Layout top - 1/2 Sanded plywood or 1/2 MDF?

You can stretch your $$ further by only using the plywood and homasote under where the tracks will be installed. Makes landscaping easier for hills and valleys.  If you need some flat areas lets say for a small city, install just the plywood in that area only.

Plywood shapes can be cut with a jigsaw and the homasote can be cut with a knife. If dust is not a problem, cut the homasote with the jigsaw.  Bill

If dust is a problem, cut the homasote with the jigsaw anyway.  Use a knife-edge blade and you'll see a big reduction.

These work wonders for me:

  BOSCH T313AW3 3-Piece 6 In. Knife Edge Special for Soft Materials T-Shank Jig Saw Blades

Check out the wavy edge.

Mike

My layout was done using the L-girder design 12" on center frame. Covered that with 1/2" OSB and 1/2" homasote. I tried the blades for my jig saw with kinda/sorta ok results. I ended up using a utility knife. Trick was changing the blades often.

Here's a nice comparison...

...which tends to confirm my own experience...

...for which my knee-jerk response to your OP for application on the layout: Plywood.

FWIW, of course...and just one man's opinion.

KD

Happy w/ OSB- the guy who did my tables convinced me it was more "stable"- less likely to warp- than plywood.  Used 5/8" I think.

I used 1/2 inch plywood sanded one side, with pink board of various thicknesses glued to top. While plywood is more prone to warping,  if have that much moisture I’ll have bigger problems than board warping. The reason for my using plywood is I don’t like to cut OSB due to formaldehyde used in its manufacture.

IMHO FWIW

I have used both Mdf and plywood. Mdf weighs a ton and is not as stable (or lays as flat) as we are led to believe. My vote is plywood with as many layers as you can afford. More layers equals more stable. I also covered the plywood with homasote.

Speaking of afford, we are talking about a few box cars as the price difference probably.

If its framed properly, the 1/2 inch plywood should work well.  You can re-use plywood over and over again, so just lightly glue whatever material you use on top. 

@Frank Mulligan posted:

I had thought about topping the plywood/MDF with 1/2 homasote, but even that is up to $43 a sheet.   I am on a bit of a budget.

My local Home Depot has 1/2 in. x 48 in. x 96 in. Acoustic Insulation Sound Board in stock for $18 a sheet. I've used this before, works good, very similar to homasote but a lot less money!

Whatever you do, revisit your decision a few days later, before buying materials.  I used ½" ACX plywood with ½" Homasote atop it.  So why did I need ACX?  I didn't, but made that decision before I decided to use Homasote atop it and didn't revisit it before acquiring all the materials, impatient to get started on the layout.  OSB would have been fine for the purpose and cost a lot less.

@dkdkrd posted:

Here's a nice comparison...

...which tends to confirm my own experience...

...for which my knee-jerk response to your OP for application on the layout: Plywood.

FWIW, of course...and just one man's opinion.

KD

I think I just learned more about MDF and plywood than I needed to know!

I think this might require a trip to one of the big box stores.  If I'm not happy with what I see, there is a local place I can also try.

@Bill Sherry posted:

You can stretch your $$ further by only using the plywood and homasote under where the tracks will be installed. Makes landscaping easier for hills and valleys.  If you need some flat areas lets say for a small city, install just the plywood in that area only.

Plywood shapes can be cut with a jigsaw and the homasote can be cut with a knife. If dust is not a problem, cut the homasote with the jigsaw.  Bill

Valleys and rivers are a concern of mine to prevent a flat-plywood world.  From your post I am leaning in that direction.  I'll have to look more into it, but I assume you sculpt these using cardboard strips and some kind of molding material?  (plaster of paris, scultpamold?)

@dkdkrd posted:

Here's a nice comparison...

...which tends to confirm my own experience...

...for which my knee-jerk response to your OP for application on the layout: Plywood.

FWIW, of course...and just one man's opinion.

KD

Very well done video, worth watching!

@Darrell posted:

My local Home Depot has 1/2 in. x 48 in. x 96 in. Acoustic Insulation Sound Board in stock for $18 a sheet. I've used this before, works good, very similar to homasote but a lot less money!

John

My search shows 27 in stock....