I was reading one of the threads on constructing with pink/blue foam and a poster commented about foam’s not holding screws. An idea occured to me and because I don’t model foam (wood is good) I thought I would lay it on you foam guys. Could you use the type of drywall anchor that resembles a large white screw with short, fat, deep threads? If you coated it with adhesive and screwed it in to the foam, it might have enough hold for skinny screws, like what you’d use to mount a Tortoise or other switch machine. If I modeled with foam I’d sure try it.
Or a little shot of Liquid Nails. Roll the screw in it and stick it in the foam. Holds super well. Just be sure to put it exactly where you want it. Liquid Nails does not release very well. Jay
I’m trying to figure out why you would want to screw into the foam in the first palce, as a primary fastener. Cheap latex adhesive caulk fastens foam quite securely to most other materials, and likewise fastens other materials to foam. Yellow glue also works for attaching foam to wood.
I use foam extensively, but have yet to find a reason to use screws with it. I even discovered that a dab of caulk will fasten a Tortoise to the bottom of the foam - securely enough that when I attempted to remove it I was worried that the Tortoise would break before the caulk joint.
Lou, that is a technique I discovered four years ago when I made a small diorama to mount my HO Lionel Challenger when I was between layouts. I covered a two foot length of 1 X 6 with 1" foam and screwed the foam core board backdrop element to the side of the extruded foam topping with two good sized plastic wall anchors. Into the wall anchor I inserted a drywall screw. I didn’t feel the need to also glue the wall anchor.
And alternative would be to dig out a volume in the foam, insert a wooden block filler covered on the sides and bottom with a suitable adhesive, and then use the wood blocking for mounting things with conventional methods.
I think you’ll find usng drywall anchors in extruded foam works well, provided you don’t subject it to a lot of abuse.
As my railroad is outside, I had one area where the foam lifted from the plywood base. I anchored it with 1/4-inch lag screws with a washer under the head to avoid over torqueing.