I have a friend who will be doing the scenery for a small museum layout. The HO layout will be reasonably long and skinny. His plan is to use 2" Styrofoam over a plywood base, but the organisation is caught up in debate on whether either the Blue or Pink brand will shrink over a long time: ie years.
Some advise that the shrinkage is as much as 2%! (?)
I don't have experience with foam as a scenery base, but with the layout going into a converted baggage car, and the likelihood of temperature/humidity swings, are the concerns valid? If so, what's a better choice?
Does anyone have comments I can take back to him?
Thanks for your feedback, George
Well, styrofoam will shrink under high temps but I do not believe that extruded polystyrene (blue or pink) will shrink except under extremely high heat - like flame impingement.
Are your sources confusing their materials?
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I've noticed no shrinkage after 3 1/2 years. My layout is in the temperature and humidity controlled environment of our family room, so it's not getting stressed out a lot.
You're more likely to have problems with the wood frame than the foam, though.
It takes an iron man to play with a toy iron horse.
I have had no shrinkage either. My layout is in my garage, but it does have heat so 45 is about as low as it goes. My first hills are against the garage door and they will get colder than 45 and I have seen no change after 2 plus years.
I will add this is the first time I have read anything on this subject. I would be more worried about the plywood base my self.
Cuda Ken
I hate Rust
The foam on my layout has been on for almost five years now with no shrinkage.
Kevin
http://chatanuga.org/RailPage.html
http://chatanuga.org/WLMR.html
I believe it is very stable. The folks who have worried about this may be using their experience with beaded polystyrene, the picnic cooler stuff, when it is left exposed. It does shrink and break up, but this is due to weathering and UV radiation. I don't imagine any UV will be contacting the foam under scenic materials, and indoors.
-Crandell
Shrinkage of the extruded foam, whether blue (Dow) or pink (Owens Corning) is a non-issue. Seasonal shrinkage/expansion of the substrate (plywood in this case) can be an issue, but as a general rule, it won't be. Plywood is extensively used precisely because it is very stable. Minimal (less than 1%) shrinkage is possible in a module that is subject to wide swings of temperature, and more importantly, humidity. Simply use a foam safe adhesive designed specifically for mounting foam to wood, and you'll be good to go. The foam adhesives have enough flexibility to accomodate any miniscule variability a module may encounter.
For complete clarity "from the horse's mouth", I would suggest going to Dow or OC's website. They have available the full technical specs for their products, including shrinkage values.
Being employed at a company that uses DOW blue board in a residential precast concrete application I'll throw in my 2 cents to assist in the debate.
We have precast concrete basement walls over 22 years old with houses on them and people living in them. Never have I once heard of a comment of foam shrinkage.
This however is not to be confused with thermal expansion and contraction. Even so, at least DOW's product is stable (I can't comment on Owen Corning due lack of interaction with it). About 2 years ago we did a informal test. We took a peice of DOW foam (21"x114"x2") that was sitting outside overnight in below freezing temps and measured it. We immediately placed it in our curing kilns and ran a cycle at 130*F for 2 hours and measured it again. At most it grew less than 1/16" of an inch on the length.
I would be less worried about the stability of the foam and more on the expansion and contraction of the materials placed on it.
Seven years in a half-uninsulated garage, my layout is ENTIRELY extruded foam based, both the Corning Pink and the Dow Blue. Not one iota of shrinkage and my layout is relatively large--24x24'. I swear by the stuff.
Tom
Tom View my layout photos! http://s299.photobucket.com/albums/mm310/TWhite-014/Rio%20Grande%20Yuba%20River%20Sub One can NEVER have too many Articulateds!
I'm agree with twhite, I also have extruded foam on my layout, and it's in our basement, and not one time have I had ANY shrinkage!!! I would ALSO be more concern about the plywood base than the foam!!!
Trainsrme1 (ie the Extruded Foam layout King)
ARTHILL wrote:Remember, it was designed as insulation for buildings and foundations, where the smallest shrinkage would distroy the whole purpose. Like the others I have had none on my layout.
Exactly. Extruded foam insulation board has certified R values to measure the ability of the material to resist heat flow. By their very nature, these materials are typically exposed to the elements and must perform while experiencing huge temperature swings. I do not see how this would be possible if they were not dimensionally stabile (think gaps around the edges if they were to shrink). Jamie
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Thanks to all who have shared thoughts about foam shrinkage. I'll take them along to Bill so he can talk with his organisation. I suspected that there wasn't a problem, and am glad to see that there doesn't appear to be one.
Thanks again, George.
wow, 2% shrinkage. I have never heard of the pink or blue foam shrinking that much . I have had my laylout in my basement for over 2 yrs and I have not noticed any shrinkage other then the size of my wallet.I have 2" of the blue styrofaom on top of 3/4" plywood and it looks the same size to me now as it did the day I put it down. So I would not loose sleep over the worry about it.