How about MDF under Homasote instead of 3/4 CDX Ply?

[Anonymous]

I've had trouble with plywood buckling over time in a number of applications, and find 3/4 MDF to be very dimensionally stable. Anybody built a layout substituting MDF for plywood in L-Girder/cookie-cutter-type benchwork?
How long ago? What environmental conditions (humidity/temperature fluctuations)? What results?
Thanks,
Ken

[nfmisso]

Ken;

MDF is more brittle, and not as strong as plywood. It is a paper product. MDF is more rigid - thus will not bend as well for grades, it will tend to break rather than bend.

Being a paper product, it will change with changing humidity, like any wood base product, it should be sealed.

I would not use CDX plywood nor MDF. I would suggest 3/4" AC grade. See:
http://www.tdhmanufacturing.com/html/common_plywood_grades.html

[IRONROOSTER]

Properly supported plywood works fine. My layout uses 3/8" AC supported every 12". In over five years I have had no problem with the plywood.
Enjoy
Paul

[cacole]

By MDF, don't you mean Medium Density Foam? If so, you still need a solid base under it, such as a 1/2" sheet of plywood because foam won't take weight or pressure without sagging.

I built the Cochise & Western Model Railroad Club's 20 x 40 foot HO-scale layout on hollow core doors. If you have a large building supply store such as Home Depot or Lowe's nearby, you can sometimes pick up damaged doors for $5 or less. Hollow core doors are a very good base for a layout because they are usually treated material that will not suffer from expansion or contraction with changes in the weather, and they are strong enough to get up onto if necessary. I topped the doors with two layers of Upson board, also known as sound board, to eliminate the drum effect, and also used cork roadbed. Overall, this turned out to be more cost effective than plywood, foam, and/or homosote, and is more durable.

[nfmisso]

QUOTE: Originally posted by cacole

By MDF, don't you mean Medium Density Foam? If so, you still need a solid base under it, such as a 1/2" sheet of plywood because foam won't take weight or pressure without sagging.

MDF = medium density fiberboard.

"MDF belongs to the hardboard family of products which are made from wood fibers glued under heat and pressure. Medium Density Fiberboard typically has densities between 33 and 50 pounds per cubic feet while High Density Fiberboard (HDF) ranges between 50 and 80 pounds per cubic feet. Hardboard was first produced in 1924 by W. H. Mason, founder of Masonite Corp. The term Masonite is therefore often used to denote hardboard products, especially HDF.

Physical and dimensional tolerances for MDF are specified in ANSI A208.2-198"


http://www.lungster.com/l/speakers/mdffaq/mdf.html

[ndbprr]

Those that don't use it have negative things to say about for the most part but they have generaly never tried it. Advantages - Uniform surface (paper), Flat (very), Can handle longer unsupported distances ( but don't push it). Disadvantage - very heavy. most people who have been around equate MDF with the old particle board which was an entirely different animal and useless for model railroads. It doesn't hurt to try a sheet and see if you like it.

[Anonymous]

MDF is not a paper product. It is medium density fibreboard and is manufactured by combining glue with sawdust and heating and pressing the mix. It is dimensionally stable for a period of time, but long-term exposure to high humidity will cause it to swell and deform badly. If you want to use it, simply seal it completely with 10 or so heavy coats of varethane or spar varnish. I do not and will not use it on my layout. Oh yes, you will find MDF is tough to nail or screw. You will find yourself drilling lots of holes to accomodate fasteners.

You say you are having trouble with plywood buckling. If you use 1/2" or thicker five ply material manufactured with exterior glue that shows A-C on the grading mark, you will not have any buckeling problems. Problems with plywood arise because , in our effort to be economical, we opt for the cheapest stuff. The three ply stuff, with C-D grade markings, glue type not specified will be cheap enough but will give you headaches in the long haul. With wood products, you really do get what you pay for (most of the time). I have used OBS, also known as flake board (looks like wood shavings pressed into a sheet which is exactly what it is) because it was cheap. With enough support, it works very well. The problem is that the price for a sheet of OBS has gone from under $6 a sheet to over $18 a sheet in the past year. Someone else with ties to the bank can use that stuff.

Sorry for the sermon, but after a lifetime in the building trades and related fields I have learned a little about wood products.

Tom

[CP5415]

I'm using 1/2" & 3/4" plywood that I haven't sealed yet, it's up in the attic where I have no control over the climate as I don't have a heat/ac vent up there yet.
I have yet to need to replace any of it yet.
The only reason for the 3/4" was it was free.
No warpage or any other defects that has caused any problems with my track.
Even with the occassional spill of a drink, I've haven't had a problem with the wood expanding.
MDF will absorb moisture as others have stated & will expand especially when you go to do your scenery.
Do not use it unless you have no alternative.

Just my 2 cents

Gordon

[ndbprr]

Have you used it to know that for a fact or are you taking the word of others as fact? I know several layouts built in the Chicago area of MDF that are not sealed and have no problems. All the builders comment about the smoothness of the paper surface and cost as a reason for usage. A lot of what we accept as fact turns out to be otherwise I am afraid.

[nfmisso]

I have used MDF for other projects, including furniture and speakers.

I would not use it for a cookie cutter model railroad layout. It needs pilot holes for all screws. It does not take to bending well, which is a requirement of cookie cutter construction mentioned in the original post.

I would use it for a table top layout with foam above, specifically 1/4" MDF with 2" or more of extruded polystyrene laminated above the MDF. This is a very stable, solid and quiet table top.

For cookie cutter, 3/4" AC plywood is hard to beat. A big part of the reason is the verticle curves comeout just right with it. With 1/2", you have to excercise care because you can easily get too sharp a transistion.

I believe that Tom is referring to what is called OSB (Oriented Strand Board) around MN and OK. In OK, OSB was by far the cheaped 4x8 sheets that Home Depot and Lowes had.

Splines of 1/4" MDF would work well (1/4" thick MDF ripped 3/4" to 1" wide, on edge) - Masonite®, Homasote®, pine, etc also work well for splines.

[CP5415]

As Nigel said, a cookie cutter style layout is not suitable for MDF.
I used a sheet for shelving a pantry I built in my kitchen last year, I would not want to use it in my model railroad application.
This was the only time I used MDF & would probably won't use it again as plywood is lighter in the applications I would need.
Plywood was easier to use for me in my benchwork as it's flexible.
The 1" MDF I used never flinched when I had to move it.

As I said in my previous post, my attic gets really hot & humid in the summer & rather cool in the winter. The plywood I'm using hasn't warped as I make sure it's securely fastened to the 1X4 risers using screws.
In my construction, my risers are no more than 6" apart on curves using the 1/2" plywood & no more than 1' apart in any other section.
This may seem like overkill, but my dad taught me to make things to last.
I made a TV stand for my tv out of 3/4" plywood 3 years ago.
There's a 3' span in-between the side supports & 115lbs of tv on top. This has sat in the basement since I got the tv & it hasn't sagged yet.
The only way plywood will sag is if it's not supported properly.

Gordon

[CBQ_Guy]

For the record, it is also very heavy and is rough on saw blades. I also believe it needs extensive support to prevent sagging, but can't recall now for sure. Information is knowledge, and all that.

[tutaenui]

I have used 12mm thick MDF road bed on my 14YO layout. I have found it exellent with no sag with supports approx 300mm spacing. One downside is the dust from sawing is very fine, gets everywhere and can be irritating. The other thing I have found is that unsealed MDF tends to get a very light coating of mould in the damp garage my layout is located in, but this is cosmetic effect only and does not appear to effect the strength of the MDF. On the plus side MDF is dimensionally stable, very flat and smooth and considerably cheaper than quality ply.

[Anonymous]

Be careful when using MDF, the glue used in making it contains stuff that can give you cancer (a study about it was just made public this week here in Montreal), so when sawing it, use a mask in order not to inhale too much of the dust, especially if you work a lot with it (more dust inhaled). I guess that model railroading is a hazardeous hobby, we have to check out for pointy objects, dangerous fumes from paint, foam (when using hot wire cutters) and now even some type of "wood".

[Anonymous]

MDF is what is typically used by furniture builders as it is very stable. It has no grain but as has been stated it is very heavy. It is an excellent product but it has limitations. It, being very hard is tough to cut and is tough on saw blades and drill bits due to the predominance of glue in the mix and is not at all flexible. It is thus not very sound deadening as well. It is very heavy (makes furniture seem very expensive) and tends to not absorb moisture as much as other wood products. Essentially, you pays your money and you takes your pick. I think that 2" rigid foam over a grid benchwork is a lot simpler to work and and work with, even for elevation changes. Just don't go kneeling on it. Bob T

[Jetrock]

I use MDF for my layout and kind of like it. There are caveats, though: My layout is totally flat (as is my prototype city) and I wouldn't try to cookie-cutter it. I drill pilot holes for every screw, but I do that anyhow because I hate splitting wood. The MDF is supported by a framework of 1x2 and 2x2 lumber, with supports every 18 inches. I also have a small layout, which means that even though MDF is heavy it doesn't weigh that much because the sections are small. And I wear eye protection and a filter mask when I cut it.

Other things about it: I don't use subroadbed--I put track nails directly into the MDF and they hold very solidly, even when removed and repositioned. I get no sounding-board effect due to the MDF's stiff, dense qualities. I also live in a very dry climate so I don't have to worry about swelling--it does warp slightly, but the framework holds it in place. I also use it for shelves, but an L-bracket of 1x2's screwed in place (with pilot holes!) makes for a very sturdy shelf (and the L-bracket provides me a place to hang a lighting valence!)

So while it's fine for my style of model railroading (a relatively small, flat-terrain shelf layout), it might not be the ideal material for large scenic vistas.

[Anonymous]

Have used 12mm MDF on my new layout with absolutely no bad results. I regard it as a perfect medium, this after being a dedicated ply user! Of course you keep excess moisture away, but that rule applies to all forms of roadbeds, flat or cookie-cutter.

[nslakediv]

Has anyone other than me heard of a 3/4" thick 7 ply and a 1/2" thick 5 ply plywood called Aruco. Good stuff, no predrilling, no voids, soft outerskin veener(good for driving track nails) and very smooth. In N.W. Ohio its running about $32.00 a sheet. I use it for table top and also rip it to 3" for framing, very cost effective.