# Spray foam for hills?



## Zante (Dec 9, 2021)

Has anyone used spray foam to create hills and mountains?
Is it any better than layered foam board?
Is it any easier to carve?


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## vette-kid (May 2, 2020)

I think a few have tried, but I do not think it will work well. For one, it is impossible to control the direction of expansion. Of you touch it while it's wet it just makes a sticky hot mess, and if you cut it the final product it will be unpaintable and require plaster cloth anyway. 

Sheet foam is easy to work with, controllable and less messy. 

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## Severn (May 13, 2016)

I have seen it on you tube or similar. I guess having used that kind of foam on exterior house projects. I would think it would be sticky and not particularly workable.

I currently favor sculpta mold on something to hold it up. However for really big efforts there may be cheaper.

Check out for example Kathy Millatt had one somewhere in this pile of vids which I can't quite put my fingers on... That was basically white glue, sanded grout, color.... If memory serves. I have not quite tried this although I have applied sanded grout onto foam, then spray glued it. And I would do this again if I wanted the texture.




https://youtube.com/c/KathyMillatt




I'm going to add some more...

The white style foam is easy to cut and you can get free pieces from packaging. Select your pieces and glue them up. I used gorilla glue which is a us brand polyurethane based glue... I think. I also took some cheap wood chopsticks from Chinese carry out and jammed them into the foam to help make it reasonably sturdy. Also had glue in them or made a hole, glue, chopsticks. Whatever worked. Obviously there's a lot of variations to this basic idea to get it all to hold together.

Then I just used serrated kitchen knife and cut it away to the shape I wanted. Then I smeared sculta mold all over it and smoothed that out.

Then after drying paint, then ground cover, static grass etc...

The exterior house pink or green foam sheets they sell here for insulation is another option, it's probably everywhere. These come in large sheets of various thicknesses.

Similar to above but it's a little sturdier product so maybe a little harder to carve.

All this works but for the 10000 pieces of foam left over. Some you can save for other projects.

I don't absolutely think hot wire cutters are necessary or an advantage ... But I have tried this as well. Makes a strong vapor.

Ok another approach is then something like window screen.. draped over anything to make the undulating terrain shape. I've seen or tried screen or even paper. Ive seen wood or cardboard sticking up to provide elevation.. or crumbled up paper, this is what I used. You drape the paper over to form the surface desired shape, you may need to home pressure points in some way and glue. 

If you used the screen, apply wet thin paper of some kind using a glue water mixture. If you're going right to paper it's going to have to strong enough to not fall apart but I would think also wet it with glue and water... I think the screen helps here myself..

Then you spray glue over it and let it dry and harden... Then what? Once again your back to various ground covering steps.

This is cheap and can produce excellent results but it's not terribly strong and this can be both bad and good.

A somewhat similar approach is the products that are a heavy foil with perhaps some kind of surface glued to them to hold ground cover.

In this scenario you crumble up the foil for the surface, partially flatten it back out and drape it over the space of interest possibly with something underneath to hold it up over spaces .

Once again you get back to the various ground covering steps from there.

So I've done carved foam, screen with paper, and the foil. And each case I've gone then to the sculpta mold next. I've never really skipped that.

I think for large spanning background hills, maybe the screen, then foam is easy, then for granite or very rocky faces the foil.


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## beachhead2 (Oct 31, 2017)

Zante said:


> Has anyone used spray foam to create hills and mountains?
> Is it any better than layered foam board?
> Is it any easier to carve?


I've done it with good results. I did sort of a hybrid method. First I made some rough forms out of pink XPS foamboard. Then I used Great Stuff expanding spray foam on top to create the surface. The key to the technique: while the Great Stuff is expanding, you lay on a thin layer of quilt batting. That will serve to contain the foam a little bit. Then as the Great Stuff sets up, you can push on the batting and sort of massage it into the shape you want. After it sets up, you can paint right over the quilt batting and apply ground cover. It works great. Here is a YouTuber with a series of videos explaining it.


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## CTValleyRR (Jul 26, 2014)

Any time you are tempted to ask a model railroading question that begins with "Has anyone ever....", you can bet good money that the answer is going to be "Yes".

I have seen a gentleman doing it at a train show. Contrary to what Vette-Kid says, he was cutting (with a hot wire) and sanding the foam into shape, and then painting it. He was getting good results.

For me, I prefer to stack foam pieces (either extruded foam or bead board; both work) to get the general shape, then cover it with a good layer of Sculptamold (which I buy in 25 pound bags).


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## vette-kid (May 2, 2020)

Interesting, maybe I used the wrong stuff. When I cut it the opened surface was VERY porous. 

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## CTValleyRR (Jul 26, 2014)

vette-kid said:


> Interesting, maybe I used the wrong stuff. When I cut it the opened surface was VERY porous.
> 
> Sent from my SM-G781U using Tapatalk


It's also possible that cutting it with the hot wire seals those pores. That said, it's not that you CAN'T paint something porous, you just have to fill them first. A quick brush with fairly thin plaster would do that, as would spackle, tile grout, drywall mud, or any of a number of other things.


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## nsmustang55ol (Sep 3, 2021)

This was my first layout, for doing a hills that aren’t so high it worked well. After I carved them I covered them in water glue and toilet paper.


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## lagales90 (Nov 14, 2021)

Severn said:


> I have seen it on you tube or similar. I guess having used that kind of foam on exterior house projects. I would think it would be sticky and not particularly workable.
> 
> I currently favor sculpta mold on something to hold it up. However for really big efforts there may be cheaper.
> 
> ...


So I ran all the numbers and order 600 board ft of tiger foam spray insulation. ($700) it should have been enough to do a whole 28 ft camper! It was not! I did about 1/3 of the camper. Won't buy the two-component again. To much inconsistency and to much to shave. Much waste!


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## sjm9911 (Dec 20, 2012)

??????????


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## OilValleyRy (Oct 3, 2021)

I saw somebody on youtube do it. I thought about trying it, then quickly turned to thinking about if I could make a lightweight stone wall for a bedroom that way? Never did though.

Side note: I find carving foam terribly inefficient and messy. I stopped doing it years ago, i learned an ancient Mayan technique. In fact let’s call it the Mayan Way. I build up a terrace like a Mayan pyramid. Then fill the “steps” with wadded newspaper, magazine pages etc, masking tape to hold them there. Cover that in tinted plaster and/or “ground goop.” No carving fuss, no mess. Doesn’t work for river banks sadly. Still gotta carve those.


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## CTValleyRR (Jul 26, 2014)

OilValleyRy said:


> I saw somebody on youtube do it. I thought about trying it, then quickly turned to thinking about if I could make a lightweight stone wall for a bedroom that way? Never did though.
> 
> Side note: I find carving foam terribly inefficient and messy. I stopped doing it years ago, i learned an ancient Mayan technique. In fact let’s call it the Mayan Way. I build up a terrace like a Mayan pyramid. Then fill the “steps” with wadded newspaper, magazine pages etc, masking tape to hold them there. Cover that in tinted plaster and/or “ground goop.” No carving fuss, no mess. Doesn’t work for river banks sadly. Still gotta carve those.


Matter of opinion ion, really. Stack your foam strategically and use a serrated knife to carve off big chunks, then do some finer shaping with a rasp. I can do a 2x2 section in about 5 minutes. Pick up the big chunks by hand, and take a shop vac to the rest. Very efficient, and, while messy, a breeze to clean up. A final coat of Sculptamold (with which you can easily make terrain undulations that don't need a full layer of Styrofoam) and you're done. I've made my share of newspaper hills, and I find foam much easier and less tedious, as well as infinitely easier to get the exact contour you want.


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## CTValleyRR (Jul 26, 2014)

lagales90 said:


> So I ran all the numbers and order 600 board ft of tiger foam spray insulation. ($700) it should have been enough to do a whole 28 ft camper! It was not! I did about 1/3 of the camper. Won't buy the two-component again. To much inconsistency and to much to shave. Much waste!


So you reopen a 6 month old thread with a comment that has nothing to do with model railroading? Sheesh.


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