I used the blue foam {same thing} one inch over open grid.
1} any FOAM SAFE adhesive material will work. I believe I actually used Gorrilla glue {if nto it was regualr white glue} I used caulk to secure track to the foam.
2} I did NOT use screws. Instead I used sandwich sized ziplock bags filled with play sand as weights {a LOT of them} to hold down the foam where adhesived while it cured.
3} Spackle will work, even a little more foam Safe caulk could work, though I had no problems scenicking over gaps without using a filler. perhaps my gaps were not as wide as your? Just sand them flat.
What do you have supporting your 1/2" foam sheet? That is pretty thin stuff and I am not sure how strong it will be unless well supported. I know that 2" foam does not sag when using 24" centers. Wome folks use 1", but have never seen a discussion on support spacing. I have used some 1/2", but always on top of something else.
Just went down and took a 2’x4’ piece and set it on 12" centers. Didn’t take much pressure to get it to sag. Granted it was not attached anywhere. Be sure you have enough support.
Why just 1/2" foamboard? I don’t know if I would even bother to go to all that trouble for 1/2" foamboard. There’s not much scenicing you can do with 1/2" foam that I know of. I would go with 2" foamboard, there’s a lot more you can do with it. I attached my 2" foam board to 1/2" plywood with drywall screws and large 1" washers. I then went back and spackled the seams and the dimples that the screws and washers made in the foamboard. Recently I took apart a major part of my layout to make some changes and the foamboard was easy to remove, just by locating the srews and unscrewing it. I don’t know how many others screw down their foam board, but it works for me.
Flynn somewhere down the line you will very likely seriously regret using half-inch foam…it is too flimsy to keep scenery and other attached items from dislodging and/or breaking into pieces the first time any weight is put on the foam. I wouldn’t use anything less than rigid two-inch foam.
Since I never climb on it, or lean on it, and don’t intend to, I don’t have a problem. It holds well and doesn’t deflect any at all. On top of it, I have also used WS inclines to vary the “terrain height”. Perhaps that also strengthens it. Those also allow for shallow gully, stream and pond, nothing deep is needed to appear that way.
I agree 1/2 inch may be flimsy, but that isn’t what he asked.
I would also recommend thicker foam. I use 2-inch. It is very stiff, and lets me dig into it for ditches and ponds.
Weight, well distributed, is also what you want to hold the foam in place while your adhesive sets. Foam just doesn’t hold screws. One of us has a fossilized dinosaur bone he uses to weigh down his foam. I use my wife’s copy of a Martha Stuart book - hardcover and quite heavy. Remember that foam will crush, so you need to distribute the weight evenly.
Sorry guys should of gave more details. I have 1/2 in pink foam on 1/2inch plywood on open grid. I’m modeling central Illinois (flatter than flat) industrial/warehouse district so other than a few shallow ditches no need for much scenery. I wanted to use foam board for sound absorption/stability. I also will have some blue point or bull frog switches so I didn’t want the foam to be to thick. Since I didn’t “need” a ton of foam thats why I went with 1/2 inch. Basically same purpose and thickness as homasote just cheaper and easier to cut/install.
Certainly better on plywood for strength, but as mentioned above there is not much below track level you are going to be able to do.
Another thing with the 1/2" is to remember to peel off the plastic film. It helps protect the foam in transit, but if you leave it on the adhesive will stick to the film, the film will peel off the foam and thus the foam will not be attached as you expected.
LION used 1/2 Celotex sheets over an open 16" grid. GO WITH THE 16" grid not a 12" grid. You will use less material AND most importantly, will be able to fit a power drill and bit in between the members because you will always want to make holes in them.
The 1/2" Celotex sheets [no longer available–fire codes, you know] have no trouble making this span, and are both lighter and more rigid, and much easier to cut than Homasote.
That being said, and having used up all 10 sheets that somebody had so nicely salvaged from some building torn down in the distant past, him went with 1" pink foam (Recommended by a Panther, so it must be ok, yes?) This element of the layout is rather tall from the floor, and so it would not be possible to lean on it even for a LION standing on a ladder. No matter, the LION thinks that this will work for ewe (he said sheepishly) .
Use Siliconized Latex for attaching. LION has any number of steel shapes liberated from the metal shop to hold thing in place while adhesives dry. If you have a metal shop filled with surplus steel shapes then you will have no need to find other weights. Books are a good substitute if you do not want to use bags of sand.
LION uses pure silicone caulk for other things, such as the attaching of Tortoise machines, and for the mounting of paper background or signs. Latex products will damage paper, and are not occlusive or aggressive enough to hold Tortoise machines while curing.
I would go with 2" foam. You could still use the 1/2 foam later. If you want anything below grade, the 1/2" will not really be effective. Well, not as effictive as I would like.
I suspect everyone is going to jump all over me for this, and maybe it has nothing to do with your original question, but here’s something to consider:
In actually experimenting with sound absorption/deadening/abatement, whatever you want to call it, I discovered that latex caulking the foam insulation to the BOTTOM of the plywood, UNDERNEATH the layout benchwork was the most effective sound deadening of all the various methods I tried out.
This was an observed, not a theoretical, experiment on my part and an observed (audible ! ) result.
Okay, you can all start trashing me out now, but it could be that once sound is transmitted through the tracks and the ballast and the layout surface, which in the case of plywood is like a drum, it gets deadened at that point (rather than travelling through the insulation into the “drum”).
Theoretically speaking, you probably wouldn’t want to screw the insulation to the underside of the plywood because the screws would transmit the sound from the layout surface and through the insulation, thereby defeating the sound deadening purpose of the insulation.