# To foam or not to foam??



## pdecesare (Nov 10, 2021)

Hello,

This is my first HO layout in a few decades! I'm finding things are very different from years ago.

I have my table/frame built. I have 3/4" sanded plywood on a 2x4 frame with double corner legs and bracing throughout. You can basically park a Volkswagen on this thing!! 

My question is: 
I have read a lot about pink foam insulation board as a base, but many people use it OVER the plywood - why?? 
Why not just attach (glue or nails is whole different topic )the track and landscape directly to the plywood? 
Other than adding 1/2 to 2 inches height to your plywood, what benefit does the insulation truly add?
I don't plan to use cork beds under my track. 

Any insight to the wonders of pink foam insulation would be great!!

Peter


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## Old_Hobo (Feb 20, 2014)

The foam helps to deaden the noise….which can quickly become annoying….that is experience talking there….


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## Conductorkev (Nov 5, 2021)

pdecesare said:


> Hello,
> 
> This is my first HO layout in a few decades! I'm finding things are very different from years ago.
> 
> ...



Foam makes it much easier to carve out rivers and streams and ravines without having to build up everything.. Plus it will help reduce the noise that you will most certainly have being tacked straight to plywood.


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## traction fan (Oct 5, 2014)

pdecesare said:


> Hello,
> 
> This is my first HO layout in a few decades! I'm finding things are very different from years ago.
> 
> ...


The main reason behind the use of extruded foam, be it the pink (Owens Corning), blue, (Dow Chemical) or green, (?) is to be able to simply carve out
below-track-level scenery features, like rivers, or road underpasses. Additional layers of foam can be glued on top to create above-track-level features like hills, and tunnels. This is easier, and somewhat less messy, than traditional "hard shell" Hydrocal plaster & paper towel scenery.

Also, foam is not always used on top of plywood. Sometimes its used instead of plywood.
A sheet of foam on top of open grid benchwork can be used as a layout base with no plywood under it. This is another benefit of using foam, it saves weight. For those who don't plan to park a 12"-to-the-foot-scale Volkswagen on top of their model railroads, a 1 x 3 frame and 2 x 2 legs are quite sufficiently strong, cheaper, and a whole lot lighter.
Model railroad benchwork only needs to support model trains, not real trains, or full-sized autos. However, a 2" thick sheet of extruded foam on top of a 1 x 3 frame with stringers every 16" or so, will support a man crawling on it, without plywood under it.

The idea of a sheet of hard, extruded foam doing any "sound deadening", is not one I agree with. The sheet of foam makes just about as effective a "sounding board" (which amplifies sound, rather than deadening it) as a sheet of plywood does.

To each his own, so if your happy with your extremely heavy-duty table, and laying track directly on 3/4" plywood, that's all that matters.
Someone could make a train table out of reinforced concrete if he wanted to, just don't ask me to help move it please! 😄

Traction Fan


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## DonR (Oct 18, 2012)

The world ain't flat...and that 2" foam, as our guys have said, makes it
easy to put some small vertical dimension to your layout. 

However, I didn't de that. Instead, I used a 1/4" paper covered
foam sheet from Walmart and Hobby Lobby to cover my plywood.
It's inexpensive and easy to cut to fit your plans. Comes in black,
white and several colors. I used black to underlay my yards and
white for the rest of the layout.
It makes a much easier surface for 'gluing' your roadbed and/or track
and also it's easy to paint it and attach various 'greenery'.

You'll be glad that you used something to cover that plywood.

Don


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## JeffHurl (Apr 22, 2021)

I decided to use foam for a few reasons:

1) Like others have said, it's easy to carve into shapes.
2) I model N scale, so adding a 2" layer of foam made it really simple to make tunnels that are 2" in height. I just add another 1/2" layer on top of the voids I leave between the 2" pieces.
3) I found it really simple to lay the N scale flex track using plain old straight pins to keep the track pinned in place. This was especially nice given that I have had to pull the track back up a couple of times in some spots to correct wiring issues.
4) Scraps of foam can be used for structures. I used some scrap pieces to fabricate some bridge piers, which was super simple since the bridge piers needed to be the same height as the ground level.

Lessons I learned along the way:
A) It takes a lot more adhesive to lay foam than I had imagined.
B) If you think you need 1.5" of clearance, shoot for 2" (trust me).
C) Be careful of warped sheets. Although, bent is probably a better word. I ended up with a few 1/2" pieces that had a warp to them that wasn't obvious until I tried to add a 1/2" layer on top of 1.5" layer (see also lesson 'B').
D) you need a lot of weight to sit on top of a piece of foam if you are gluing it down.

Also be warned about solvent based glues and paints. Most will dissolve the foam, including rattle can spray paint.

But all in all, I am very happy with foam so far.


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## cv_acr (Oct 28, 2011)

Conductorkev said:


> Foam makes it much easier to carve out rivers and streams and ravines without having to build up everything.. Plus it will help reduce the noise that you will most certainly have being tacked straight to plywood.


Carving scenery detail below the track level is the main reason.

It is not the only approach. Model railroads were built without foam for years before the technique was introduced, and at least some model railroads will be built without it for years as well.

Like a hammer, it's handy, but needn't be the only tool in the toolbox...


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## Mixed Freight (Aug 31, 2019)

traction fan said:


> The main reason behind the use of extruded foam, be it the pink (Owens Corning), blue, (Dow Chemical) or green, (?) is to be able to simply carve out below-track-level scenery features, like rivers, or road underpasses. Additional layers of foam can be glued on top to create above-track-level features like hills, and tunnels. This is easier, and somewhat less messy, than traditional hard shell plaster & paper towel scenery.
> 
> Also, foam is not always used on top of plywood. Sometimes its used instead of plywood.
> A sheet of foam on top of open grid benchwork can be used as a layout base with no plywood under it. This is another benefit of using foam, it saves weight. For those who don't plan to park a 12"-to-the-foot-scale Volkswagen on top of their model railroads, a 1 x 3 frame and 2 x 2 legs are quite sufficiently strong, cheaper, and a whole lot lighter.
> ...


Yup. Agreed. Every last word.


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## pdecesare (Nov 10, 2021)

I try some foam!!! What is the minimum to use as a base over the plywood? 1/2" ? 

Can the foam be attached to the board with screws with washers, rather them glue?


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## vette-kid (May 2, 2020)

Another reason I use foam is that you can carve out a tunnel for wires and then easily hide it with scenery or even sculptamold. I'm modeling on top of a wood counter with drawers in it, so wiring under isn't an option. With the foam you have lots of options for just about anything. 

Sent from my SM-G781U using Tapatalk


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## CTValleyRR (Jul 26, 2014)

Reasons to use foam:
1) Easy to create elevation changes below track level (how thick the foam should be depends on how deep you need that terrain).
2) It' a heck of a lot lighter than plywood.
3) It is a sound insulator.
4) It's much more dimensionally stable than plywood.
5) It's easier to cut / drill through.

My last two layouts have no plywood under them. 2" or 4 " of foam on L-girder joists.


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## Severn (May 13, 2016)

I have foam. I'm not sold on foam. If I redid what I've done, I might "peg up" where the track will go on some kind of thin wood so it's a few inches above the base. 

So then the whole track plan I guess we'll call it is floating... Then I'd fill in the gaps between the track runs with mesh, paper, something to make the terrain base which I'd further cover with finer details as I find interesting.

Never done it. But seen this idea on a few vids.

So while foam is readily available it's kinda a pain to cut, mold, sand, all that. I mean it's messy as heck. And you're a bit stuck with whatever thickness you get down in terms of going below track grade. It's definitely easier to build up with it or out. 

For that I glue it up in layers -- the rough shape I want, then chop off the rough edges to get reasonably close to the final shape. I use a serrated edge knife, a kitchen knife basically. Heat wire works but it produces a smoke.

Then I smear sculpta mold over that -- which is the key to it really. Sculptamold to ground coverings.

I also think the white foam while crumbly is easier to work with as far as that goes.... 

But again from the vids, the pink foam holds finer details if that's desired like a brick pattern etc...


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## DonR (Oct 18, 2012)

It is much more advantageous to use glue to attach the
foam to the plywood. But, very little of it...dab here and
there...same with attaching the track to the foam...very
small dabs spaced widely will be all you need to hold
the track in place. If you are using Flex track you may
want to temporarily anchor it with stick pins until the
glue sets.

Don


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## mesenteria (Oct 29, 2015)

You have lots of great thinking expressed already. If you can stand one more relating of experience and some scientific explanation....?

Extruded foam IS a sound board. It will be at least as noisy with EZ-Track or Kato Unitrack set on it as it would be on plywood. _At least_ as noisy. 

If you use those tracks, or even flat sectional lengths, or flex track, but held in place with a bead of acrylic caulk, you'll find it a lot quieter. If you glue a thin layer of, say 1/4" plywood or even MDF to the bottom of the foam, you'll create an acoustic deadener of 'dual density' that will really lower the sound. 

A lot of the noise on anyone's layout comes from direct contact between ballasted, hardened ballast, tracks and whatever surface they rest one. So, if you use the caulk, but then pour and groom ballast grains, and then infuse the ballast with a thinned glue mixture, and wait until it hardens, you have created that soundboard effect all over again and undone the advantage the softer caulking gave you.

So, how do you fix this problem...IF...IF...the noise drives you crazy (not everyone agrees, not by a long shot, that noisy layout tracks are a problem)? Lay a sub-roadbed, top it with cork or foam roadbed, and make sure your glued ballast doesn't cover all the roadbed and make direct contact with the sub-roadbed, whatever that is...1/2" exterior grade ply is all I ever use. Remember, you want dual densities at least, but not hardened ballast coming into contact with whatever nether surface there is supporting your tracks. That's the key.

I have set up temporary trackage on slabs of drywall while finishing a room prior to building the layout. Amazingly quiet!! Quieter still is a train running over a bridge of any construction supported at both ends, say a long truss bridge on two piers/abutments. Dead stinkin' quiet! Why is the bridge quiet? It sits on two abutments of material X, which sit atop wood or molded plaster, or whatever. Dual densities.


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## Severn (May 13, 2016)

I ended up with me flex track on cork on foam on plastic table tops. That was more to do with what I had on hand than actual planning. However I started with plastic base track. I found the me combo to be about 10 db quieter according to my phone based app and so went with that. At slow speeds I only hear the decoder sounds which I turn down a bit from factory settings anyway... And to me this is exactly what I was after. The table tops are not ideal but I never intended for anything long term. So they are ok. The biggest issue of course is that the track once down has to be level enough to function in terms of disconnects or derails. I admit what I did is not ideal there and I've had to go around and fix a lot of spots with shims to bring a spot up or cut outs to being a spot down... But it works.


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## pdecesare (Nov 10, 2021)

mesenteria said:


> You have lots of great thinking expressed already. If you can stand one more relating of experience and some scientific explanation....?
> 
> Extruded foam IS a sound board. It will be at least as noisy with EZ-Track or Kato Unitrack set on it as it would be on plywood. _At least_ as noisy.
> 
> ...


Lots of good input on foam!!!

Have you ever tried adding a sound absorbing layer between plywood and insulation? Maybe something like this: 
https://www.amazon.com/Soundsulate-...86B2ZRVY/ref=pd_lpo_3?pd_rd_i=B0733VC7JM&th=1
Dual density??

Just curious if anyone has ever tried this material


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## traction fan (Oct 5, 2014)

pdecesare said:


> I try some foam!!! What is the minimum to use as a base over the plywood? 1/2" ?
> 
> Can the foam be attached to the board with screws with washers, rather them glue?


The minimum thickness of foam to use would depend on what you want the foam to do on your layout.
If you're using it just for "sound deadening" then I wouldn't use extruded foam at all. You might use Homosote instead. It has been used successfully as a sound deadening material for may years. 
However, if you want to carve scenic features out of the foam then the thickness required depends on what you want to carve out of it. If you just want shallow drainage ditches the 1/2" would do. On the other hand, if you want a bridge over another track, then you would use several, stacked layers of fairly thick (1" -2" ) foam to build up enough elevation in the scenery on either side of the bridge so that trains can pass under it.

Normally foam is glued down, rather than attached with hardware. A common "glue" used for this purpose is Latex caulk. On your railroad, you can anchor your foam any way you want, including with screws & washers. For what its worth, I've never heard of anybody using screws & washers to attach foam, but that doesn't mean you can't.
Screws are very solid, which means they are very good at carrying sound. So any "sound deadening" That some believe foam provides, would be bypassed by the screws, if they went through the track, roadbed & plywood. If they only pass through the foam and into the plywood below, then I don't think any "sound deadening" would be lost. However, I don't believe hard extruded foam is a sound deadening material in the first place, so what is there to lose?

Traction Fan


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## pdecesare (Nov 10, 2021)

traction fan said:


> The minimum thickness of foam to use would depend on what you want the foam to do on your layout.
> If you're using it just for "sound deadening" then I wouldn't use extruded foam at all. You might use Homosote instead. It has been used successfully as a sound deadening material for may years.
> However, if you want to carve scenic features out of the foam then the thickness required depends on what you want to carve out of it. If you just want shallow drainage ditches the 1/2" would do. On the other hand, if you want a bridge over another track, then you would use several, stacked layers of fairly thick (1" -2" ) foam to build up enough elevation in the scenery on either side of the bridge so that trains can pass under it.
> 
> ...


Thank you for the explanation! This is all starting to make sense... 
I live in the midwest and Homasote board seems to be very hard to get right now. Both Homedepot and Lowes are sold out!! 
Would 1/2" cork sheets be a good alternative for sound deadening over the plywood?


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## MichaelE (Mar 7, 2018)

Cork works well. A lot of roadbed material is cork.


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## traction fan (Oct 5, 2014)

pdecesare said:


> Thank you for the explanation! This is all starting to make sense...
> I live in the midwest and Homasote board seems to be very hard to get right now. Both Homedepot and Lowes are sold out!!
> Would 1/2" cork sheets be a good alternative for sound deadening over the plywood?


Yes, cork will work well, as long as you keep the track completely isolated from the plywood sounding board. That means no screws, or nails, through the track & cork and on into the plywood. Each one of them will be a very efficient sound carrier, passing train sound from the track, right through the cork, and into the plywood.

Instead, glue the cork sheet over the entire area of the plywood top. Then glue your track, ballast, & scenery materials, only to the top of the cork sheet. Don't create any sound paths of hardened glued ballast or dirt, that connect to the plywood. The whole idea is to keep the entire model railroad only on top side of the cork, and the plywood only on the bottom side.

Latex caulk makes a good glue for this job. Either caulk, or Elmer's glue, will hold the cork to the plywood. Elmer's will not hold plastic bottomed track to the top of the cork well enough to be relied on. (despite some claims you may see here.) Yes it holds a little, temporarily, but your track can be pulled right up with no real effort, or intent, if all that's holding it down is white glue. Elmer's is not made for gluing plastic.
Use caulk for the track-to-cork bond. A drop every 6" or so will work. Use weights (bricks, canned food) to hold the track down overnight, to give the caulk time to set up firmly. If you want the realistic appearance of the embankment found under real railroad track, you may want to glue some cork roadbed down to the main cork sheet along the route your track will be laid. Later, you can ballast the track and it will look like the real thing, raised up above the surrounding landscape.

Good Luck & Have Fun;

Traction Fan


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## MichaelE (Mar 7, 2018)

No foam was harmed in the building of this layout...brought to you by the AFPS.


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## OilValleyRy (Oct 3, 2021)

I always used foam, and always had trouble with turnout machines… both reaching and mounting.
My next layout (my 5th?) will combine those answers. To foam? Yes. Not to foam? Yes.
Plywood sub roadbed on risers, mainly for switch machine mounting. 2 inch foam butted up against that in most areas for carving depressions, but some areas of plaster shell over open grid too.


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## Geno the Viking (Feb 29, 2012)

pdecesare said:


> Hello,
> 
> This is my first HO layout in a few decades! I'm finding things are very different from years ago.
> 
> ...


I do plywood covered with homesite and pink insulation board wherever I need elevation gain as on hills. Foam is wonderful, easy to cut, glue and paint. The only way to go. I put plaster over the foam in some areas as needed.


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## Geno the Viking (Feb 29, 2012)

Geno the Viking said:


> I do plywood covered with homesite and pink insulation board wherever I need elevation gain as on hills. Foam is wonderful, easy to cut, glue and paint. The only way to go. I put plaster over the foam in some areas as needed.





Geno the Viking said:


> I do plywood covered with homesite and pink insulation board wherever I need elevation gain as on hills. Foam is wonderful, easy to cut, glue and paint. The only way to go. I put plaster over the foam in some areas as needed.


Homesote. darn spell check. Ha.


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## scenicsRme (Aug 19, 2020)

It really depends on what you want your finished layout to be like. Do you like a lot of detail, weathering, realism, or are you more interested in a run them as they came out of the box, with simple painted (or unpainted in the kit colors) plastic buildings set around as scenery and watching trains go around in circles like on xmas morn? putting track down on a flat surface no matter if it's plywood, foam, cork or homosote, you are still going to end up with the train around the xmas tree look, because even Kansas isn't perfectly flat. If all the track, roads, buildings are all on the same level there is not much choice. very few places don't have any water courses either, otherwise they would flood with every rain.
In most of the world railroad track is relatively flat on it's roadbed because there was a lot of earth moving, cutting and filling, bridge building etc to make it that way, whereas except for maybe modern expressways, roads sit on and follow the contour of the land, Building are primarily placed wherever there is enough space, some flattening, re-contouring of the immediate area may be done to allow the building to sit level or for landscaping or drainage purposes, but the surface still undulates above and below the level of the track, and buildings sit above and below track level.


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