Plywood Thickness Question

[dave9999]

QUOTE: Originally posted by H-Liner

I prefer 1/2" ply because it's stiff enough not to sag when supported every 16" or so but bendable for vertical curves at changes in the grade. 3/4" won't bend and 3/8" is too flexible. By the way, 11/32" ply would be undersized 3/8" not 1/2". Last I heard, plywood is supposed to be its full nominal size. Then again, I'm old enough to have worked with 2x4's which were 1 3/4" x 3 3/4" when I was in grade school. I'm planning a new layout and this one will be a combination of steel stud shapes for the skeleton and 3/4" x 3" cut from birch plywood for everything else. The subroadbed will be splines ripped from 4mm luan or baltic birch.

Your right, 1/2" is actually 15/32". My mistake.[oops]
Although when ordering you just request 1/2" and you'll get 15/32".
And kiln dried wood is 1 1/2 x 3 1/2 for 2 x 4. Pressure treated wood is usually closer to 1 3/4 x 3 3/4.

[Anonymous]

I prefer 1/2" ply because it's stiff enough not to sag when supported every 16" or so but bendable for vertical curves at changes in the grade. 3/4" won't bend and 3/8" is too flexible. By the way, 11/32" ply would be undersized 3/8" not 1/2". Last I heard, plywood is supposed to be its full nominal size. Then again, I'm old enough to have worked with 2x4's which were 1 3/4" x 3 3/4" when I was in grade school. I'm planning a new layout and this one will be a combination of steel stud shapes for the skeleton and 3/4" x 3" cut from birch plywood for everything else. The subroadbed will be splines ripped from 4mm luan or baltic birch.

[cwclark]

I'm convenced that 3/4" plywood is the way to go...using 1/2" and 3/8" is ok until it's time to nail in the track spikes...there is too much play in the thinner boards and I end up bending more nails than nails I get set when i tap them in when using the thinner plywoods...also i've found that 3/4' plywood makes better looking, more defined roadbed ...it's stiff and hard to work with but the results are fantastic....Chuck [:D]

[n2mopac]

I use 3/8" with little problem. The key is to watch areas where it strecthes around curves and use extra bracing anywhere that you can push it down and bow it with minimal force. as long as you braing is good 3/8 works great.
Ron

[MAbruce]

Another way to fight the effects of humidity (besides beefing up the lumber) is to seal your bench work before you start putting anything down on it. I primed mine and also use a dehumidifier. I used ½” plywood braced by 1x3 strapping, 2x3 for the legs (Yes - I had to go through a lot of lumber at Home Depot to find straight sections), and all held together by drywall screws. It’s not very "pretty", but it’s solid and I've had no problems so far (three years). Even a small warp/shift would cause me all sorts of headaches in N-scale.

Of course I'm talking about a table top style of bench work, so I’m not sure how much sealing would help an open grid style.

[Anonymous]

Dougal,

I guess I'm running against the grain here. I use 3/4" cabinet grade plywood because I don't want any problems with warp or sag. Most supports are on 18" or less centers. I have used 3/8"and 1/2" plywood in the past and have had sagging and warping issues. Many of these problems took years to manifest themselves.

BTW: Another high quality ply is the Luan Mahogany (solid wood plys and no voids)

My 2 cents,

Guy

[ham99]

For a really nice bench, use 3/8" Baltic Birch plywood. All the plies are birch, and there are no voids. It bends nicely for grade changes. I find 1/2" a little stiff for grade changes, but maybe not if you are using construction grade fir ply. Baltic Birch comes in 5'x5' size, not 4'x8', and is a little more expensive per square foot, but it is really nice to work with. I use 16"OC braces under the benchtop. harrym

[dave9999]

The reason I recommended 1/2" (11/32") is that I live in a high humidity area of the country.
I have actually returned to a job the next morning and found a sheet of 1/2" plywood shaped
like a rocker on a rocking chair. It hadn't rained on it, it happened just from laying out in the humid
air all night.

Ray's suggestion of 16"-18" on center crossmembers is a good idea if using 1x4 lumber. I personally
use 2x4 only because of the high humidity. And even with 24" O.C. crossmembers I can stand on
my table and it doesn't give.

But, as I said before use at least BC grade. CDX will delaminate and warp, especially in humid conditions.
The extra cost will save you a giant headache in the future. Good luck
Dave

[IRONROOSTER]

I use 3/8" thick supported on 12" on center. It may be overkill, but I haven't had any problem in several years.
Enjoy
Paul

[orsonroy]

11/32nd is 1/2"....sort of. Wood is sold in "nominal dimension", meaning that when you ask for and buy 1/2", you're really getting 11/32". If you measure a 2x4, it's really 1.75"x 3.5" (or something like that).

[Anonymous]

is 11 32ths good enough?

[orsonroy]

Actually, it all depends on your bracing. True, virtually all model railroad benchwork is WAY overbuilt (there's no reason for 2x4s, people!), but plywood is one area where most people UNDER build.

Plywood will sag, no matter what you do to it. How MUCH it'll sag depends on how much bracing you add underneath it. The further apart the supports are, the greater the chances of noticeable sagging.

You should be fine with 1/2" plywood, so long as your supports are less than 2 feet apart. Realistically, 16"-18" would be better.

[dave9999]

Hey Mark,
1/2" will work fine, just make sure to use at least a "BC" grade. Also make sure your cross members in your bench work are no more than 2' on center. This will prevent warping. And screw, don't nail, the plywood to the benchwork. You may
also want to glue the plywood down, as well as screw it.
Dave

[EL PARRo]

½" is plenty. In fact, a lot of the layouts that I see only use 3/8" plywood. I use ½" plywood on my layout, and it's plenty strong.

[Anonymous]

Is 1/2 inches good or should the plywood I use be thicker[?] Thanks[:)]