I went to Home Depot to find some 1/2" plywood to use for a sub roadbed. I looked mostly at 2’x4’ sheets as opposed to 4’x8’. Unfortunately most of the sheets I came across were not flat, i.e. quite warped. I ended up getting a 2’x4’ birch plywood sheet which seems much more solid than others and much flatter.
Question: Is there a “type” or “grade” of 1/2" plywood to use to make sure you have a good FLAT sheet? Or is this the nature of the beast? How do you ensure a good flat surface for laying down the cork roadbed and track?
Most ‘grade’ designations, particularly at the big box stores, are only concerned with appearance. Fewer knots, cracks, footballs, etc.
Plywood warps, that’s the nature of the beast. Getting a higher number-of-ply plywood helps (more plies to stress against each other and cancel out the differences), but lateral reinforcing and cross bracing is the only reliable way to control warpage.
Plus, lower ‘grade’ plywood is more likely to have deadly splinters. Ouch!!
Birch plywood is nice stuff and if that is what it takes to get flat plywood, spend the money. I myself bought 2x4’ “handi-panels” from big box stores, all of which were stored and sold flat and on the floor, and had no warp. When I needed a few more and the store was sold out, I bought a 4x8’ sheet of normal grade plywood and had it ripped into four 2x4’ panels (my car can’t handle a 4x8) thinking it would be ok but that 4x8 sheet was stored and sold suspended by two supports at the far ends, and had a built in warp both lengthwise and widthwise. And while both sides of the handi-panel were smooth and usable, one side of the full 4x8 was obviously rougher in texture with lots of “football” shaped plugs. I used what I bought but there clearly was a big difference, and the warped plywood had to be bulled into submission and used lots more screws.
Similarly a big box store had slightly damaged handi panels that they stored and sold on edge in a bargain area away from the main display (in a roofed but outdoor unheated part of the store) and by storing on edge those too gained a permanent warp. So it isn’t just the quality of the plywood per se, but also how the store elects to display and sell them: flat on the floor is best (and in the heated part of the store).
Once you added in the slight charge for ripping the 4x8 at the store, the cost advantage to the “cheaper” plywood disappeared.
When I built my helix (32” R) I needed thin plywood and ran in to the warping problem also. That was back in the late 80s and even though everyone’s advice was not to use OSB that was the only ¼” thick I could find that wasn’t warped. Well 30 years later it is as good as new, I had to drill holes for everything because of the hardness but it really came out perfect.
I glued Midwest cork to the ¼” OSB making the total thickness of the helix ½” + code 100 flex track.
Welcome to my world! I live in northern Virginia and have looked at plywood at Home Depot and Lowes with dismay. Most of what I’ve seen was very bowed or warped too. And since the pandemic, the prices have risen dramatically to add insult to injury.
I don’t use plywood at all, but instead use OSB. I’ve been using 19/32 thickness OSB for my sub road bed and 13/32 (7/16?) for sheet areas where I’ve mounted Homasote on the open grid benchwork.
The OSB I’ve been using seems to be pretty flat and work well for my benchwork.
My wife and I bought some birch for our bathroom tub frame. If what you got is like that, it’s way too nice for benchwork, and probably quite expensive.
Here are some photo’s of my OSB benchwork. Before the pandemic the 7/16 OSB was about $9 at Lowes - cheap and cheerful. I see the 19/32" OSB is $36 presently! Dang! Fortunately I’ve gotten 95% of the wood I need for my layout before the prices shot up. Pandemic evidently to blame for lumber price hikes.
This is a sandwich of OSB and Homasote for the staging yard:
Here is 19/32 thickness OSB I’m using for subroadbed. It’s a bit thicker than half-i
The 3/4 ply I got from Lowes isn;t warped, at least not in any way that won;t be flat if attached to a flat support structure. So there’s a bow across the sheet - you aren’t going to just ley it on the frame and hold by its own weight, are you? Any slight hump is going to be pulled out as soon as you screw it down.
Using it for the side panels of a cabinet or something - that’s a different story.
I’m uncertain as to the need of a flat sheet: if you’re using it in sheet-form, the usual practice is to secure it to a framework of some sort, using nails, screws, or construction adhesive.
The majority of my original layout used 3/4" firply, good-one-side, but all of it was used mostly as cut-out curves, supported on risers above the open grid framework (select pine 1"x4") which provided the base. In some areas, I used remnants of plywood (mostly 3/4" or 1/2" leftover from building my house) to support structures, and most of that was on risers, too. Areas where straight-ish track was needed was mostly atop either strips cut from the 3/4" sheets or 1"x4" boards, also on risers.
When I added a partial second level to the layout, I used 11/16" T&G sheathing plywood, also good-one-side, but it was attached to the open grid framework (1"x2" and 1"x4" select pine) as sheets, using screws. The T&G allowed me to use leftover parts of the cut-up sheets, whereas, without that feature, I would have needed a couple more sheets.
The original portion of the layout (still not “finished”) has been in place for over 30 years, with no sagging, warpage or any other anomalies, and the partial upper level for 5 or 6 years (I think), also with no issues with warping - it’s screwed to the wall studs, and supported by custom-welded brackets which are lag-bolted to the studs. I have, at least once, lain atop the upper level in order to paint rails which were otherwise out-of-reach… no sagging, no warping, no problems.
Here’s a portion of the original construction (it forms the grade to the partial upper level) showing some of both the open-grid framework and the risers used to support th
When I started my layout about 12 years ago, both Home Depot and Lowe’s carried a grade of 1/2" plywood they called “Hardwood Plywood.” This was really nice 7-ply plywood, finished both sides, no voids in the inner layers, and significantly cheaper (around $26 per sheet) than high grade birch plywood. I used this Hardwood Plywood to build all of my open grid benchwork and it hasn’t warped even a fraction of an inch since. When I added a new yard to one end of my layout a few years ago, I found that the Hardwood Plywood product was long gone. The plywood available at big box stores today is abysmal, sometimes not even having the same number of plys at both ends! As I wanted the same benchwork quality as the rest of my layout, I was forced to go to a real lumber yard and buy a sheet of 1/2" birch plywood for $60!!!
Another option might be “cabinet grade” plywood as it is meant to be dimensionally stable, clean and smooth, but not visible without crawling into a cabinet. This stuff should be high quality and possibly cheaper than true birch plywood.
1/2" MDF would be suitable. I hate the fine powdery sawdust it makes when cut but apart from that it is a good product for this use.
OSB (Aspenite was one of the first) is way overkill for this purpose and really hard to drive fasteners into. It’s designed for exterior use and power drivers for fasteners. It’s very strong, for the purpose it’s intended it’s far stronger than plywood.
OSB is basically horrible stuff to use. Indoors it should be subfloor not exposed inside the home. The resins used are not really intended for interior use.
MDF is commonly used indoors in furniture frames and for cabinetry as well as for wall mouldings. It replaced most particle board applications.
The disadvantages to MDF are that it is HEAVY, difficult to drive fasteners into without first drilling pilot holes, fasteners often tear out over time, and while it doesn’t warp, it will sag significantly if not well supported (more MDF and more weight).
OSB is used here in Southern California as shear panel (earthquake resistance) and is NEVER meant to be seen.
I would never buy plywood at Home Depot for my layout surface. I always buy from our local lumber yard. On my new layout, I bought 1/2" cabinet quality grade plywood, B-2 grade, with absolutely smooth surfaces on both sides, no warping whatsoever. My cost per sheet for a 4’ x 8’ sheet was $45.
5 years ago when I started my new layout I decided on using 1/2-in x 4-ft x 8-ft Douglas Fir Mdo Plywood from Lowes. Only problem with this material is the price.
I went to a lumber yard and bought 1/2" AC plywood when I started to build my layout. The big boxes don’t sell that grade of plywood, and it did cost more. I went for the quality. Since I was not using a cookie cutter design, I did the following:
I had the lumber yard cat my sheets to the lengths and widths I needed. Next, I let the wood acclimate in the train room for about a week. Then I painted the underside with a ceiling white paint and the top and side with a gray color paint since I couldn’t find a good ‘earth’ color to use.
The plywood did not warp and since I have built my cross supports on 12" centers, I’ve basically eliminated any type of warping. The most important things I learned was to let the wood acclimate and then seal it before putting down any type of cork or ground cover…
There has been some good suggestions so far. All I can find down here in 1/2" or 15/32" plywood is cheap garbage.
I do have a marine lumberyard nearby. They have 3/4" plywood that is perfectly smooth on both sides, and has seven plies. This is very strong, and all sheets I have bought have been perfectly flat.
It also has very tight grain and does not splinter as it is cut, routered, or sanded. I do not know what it is exactly called.
Sorry I cannot help with the 1/2" specifications.
This riverbed shows the kind of 1/2" stuff I can get from a big box store down here.
Clarifying assumption: I will be screwing down the plywood to the underlying benchwork. I was concerned that that may not “be enough” to “fix” the bowing of the wood that I saw. I am hoping that would help straighten and flatten the sheet where it was bowed, but don’t know if that will remedy things?
If your benchwork is strong enough to support the plywood then screwing down 1/2" plywood will flatten out any bowing. Twisted panels on the other hand will cause problems. Plywood, or any sheet wood product, is far heavier and stronger than is needed for model railroad benchwork. We used some 1/4" birch ply, even poor quality, and it’s plenty strong enough.
MDF and OSB are both heavier than plywood. OSB suffers from warping. MDF cannot warp. I’m not sure why a traditional benchwork aficionado would worry about the trivial weight difference. Use foam sheet for less weight, a lot less weight. It’s the benchwork framing that is the supporting structure. The table top, or trackbed if you use the cookie cutter style, needs very little structural strength of its own.
The idea that MDF is not water resistant is frankly absurd. It’s not particle board which does not recover from water exposure. MDF is certainly water resistant enough for our purposes. I wouldn’t drape it directly with plaster cloth but then why would you?
Menards has shelves that are 2’ wide and range from 4’ long up to I think 10’. I usually use the white ones, they have ones with the natural wood grain but I figure no one’s going to see it under the layout scenery. They’re very strong and so far have all been very flat.
