1/2" MDF vs plywood for sub-roadbed

I went with 3/4" MDF on top of 1x4 benchwork with cross bracing at 16".

 

It is easy to cut although dusty.  Each piece has the exact same measurements.  It is perfectly flat - as in not warped or bowed. And it is acoustically dead so it shouldn't transmit as much track noise.

 

But you have to seal the MDF.  I did two coats of polyurethane on both sides and all edges.  That amounts to a lot of extra work.

 

4x8 3/4" MDF is @ 25.00.  Half the price of quality grade 3/4" plywood.

 

I'm happy with how the MDF turned out but for my next layout I'm going with 3/4" plywood.  The sealing is too much work.  And you can't bend MDF like you can plywood for grades.

 

George

I used 1/2" MDF for my previous layout. I had a water problem before I could properly seal some of it and it started warping on me. I have re-used most of it in my present layout, but have used 1/2" birch plywood for all new construction.

 

My framing was all 1 X 4's, 2" square legs, and on 24" centers. Plenty sturdy enough for me. 

 

MDF is heavier, has horrible sawdust, is prone to warping if not sealed, has no splitters, but is less expensive. After using both, I would use plywood.

 

Art

1/2" Fir Underlayment plywood

 

not cdx plywood-not southern yellow pine plywood-not osb-not mdf

 

that is my opinion

 

with 1/2" homasote on top-but you didn't mention that

use Fir Underlayment for plywood-you won't be sorry you did 

I was a big fan of MDF for all the reasons stated above. To me, it's harder to cut. For the layout we are building now, I am going back to plywood.

YIKES!And I was about to buy a 'biscuit cutter/joiner', which I'm told works well with MDF, but not with plywood.  You have made me reconsider the entire concept.  I had thought that it was BETTER than plywood re:  warping...not worse!

 

Also, I'd like to learn more about sealing it: Does it warp over time if untreated?  And what are the sealing options?  BOTH sides?

 

BTW, I DO plan to use homosote anf Homabed.

 

Also, part of my new layout will be flat & conducive to 4 x 8's; part will need the 'cookie-cutter' method for grades, and part will be 'around the room', requiring only 1 - 3' of 'shelf-like' sub roadbed.  Comments regarding the 2 materials for each of thes areas would also be appreciated.  I.e.; I'm wondering if some of each might be a good plan...

 

Thx for the input thus far.

Plywood.

I've tried biscuit joints on 1/2" plywood and 1/2" MDF, and I had excellent results with the plywood.  I'm building with plywood...

Don't be cheap on that is the basis for your layout......go plywood.

 

TEX

Steve

Thanks, fellas.  'Cheap' was not even an issue in my considerations, but it looks like I should stick with high-quality plywood.

The problem I've encountered with plywood is when a sheet gets warped before I can use it.  That situation creates huge problems getting to into place on girder bench-work.  Seems like plywood is getting cheaper in construction, even the A/C we're using, perhaps it's the glue.  Something is causing it to warp; didn't used to happen in the dry heated basement.

Kerrigan, I have always used "marine" grade plywood in all my past layout projects.  The plywood is stored by the vendor indoors and away from any moisture.  Marine grade plywood I have found to be the best plywood as far as glue quality and resistance to any warp problems.

 

TEX

Steve

I didn't have any trouble with the MDF once cut and down.... that layout was in for about 5 years..... some of it got painted on the top and some hadn't yet whenI pulled it down.... I like the straight and smooth.... I plan to use it for the base for the city sections but want to try plywood this time - 3/4" - for the subroadbed..... We are going by to buy our sheets today.....

Being a professional layout builder, I've used plywood, Homesote, Masonite and MDF and combinations of the four. MDF works best with biscuits and a biscuit cutter over the others.

Have NEVER heard of having to "seal" MDF. I have heard of sealing Homesote and priming plywood. In EVERY case where I used MDF, it has never warped or caused any of the problems mentioned above. Yes, I suppose if it gets wet it may warp, but so will the others. Yes it is dusty when cut, but that's a minor point when all the positives are weighed in. I've used the 1/8th inch for the curved fronts of layouts. Works well, takes paint well and looks good. Takes screws far better than Masonite.

I have had to seal Homesote but that still does not stop it from swelling and changing its shape over time, even in a very dry climate. Using Homesote over plywood is NOT a good idea. Over  time due to its qualities it will cause bumps and dips in the track work and be a high maintenance nuisance.

Of all products used MDF is the best for sub-roadbed in my opinion. If a customer wanted to use expensive high grade ply, I would certainly use it but that would jack up the cost of his layout about 30-50%.

MDF is used in high quality molding work, even expensive Crown Molding. My carpenter uses it almost exclusively and never "seals" it.

 

I will try to post photos tomorrow showing samples and technique of some of the products.

Phil,

 

Don't use MDF.  It's heavy, has very little structural strength, warps when wet, will crumble rather than cut neatly.

 

Go with a good grade of plywood, minimum 1/2" (but I would go with 3/4").  Trust me, I have learned the hardway about skimping on subroadbed.  I am still paying for that lesson.

 

George

I used 5/8" AC from indoor storage at a local lumber yard.  Usually it has been fine once cut and down.  Also use Homaboard 440 which is supposed to be resistant to moisture but I paint it with latex when it's down glued to the plywood.  So far, which is down (and some has been down for 7 years) hasn't warped or lifted the track.

It's recent plywood that has developed a warp while waiting in the heated garage to be used ...  also noticed the recent purchase was a slightly different thickness than previous sheets purchased at the same place.

 

I've used 1/4" MDF as the surface of all of my benchwork, and have found it to be very dimensionally stable. I've never suffered any warping, even on a couple of sheets that got soaked when my boiler exploded last year. They were fine after they dried out. It's easy to cut, and provides a good strong, smooth and stable surface provided it is supported properly. It does produce a lot of dust when cutting, but this is easily cleared up with a vacuum cleaner. I've also had no problems with curving it for inclines. I would suspect that those having problems are trying to use too thick a board. I build the strength into my framework, and use the MDF as a surface skin, not as a major structural member. A well designed space-frame can use much lighter elements, which is important to me, as I have to carry everything that I build.

So you don't seal the MDF.  What happens when you get it wet?  When you glue ballast in place for instance (assuming you watered down the glue)?

 

With a couple of coats of polyurethane the water will bead up and sit there until you wipe it away or it evaporates.  Not so with an unsealed piece.  It does a good impression of a puffer fish.  Especially if you get some water near the edges.

 

And then there is the outgassing issue...

 

George

3/4" birch with 1/2" homosote

MDF has it's place in layout construction. I use UL ( ultra lightweight) MDF because of it's structural properties and it's weight. I use 3/4" mdf ul instead of plywood for large flat areas. It is flat,easily glued and screwed, providing a sound substrate for our trains.  Some if not much of the plywood you see at the "box stores" is asian and not very stable.  They just don't dry their substrates in China as carefully as we do.  This tends to produce inferior, warp and bow phoned plywood, but it is cheap.  Most MDF is domestically produced or South American produced and of very high quality. I think all the MDF UL is from South America. The thing to keep in mind when building with MDF is that it is not as strong as plywood, but in the O gauge world we are talking about it is often more than adequate. Regular MDF you find at the box stores weighs about 90# a 4x8 piece,  for all us old guys building layouts that is very heavy.  MDF UL is about half the weight but works just as well.  See your lumber yard and have them get this for you, you will like it. Fred

My layout is 3/4" plywood on 2"x 4" centers. Built like a tank but I am on top of it often. Paid more for materials but as a previous member already mentioned, we pay $1000s for our trains, we shouldn't go cheap on layout construction.

IMO, Homosote/plywood.

 

But that is only a portion of the story.

 

Specs and technique contain the rest of the story.

 

Using marginal product reduces or eliminates redundancy.

 

Redundancy keeps Murphy out of the train room.

 

Don't go cheap unless it is a 4 week exercise in December for holding a Christmas tree. tt

 

www.curvedbenchwork.net

MDF does not crumble.  At least not good MDF.  I prefer good birch plywood over MDF for roadbed, but I ribbon cut, so I don't buy very many sheets of whatever I use.  But, I have built carefully designed shelves with MDF and a number of other things.  Crumble it does not.

 

Note: MDF is not "particle board", which does crumble.  The stuff that cheap stereo cabinents and the like use is not MDF.

 

Mike

I think you hit the nail on the head. MDF is very smooth, dense, strong, and about the same weight as plywood, maybe just a tad heavier. Takes all kind of glue very well including crazy glue, the thick kind.

Does NOT act strange or puff up when water hits it as described in some of these posts.

Check out Wikipedia:  http://en.wikipedia.org/wiki/M...m-density_fibreboard

GOLLY WHIZ!!  This thread now reminds me of politics, or religion:  How can seemingly intelligent/knowledgeable people have such opposite views on a given subject?

 

 My mind is swirling!!  I sure didn't expect such a widely-varying bunch of opinions....

Because successful benchwork can be built using a variety of different techniques and materials. After building a few successful layouts, most of us tend to stick with certain combinations of materials with which we have become familiar and which are readily available in our geographic area.

 

The important thing is that the subroadbed be well-supported with sufficient bracing.

 

Also, we all have different budgets which influence our choices. For example, top-of-the-line plywood is nice if you can afford it, but good construction techniques can produce sound benchwork with much more economical products.

 

For example, all my layouts have been built with that much-maligned, but very economical 1/2" CDX plywood mentioned above. Most of those layouts have lasted 20 years or more with no problems.

 

Jim

I've got a table-top layout that over the years has grown from 9'x9' to 10'x17'.  I've used 1/2" plywood over a 1"x3" frame with 16" intervals, with 2"x2" uprights.  This foundation has been plenty strong to support my (slowly growing  ) 190 lb. body, and I will confess, I spend a lot of time on top of the layout!

 

My only advice with using plywood would be that make sure that all you use is the same thickness.  There are slight variations in the thickness of plywood and it is easy, on different trips to the store, to buy plywood that is slightly different thickness.

 

I guess I don't really understand why folks have problems with warpage?  I guess it might depend on the method of construction?  Many layouts are constructed with the wood based secured to a framed so if the wood starts out reasonable flat and is screwed down, there should be no warpage.  Msybe if one uses a cookie cutter approach to the layout, a thicker, higher grade wood would be of value.

 

I also don't understand the comments that MDF is not structurally strong?  Look at any new house that has been built within the last twenty years.  You will find a lot more MDF used to built the house than plywood. 

 

Jim

 

 

It isn't MDF that is used extensively in home construction.  It is OSB

MDF = medium density fiberboard.  It is used in finish applications where a super smooth surface is desired.  It is basically sawdust and glue.

OSB = oriented strand board.  Itis chips of wood and glue.  7/16" OSB is structural as a shear panel on wood frme walls.  Not when laid flat.

 

Both are harder to work with than plywood in layout construction.  MDF is super dense and heavy.  OSB is garbage for anything else except what it was made for.  Wall sheathing.  That's why I use 1/2" FIR Underlayment grade plywood.  You won't be sorry when you have to cut a 30" turntable round hole with a jigsaw, for example.

seemingly

Time to unsubscribe from this one, I though I could argue a point!  I'm a piker I can see.

Plywood!

I used OSB on my modular layout. Great so far.

Rob

I used 1/2" Medium Density Overlay (MDO).  Designed for exterior sign use one side or both are easily paintable with no prep.  Framing is 2"X4", 16" OC.  A 1/2" AC plywood would also work well.  A grade on one side, C grade on the other.

 

 

 

A/C plywood.

i used 7/16" osb and covered it with 1/4" cork then green felt. strong, flat and quiet.

It's just different results using different material, Phil.  You've seen ours with the girder structure, 5/8" ply with 1/2" Homoboard 440 glued on it, painted with latex.

It works and doesn't warp, but I'm sure others have had a different experience.

The warping problem we've had is with some "raw stock" plywood before it's put down.  Once down and secured it stays in place.

Fairly quiet, easy to screw track onto, and hopefully resistant to swelling when we ballast due to the latex coat.

The homoboard is very dusty to cut I'll give you that.  That's why we do the cutting in the garage rather than the layout room.

 

William,

 

You are absolutely correct.  Not enough caffeine this morning to remember the difference between MDF and OSB.  I shouldn't post until I drink that second cup of coffee is the morning!

 

Jim

p.s. I would also add that you can get a nice cut with 1/2" birch as well, as I used this for the construction of my turntable.

OK, folks....I guess we've all had just about enough.  I shall re-read all contributions, AND if I feel then as I do now, I will TRY BOTH!  After sufficient personal experience, I should be able to decide which way 'works best for me'.

 

  I shall even pour some H2O on a test piece of MDF.  I MAY even buy a biscuit-cutter/joiner, and try it with both material, altho' I believe using some thin steel straps from SIMPSON STRONG-TIES may be the way to join sections together....

 

BTW, I DO plan to use Homosote on top of my sub-roadbed.  Also, some of my layout will use 4 x 8's, some using the L-girder method, and even some via the 'cookie-cutter' technique.

 

Lots of excitement ahead!

These type of threads are good.  They spread out the various ways we all build.  No real one right way.   No matter what you use for material it is in the execution of the job that determines the quality of the finished product.

 

I have used 5.5mm, 6mm, 1/4", 3/8" 1/2" 3/4" & 1" A/C, A/B, A/A, Birch & Fir plywood, 3/8", 1/2" & 3/4" MDO(G1,G2). 1/2" & 3/4" OSB and 3/4" Sturdifloor for decking and/or subroadbed.  Granted, vastly different prep on some of these jobs, but no failures over the years. 

 

Budget, client supplied material, portability, etc pushed the different materials.   I used MDF twice.  Never again.  Problems above.  Plus the friable dust is a mess.

 

I have seen a lot of benchwork jobs, both professional and D.I.Y., IMO, if you want to see what I consider to be the very best workmanship and material selection in benchwork ya' juss gotts ta wrangle a visit to greg410's RR.  No one else including myself comes close.  Just flat out exquisite. tt

Just got back from a trip and saw this thread. I agree that some contributors must have confused MDF with particle board. MDF is very heavy and dense and it cuts well. Leaves a clean cut, but you do have to dress up the fuzz on the edges. I work with it quite a bit but I am using plywood for my layout, due mainly to weight. Moisture isn't a big issue here in southern Arizona. One thing about MDF as opposed to plywood, it loses strength if it is sliced thin, as in a lock miter or rabbet joint. I built a piece of furniture out of MDF and tried to do a lock miter, but the interlocking rails were too thin and it tended to break. I can do the exact same lock miter with the same thickness plywood and it holds fine. 

 

Personally, I like MDF for making shop jigs and plain, utilitarian items of furniture. It's great when you need stability - the "Wood Works" TV show once did an episode on building a dead-flat assembly table out of MDF. I'm going to build that one of these days. For train layouts I prefer plywood.