

The main structure will be made from standard 2x4's, no more than 16" on center, with 1/2" plywood glued and screwed to it. I'll build the entire sub roadbed, complete with elevation changes and elevated curves using 1/2" plywood supported on 2X4's cut into pillars. Once it's all correct I'll cover the entire thing with either 1/2" or 3/4" insulating foam for deadening and additional smoothening out of the layout. Cork roadbed will then be glued on top of that. Other than the foam, there will be no problem walking on the layout. I'll swap foan with plywood in a few areas away from the track so I can walk on it. As I get closer I'll be posting the layout design and progress.

Mark in Utah