Large Scale Central

Rigid foam exposure

General Discussion
#1

The 1-2" insulation foam that everyone likes to build with, how long with it last outside without paint?

Or if I paint it, I know I can’t use rattle cans so what do I do?

The reason I’m asking is, I want to mock up some buildings, roads, etc on the layout. Not the final permanent structures but the eventual base layer.

Or a better question is what have people used for mock ups? I’ve got a few small buildings I’ve made with the paperback foam core but those wouldn’t last long outside 24/7.

My idea was to have something fairly easy to build as a mock-up until I can get the final product done.

I’m getting impatient looking at the backyard and not seeing stuff on the layout. :joy:

#2

Craig,

Our foam buildings have been outside for years. The one we are currently rebuilding never left the railroad. The foam core showed no damage, whether from bugs or weather. Surfaces were clad with crabstick.

Other buildings have held up equally well. The paint may peel, the crafsticks rot, or panels fall off, but the foam lives on.

Eric

#3

you use exterior-latex paint.

but with your quick-modelling, it might be better, to beg or buy off-cuts from a carpenter, build up some buildings like with toy-blocks, glue and paint them with oilbased paint.

they endure the wait, until you finished your actual building project, are children-resistant and offer no home to wasps and bugs. :wink:

#4

I’m sure the same amount of time with or with out paint. My project has been outside for 18yrs (year round) in PA with latex paint. So basically long enough for you to decide on your next step.

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#5

I built a bridge using 2" foam that I stuck together with glue. I had heard that ants would eat into it so I placed it on gravel to avoid direct contact with dirt. The top is a piece of hardi backer board. After scribing it to make it look like blocks I gave it a good coat of latex paint then used various other shades to make it look more real. Last year the bridge celebrated it’s 10 year anniversary. I never expected it to last so long but it is still solid.
Here it is just before it was installed.

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#6

I have bridge abutments that have been out at least 8 years, one set in full sun the other in total shade no difference in weathering.

I primed them with exterior white latex then over sprayed them with various rattle can colors. I know people say you can’t do that but it seems to work fine.

This wall behind Fields Landing has only been out a couple of years now. It was brushed with a gray exterior latex then sprayed with a couple of colors of stone texture paint. No problems.

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#7

Thanks guys. This gives me a bit of confidence moving forward. I may have a pile of scrap foam after the 2nd week of July. Our church is doing our VBS program and I believe one of the suggestions for decorating is to use rigid foam for animal cut outs etc.

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#8

The primer protects the foam from the solvents in the spray paint.

I had a bridge pier made from pink foam and painted. It was out for 10 years or more, directly on the dirt, with no issues. I think I found it while packing and decided to keep it!

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#9

What glue do you use on foam?

#10

I have had good luck with Titebond III… It is mostly waterproof and does not expand like gorilla glue. It will take paint pretty good but best to keep it off the exterior surfaces.

#11

Yea, Titebond III is all I use for glue on foam board. I also use tooth picks and/or drywall screws to secure the joints.

#12

You can also use just plain old exterior caulk for an adhesive.

I have heard it works pretty good.

#13

We would second that. We also reinforce joints by sticking toothpicks into the foam and pressing the pieces together. It holds things in places as the TiteBond III sets.

Eric

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#14

This works well for sticking non-porous material to the foam. We found gutter flashing glue was the only thing that held metal to foam, though.

Eric

#15

I made a mockup of a large mine structure years ago, and used panel adhesive (though I’m sure TB is just as good). A big help was coarse-thread drywall screws, which held everything without clamping.

With TB glue + DW screws, especially if you put glue on the screws, there’s no way that joint’s coming apart except for destroying it.

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#16

Good to know about the Titebond and screws.

I’m thinking about using the foam as a base for roadway as well. Lay it flat then skim coat it with something (making sure to add the appropriate slope).

#17

On Facebook a while ago I was following Chris Walas efforts to build an outside backdrop out of 2 inch pink or blue rigid insulation foam. He shaped it to size and desired form then coated it with a sandy stucco that was then latex painted. The results were really nice and it’s apparently still in place today

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#18

FWIW Craig, here’s my old model.

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A word of advice: don’t bother with window & door openings in foam!!

Except for those, all else was a piece of cake.

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#19

Why Cliff?
…and for 20 characters…

#20

Probably because they are a pain to cut out and don’t really add anything to a mock-up.

What’s the consensus on what thickness foam? 1.5" or 2"? I’m guessing the 1" stuff is just a tad to small?