I have been reading the forums and picking up lots of usefull info on building a layout, for i am a noob at this. And one thing keeps jumping out at me, when using foam as sub roadbed on top of plywood why does everyone use extruded foam instead of expanded foam?, has anyone built with expanded foam and if so what was the result? Don’t have too much experience with foam insulation so good solid facts and reasonable explanations will be appreciated.
If by expanded foam you mean the picnic cooler stuff, or the molded shapes that your DVD player came in, it is okay in a pinch, but it pills something terrible when you go to cut and shape it for hills, gouge it for ditches and rivers, etc. It also crumbles easily. Generally, we advise against it unles…
Extruded foam is more like sponge toffee as far as being homogenous. If you were to cut it, you would do a score along the cut line, then snap it to get a clean break. Doing that with expanded foam, the beaded stuff, will net you some odd-shaped chunks an a lot of little beads.
The extruded stuff is either pink or blue. It can be shaped realitvely easily with sanding blocks, wire brushes, carving knives, etc.
Thanks, Thats exactly the straight forward and to the point answer i was looking for.
Most of us have found that when we use 2-inch thick extruded foam, we don’t even need the plywood. It is stiff enough by itself to get by with just supporting rafters (I use 1x3’s for them) every 16 inches or so.
Without plywood, though, you can’t climb on top of your layout, even during the construction phase. Once you put down the foam, though, you can’t climb on top of it anyway.
The only disadvantage is not being able to mount stuff securely underneath. Are there any Tortoise-users out there who use just foam? How does that work?
Actually guys, just for terminology, expanded foam is what comes out of a “spray can”, foam insulation. The stuff used for packing is called bead or bead board. The expanded is usable but a pain to control and form. The beadboard is good for starting trash fires.
To mount stuff under foam (like TO motors) I glue on pads made from 1/8 basswood with RTV silicon and then screw whatever to the wood after it’s cured.
There are 2 manufacturers of extruded foam insulation – Dow (blue) and Owens-Corning (pink). They are basically the same stuff.
I’ve been using the blue stuff and it’s great to work with. It comes in 1/2", 1", 2", and 4" thicknesses. I use Liquid Nails foam glue (in caulking gun tubes) to secure it and it works well.
Good luck…
I wouldn’t be downwind of burning beadboard foam - like styrofoam cups that stuff gives off some nasty stuff. The MSDS for the extruded pink and blue stuff, however, indcates that it is not toxic - another reason to use the pink or blue over the beaded stuff.
–Randy
Can anyone comment about the foam board bowing? I picked up two sheets at my local home depot and they all seem to be somewhat bowed. Makes me nervous to use it alone???
Hmm, can’t say mine was bowed in any way, I have the 2" thick stuff, barely deflects when you hold it bt he ends. I used mine in top of wood grid benchwork, no plywood. I used yellwo glue to attach the foam to the wood, and weighted it with my stacks of MR mags for a day or so til it dried. Nothing has pulled loose yet, and that was almost 2 years ago now.
–Randy
I have not noticed my pink 2" foam being bent at all, But even if yours is a little bowed, after gluing it to your bench framework, it should flatten out nicely, just make sure you place some weight on top after you glue it down until it sets.
I am using foam on top of plywood because I wanted a better mounting base for things underneith, and , I have a 4’ wide bench over 16’ of the running space.
Mr Beasley Someone on this Forum or the General forum, had an article about mounting Tortoises into foam, they work out very nicely as I recall. I also read an article in a past issue of MRR, maybe a year ago I am guessing.
I forgot to mention, Randy, you are not only correct about the beaded foam being nasty to smell, it IS hazardous to breathe, there are warning by Woodland Scenics about which type to use and not use when using a hot wire knife. I also checked on the internet doing a Google search, and they have MUCH info on foam types, do’s and don’ts. They would never OK using the wrong type ( beaded type ) for home insulation because of fire…it would give off hazardous fumes and cause possible death to those trying to escape a house fire. We hobbyist on the otherhand, need to be aware of the dangers in the products we use.
hehe the Torotise thing was Tom (tstage) he took what I posted (not my idea, I got it from the North California FREEMO group) and took a series of pictures showing it and posted them here. I did all mine that way.
–Randy
RANDY I just checked out you home page for the 1st time, I must commend you on an EXCELLENT web site, and a great job with layout!!! A1 job Randy, VERY impressive.
I’ve never had 1 1/2 or 2" foam bow. But, it’s also not always “true” either. I’ve often gotten pieces that are a little thick or thinner at the edges. I just dress it up, with either a surform tool, or some drywall mud.
Nick
One other thing…
A lot of people say that they use foam but then cover it with plaster for the final scenic contour. For the life of me I can’t figure out why they do that. Seems like we can just contour the foam and paint it and be done with it. Maybe apply a little sculptamold in a few places for special details but I sure don’t get the cover the world in plaster trick.
george
Yes, it can be sculpted and decorated without any plaster or mud, I thinks its’s just a mind set and/or they are doing what they know (plasterwork). I carve mine with a knife and hot wire, sand it, surform it, blah blah. But there are not many wrong ways to do this stuff, esp if it works. Fred
It probably is not necessary, but if you wi***o add plaster rocks or other moldings, it will adhere better to a plaster than it will to the foam. So, some people (myself, included) use strips of the plaster cloth to cover gaps,cover steep slopes on which rocks must be placed, and so on. I do not cover the foam otherwise. Latex paint and ground foam do that nicely.
George wrote: A lot of people say that they use foam but then cover it with plaster for the final scenic contour. For the life of me I can’t figure out why they do that.
my response: I suspect carving foam is an exercise in patience that many of us do not have. With plaster OTOH, patience is not a virtue due to its fairly quick setting time.
Another reason for favoring plaster is that for many of us, construction by addition - adding the plaster until we get the contour we want - comes more naturally than construction by subtraction - carving the foam away until we get the contour we want.
I cannot say how valid these reasons are until I try carving foam myself; I’ve only worked in plaster so far. But I am aiming for a much lighter weight layout - bookshelf style - on the next PG&W (starting this summer).
Or was your comment rhetorical?
Fred W