Plywood Panic

Bob, here's my thought, and remember that since you are paying nothing for it, that may be what it's worth!

Rather than tearing up the 3/8 and replacing it with 3/4, what if you added another layer of 3/8 on top of the existing 3/8?  Here is my reasoning:  this would give you additional strength, AND the two separate layers might do a lot to decouple the sound waves and give you a quieter layout.

It makes sense to me, but I'll wait and see what others think about my theory.

 

Glad you're building - you're ahead of me!

 

Tom

Are you driving trucks on your bench work or setting up toy trains? 3/8 should be fine, I used 1/2 inch with 24" spacing in my 1x4 and it's more than enough. I've used 3/8 on 24" spacing on HO SCALE AND N SCALE AND THATS MORE THAN ENOUGH.

add more 2 by 4 stringers.

How many plys does your 3/8" CDX have?

3/8" CDX is probably strong enough, but it will warp if you don't fasten it down well and with enough bracing. I would do as F&G RY says and add more cross braces.

 

I used 1/2" sandply (5 ply), it is quite strong and does not warp. 

I agree with what others have said.  While you can probably get by you need to make sure its well screwed down and add additional 2x4s.  I went 16" centers and used 3/4" AC grade sanded material with 7 plys.  It has not warped at all.

3/8's should be perfectly fine in my opinion. I am structural engineer and your not going to see a difference between 3/8 and a 1/2 in my opinion for what weight is there. 

 

What are your 2x4's spaced at 16 inches on center or 24 inches on center? I would not add a layer of plywood on top because they is going to increase the weight on your original layer. They will not act as a composite member in my opinion. If you are that worried about it I would add extra 2x4's below, so if the original spacing is 24 inches then add a board in between cut it to 12 inches on center. The plywood just gives you a surface between the joists and its job is to transfer the weight of your layout to your 2x4's with in that 24 inch spacing for example. 

 

Chris

 "I have been crawling on it with all 190 of my lbs with no consequence, but I want it to last, so I am asking your expertise.  Thanks!"

 

    If the top wasn't flexing with your weight it shouldn't have any problem with some trains on it. How far apart are the cross braces( or what is the span that the plywood has to support)? For 3/8th inch plywood I usually try to keep the span to 16 inches or less....DaveB

I do agree with others on properly securing the plywood and if need be add "braces" perpendicular to your main supports to get the middle fastened. I don't think you need braces for load, but more for warping if you think you have an issue. 

 

Chris 

Yeah, I don't think you need to worry about the plywood, as long as it is well supported to prevent warping.  Two-by-fours wouldn't even be needed for that.  Any size down to 1X2 should be suitable for that purpose, given that you have already framed the table with 2X4s.

 

Have fun, and do post photos of your progress.

I am not at all qualified in engineering but there is one aspect that I think may have an impact on your situation.

 

i have found that higher than normal moisture/humidity levels has an adverse effect on plywood (and trains) over time.  

 

You didn't mention where your layout is, basement, garage, etc.

 

Ed

 

 

It is a whole lot easier to put in braces to prevent warping than to try to get rid of the warping later. Humidity and warping go together.

Sounds like a decent enough stress test, but stay on that diet....

Thank you so much for all of your replies.  I will add some more 2x4's for support for sure.  The pictures and suggestions have been tremendous for my peace of mind and direction going forward.  

I am a big believer in glue and screw. When I first started using glue in addition to screws when securing the top to the frame, I was amazed at how much rigidity and strength appeared to be added.

As others have written, I think how the table is framed is important. My standard construction technique to frame a 4 by 8 sheet is to have 1x4 around the perimeter, with cross pieces every two feet.

I think that If I was building a table today, I'd have some plywood ripped into six inch wide pieces to make the frame. The lumber I see in our local yard is rarely straight, and I am not particularly good at finding the useable pieces.

On another forum a member who writes articles mentioned he used 3/8" and should of know better the minimum should be 1/2" as 3/8" will warp I use 3/4 I guess if you would do criss cross 3/8" and screw it down very often you would be okay. I would go with at least 1/2" if not 3/4" thou it's better now than later if you should have a problem and if your already seeing warping I would say it's time to go thicker now.

The problem is rigidity and warping.  A long time ago, Tony Koester of RMC and MRR fame indicated he used 3/4" ply and would have used 1" ply if he could have obtained it.  The problem is not the weight of the trains or the person on top of the table but keeping it rigid and avoiding warping.

I use 3/4" AC Exterior and sometimes 3/4" birch ply (when I can get it) on 16" centers.  I also use 3/4" birch ply ripped into 1x4's for the frame.  So far, I have had no warping and minimal expansion/contraction due to humidity.

Let me put it another way:  You spend thousands of dollars on trains and countless hours building your RR, why skimp and/or take a chance with minimal carpentry?

Just my $0.02.

Ed

"The problem is rigidity and warping.  A long time ago, Tony Koester of RMC and MRR fame indicated he used 3/4" ply and would have used 1" ply if he could have obtained it.  The problem is not the weight of the trains or the person on top of the table but keeping it rigid and avoiding warping."

 

    Rigidity comes from proper framing, not from thick plywood. I've built 25 foot sail boats with 1/4 inch ply skin that were perfectly rigid while I have a piece of 3/4 inch plywood out in the shop that someone recently gave me which is warped due to improper storage. Rigidity is determined by the thickness of the section , 3/4 ply over 3.25 inch framing has an effective thickness of 4" " as does 1/2 ply over 3.5 " framing. Using thicker ply can slightly increase the rigidity but not as great as using wider framing members and spacing them correctly. The downside of thicker plywood is more weight to carry around and more thickness to run switch motors throw wire thru. I usually go with a good 5 ply 1/2 inch plywood as the best compromise between cost,weight and screw holding ability.....DaveB 

Daveb,

Interesting points.

Question:  What thickness of ply would you use over 16" centers?

Ed

We build our modules for the modular club with 1x4 framing and 1/2" plywood.  We have never had any issues with warping or rigidity.  I can walk around on a module with no fears of breaking anything. I've seen a couple of layouts that used 1/4" plywood, they didn't seem to have any issues.

 

If you can't walk on a layout with 2x4 framing and 3/8" plywood, there is something seriously wrong in the universe!

 "What thickness of ply would you use over 16" centers?"

 

   Hi Ed, I think it depends on a lot of factors. A layout framed for a solid plywood top can use thinner ply than a layout framed with uprights supporting narrow roadbed width plywood for example, a  layout with sheet foam over the plywood will also require less plywood thickness as the foam although not strong still adds to the stiffness of the complete section measured from track to bottom of framing. I've had modules with solid 1/4 inch plywood tops glued and nailed to 1X4 framing at 16 inch on center and they were stiff enough. Generally I don't like to go less than 1/2 inch ply just because it takes and holds screws for things like switch motors or wiring terminal strips better than thinner ply. For an O  layout that is open on top with just the plywood roadbed I'll use 3/4 inch ply cut to the width of the ballast base as narrow pieces of ply are less stiff than full sheets nailed at the perimeter. Anyone building a layout should base the decision on their type of scenery and framing desired but 3/4 inch should be plenty strong for every application as long as it is supported adequately.....DaveB

Hey, which thickness of ply would you recommend for Mianne benchwork in a basement

environment?  It is poured concrete with no water problems thankfully, but humidity

runs about 65 pct. in the summer.  Thanks for your replies.

 

     Hoppy

 "which thickness of ply would you recommend for Mianne benchwork in a basement

environment?  It is poured concrete with no water problems thankfully, but humidity

runs about 65 pct. in the summer. "

 

   What kind of track and scenery will it have? Will the benchwork be covered with a continuous table top or will it be just narrow plywood roadbed under the tracks and plaster or foam elsewhere? Is there any wooden furniture or other items in there that give a clue to how wood does in there? .......DaveB

Dave, the railroad will be 7' X 16', topped overall and no foam, etc.  Lionel tubular

in Johnson rubber roadbed.  I won't need to walk on it.  We've been in the house for

16 months and so far, any wood furniture down there is fine (doors & drawers operate

properly).  I have a dehumidifier that I run during summer and it seems to need only a

few hours a week, if that.

 

     Hoppy

 "so far, any wood furniture down there is fine (doors & drawers operate

properly)."

 

   Sounds like you should be fine then. Does Mianne have a recommendation for table top thickness? If not I'd go with whatever you think feels the best from a strength,and weight stand point. If the supports are 16 inch on center I'd be comfortable with a good 5 ply  1/2 inch top , if the cross members  are 24 " on center maybe 5/8" or use 3/4" if you don't mind the weight. On my latest layout I got some 7 ply approximately 1/2 inch sheets at Home Depot that are stiff and smooth, some kind of foreign wood that resembles luan but is more stringy in the grain. I don't know how it would react in a basement because the layout is in a spare room in the house.....DaveB

Thanks Dave.  Now a question:  does 'sandply' mentioned in this thread, go by another

trade name.  It comes up 'not found' on home supply sites.

 

     Hoppy

1/2" sandply is available at Home Depot, at least in my area. Might try searching 'plywood'? That will be just fine for your basement and Mianne bench work. I have the exact same setup, concrete basement and all. I started out to get 1/2" birch plywood, but the sandply had more plys and the more the better. It was the same price as the birch, about $30 something a sheet. Had Home Depot cut it into smaller pieces I could handle. Getting old, and can't handle a full sheet anymore. Tim (from Mianne) also recommended the Home Depot sandply. That is also what he supplied with the Mianne transformer cart I ordered after getting my layout setup. Lowes near me doesn't have it and there are no Menards near me, so I don't know what they carry?

 "does 'sandply' mentioned in this thread, go by another

trade name.  It comes up 'not found' on home supply sites." 

 

   It might be a Home Depot exclusive product, I see something called sandeply on their website. This stuff might be what I got for my latest layout, sounds about the same, lots of plys some quite thin with a smooth surface. Another part of my layout uses 5 ply 1/2 inch  fir maybe ACX or ABX grade that was fairly reasonable few years ago. The fir doesn't look quite as fancy but I know it's sturdy as I bought a lot of it for new  sheathing when I rebuilt my house roof, some left overs were used for the layout. I didn't have enough of the fir ply left to do the whole layout so bought a sheet or two of the foreign wood.....DaveB 

Not all of the home centers carry sandply. It might be a regional product.

One website says that it is "typically southern yellow pine a.c. grade exterior that is sanded on one side ready for paint."

Not available at our Home Depot or Lowes.

Sean

Ok, I looked it up, here is a link Home Depot Sandply plywood. They call it Sande Plywood on their website. It could still be a regional item for them? All the stores around here carry it? Mianne is in Massachusetts and they have it there as well, at least they supplied it with my transformer cart anyway.

 

They say it is a Home Depot exclusive. It is listed under Hardwood Plywood on their website. It is not yellow pine, which is a softwood. (Yellow pine is actually pretty hard and strong, but classified as softwood.) BC grade is all that I have seen around my area and all the yellow pine plywood I have ever used had warping problems (including 3/4") unless really fastened down well. I stopped using yellow pine plywood many years ago.

A friend of mine  built his with 2X3s 1/4" plywood 16" on center and I was sitting on it Im 6'3" 349lbs and it held no problem

In truth, if it's framed well, 1/4" plywood is fine.  I think the one comment about having a bit more wood for screws is the major argument for thicker plywood.  More than 1/2" is truly overkill, I can't imagine that being a problem with proper framing.

 

Thanks for your replies re. 'sandply'.

 

     Hoppy