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Patching gaps between foamboard?

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Patching gaps between foamboard?
Posted by -matthew on Tuesday, January 24, 2017 8:50 AM

I'm working on my first "major" layout, the base of which is 2" foamboard.  The reason is that I bought a bunch of it about 6 years ago to do an insulation project before realizing that the labor required for the project will not outweight the savings.  And so for the past 6 years, I've had numerous sheets of 2" foamboard sitting in my basement.

Ok, so I'm using the foamboard as a base on my layout but the pieces don't fit together snugly.  I was thinking of using sculptamold to fill the gaps but I've never used it before and wasn't sure if it's the right thing to use.  The layout's in my basement so pretty constant temperature and humidity (there are two dehumidifiers down there.)

Is sculptamold the right stuff or is there something better?


Thanks

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Posted by UNCLEBUTCH on Tuesday, January 24, 2017 9:47 AM

I use recycled 2in foam,not even close to a good edges. On the ones that are kinda close, I run a fairly large bead of caulk between them, push em togeather, when cured, fill any void with drywall mud.Or,, I'll tape and mud the joint. just like a wall joint. I use a fiberglass meash type of tape, can span a little further then the paper.On really bad spots, bridge with "for sale sign" or a like material' don't use card board with mud

Never used sculptamold,cant help you there

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Posted by BroadwayLion on Tuesday, January 24, 2017 9:49 AM

Foam board is not affected by the weather, humidity or temperture... But it does breathe, that is it can shrink as the foam continues to cure. LION got such gaps on the layout of him. You could try spary foam, but that stuf expands rather agressively. I plan on using it to make hills and other layout features, I would not think of filling the gap with that.

As a matter of fact, the LION did NOTHING to fill the gap. The foam is the Under board, and will not be seen when the layout is finsihed. Ignore it, and just build scenery right over the top of the gap.

 

ROAR

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Posted by selector on Tuesday, January 24, 2017 10:02 AM

Almost every household has a tube of spackle or drywall patching/mudding compound lying around from five years ago when you accidentally put your fist through the light switch.  Well, beside it, actually, because....never mind.  Anyhoo, any of those, or Durham's Water Putty if you don't mind mixing it, acrylic latex caulk,...basically anything that can be applied easily, that won't drip or glob onto nether surfaces (it will stay where you want it)...it's what I have used.

If possible and reasonable, I would apply a length of painter's masking tape below the joint and then gently fill in the gap.  Every little bit helps.

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Posted by RR_Mel on Tuesday, January 24, 2017 10:54 AM

I built my mountains 25 years ago using 12” x 18” x 2” foam packing blocks.  I purposely left space between and around the blocks to get more mileage out of the blocks.  I used several layers of damp newspapers to form a base for the groundcover filling all the gaps in the foam blocks.  I let the newspapers dry for several days before I started a thin layer of Paper Mache forming ground, rocks and such. 
 
I used very thin layers of Paper Mache on top of the newspaper for strength and weight.  You have to be careful with Paper Mache because it shrinks, a 12” x 12” section of Paper Mache will shrink from ½” to ¾”.  There is some shrinkage with spackle and joint mud too.  If applied thick it can pull the newspaper and foam leaving cracks creating problems.  Using fiberglass joint tape will minimize cracking with spackle and mud.
 
One of the fellows on this forum put me onto Sculptamold and it works great, no shrinking!  I no longer use Paper Mache favoring Sculptamold.   
 
I learned a trick to prevent Paper Mache from screwing up the foam base, place Saran Wrap over the area then applying Paper Mache on the Saran Wrap prevents the Paper Mache from dinging the base.  Another advantage of using Saran Wrap is the ground section is then easily removable, it retains its basic form and fits perfect when you put it back.
 
 
Mel
 
Modeling the early to mid 1950s SP in HO scale since 1951
 
My Model Railroad   
 
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I'm beginning to realize that aging is not for wimps.
 
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Posted by Grampys Trains on Tuesday, January 24, 2017 10:56 AM

I used foam in a few places on my layout, I used plaster cloth to bridge any gaps, covered with my mix of Sculptamold/Structolite.

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Posted by DigitalGriffin on Tuesday, January 24, 2017 11:19 AM

Grampys Trains

I used foam in a few places on my layout, I used plaster cloth to bridge any gaps, covered with my mix of Sculptamold/Structolite.

 



I wish I could get you to teach me how you do those great scenes.  While I'm great at electronics & track, I'm horrid with scenery.

You sir, are an artist.

edit:  Sorry I hi-jacked.

Don - Specializing in layout DC->DCC conversions

Modeling C&O transition era and steel industries There's Nothing Like Big Steam!

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Posted by riogrande5761 on Tuesday, January 24, 2017 11:24 AM

There is a host of things you could use to patch cracks between foamboard.

Plaster, Drywall Mudd, Sculptamold, even some plaster cloth first and then a layer of plaster.  Spackle sure.  You name  it.

Rio Grande.  The Action Road  - Focus 1977-1983

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Posted by MisterBeasley on Tuesday, January 24, 2017 11:43 AM

I filled the cracks for a while, early in the layout-building process.  Then I stopped, because the pink foam always ends up getting covered by scenery. 

It takes an iron man to play with a toy iron horse. 

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Posted by carl425 on Tuesday, January 24, 2017 11:50 AM

Try "Great Stuff".  It works well to glue foam together, fill gaps and as the scenery base itself.  Check out Ken Patterson's videos on youtube.

http://greatstuff.dow.com/

Ken uses the "pro" version most often.

I have the right to remain silent.  By posting here I have given up that right and accept that anything I say can and will be used as evidence to critique me.

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Posted by -matthew on Tuesday, January 24, 2017 11:53 AM

Thanks for all the responses!  I have a tub of drywall plaster from joining the backdrop that I will try that first.  

 

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Posted by 7j43k on Tuesday, January 24, 2017 12:03 PM

BroadwayLion

Foam board is not affected by the weather, humidity or temperture... But it does breathe, that is it can shrink as the foam continues to cure.

 

 

This foam is closed cell.  Temperature will change the pressure inside each cell.  And it will shrink and grow accordingly.  I saw it demonstrated on my layout when cracks in the scenic surface happened in hot weather.  And lessened when the weather cooled.  The temperature range was, very roughly, 30 degrees.  If your foam is in a conditioned space, you will likely not see much dimensional change.  If not, you likely will.

And, being closed cell, it does NOT breathe.  If it did, it would be called open cell.

It does shrink over time, apparently.  That's been demonstrated at the end of Free-mo modules where, over time, the track starts dipping down after it crosses the wood ends onto the foam--sometimes enough for coupler disengagement.  I do wonder at the rate of shrinkage.  It would be almost fun to buy a "fresh" piece and measure the thickness regularly.

 

Ed

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Posted by mlehman on Tuesday, January 24, 2017 2:03 PM

Sculptamold will work great for this. If it's what you're using for the rest of the scenery, then it's even better, because it will all blend together with nothing else required.

Just mix it on the dry side, then slobber it over the gap. For 3/4" or less, probably no need to stuff anything, it will naturally fill as deep as it needs to be. Bigger than that and you may want a little fill the gap sort of thing, but newspapers, whatever, should work.

Thta's pretty much how I built this, all 2" foam and Sculptamold, plus some other stuff...Smile, Wink & Grin

Mike Lehman

Urbana, IL

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Posted by rrebell on Tuesday, January 24, 2017 2:11 PM

6 years should be more than enough aging so shrinkage should not happen, the 2% shrinkage they talk about is for new stuff.

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Posted by BigDaddy on Tuesday, January 24, 2017 2:59 PM

rrebell
6 years should be more than enough aging so shrinkage should not happen, the 2% shrinkage they talk about is for new stuff.

Well the man says he has gaps, so it may be an issue with squareness or how he has laid the foam to the benchwork.

Henry

COB Potomac & Northern

Shenandoah Valley

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Posted by -matthew on Tuesday, January 24, 2017 3:11 PM

BigDaddy

 

 
rrebell
6 years should be more than enough aging so shrinkage should not happen, the 2% shrinkage they talk about is for new stuff.

 

Well the man says he has gaps, so it may be an issue with squareness or how he has laid the foam to the benchwork.

 

I definitely have some squareness problems.  The same night that I bought the foamboard, I bought a piece of furniture and they weren't both fitting in the SUV I had borrowed.  So I tried tying the foamboard to the roof with bungie cords.  That worked... for a while.

About half-way home the foamboards on the roof of the car tore apart and scattered in chunks across the road.  I happened to be passing an RV repair place and the guy was working and heard it from inside his shop and came running out to see what happened.  So yeah, not all the pieces are what you'd call "square and smooth".

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Posted by UNCLEBUTCH on Tuesday, January 24, 2017 4:04 PM

-matthew
About half-way home the foamboards on the roof of the car tore apart and scattered in chunks across the road. I happened to be passing an RV repair place and the guy was working and heard it from inside his shop and came running out to see what happened. So yeah, not all the pieces are what you'd call "square and smooth".

 As I stated above,I used recycled foam,so I have 2/3 more seams then if you used new.The only cracks I see are where I did not use tape with mud. The caulked joints are still all tight, its been <10yrs>

Without going down to look , I can recall 4 places that cracked,3 are well hidden with scenery. I'm still debateing about tearing it all down to build a new one, so I didnt bother to fix it, [the crack]

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Posted by Anonymous on Tuesday, January 24, 2017 5:06 PM

I used Liquid Nails between the sections of foam and Joint Compound (green lid from home depot).  Did not have any cracking in the 3 years my layout existed, but it was in a relatively well controlled climate.

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Posted by CraigN on Wednesday, January 25, 2017 10:42 AM

Woodland Scenics makes a product called Foam Putty

Their words :

"A non-shrinking, easily sanded and lightweight filling material having the same characteristics as foam. Fill cracks and gaps on foam and sand when dry."

 

I used it in a few places a couple of years ago and covered it with plaster and I don't have any cracking in that area.

Craig

 

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Posted by speedybee on Wednesday, January 25, 2017 10:59 AM

rrebell

6 years should be more than enough aging so shrinkage should not happen, the 2% shrinkage they talk about is for new stuff.

I did not know about this... About how long does this take? I'm planning on building a new layout soon ish, maybe a month or so from now, so should I buy the foam now and let it sit?

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Posted by kasskaboose on Wednesday, January 25, 2017 4:00 PM

Perhaps I'm late jumping on so please forgive.  I also suggest using some joint or spackle compound to fill in the gaps.  To secure the foam to wood, I used liquid nails.  My layout has 1x4s going across the layout as an L-girder.  This style allows me to put wire thrugh the foam w/o going through wood.

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Posted by woodman on Wednesday, January 25, 2017 5:24 PM

Ihave always used lightweight joint compound, I have never had any issues with expansion or cracking.

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