Pre-shrunk foam

[rrebell]

PED

I had my 2" foam sitting around about 6 months before I was ready for it and I noted that it had developed a wavy pattern with ridges about 2" wide along the 8 foot length. No ridges across the 4' width. However, i also had some 3/4" foam sitting with it remained smooth and it did not develop the ridges. As a result, I am laying the 3/4" foam (smooth) on top of the 2" foam (wavy) to ensure I have a flat surface to lay my Kato Unitrack on. Appears the thicker foam is more susceptable to developing irregularities that may be related to how it is extruded at factory. In hindsight, I think building up with thinner sheets might be prefered over a single thick sheet.

 

That is why I went with the white beaded stuff, much more stable, even before the off-gassing.

[rrebell]

7j43k

 

 

rrebell

Don't know how they pre shrink, it could be just from storing but more likely some other method, haven't resurched that as it is ussually not a local big box store item, yet.

 

 

 

 

 

So, how did you find out about this stuff?  Where have you seen it?  Was there something on the packaging that said it was pre-shrunk?  Was there some particular brand or something?

 

Ed

 

Saw it for sale at one of the big box stores online dept., it just caught my attention because it has been a problem with home builders as their stuff is ussually really fresh due to bulk buying.

[PED]

I had my 2" foam sitting around about 6 months before I was ready for it and I noted that it had developed a wavy pattern with ridges about 2" wide along the 8 foot length. No ridges across the 4' width. However, i also had some 3/4" foam sitting with it remained smooth and it did not develop the ridges. As a result, I am laying the 3/4" foam (smooth) on top of the 2" foam (wavy) to ensure I have a flat surface to lay my Kato Unitrack on. Appears the thicker foam is more susceptable to developing irregularities that may be related to how it is extruded at factory. In hindsight, I think building up with thinner sheets might be prefered over a single thick sheet.

[7j43k]

rrebell

Don't know how they pre shrink, it could be just from storing but more likely some other method, haven't resurched that as it is ussually not a local big box store item, yet.

 

 

So, how did you find out about this stuff?  Where have you seen it?  Was there something on the packaging that said it was pre-shrunk?  Was there some particular brand or something?

 

Ed

[rrebell]

Don't know how they pre shrink, it could be just from storing but more likely some other method, haven't resurched that as it is ussually not a local big box store item, yet.

[7j43k]

rrebell

Did you know you can get pre-shrunk foam now so that you don't have shrinkage.

 

 

Nope.  

Please tell us more.

 

Ed

[rrebell]

CentralGulf

https://foursevenfive.com/foam-fails-reason-5-excessive-shrinkage/

CG

 

 

Thats why you use aged foam. The panels I bought were 2'x4' for my layout but in reality they were up to a 1/4" less when layout built. I pre aged mine myself (just let them sit for around three months) before I started building. Most of the noise you hear about foam is just noise or people who do not know how to use the materials or use the wrong materials. I chose to use beaded foam and I tested everything myself to just confirm that I had the right info. Beaded foam I tested was taken from freezer to hot sun a few times and there was no visable shinkage. I also tried to set it on fire with burning wooden matches thrown on a panel and hot souldering irons left on the surface. Also tried to start a fire with a electrical short, couldn't even get a fire started that way or with the iron and the matches just stopped burning as the foam melted away. As far as cutting, if you use a controled cutting temp cutting meathod you get no toxic fumes (just bad smell) as long as you keep temp below 467 degrees.

[BigDaddy]

That article cites a 2% shrinkage which is almost 2" over a 8' span.  Ken Patterson showed shrinkage on his layout, but it looked like it was more like 1/8" 

Our application is different than sticking up in a barn roof, but nobody would be using it for layouts if they were getting 2" gaps.

My Home Depot doesn't mention pre-shrunk.  Where are you finding this product?

 

[CentralGulf]

https://foursevenfive.com/foam-fails-reason-5-excessive-shrinkage/

CG

 

[7j43k]

jrbernier

  Of course you can leave the foam outside in under 60 degree temps - The 'shrink' happens as the air pockets collapse in the foam(at least from what I have been told).

Jim

 

 

In my experience, those air pockets swell right back up later, when the temperature goes up.

The foam can change dimensions because of changes in ambient temperature.  Pretty much forever.  I noted the phenomenom when the coating I put on over the foam developed cracks long after it had dried/set.  Co-incident with termperature rises.

The shrinkage-only would be a separate thing.  I've seen that, and it never puffs back up.

Aging for six months has been represented as a cure for the latter problem.  I do suspect that the six month term was not scientifically determined.  Consider:  someone has to store the foam at least six months, measure it "frequently" to determine the cut-off time, and do the measurements under temperature controlled conditions.

Anyone done that?????

 

Ed

[jrbernier]

  Of course you can leave the foam outside in under 60 degree temps - The 'shrink' happens as the air pockets collapse in the foam(at least from what I have been told).

Jim

[mbinsewi]

Evidently I live under a rock, as I've never heard of pre-shrunk foam.  You wouldn't mind explaining it to me, would you?

Thanks,

Mike

[rrebell]

Did you know you can get pre-shrunk foam now so that you don't have shrinkage. I had to let mine foam sit for months when I built my layout because at the time pre-shrunk wasn't available.