Thickness of benchwork plywood?

[pcarrell]

Excellant idea selector! Time to dig out the straight edge again.

[selector]

P. Carrell, I think you are okay.

It really isn't the luan sagging, especially if it is well supported, as I believe you are, but the thinner luan sagging because your 1X3's are immeasurably sagging over time when they are too long and/or not supported well enough near their middles. However, in your case, they should be good on their edges as you describe, like joists.

What you could do, with a few minutes of your time, is use a level and straight-edge to mark the 1X3's average middle-span sags (if there is any) at each of the end beams of your bench. Put a mark with a date. Three months later, repeat the measurement and see if you can detect any sag. If more than 1mm in three months, I'd say you were slowly losing the struggle against Mother Earth. You would want some form of support along them.

[Bikerdad]

If you live anywhere that has either a hardwood dealer or a sheet goods dealer, go visit them. Last week, my buddy purchased 6 sheets of 5'x5' 1/2" Baltic Birch plywood from McKillican's (they have stores in several states) for $20 each. 1/2" BB is 9 ply, shop grade (i.e. paintable and stainable) both sides. BB is available in other thicknesses as well.

[pcarrell]

Oh, I used only quality wood for the benchwork (clear poplar).

[pcarrell]

selector,

The layout depth, and consequently the supports, are 4 feet deep and they are not layed up on their sides. They stand up with the skinny side on the top and bottom. They are cut to fit within the 1x4 frame and they are double screwed on each end with 4 inch deck screws countersunk into a pilot hole. Seemed pretty solid to me but with the luan being only 1/4 inch thick I didn't know about sagging over time.

The scenery will be light and will be mostly plaster soaked paper towels except for a pop out hatch that will be foam board (2 inch thick).

The setting is late 30's coastal and near coastal backwoods Maine and so trains will be mostly short (10 or 12 cars at the longest).

Any more input is welcome as I right now have a plan, 1/3 of the track down, and a head full of ideas.

I'd rather make changes now then later, so bring it on!

[selector]

P. Carrell, yes, what you describe should be plenty strong for light trains and structure, such as plaster cloth mountains, especially with the 12" support spacing underneath. One question, though: how long are the 1X3's that are spaced 12" apart? In other words, how wide is your layout, because I am assuming that those 1X3's are like floor joists in orientation? If they are longer than about three feet, and oriented on the flat side up against the luan, then a stronger beam running longitudinally under their centers might give them a bit of insurance from over-time sag.

[Leon Silverman]

Riverotter:
Checkout www.howelumber.com/osbply.htm. This explains the difference between OSB (Oriented Strand Board) and regular plywood. Plywood has the wood grain appearance whereas OSB looks like chips of wood laid in random directions. OSB should be cheaper since it can be made from small trees. It has about the same strength as plywood of similar thickness but will lose strength is countersunk.

[pcarrell]

Larry Boyd brings up a good point.

I used 1/4 inch luan with 1/4 inch foam sheets over the top. I placed this on a boxed framework of 1x4's and used 1x3's for cross braces on 12 inch centers. I'm using the cookie cutter method. I just built this a few months ago in a climate controlled room. I don't climb on the layout, humidity isn't an issue, and the temperature is constant year round.

My question is will this be enough support for the long haul or should I make an I-beam setup to go under the luan between the 12 inch supports?

I want it to last but I don't need a 2 million pound monster in my train room.

[selector]

Any manufactured or natural wood product, unless it is completely sealed in a non-porous medium, will begin to change shape as the ambient humidity changes. That is why layouts in garages and basements, and those in non-air conditioned homes, will have problems with continuity, displaced and separated structures, dislodged castings, and faults along the terrain that mirror the San Andreas fault....unless they have a decent dehumidifier nearby.

I don't know why a person wouldn't spend $200 on a dehumidifier, and spend another $30/year operating it, to protect a much more substantial investment in their hobby.

[riverotter1948]

This is exactly the forum I've been looking for. I recently moved to the Midwest where humidity definitely is a problem. For my first attempt at a new layout I used Mianne benchwork and 5/8" B/C plywood as recommended by MR et al. First thunderstorm we had (100% humidity), the 2' x 6' sections I had cut and screwed into the benchwork warped almost 2" east-west; pulled those wood screws out like they were greased. The fellow at Home Depot suggested I consider laminate (you know, compressed sawdust); he said that stuff never warps. Doesn't sound right to me. Thanks to everyone for sharing their thoughts on this. P.S. What is "OSB"? Sorry to be so dumb; I'm in information technology (IT) & we're acronym crazy, too.

[WilmJunc]

I am currently using 3/8" plywood supported 16" O.C. Once everything is connected it becomes quite strong.

[howmus]

QUOTE: Originally posted by Robert Knapp
I would like to add to this. Check out the ply at a local quality lumber yard first. They will carry a far better grade of ply than the big box stores. Plywood, whether 3/8 or 1/2" can be found in Douglas fir graded for underlayment (3/8, 1/2 PTS or termed plugged and sanded). This is still a relativly inexpensive ply for the quality. Most big box stores will have only pine and found to be inferior.

Absolutely! A few years ago I bought some plywood at a local HugeCo "we sell cheaper" (meaning quality) store. The plywood was purchased to be cut up to make stands for a backdrop for a Christian Rock Group sponsored by the Presbytery. When it was cut it completly delaminated. I took a couple sections back to them and they said they were really sorry and would replace it (with more from the same pile of crap). When the replacement sheets did the same thing, they said, "Oh these aren't really made to cut and should be used whole". Yeh! Right! IMHO go to a quality lumber yard (the kind owned by people in your community who care about the stuff they sell to you) and get quality (5 ply) plywood that will not warp or fall apart on you. In the long run it will be a lot cheaper.

[Anonymous]

jshrade

I have a shelf railroad that is 24" wide and in 8 foot sections and is framed with 1 X 4's with 1/8" lauan glued and screwed to the top. It has 2" foam glue to that. Its stronger than most without the heavy layup. Why most people think you have to have plywood thick enough to walk on is beyond me.

Larry

[Anonymous]

I decided on 15/32" 3 ply plywood for the layout. I took one look at what was available in 3/8 at my local lowes, and really wasn't thrilled, but the stack of 15/32 right next to it looked so much better, and was only marginally more expensive ($1 more per sheet) and marginally heavier, but considerably less flex. I would've liked to have found 4 or 5 ply, but the 15/32" they had seemed like decent quality and now that I've got it temporarily placed on the layout benchwork, I'm quite happy with it. Had to install a ceiling fan last night in the layout room, and sat on top of the plywood for nearly an hour as I hooked up the fan, with no sag, and no problems whatsoever with my benchwork wobbling or anything. Once I actually screw the plywood to the frame and joists, I think it'll stiffen things up even more. Thanks for all the advice guys!

[bogp40]

QUOTE: Originally posted by howmus

jshrade, given the fact that you will have to climb up on the layout changes my recommendation to you! You would be better off, given what you are doing to use 1/2" plywood. Also get the 5 ply stuff as it is considerably stronger than the 3 ply. 3/8" plywood can be found in both, most 1/2" is 5 ply (that is, it has 5 layers of wood used to make the plywood). Again, how you are using it makes a big difference in what you should be using. Have fun!

I would like to add to this. Check out the ply at a local quality lumber yard first. They will carry a far better grade of ply than the big box stores. Plywood, whether 3/8 or 1/2" can be found in Douglas fir graded for underlayment (3/8, 1/2 PTS or termed plugged and sanded). This is still a relativly inexpensive ply for the quality. Most big box stores will have only pine and found to be inferior.
Last week I needed 40 sheet of 1/2" CDX, my regular supplier was $.30 less than HD for fir instead of pine. All the sheets were flat w/o the curl as most lesser grades will tend to have.
Some people love these big box stores, I personally don't have the time to deal with them and then end up w/ a lesser product. I deal with lumber on a daily basis, Pull up to the lift load it and get to the job with a good product to work with for a quality job. Not All Plywood Is Created Equal...
Bob K.

[Anonymous]

Well, I got to thinking more about it, I'm definitely going with 1/2" plywood (well, down here they call it 15/32 but that's basically the same stuff (5 ply), my joists are 12" apart, but considering where I'll need access in the long run, I'm certainly going to have access hatches instead of climbing on top. Only issue I really have will be the hidden double tracked mainline and part of the reverse loop section, which will be out of reach from the edge of the tables, but my plan is to have that track as bulletproof and derailment free as I possibly can, so I won't have to go back there but every so often. I have plenty of room under the layout to access the back side, just have to cut in some 'hand holes' to be able to reach things. Shouldn't be too hard if I hide the holes with buildings, instead of complete removable sections.

[selector]

Cletus, you raise a good point. Aboslutely, DO NOT walk, kneel, even pray up on your foam sheets without using a weight-distributing length of board, plywood, or another piece of unused foam. Otherwise, your heels, tools, or knees will leave unwanted marks and marr the surface. My preference was a piece of plywood as it was stiffer and better at holding my weight in distribution.

[cwaldman]

All it depends on is the spacing of the supports underneath. What load it is gooing to carry, over an above the normal railroad. If you are going to walk around on it then you probably will need to do one of two things. Use thicker plywood or use more suppost under it. It is probably a trade off your making by spending more on support or more on thicker plywood.

it has been recommended before to seal the wood to prevent warping if humidy is a concern.

I wouldn't recommend walking around on styrofoam of any thickness.

Cletus

[tsasala]

If humidity is an issue, you might want to try OSB instead of plywood. It holds up better, but I think it's usually more expensive.

I put foam directly over my frame without any underlayment. But I'm modeling HO and have no reason to stand on my layout. In fact, my layout will be hoisted to the ceiling when not in use, so weight was a concern for me.

-Tom

[howmus]

jshrade, given the fact that you will have to climb up on the layout changes my recommendation to you! You would be better off, given what you are doing to use 1/2" plywood. Also get the 5 ply stuff as it is considerably stronger than the 3 ply. 3/8" plywood can be found in both, most 1/2" is 5 ply (that is, it has 5 layers of wood used to make the plywood). Again, how you are using it makes a big difference in what you should be using. Have fun!

[selector]

Oh well, I'll jump in myself, and add my three Cdn cents.

My layout has three 4'X8' sheets of plywood set long side by long side to make a 12' X 8' layout. The plywood is 5/8", good on one side (GIS). I have threee two-by-four 41"-high pony walls spaced 24" apart holding up the entire layout. On top of the plywood is one layer of 1" foam. I danced on that layout many times rasping foam with a wire brush, and I got lots of movement, but it was sideways, strangely, in time with my arm movements as I brushed the foam. A few diagonal braces soon fixed that!

The 2X4 ponywalls were definitely over-kill, but not the 5/8" plywood. I believe that I would have experienced some sagging if my 'walls' had been spaced another two or three inches apart.

If you want my considered advice, I would use not less than 1/2" plywood if you will rely thereafter only on the glue holding together two layers of 1/2" foam, and then only if the joists or supports are no further than 18" apart. I say this with your claim in mind that you will have to climb up on it from time-to-time.

[Big_Boy_4005]

QUOTE: Originally posted by howmus

I have used everything from 1/4" up to 1/2 inch plywood on the layout. What I use depends on where and for what purpose I am using it. I would recommend that you use 3/8" plywood and keep the supports no farther than 16" apart. Gluing the plywood is also a good idea. Much of my 3/8 inch base has been down over 20 years and has not warped at all. However! The conditions in my basement stay reasonably the same year around. If your room has wide swings of temperature or (more importantly) humidity, you may want to go 1/2". IMHO 3/4 is major overkill unless you only put supports in every 4'. Consider your total cost for the construction, not just the cost of the plywood.

Have fun!

Actually, 3/4" plywood can get kind of springy if you don't support it about every 24". In order to cut material costs, I cut the sheet into strips. Being in O gauge, that means 4" per track. In the photos above, there was less than one full sheet used to do 30 feet of railroad. In those areas where I need to climb on the layout, I just deck it, but that's only a couple of places.

[Anonymous]

Well in my area, 2" foam isn't readily available, so I'm only going to use two layers of 1/2" foam (which is available) and my layout is around the wall but is 48" wide. The walls/ceiling of the room slope inward (bonus room over the garage) so I will need to climb on top of the layout when laying track along the walls (the hidden main loop). So it will need to support my 250lb fat butt. I think I'll go with 1/2" ply with 12" joist spacing, glued and screwed.

[grayfox1119]

You are correct Ray, you use what you need depending upon what your layout needs for strength. I have tables that will be 30" wide and wider. I may need to get up on these tables at times, I weigh 185#. I also want the room underneith un cluttered for staging, so my supports are every 4 feet. I also have a well temperature controlled basement location ( as you stated also Ray). This makes a big difference. There is a correct answer for each layout, but that answer depends upon all the factors mentioned by all the guys that answered this thread, bookshelf layouts to not need 3/4", table layouts of 24" or less do not need 3/4"....the layout dictates the construction design required.

[howmus]

I have used everything from 1/4" up to 1/2 inch plywood on the layout. What I use depends on where and for what purpose I am using it. I would recommend that you use 3/8" plywood and keep the supports no farther than 16" apart. Gluing the plywood is also a good idea. Much of my 3/8 inch base has been down over 20 years and has not warped at all. However! The conditions in my basement stay reasonably the same year around. If your room has wide swings of temperature or (more importantly) humidity, you may want to go 1/2". IMHO 3/4 is major overkill unless you only put supports in every 4'. Consider your total cost for the construction, not just the cost of the plywood.

Have fun!

[chateauricher]

QUOTE: Originally posted by Big_Boy_4005
There is no way I could work with a foam only layout. There are places where I need to stand on my layout. Beside, working in O gauge, it is possible to have 10 pound locomotives. For my upper deck I'm thinking about 1/2" OSB with 1/2" foam over that. The lower level is 3/4" plywood with foam or homasote roadbed.

With the larger scales and their heavier equipment, I can see where you would need the extra support of plywood.

And if you had a layout where you needed to stand on portions of it in order to reach other sections, then, yes, plywood would be a good idea.

However, what about for smaller scale (eg: HO, N, and Z) layouts where all areas can be reached without standing or leaning on the layout ? [%-)]

[Big_Boy_4005]

QUOTE: Originally posted by chateauricher

But is a plywood deck of any thickness really absolutely necessary if you are using 2" of extruded foam? Let's presume, of course, you have an adequate support frame underneath. Is the foam not rigid and strong enough to support the tracks and scenic elements without resorting to expensive plywood?

By not having a plywood deck ...

wiring would be simpler -- no holes to drill (in the wrong place), just poke a hole in the foam with a coathanger or awl;

undermounted switchmachines could be mounted closer to the surface by simply cutting a hole for it;

no worries about seasonal expansion/contraction.

There is no way I could work with a foam only layout. There are places where I need to stand on my layout. Beside, working in O gauge, it is possible to have 10 pound locomotives. For my upper deck I'm thinking about 1/2" OSB with 1/2" foam over that. The lower level is 3/4" plywood with foam or homasote roadbed.

[chateauricher]

But is a plywood deck of any thickness really absolutely necessary if you are using 2" of extruded foam? Let's presume, of course, you have an adequate support frame underneath. Is the foam not rigid and strong enough to support the tracks and scenic elements without resorting to expensive plywood?

By not having a plywood deck ...

wiring would be simpler -- no holes to drill (in the wrong place), just poke a hole in the foam with a coathanger or awl;

undermounted switchmachines could be mounted closer to the surface by simply cutting a hole for it;

no worries about seasonal expansion/contraction.

[grayfox1119]

Notice I said...for smaller widths ( ie shelf layouts), thinner plywood is fine. I am taking about layouts on benches, and layouts 30" wide and wider. No one is going to need to climb on a shelf layout.