I never stood on my previous layout and I don't plan on standing on my future one either.
Has anyone ever had one collapse because of weight? Or issues with warpage?
@gunrunnerjohn posted:I have to stand on mine at times to reach everything, I'd feel a little endangered standing on 1/4" Lauan plywood on 24" centers. I think I'll pass on that idea.
John, You miss the point. I never stood on my layout of 5 X 13. The Luan is referenced as an alternative to higher priced materials. I've seen your new layout. I don't know why you or anyone would need to stand on smaller layouts?... The warehouse sized, well, I think that is a different story'....
True Ted, if you don't plan on putting weight on it, the 1/4" would certainly support anything you might put on a model RR. OTOH, the other issue is the possibility of the 1/4" plywood warping.
I agree with John. If it’s up for an extended period I think you’ll notice a bend in 1/4 inch for most layouts. It might be awhile but you’ll notice it.
@texgeekboy posted:I agree with John. If it’s up for an extended period I think you’ll notice a bend in 1/4 inch for most layouts. It might be awhile but you’ll notice it.
no, like any thing, made from wood, its how its supported, and assembled (glue, screws, ect) For the last 60 plus years there have been countless publications, and articles On how to frame and build a model rail road with out raising a floor op to waist level ,and strong enough so 12 guys can walk on it.
@Frank Mulligan posted:I never stood on my previous layout and I don't plan on standing on my future one either.
Has anyone ever had one collapse because of weight? Or issues with warpage?
Falling no. Warpage yes. I had 28 feet of table built. It bowed, warped and twisted after it was built. It was not usable so I took it all apart and scrapped it.
I've had plywood bow after I cut it into 4" wide strips. I started using red oak 1x4's and have a couple of 4x8 tables built. But my saw mill guy passed away and the kid's closed it down. No more red oak anywhere around here. Oh I did have a 4x8 sheet of plywood bow something fierce.
I've seen a lot of warped plywood in a host of applications, so it does certainly happen. In any case, the difference in price from the plywood to the really nice Baltic Birch at the time was minimal, so I went with the really nice wood.
Hello!
Go to Lowes or HD and buy their APA exterior grade (green stripes painted on end) 1/2 inch plywood. (Not the interior grade junk with black stripes painted on the end.) Look on the underside of the sheets, and they will be stamped with a black APA Approval Stamp, stating that it is Grade 1 Exterior. This will cost you about $60 to $70 per sheet.
I'm not talking about "treated" green plywood, but the plywood which uses waterproof glue between the layers, so it can take lots of direct water and damage for months before it fails.
The exterior grade is rated BC, with a nice filled and sanded B side up, and a good grade C on the bottom with no voids from fallen knots. If you want it to have an A side up, then buy a small palm orbital sander, and in about 45 minutes, you can sand it to an A looking side.
Assuming that your joists are strong enough, you can glue and screw this plywood down on them (using Loctite PL8x construction adhesive), and it will be incredibly strong. You will be able to walk on it with almost no flex. I am not sure why you are concerned about voids in the middle of the layers, since you are going to use a screw or nail to hold track and accessories down on the table and the plywood is 4 layers thick. If you want the top to be even stiffer, then spend an exrta few bucks and get the 5/8ths plywood, which HD generally carries but not Lowes.
CDX is absolutely the worst plywood you can buy for construction, and has a C side up and a really terrible D side on the bottom full of holes where the knots have fallen out. It is only used by contractors who want to build roofs with the cheapest junk available that meets the minimum building code standards. Walk on the roof of a "modern" house build with a CDX roof (which sadly today is 95% of new houses.) It bouncec like a trampoline. It sags in the middle of the rafters and creates low "channels" or valleys between all of the rafters. Drive down the street of any modern subdivision after it is 5 years old, and you will actually see all of the vertical channels (they look like long gray shadows.) The older the houses get, the deeper the channels get.
I understand that people like birch plywood, without voids, but unless you are building cabinetry or just don't want to see the occasional gap in the side edges of the plywood where a small interior void is present, I'm afraid I don't see the point for a train table top. I am always looking to learn though, so if there are any substantial reasons why the birch would be better, I would like to hear about them.
If you paint the top and edges of the BC exterior plywood with a good grade primer before you glue and screw it down, and then go under the table and prime the areas between your joists, the BC plywood is extremely stable and any expansion or contraction will be almost imperceptible.
Hope this helps.
Mannyrock
P.S.- As for plywood "bowing".
The inside of Lowes and HD are extremely dry, and the stacks of plywood are extremely dry. Consequently, when you bring a sheet home a place it in any environment where the moisture is higher than the store, the wood will absorb it and the sheet will start to bow, almost overnight. After 3 or 4 days, forget it, it is ruined!
So, when you bring it home, take it to the driest room of your house, lay it flat with the good side down, and weigh the entire sheet down, particularly the middle and on the ends. I have several heavy tool boxes, so that is what I use.
The weight will minimize or prevent the sheet from bowing.
Cut and prime the plywood on the same day you bring it home, and glue and screw it down on the table by the end of the following day. If there is minor by this day, then weigh it down flat on the framework once you have the glue on the joists. After you glue and screw it, those bows will be gone forever. Prime the underside by the end of the second day.
Your table will not bow after that.
I am very lucky that I have an extremely dry basement, which I keep at around 35% humidity with my dehumidifier. But even at that, new plywood and timber will start to bow down there if I don't weigh it down immediately.
Plywood can be pretty unforgiving. I have learned the hard way that you can't cut it into strips and leave it for couple of days. It will bow in the extreme and you have to trash it.
Again, I hope this helps.
Mannyrock
@Mannyrock posted:I understand that people like birch plywood, without voids, but unless you are building cabinetry or just don't want to see the occasional gap in the side edges of the plywood where a small interior void is present, I'm afraid I don't see the point for a train table top. I am always looking to learn though, so if there are any substantial reasons why the birch would be better, I would like to hear about them.
Thanks for making my case for using the Baltic Birch. 
I had the wood in my basement simply laying flat on the floor for months before I started using it. Absolutely no bowing or other deformity was observed when building the layout, the birch sheets were as flat as the day they were manufactured.
If you're looking for my justification for using it, simply read your last couple of posts. I didn't have to deal with any of those issues, and the material is a pleasure to work with. Dimensionally, it's far more stable than regular pine plywood, and the difference in price between this and standard plywood for my 12 x 24 layout was less than $100.
Obviously, you can build a layout any number of ways, but I've worked with standard plywood a lot on a variety of projects, and when Baltic Birch was recommended, I decided to try it. If I were to build another layout, I'd be using it again.
@TomSuperO posted:(Am going to use 1/2". Not willing to ck off to 3/4 - using L girder and cookie cutter ) Am having no luck at finding 4x8 5 to 7 ply either birch or maple plywood in the Northern ATL area. All Lowes stores that say they have some in stock - don't. So question, did find at Lowes a 7ply 1/2" 4x8 blondewood - primed on one side. Does anyone have any experience with "blondewood". I looked it up, can contain various types of wood, typically foreign made, doesn't appear to have voids / hollow spots. Our joists r 12" to 14" apart so not spaning 24". Really want the 7ply birch; it ain't happening. Maple - nada. Frustrating. Did find 1/2" 4x8 homasote at Capitol Materials near Cumming, GA. $64 for a 4x8 sheet. Sheesh
Tom
How about particle board, very strong and is made of pieces of wood glued together under high pressure.
@ThatGuy posted:How about particle board, very strong and is made of pieces of wood glued together under high pressure.
IMO particle board is a terrible base! If you think plywood might warp, wait until you see what happens to particle board! A very long time ago(50+ years), I made some shelves using particle board. Even though they were supported quite well, the particle board bowed between the supports, and in addition after a few years it absorbed moisture and start flaking at the edges. Yes, they were painted with a couple of coats of paint, that didn't make any difference! IMO, that's likely the worst possible choice for a layout base!
Oh, and it's really not that strong, I can take an 8" wide piece of 1/2" particle board and break it by hand quite easily, try that with an 8" piece of plywood!
Thanks as always for your input John.
If somebody can't schedule things so that they cut and mount their table top in one or two days, or they are building ramp and grade sections, which take a lot of time, then Birch is definitely the way to go!
It makes zero sense for folks to plan on building a layout, and devoting several hundreds or thousands of dollars to it over several years, to try to "go cheap" and save $50 on the most important structural feature, being the table top. :-)
And, particle board is definitely not the way to go. If it ever gets wet, it likes to promptly blister and dissolve.
Mannyrock
@gunrunnerjohn posted:IMO particle board is a terrible base! If you think plywood might warp, wait until you see what happens to particle board! A very long time ago(50+ years), I made some shelves using particle board. Even though they were supported quite well, the particle board bowed between the supports, and in addition after a few years it absorbed moisture and start flaking at the edges. Yes, they were painted with a couple of coats of paint, that didn't make any difference! IMO, that's likely the worst possible choice for a layout base!
Oh, and it's really not that strong, I can take an 8" wide piece of 1/2" particle board and break it by hand quite easily, try that with an 8" piece of plywood!
Where do you get your information? Particle board is used in mission critical construction all the time. The boards are fine like anything if you use it wrong it will fail.
The greatest benefit of using particleboard is its greater dimensional stability. As a result, it won’t lose shape due to temperature fluctuations and other similar environmental changes. Besides, particle boards don’t have any natural defects. Therefore, they provide adequate thermal and sound resistance.
Affordability
Particleboard is considerably more affordable than both plywood and solid wood. When undertaking a project that requires hundreds of sheets, particle boards will save you a lot of money. You can save up to 12% of your budget when installing kitchen cabinets, for instance.
Lightweight
Although particle boards are dense, they are incredibly lightweight. This makes transportation and handling relatively easy. It’s common to come across people who consider density a key consideration when purchasing wood.
However, it’s best to keep in mind that the denser a carpentry material is, the harder it is to work with. The denser wood is certainly heavier and more difficult to work with. The particleboard is strong but incredibly lightweight, which means it’s easy to move it to and from and around the job site,
Easy to Hold Nails
Particleboard has a higher capacity to hold nails and screws compared to MDF and plywood. As a result, it won’t crack or break when you drive nails or screws into it. Besides, the nails and screws will stay in place without moving, thanks to the dense composition of the boards. Furthermore, cutting, drilling, milling, gluing, and painting particle boards is easy.
Eco-Friendliness
Particle board is typically made from wood scraps, shavings, bagasse, and sawdust, which are considered waste. Most manufacturers make particleboard from leftovers that would otherwise be an environmental hazard.
Therefore, there’s little waste when manufacturing particle boards. Besides, extra logging needs to be done to produce particle boards. Some manufacturers even produce particleboards without using formaldehyde, which minimizes their environmental impact all the more.
Ease of Lamination
Particle wood provides a flat and smooth surface to work with. It’s easier to stick wood veneer or decorative laminates on particle boards to add beauty and even more aesthetic value to your project.
Cons of Particle Board
The biggest drawback of particleboard is that, despite its considerable strength, it can’t support heavy loads. Therefore, it may not be suitable for use in places such as kitchen countertops. Furthermore, continuous exposure to moisture and humidity will cause the boards to warp.
When compared to fiberboard or even some types of plywood, particleboard is low in strength. This means it’s more susceptible to damage when handling. It also limits the application of particle boards to only specific projects.
so you can see properly supported with framing and it will be fine.
@ThatGuy posted:Where do you get your information? Particle board is used in mission critical construction all the time. The boards are fine like anything if you use it wrong it will fail.
The greatest benefit of using particleboard is its greater dimensional stability. As a result, it won’t lose shape due to temperature fluctuations and other similar environmental changes. Besides, particle boards don’t have any natural defects. Therefore, they provide adequate thermal and sound resistance.
Believe what you like. IMO, particle board is a lousy base for a layout, and I'll keep saying that until my dying breath! What "mission critical" applications are we talking about, the Space Shuttle?
- Particle board has low strength as compared to other fiberboards. It has low density so it can be easily damaged while transportation.
- In presence of moisture, particle board expands and warps. Also in extreme conditions discolouration can occur.
- As it has low strength and gets damaged in presence of moisture, particle boards have low durability and less life as compared to medium density fiberboard and plywood.
- It cannot support heavy loads as it is weak in strength.
- Particle boards can be toxic, as they are manufactured using urea formaldehyde resin which is the source of formaldehyde gas. Even after years of installation, the resin can break down and release formaldehyde gas, which carcinogenic for humans i.e. causing cancer.
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I don't even see particle board around anymore. I see MDF and I hear plenty of people mistakenly call MDF "particle board". MDF is pretty stable. Maybe the two are being conflated?
John
It's not fair to generalize something to death.
MDF and particle board are not the same. Not even close. Particle board got it's bad name starting 50 years ago for good reasons. GRJ has mentioned a few, including sagging and water sensitivity.
MDF's close cousin, MDO, or Medium Density Overlay, which has an MDF core and a tough paper overlay, is used extensively by state highway departments for road signs. It paints nicely and holds up very well under adverse weather conditions, so water isn't a problem.
MDF can sag over long distances, but nowhere near as much as particle board. With structure underneath on 16" centers it will be fine.
Neither particle board nor MDF are currently made with formaldehyde. It was phased out at least 10 years ago after it was discovered to be a problem in sprayed-in insulation.
Like the baltic birch MDF machines very nicely, with sharp edges, perfectly flat surfaces, and with one advantage over birch-- the ability to accept very small details, via router, carving tool, or small saw.
John, the bookshelf in your photo needs to be made out of MDF, and supported underneath it's front edge by an MDF stringer (1x2 dimensional, or 3/4" x 1-1/2" actual) with it's wider dimension oriented up and down. Do that and it won't sag.
I've used MDF extensively without any issues. You can have zero problems with it too, as long as you use a little common sense. (Contrast this with particle board, which nothing can save).
Mike
@Craftech posted:I don't even see particle board around anymore. I see MDF and I hear plenty of people mistakenly call MDF "particle board". MDF is pretty stable. Maybe the two are being conflated?
John
Still piles of it available at the big box home supply stores, it's around. I wasn't conflating anything, I do know the difference between MDF and particle board. 
@gunrunnerjohn posted:Still piles of it available at the big box home supply stores, it's around. I wasn't conflating anything, I do know the difference between MDF and particle board.
Didn't mean you were. I thought maybe ThatGuy might have been. And if he wasn't my apologies.
John
@Craftech posted:Didn't mean you were. I thought maybe ThatGuy might have been. And if he wasn't my apologies.
John
While MDF and particleboard are different the trade name when making a purchase is still particleboard. It is used extensively in construction especially new construction for flooring base roof underlayment and anywhere plywood has been used in the past. The largest manufacturer Weyerhaeuser, calls MDF particleboard you can order it either way it is cheaper and just as Durable as plywood as long as it is properly supported and we can make an assumption that your layout is not going to be out in the rain you could also get MDF/particleboard water resistant I believe the color is blue. Of course I am not an expert on everything like some people on this Forum, I have just built well over 200 homes as a major contractor and went back to school and received my PE in engineering.
No offense intended, but you are totally wrong. What you are thinking of is OSB - oriented strand board. Particle board is used for things like cabinets, certainly not roof or floor sheathing. Go back to school maybe. If you’ve been using particle board for roof sheathing I hope you have a good lawyer, cuz you’re going to have issues.
Just use anything, it’s a toy train layout for goodness sakes. By the time you are thru debating this you could have been working on scenery by now. The prices aren’t going down anytime soon, I get market reports twice a week on all the lumber products. So just buy whatever and build a layout already.
@William 1 posted:No offense intended, but you are totally wrong. What you are thinking of is OSB - oriented strand board. Particle board is used for things like cabinets, certainly not roof or floor sheathing. Go back to school maybe.
Just use anything, it’s a toy train layout for goodness sakes. By the time you are thru debating this you could have been working on scenery by then. The prices aren’t going down anytime soon, I get market reports twice a week on all the lumber products. So just buy whatever and build a layout.
I have never seen a place like this osb is perfected mdf is also used and is called PB. But who am I just a guy who built commercially and followed all the codes, this started with an expert telling him only use plywood, after he said he was having trouble getting it. This reminds me of another expert telling me PENN Central engines are black……..uhhhhhhhhhhhhh nope.
Never thought I'd see the day when a sheet of plywood, or particle board, or whatever, would have us arguing like it was politics or religion. I am thinking this forum would be a lot more fun if we went on to some other topic.
Thank you.
Papa Dave,
Don't bother. There will be arguments on that topic too, whatever it is.
Thanks for trying though ...
Mike
If the Original OP is still around... and, if you still can't find Homasote look for 'Sound Board' it has the exact same cellulose fiber construction as Homasote with a water resistant coating (it's black in color). I used it because it's readily available here in the south and it was 12.95 for a 4x8 sheet at Lowe's. It was in stock today.
Here is what it looks like...
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OSB can be very strong to be sure, but if it gets damp or wet, it will blister, disintegrate and fail very quickly
Just finished a lengthy repair on an OSB floor. The owner had a window with a very slight leak. The water come in, went down inside the studs to the bottom plate, and from there under his vinyl snap together floor on to the OSB subfloor.
Not only was his floor "soft" but the exterior stud wall, supported by on the OSB, started sinking/slanting/falling inward, about 1/2 inch, as the OSB failed.
When I opened it all up, the 3/4" OSB was black, and I could push my finger through it. Easy to pull up big chunks with my hands.
Bottom Line: OSB would probably be OK as a layout table top, as long as you don't let it get damp or suffer any water spill. (Basements are full of overhead pipes, and some folks have windows near their layouts.)
Clean both sides lightly with mineral spirits, and paint both sides with primer and it should be fine.
No, OSB is not as good as plywood. That's why it only costs about 30% as much as plywood.
Every floor I repair or rebuild, I use the 3/4 inch exterior grade plywood.
Mannyrock
@Mannyrock posted:Every floor I repair or rebuild, I use the 3/4 inch exterior grade plywood.
Ask any flooring contractor how much particle board they use for underlayment. Hint, unless they're a fly-by-night contractor, the answer should be zero.
@Papa Dave posted:Never thought I'd see the day when a sheet of plywood, or particle board, or whatever, would have us arguing like it was politics or religion. I am thinking this forum would be a lot more fun if we went on to some other topic.
Thank you.
@Mellow Hudson Mike posted:Papa Dave,
Don't bother. There will be arguments on that topic too, whatever it is.
Thanks for trying though ...
Mike
Red Green is on it... https://www.youtube.com/watch?v=fEnBYTI8TE8
FYI
Mianne Customizable Benchwork’s I-Beams are made of MDF boards with edge caps & end caps made of poplar wood. Mianne customers on this forum highly praise the stability & strength of the Mianne I-Beams.
I am building a layout with LCCA Lionel FasTrack module kits supported by Mianne poplar 48” legs and lower Mianne I-beams.
As recommended by LCCA, I am using 1/2 “ birch veneer plywood for the module tops.
To kitbash this system further, I have ordered Ross 29” straight, O-72, & O-84 track sections. Based on various threads on OGR Forum, Ross track & curve system is praised as one of the most reliable O-gauge track systems.
Well I've had a 12 foot section 30 inches wide of particleboard for over 20 years in a damp basement, solid and flat as the day it was brought home. Given the plywood issues it may be part of my expansion since it has worked quite well. We are building layout bases, not custom furniture for the rich and famous, function trumps esthetics.
@Mannyrock posted:P.S.- As for plywood "bowing".
The inside of Lowes and HD are extremely dry, and the stacks of plywood are extremely dry. Consequently, when you bring a sheet home a place it in any environment where the moisture is higher than the store, the wood will absorb it and the sheet will start to bow, almost overnight. After 3 or 4 days, forget it, it is ruined!
So, when you bring it home, take it to the driest room of your house, lay it flat with the good side down, and weigh the entire sheet down, particularly the middle and on the ends. I have several heavy tool boxes, so that is what I use.
The weight will minimize or prevent the sheet from bowing.
Cut and prime the plywood on the same day you bring it home, and glue and screw it down on the table by the end of the following day. If there is minor by this day, then weigh it down flat on the framework once you have the glue on the joists. After you glue and screw it, those bows will be gone forever. Prime the underside by the end of the second day.
Your table will not bow after that.
I am very lucky that I have an extremely dry basement, which I keep at around 35% humidity with my dehumidifier. But even at that, new plywood and timber will start to bow down there if I don't weigh it down immediately.
Plywood can be pretty unforgiving. I have learned the hard way that you can't cut it into strips and leave it for couple of days. It will bow in the extreme and you have to trash it.
Again, I hope this helps.
Mannyrock
This stuff bowed immediately after I cut it into strips. A C was the grade I bought from a lumber yard.
Apply 2 thin coats of primer paint to all sides of the particle board before using it for a model railroad project.
Then apply the cover coats.
Andrew
Gunrunnerjohn, what you call particle board has changed dramatically since the 50 years ago when you used it, yes it was crap back then. Now it is dimensionally stable and some brands are water proof, being able to be immersed and when dried out still have their integrity. Any board made into a shelf as you describe will sag and warp without proper supports for the material being used. I would not hesitate to use the new stuff, but I have used 3/8 plywood over 12 inch square open grid openings with the 1X4 stringer assembled in interlocking fashion for a table top forever, with no issues.
@CBQ_Bill posted:Mianne Customizable Benchwork’s I-Beams are made of MDF boards with edge caps & end caps made of poplar wood. Mianne customers on this forum highly praise the stability & strength of the Mianne I-Beams.
For your own personal amusement, ask Tim at Mianne if he would recommend particle board for finishing the Mianne benchwork. I can take a Mianne I-Beam and break it over my knee pretty easily, try that with a similar sized piece of 1/2" plywood! FWIW, I can also easily break a 1/2" particle board of that size over my knee as well.
FWIW, the Mianne I-Beam depends on the lateral strength of a piece of MTF, not it's resistance to sagging when laying flat. This is the same as any other composite engineered wood I-beam. It's the axis the force is applied that makes all the difference. Note that they use OSB in these as I suspect it has greater lateral strength.
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When I ran HO, I built 1x3 grid on 20” centers and put 1” Dow Foam as the base…my 12 year old son who forgot his key, had to crawl through the basement window and walk across 6’ to open the door-it held him.
Now that I run O, and it’s a shelf layout, I started with 1/2”, but ended up with 3/8”….the O-54 reverse loop has 1x3 grid on 20” centers, and I put all of my 265# on it to relocate a turnout.
I have areas where the weight of the Engine and the cars cause the plywood to flex…doesn’t bother me.
Adds realism.
And I see anything-wood, brackets, wire, screws, as money spent not on trains or track-and I minimize that expense all day long.
And if I’m so lucky as to add “scenery” to my road-it will be pictures and snow.
Because when I watch real trains, I don’t notice trees or track😁
But that’s the great thing about this hobby-nothing is truly wrong…as long as the trains are running and staying on the track, it’s all right😁
The MISC
The Manchester Intermodal Service Center
And I need to make a newer video😁
Well...you guys arguing over particle board/MDF/plywood...what you need is a common enemy to argue against...you know--something that all of you think is bad. Maybe I can supply the common enemy.
My 16x17 layout, up for about 2 years now is made of sandwiches of 2 inch foam and 1/8 inch plywood. In some places, I used 3/8 inch plywood if the sandwich got thick and seemed to need extra support.
All the foam/ply sandwiches are glued together using liquid nails or similar standard foam adhesive. Risers to lift track up for hills and such are made of 2 inch foam which is gorilla-glued to the sandwich. The layout only has 2 flat parts--the engine terminal and the yard. All the rest is hills and valleys and bridges and tunnels. So the track is almost always up on foam risers.
On top of the risers is a sandwich of 1 inch foam, 1/8 inch plywood and Midwest cork topped by Gargraves track. Sometimes clearances did not permit the 1 inch foam so in places the track sandwich is just the 1/8 inch plywood and the cork.
My basement is not wet--it is VERY wet. So far, I have had zero problems with warpage. I surveyed the net and it appears that testing had shown extruded polystyrene foams (XPS) to be resistant to humidity changes. Here's one: "Results indicate that humidity levels [do not] play a significant role in XPS performance." (from "Experimental study on the effects of humidity and temperature on aerogel composite and foam insulations" by Jedediah B. Alveya, Jignesh Patela and Larry .D. Stephenson)
Anyway, bottom line is that some kind of foam/luan/cork sandwich should be included in the argument. I'm no good with wood (some of you guys are woodwork artists and don't even know it!) which is why I went with foam. But in the end, it has had many advantages and no disadvantages for me. YMMV. Pix below.
BTW, when I started this, the foam was much cheaper than plywood. Last time I went back for more foam, foam prices had doubled! That's not inflation--that's robbery.
Don Merz
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Wow Feet, thanks for that information. I've never had strips of plywood bow immediately after buying it, but I can tell you what may have happened.
I should have mentioned in my prior posts, that I never buy the top sheet of plywood in a stack. I always buy the 3rd or 4th sheet down. This true even if I buy it at a lumberyard.
If that sheet of plywood was on the top of the stack in a lumberyard for a few days, then the top of the sheet itself dried much more than the bottom of the sheet. Consequently, the top of the sheet was trying to contract, while the bottom of the sheet was trying to expand. So, the sheet itself was under internal tension and wanted to snap and bow like a mousetrap, but the tension was not yet powerful enough to lift up the entire 50 pound weight of the sheet. (A few days later, it would have).
When you brought it home, and cut it into strips, especially if you cut them long-wise with the grain of the top, then they would immediately bow because the weight of the strips was much much less.
So, perhaps this is what happened in your case.
In line with this, I also should have mentioned earlier that you should never ever set a piece of plywood so that sun is shining on it, even if it is in the basement. The sun will dry out the top and the brand new sheet will bow up in a matter of hours!
Gunrunner: About 20 years ago, they started making 3/4 inch sheets of OSB subflooring, with tongue and groove sides, specifically for building house floors. It was a cheap substitute for the standard "Sturdi-Floor" 3/4 inch plywood that is tongue and groove, and yes, it costs only about 30% as much.
This cheap flooring has been used widely in new houses here in Virginia for 20 years, especially in really big expensive homes that will have lots and lots of flooring space, even in kitchens where water spills are fully expected. Again, contractors use the cheapest junk they can get by with. It is so bad now, that when you tell them you want the expensive stuff, they don't even know where to buy it! If I use a contractor or subcontractor for any work at my own house, I order all of the materials in advance and have it sitting there ready to go. I also immediately fire the person if I catch them taking any shortcuts or trying to cover something up.
Back to train tables: Plywood is great if you treat it like the clock is ticking and it will turn into a pumpkin at midnight!
Mannyrock
@third rail posted:Why do you want birch or maple plywood? Those are cabinet grade products. After you put down your track and scenery, you won't see any of it. If you want to save money go for some cheaper grades and use the higher quality stuff for the front aprons.
While I mostly agree, birch and maple are a little bit more moisture resistant, and less prone warping.
OK TomSuperO,
Having read all of the foregoing, you can either spend the next two to three weeks trying to find the superior sheets of Baltic Birch, or you can go to Lowes this morning, buy the plywood and adhesive I have recommended, plus Kilz II Primer, plus a box of 2.5 inch PowerPro #9 self driving screw, and be totally finished with installing your layout top by this evening. :-)
If you choose the second route, then be sure to have somewhat help you lift up the sheet and carefully and lightly set it down in place on the adhesive squirted joists, because the adhesive has almost instant grab, and in about 10 seconds, you will never be able to shift it. Make sure you have a heavy hammer at hand to quickly tap it for finally adjustments, and don't push down on the sheet until it is exactly in place. Have a clean rag, wet with Jasco's Mineral Spirits, standing by to quickly wipe off any excess adhesive on the sides. And for gosh sakes, make sure you have the basement door and windows open, because the adhesive and mineral spirits fumes are very strong. But, they will disappear in about an hour.
Mannyrock
