My last couple layouts used just 1/2" CDX plywood for sub roadbed. Gave up on Homasote years ago. I’m thinking about trying 1/2" MDF for my new layout. Has anybody used MDF? Thanks - Bill
MDF is just not stable enough IMO to use as subroadbed. You’d need very close supports to make it work, say 12" centers.
Look at any cheapo bookcase after a few years. Even if it’s not full of books, the shelves are sagging just from the weight of the material+ gravity.
Guess I had the misconception that MDF is actually more stable than plywood. Although I’ve never seen a bookshelf made from MDF. Only that cheap “pressboard” that does indeed warp from moisture effects. Thanks - Bill
I have MDF as a subroadbed. I wouldn’t do it again, I would try something else. I haven’t noticed a sagging problem, as you would with particleboard, but its main problem is that it is difficult to screw into.
It seems to be extremely hard and dense, and it must have some countersinking work done in order for wood screws to set flush. Overtighten the screws, and the MDF strips easily and the screw just spins.
I resorted to predrilling holes and used finishing nails and wood glue to hold the mdf table top. The stability and durability has been fine, mdf is just harder to work with than plywood, IMO.
There’s roadbed and sub-roadbed. MDF can be used on either one, but not without support. On edge, laminated about five or six deep as splines, it makes fantastic and stable sub-roadbed. It also makes great roadbed adheared to properly graded and smoothed sub-roadbed, but not if you are going to drive spikes and track nails into it…good luck with that enterprise. If you use a thin sheen of latex caulking to adhere your track elements to MDF, that’ll work just marvy. The strips of MDF on their side make very smooth roadbed…no prep necessary exept for setting it on a proper sub-roadbed that won’t make the MDF roadbed undulate or yaw.
-Crandell
There are multiple kinds of ‘particle board’ and there are multiple types of products that tend to be lumped together as “MDF” and they are not the same at all.
The most commonly seen ‘particle board’ is the kind with the giant flakes of wood - that stuff has absolutely no strength to rest unsupported over any reasonable distance and not sag. Also does not hold screws driven into the edges. Not suitable for railroad use except maybe to make angle gussets for the legs. There is another kind that is more or less sawdust in a binder. I used this on a little shelf layout, supported on those metal shelf brackets every 16". Above the layout I had another shelf of the same stuff which I filled with issues of MR and railroad books. No sag either on the layout shelf or the bookshelf. I screwed a little fascia to the front edge - no problem taking screws. I had the full sheet cut to size before I brought it home, cutting this would not be easy, and it was extremely heavy. But it did work without the dreaded sags.
Under the heading of “mdf” we have the thing, flexible stuff people use for fascias and backdrops. Too thin and flexible to use as a base surface, but cut into narrow strips and splined together it can make very good subroadbed. Then there’s this 2x4 sheet of stuff I have, it’s more like 3/4" thick, and very heavy - much heavier than the same size sheet of 3/4" plywood. It’s also very strong and dense - I can knock on it and you barely hear it. It’s been standing on edge for almost a year - the sort of thing you generally do not want to do with sheet goods, lest they take a bow. It’s still perfectly flat. I don;t think sagging would be an issue with this material. Cutting - probbaly would be difficult. It’s much like that high density partical board I used, though a bit lighter. I still have to get around to gluing on some WS roadbed, cork, and Homabed, and putting on pieces of track, to see how loud it
I was speaking generically of pressed fiber products. Yes, there are differences in quality and some of it is suitable – sorta – for subroadbed if one is careful. Thus my commentts about the need for support. The issue is once you get to the better grades, you’re spending as much or more than you would on suitable plywood – and needing to be considerably fussier about the kind of construction needed for subroadbed use.
I was careful to say that was my opinion about such use. On balance, you’re better off with plywood. in terms of the tradeoffs, again IMO. Nothing to prevent you from doing it, of course, just want to go in with your eyes open. There are plenty of horror stories of folks using various grades of this stuff for subroadbed. And a few reports of success for those smart enough to spec the right stuff and disciplined enough to use it within its limitations. For the average model railroader, plywood is far more forgiving and easier to get suitable results.
Thanks everybody for your replies. It looks like MDF might work but probably does not have any advantages over plywood except maybe for it’s smooth non-splintering surface. Modern MDF is indeed very stable and I use it often for jigs etc in the workshop, however I agree it does not hold nails and screws well. That’s an issue I hadn’t thought of. Also the extra weight and higher price make it less desirable for carrying home from the store. So I’ll stick with tried and true CDX plywood. - Bill
Gidday Bill, I was going to wax lyrical about the merits of dressed 4"x1" radiata pine framing and 9mm ( 0.36") MDF for subroad bed but find it interesting that ply is cheaper for you than MDF. Only packing case grade plywood is cheaper here, and I certainly would not recommend using that as thickness can vary. Besides sticking with what you are comfortable with is often the best.[:)]
Cheers, the Bear.
I used MDF on my last layout for the sub roadbed. I used 3/4" with supports between 14-16" and had no issues with sagging, twisting or warping. I drilled holes and used wood screws and sheetrock screws to attach it to the dimensional lumber and plywood supports. It’s creates a lot of dust when drilling or cutting it. I’m planning a new layout and will probably use it again as the plywood I’m seeing at the lumber yards and places like Home Depot & Loew’s is really crap.
My 2¢
Roger Huber
Like Roger I have used MDF in some areas and have had good results with it. My only complaint, in addition to the dust, is that it wears out saw blades a little too quickly.
Joe
Hi, Bill
Maybe you would want to look at A-C plywood rather than CDX. The A-C is a little better grade “plugged & sanded” that should have fewer defects and smaller knots. CDX is more of a sheathing grade and is (almost) at the bottom of the heap.
Some of the stuff rated as “sheathing” is actually cut smaller than 48 x 96 inches to allow for spacing in construction applications. Even the thickness is rated by the joist span, 16-32 for instance.
Anyway, for the cost difference you might have less hassles with the A-C grade rather than the CDX.
Ed
You might also look into 1/2" thick “hardwood plywood” as sold by Lowes and Home Depot. This stuff has seven plies instead of five, no voids in the inner layers and a very nice sanded finish on BOTH sides. Yes, it is more expensive than CDX or A-C plywood but the quality is worth the price.