Plywood under 2" pink foam or not?

[rfross]

I'm using Sievers benchwork on my shelf layout which on average is 18" deep and I will be using 2" pink foam board. I keep going back and forth between whether or not to fasten the foam board to 1/4" plywood first, or just attach the foam to the benchwork. Virtually all of my framework has cross braces every 12" so I'm not sure the plywood is necessary from a structural standpoint.

I'm leaning towards the plywood because it certainly can't hurt. Some have suggested that the addition of plywood helps to quiet the foam. But the plywood complicates the construction somewhat because I would need to add cleats to the framework so I could run screws up from underneath so as to not end up hiding screws under scenery. And it obviously increases the cost somewhat.

Any real world observations that I should consider?

[CP5415]

Personally, I would go with the 1/4" plywood underneath just in case.
2" foam board is rigid, just how rigid is something I don't want to find out after the track laying & wiring is completed.

Just my 2 cents

Gordon

[dehusman]

I would be more afraid of the 1/4" plywood warping than the foam. Several of the more experienced modelers use the 2" foam with no plywood. If you have supports every 12-16" underneath, the plywood wouldn't really be necessary.

Dave H.

[rrinker]

I've built my layout using just the 2" pink foam, no plywood. The framework is 1x4 lumber on 16" centers. I've had no issues with the foam sagging or not providing suffcient support, even after I punched holes in it to mount Tortoise switch machines - and I don't mean drilled holes for the throw bar, I mount the entire Tortoise machine from the top. I have some pictures of it on my web site.
I did this part of the layout mainly as a test, but I am more than satisfied with the results and will continue to build using these same methods.

--Randy

[Anonymous]

rrinker... you aint kidding about punching down thru the foam.. that was a great set of photos.

[rrinker]

And it's pretty easy to do. I mount the Tortoise to the PC board first. Place the track and mark the location of the throwbar, and trace around the PC board onto the foam. I have a cutting attachment for the Dremel that came with a depth stop, sort of makes it into a mini-Roto-Zip. Works great on foam - depth stop set to the thickness of the pc board, shop vac hose in hand, and I rout out the square. Then I use a kitchen knife to cut out a block in the middle of that to clear the body of the Tortoise and the pivot piece. Drop the Tortoise in, make a hole in the roadbed, drop the turonout in place, and that's it.

--Randy

[rfross]

Randy - did you assmble the foam to the framework using Latex Liquid Nails? If so, is it a pretty solid bond?

Because I'm using the Sievers modular benchwork I want to be able to disassmble everything if I move so the foam sections will be installed to fit the benchwork sections with gaps in the foam at the section joints.

I just want to make sure that if I go foam directly attached to the framework that it is a tight enough bond to survive moving day when the time comes.

[eng22]

I did a 5X9 on 1x3 frame work. Crossmembers every 12 inches, no plywood. I love it. Very as easy to build, great to work with. Very light.

[grayfox1119]

rfross: I prefer to use plywood as a sub base. Although 18 inches depth is not really that much to worry about, having an accident later can be a real pain! The cost is minimal for the 1/4" plywood. Warping will only be a problem if you are in an area where humidy in the room can be absorbed into the plywood, and, if you have insufficient bracing undernieth. If humidity "is" an issue, you can seal the plywood and this will prevent warpage, but with only 18" depth, I really don't see this as a concern.

***

[rrinker]

QUOTE: Originally posted by rfross

Randy - did you assmble the foam to the framework using Latex Liquid Nails? If so, is it a pretty solid bond?

Because I'm using the Sievers modular benchwork I want to be able to disassmble everything if I move so the foam sections will be installed to fit the benchwork sections with gaps in the foam at the section joints.

I just want to make sure that if I go foam directly attached to the framework that it is a tight enough bond to survive moving day when the time comes.

I did a test prior to this and used Liquid Nails to fastent he foam to some wood. It did not hold well at all, even after leaving it sit for days with stacks of my MR collection piled on top. So when it came time to do the actual layout, I used Elmers Carpenter's Glue, the yellow stuff. THAT hold, and holds well. I actually had to pick up and moe the entire 8x12 to push it back into the corner, and everything stayed attached. Now, if I go underneath and slam up on the bottom of the foam, it will likely pop off, after hitting it a LOT. I would never try lifting it by the foam. But there are plenty of people building modules for modular layout using similar methods, and those get transported around a lot with no problems, so I am not worried about this.

--Randy

[TurboOne]

Thanks for the answers to some more of my questions. Randy your layout is great. Pictures are fantastic help for us newbies. Rfross good questions, thanks for asking them.

Thanks

Tim

[twhite]

I've constructed my 24x24 mountain layout with no plywood under the foam at all, and it's quite sturdy. I have cross-braces every 12", and no sag whatsoever. And the foam is VERY quiet, as far as running goes. I used Woodland Scenic risers for the track, filling in with 2" stacked foam where needed, and if anything, the stacked foam increases the rigidity extremely well. I used Elmer's Carpenter glue to lay the foam on the cross-braces, helped a little with 2/12" countersunk wood-screws and nothing shifts. I'm very happy with it. Only wi***he foam came in a color other than pink--before I got the scenery started, my layout looked like a strawberry sundae.
Tom

[rrinker]

If you can find the Dow brand of the same thing, it's blue. But around here all I can find is the Owens-Corning pink. It does all look kind of surreal. On the test piece I have seperate from the layout I got as far as ballasting the track, looks 110% better with ballast on the track, at least you don't see the pink immediately under the wheels anymore.

--Randy

[SpaceMouse]

FRom a purely strucktural point of view, the 1/4 ply will give you a tortional (sp?) stability that the foam can't. In other words, if you bump it with your belly when you reach, it will stabilize the table (the legs have to be strenghtened with bracing.

[rrinker]

Possibly, but the foam is pretty strong. My tables tended to twist a bit if you lifted on one corner, even with the legs all braced. Once the foam was glued on - solid as a rock. Like I said, I picked the whole thing up and slid it about 2' across the floor to get it in the final position, and came loose.

--Randy

[SpaceMouse]

QUOTE: Originally posted by rrinker

If you can find the Dow brand of the same thing, it's blue. But around here all I can find is the Owens-Corning pink. It does all look kind of surreal. On the test piece I have seperate from the layout I got as far as ballasting the track, looks 110% better with ballast on the track, at least you don't see the pink immediately under the wheels anymore.

--Randy

Dumb sidetrack, but don't you paint the foam in the general color of the landscape before you lay the track?

[rrinker]

Ah but then how do you draw the lines on it to see where the track goes? Or, not sure if i will bother, but a common technique to 'weather' the track is to take a couple of spray cans and go at it after the track has been laid. Natrually this will get all over your nice 'brown' earth color. Might as well wait and paint the brown AFTER everything else is in place, then ballast and add ground cover.

--Randy