Working with foam board
I was recently asked the following question on one of the mailing lists to which I subscribe:
> I need some info on what I need to cut foam. What's the best tool for
> this, and where do I get it?
This led to a long and rambling answer about tools and techniques I've developed over time, working with one inch and thicker foam board insulation as both the base board and the main scenery component for model railroad construction. This is (I hope!) a bit more refined response, going into a little more detail and including some photos. (Well, I'll add the photos of the tools soon - running out of time right now!)
Anyway, into the breach...
I've been doing a LOT of foam construction lately... both on N-Track and BendTrack modules, and on my new permanent layout.
Some of the tools I use, and their applications:
For long, straight cuts down the middle of a piece (for instance, cutting a 4x8 foot piece into two 2x8 foot pieces) I use a fine hacksaw blade, 24-32 teeth per inch and about 10-12 inches long. Not a hacksaw, JUST the blade. Hold it to cut on the draw rather than the push. Don't try to work it too fast. It'll make SOME "foam dust", but it isn't excessive. Keep a shop vac handy for periodic cleanup as you go... and put a bag INSIDE the shop vac to make cleaning IT out easier. (Don't ask...) You can wrap some duct tape around one end of the blade to make it a little easier on your hand (though if it feels like it's cutting your hand, you're holding it too tight) and remind you which end to hold. Why shouldn't you use a knife? Foam is VERY hard on a blade, and they dull quickly. Single edge razor blades aren't _quite_ long enough to cut one inch thick foam, and utility knives are both too short AND too thick, which gives too much resistance when cutting.
For _small_ shapes, the hot wire cutter from Woodland Scenics works well and leaves NO foam dust. Very easy to clean up after. If money is no object, you CAN build a LARGE hot wire foam cutter for large shapes yourself (the nichrome wire should be available anywhere that supplies the RC Airplane hobby), but it's not generally worth the time and effort - we're not making wing cores for RC planes. IMHO, the cheap battery powered cutters from the craft stores are a waste of money (too small and constantly replacing batteries), and the "hot knife" unit you see advertised in the hobby magazines is awfully expensive for what it does... though it DOES use heavier wire that will hold a shape - you can cut roadbed and ditches in a single pass.
For forming hills and such, use a small Surform tool (they look like a cheese grater). It makes a LOT of foam dust, so keep that vac handy! Sometimes I'll even do the shaping with one hand with the vac running, hose in the other. Get the Surform tools from your hardware store.
Cut roadside or trackside ditches with a large round or V shaped stone (or a sanding drum held at an angle) in a Dremel, guiding off the roadbed.
For sedimentary rock, use a wire brush in the foam - fast and simple. For igneous rock, a square-tipped Xacto chisel blade (I don't recall the number) works well. Push in and twist, snapping out chunks.
(I'm not using ANY plaster anymore - just shaping the rock right into the foam.)
To smooth or build up surfaces, use lightweight spackling from Lowes or Home Depot. (For example, DAP Gallon Fast 'N Final Lightweight Spackling, Item #: 41404 on the lowes.com web site.) It's the same thing Woodland Scenics sells in quart containers at four times the price. I buy a gallon at a time.
With the foamboard, I use LOW TEMPERATURE hot glue to assemble the pieces. Keep the size of the pieces manageable so the glue doesn't harden before you get it all on and have a chance to press it into place. I also use the hot glue gun for laying roadbed... it goes FAST!
Be sure to peel the plastic vapor barrier off the foam before putting it down or assembling pieces. It can be peeled off the entire 4x8 sheet if you start in a corner. If you don't peel it, you'll get very noticeable join lines in the finished scenery that are difficult to eliminate.
I don't trust glue or adhesives to attach the foam to the framework. I had the top of one of my first BendTrack modules (Foam attached to the wood frame only with adhesive) come off! I use 1 1/2" deck screws (into wood) or self-drilling sheet metal screws (into steel studs) to attach 1" foam. Put the screw through a 1 inch or larger fender washer before putting it through the foam into the frame. Pull the screw down tightly enough that it pulls the washer into the foam about 1/4", and fill the hole with the lightweight spackling laid on with a putty knife.
Some folks tout construction adhesives like "Liquid Nails For Projects" for working with foam. Be very careful with such stuff. Regular construction adhesives will eat the foam! Be SURE the product you get is "foam safe".
I don't like adhesives for several reasons. I don't trust them (see above) and they take too long to dry to where you can work with the material. Some, like Elmer's glue, are foam safe... but can literally take MONTHS to dry in the middle of a large area. My build time is limited, so I'd rather assemble the parts with the hot melt glue, wait a moment or two, then go to work shaping the scenery. The hot glue gun makes my use of available time MUCH more efficient!
Here's a sample of rock work done directly into foam:
The strata were done with a wire brush and nylon cone brush in a Dremel tool. The result was painted with acrylic crafter's paints, starting with a thinned black and then drybrushing two or three progressively lighter colors over it, ending with a very light drybrushing of white.
The water is the Woodland Scenics "Realistic Water" and "Water Effects". A word of warning: If you use this over foam you MUST completely seal the surface of the foam (Spackling works well!). It WILL bubble out on you, making your beautifully finished water look like a bubble bath, and it might not show up for a couple of weeks!
