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Building a Hollow Mountain out of Foam

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Building a Hollow Mountain out of Foam
Posted by RideOnRoad on Wednesday, December 3, 2014 1:12 PM

Is it possible to build a hollow mountain or hill out of foam? I would like to hide a return loop inside of a mountain with a pair of tunnels. I want be able to access to the hidden track, thus the need for a hollow mountain.

Richard

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Posted by cowman on Wednesday, December 3, 2014 4:10 PM

There's no reason it shouldn't work well.  Have some pieces wide enough to overlap, so that your shell won't get to thin when you shape it the way you want.  Use foam friendly caulk to hold it together.  You could use Sculptamold or similar product to help shape it or just use a Surform tool to shape it and keep it at it's lightest.  2" foam could even be used on edge to simulate a verticle rock face, with a little carving.

You can either leave the back open or make a section that would lift off for access to the tracks.  If you use an open grid framework, I think you could even access from below.

Good luck,

Richard

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Posted by bogp40 on Wednesday, December 3, 2014 4:11 PM

You sure can. Just stack the foam (2" works better), Start w/ the basic footprint and you can carve each layer as you go, stepping back to the hill grade. Just start w/ a wider base to allow added support for the layer as you build. Hot wire will do a better job, but a serrated knife or Drywall saw will work but somewhat messy. Once the contours are set for the base piec, I will lay dry place the next layer hold and under scribe the bottom. As you cut angle to the shape and steepness desired.

Fore a hollow hill, I have found that constructind wood supports and staple/ glue cardboard strips to work better than all the work and mess w/ the foam.

Smaller hills open underneath are OK w/ foam, but something like this was done w/ cardboard webbing due to the shear size height (26") and length (12ft) We needed complete access to the double track.

Modeling B&O- Chessie  Bob K.  www.ssmrc.org

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Posted by BroadwayLion on Wednesday, December 3, 2014 8:49 PM

Easy. Lay the track, then box out the tunnel with wood, cardboard or even foam, then lay the foam as you would for a solid mountain, the third piece ought to bridge the two sides of the tunnel.

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Posted by riogrande5761 on Wednesday, December 3, 2014 8:50 PM

I use the cardboard strips method like the above.  It works best for hollow - foam is better used where the thickness doesn't matter.

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Posted by mlehman on Thursday, December 4, 2014 2:42 AM

If you need to have it hollow, then reinfore it with bamboo skewers. Be cuatious with them, but I use them in conjunction with adhesive and find it makes everything stronger.. I clip the protruding part of the skwer off with rail nippers.

Mike Lehman

Urbana, IL

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Posted by RideOnRoad on Thursday, December 4, 2014 7:50 AM

Does anyone know of a good tutorial for learning how build a mountain using strips?

Richard

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Posted by JoeinPA on Thursday, December 4, 2014 8:18 AM
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Posted by RideOnRoad on Thursday, December 4, 2014 9:55 AM

Richard

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Posted by mlehman on Thursday, December 4, 2014 10:33 AM

A couple of more thoughts. I also use Sculptamold -- lots of it. But I tend to shape the foam more and use thinner layers of Sculptamold when doing large liftouts, as it does make a difference in how easy they are to handle. Some of mine are ~6' long, but work OK.

This one has a supporting wood frame, but lots of track under it. I also use Rubber Rocks to keep weight and thickness down.

Also, consider using multiple parts if it's really big. Also, remember that overhead clearance may limit how high it can be lifted as well as other restrictoins on movement, watch out, don't build something that won't clearn the hole coming out.

Structurally, getting a good flat base is really important. If you have a tunnel going through, you might have two bases, one on either side of the track. One option is to build up far enough to clear the equipement on either side, then start another base for a the main part of the mountain that would set on top covering the "trench" where the tunnel is.

 

Mike Lehman

Urbana, IL

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Posted by BATMAN on Thursday, December 4, 2014 10:48 AM

On my current layout I use cardboard strips with Plaster Of Paris and foam and on other parts just foam alone stacked so the moutain is hollow.

Here is a spot where I cut out the foam and raised it up. I hot glued it to the spline and added support on the other side.

Here is a spot where the stacked foam is further along.

 

Brent

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Posted by RideOnRoad on Thursday, December 4, 2014 11:01 AM

I think I am still leaning toward foam. It is not a very large hill, maybe 27x30". It will rise steadly until it hits the back wall and will be bounded on both sides by facia. I will have a cutout below for access inside.

Mike and Brent, those are some impressive pictures. Thanks for the help.

Richard

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Posted by mlehman on Thursday, December 4, 2014 2:10 PM

Richard,

No problem, ask away. There's a lot more pics here in my Cascade Branch thread: http://cs.trains.com/mrr/f/88/t/219241.aspx?page=1

About 80% of its scenery is liftouts. It's most completed to the roughed in stage. Lots of track to come, which would normally be a problem. But it all comes apart where it needs to and I can run nominal services along the line until that happens. There's all kinds of details in it that might be useful, so worth at least skimming if you want to know how I solved lots of problems.

One more specific tip. Many of the adhesives that work with foam need air to circulate to them to cure properly. On big pieces, do big Ss with the tube/caulking gun you are using to allow air to penetrate. Don't form a neat little border aorund the edges as that will cut off the airDead

Press together as usual, that's when I use the skwers as needed for strength. You can also use the skewers just until the glue dries, in which case leave them long and pull them out when ready. Sometimes you want to carve without skewers in the way.

Mike Lehman

Urbana, IL

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Posted by bogp40 on Thursday, December 4, 2014 3:43 PM

RideOnRoad

I think I am still leaning toward foam. It is not a very large hill, maybe 27x30". It will rise steadly until it hits the back wall and will be bounded on both sides by facia. I will have a cutout below for access inside. The 3rd pic in my post above has 3/8" plywood behind the Cripplebush rubber rock. When doind so always allow distance clearance for the veneered carved foam, or castings, had to tear out a large section due to clearance issues.

 

Mike and Brent, those are some impressive pictures. Thanks for the help.

 

If part of the "hill" will have a fairly large cut where carved foam or rock castings can be used, build that portion with a sub base of plywood. You can stack thinner pieces of foam or plaster castings and glue to the wood. This will allpw for more strength, build up faster and allow more interior room/ clearance for access.

Modeling B&O- Chessie  Bob K.  www.ssmrc.org

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Posted by RideOnRoad on Thursday, December 4, 2014 4:27 PM

Hey Bob, I didn't mean to slight you. Embarrassed Yours, too, are excellent pictures along with good counsel.

Richard

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Posted by bogp40 on Thursday, December 4, 2014 5:48 PM

RideOnRoad

Hey Bob, I didn't mean to slight you. Embarrassed Yours, too, are excellent pictures along with good counsel.

 

Just lending a helping hand, with all the great stuff on the Forum, yours will look great also.

Modeling B&O- Chessie  Bob K.  www.ssmrc.org

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Posted by rrebell on Friday, December 5, 2014 12:09 PM

All my mountains are foam including one about 3' high!

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Posted by Marc_Magnus on Monday, December 22, 2014 4:20 PM

CoolThe most dangerous ennemy's of our railroads are dust and foam particles.

So I avoid the use of foam and plaster in my train room; we made already enough dust construction whithout them.

My mountain are braced whith gator foam.

The countours are made of cardstock lattice glued whith hot glue gun; fast and easy.

The hardshell is red rosin paper glued on the lattice and covered whith full strenght white glue, no dust, no particles whith hard and strong rigidity.

Rock molds are made, painted, and wheatered at the workbench and glued on the hardshell; still no dust.

Any scenery materials can be glued on the hardshell whith conventional method.

The whole structure is lighter than foam whith extreme rigidity.

Fast, whithout dust and easy to do, whath elseCool

Following some pictures how I use this method.

I don't understand why nobody speak more about it.

Gator foam brace glued to plywood base whith hot glue.

Brace covered whith cardstock lattice glued whith hot glue.

Paper hardshell glued and covered whith white glue.

Rock molds glued on the hardshell.

Hardshell painted and covered whith WS cluster.

Finished scenery.

 

 

 

 

 

 

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