We've all seen it. At our friend's house or the
FLGS. Foam hills with chips, cracking paint and broken edges. Sure it's not the end of the world, but having white, pink or blue peaking through your earthy-colored terrain can really mar an otherwise beautiful table of scenery.
Beaded styrofoam and small cell insulation foam are great for terrain because of their easy shapability and light weight, but the material it'self -even strong insulation foam- is prone to breakage.
But what can you do about it? Following are a few suggestions for building tough hills. Note that these hills will stil chip if dropped, and if stored, it's probably good to put a bit of paper between them, but they should be considerably stronger than most hills.
Important tools and supplies have been underlined
1) A base. This step is often left out, but it's among the most essential. Lack of a base is one of the primary reasons that hills chip and
de-flock at the edges. A base protects the fragile lower edge of the foam. Any sort of thin chipboard will do. It's cheap and can be easily cut with a
coping saw. Check the IKEA scratch and dent section for sheets of the stuff for under a buck. Most board of any kind will have a touch of curve to it, just make sure that you use it so it curves down so that the edges meet the table. Here's an example of a coping saw.

It's like a heavy duty jewlers saw that cuts through chipboard like butter. The blade can be rotated to allow you to cut complex shapes and curves.
2) Attaching to the base: White glue is ok, but I prefer
tile adhesive/grout. It's another substance that is available quite cheaply at your local hardware store. It will stick the styro to the board, and you can use it to fill in any gaps between the board and the edge of the Hill that might result from a warped board or foam. Also it has a nice texture to it. For a smoother texture choose "unsanded" grout for a rougher texture chose "sanded" grout.
3) Cover the hill with a putty/plaster. Especially with insulation foam folks often skip this step. Back in the day, Wood filler was widely considered to be the standard for this. However, consider
latex spackle instead. It's as cheap as wood filler, but it has a bit of flex to it. Despite the desire to have a hard-as-nails covering, a protective covering with a bit of flex is better for materiels like foam which have a bit of give to them. Covering the hill with a latex spackle
4) Paint. Don't use model paint. It's a waste of expensive paint and it doesn't cover as thickly. Head to your local home improvement store and buy a gallon of the cheapest
house paint they have and have them match a color you want or just pick one off the wall. Remember that you can use any color with any brand of paint. Just because you like a color from the premium wall, you can still have it mixed with the cheap store brand paint. My last trip to Menards they mixed me a gallon of brown for 9 bucks!
Even the cheapest paint will cover thicker than model paint. Be sure to completely cover every bit of the hill. Do a second coat if necessary. No pinholes at all.
5) Dip the hill. This is an optional step, but it's kind of my secret weapon for durable hills. Don't dip the hill in a bucket of Quickshade. Buy some
Minwax Polyshades and brush it all over. Make sure you've completely covered the hill in paint, as the quickshade can melt the styro a touch. If there is a touch of leakage, don't worry it won't make much difference, and sometimes even makes a nice bit of surface texture. As well as being a nice wash that will darken the crevases of any hill or cliff, applying polyshade essentially creates a protective layer of plastic over the hill. It's strong, and being plastic, it's not brittle and has a bit of flex, like the latex paint and the latex spackle. I recommend the "Antique Walnut" color as it is very close to ArmyPainter's Quickshade Strong Tone.
6) Matte Spray. Finish the hill with a nice light dusting of matte spray. The stuff from the hardware is just fine. It will take away the shine from the dip, seal in your drybrush (you should drybrush the texure after the "dip") and provide a final protective coat to the hill.
Here are a few hills/cliffs I recently made with these techniques.
Nothing groundbreaking, but they are quite sturdy.
The exact process was as follows:
1) Cut and glue Styrofoam to shape with foam cutter and knife. These hills are made with the cheap white beaded styrofoam often used for packaging.
2) Cover with Latex filler (these are covered partly latex filler and part of some wood filler I had left over, but latex all around is better)
3) Cut chipboard base with coping saw and attach to hills and cover join with Tile Adhesive/Grout.
4) Glue kitty litter to edges of cliffs .
5) Paint with brown Housepaint.
6) Paint ("dip") with Minwax Polyshades Antique Walnut.
7) Spray with rustoelum texture paint spray. Heavy on the flat tops and lightly (to give the upcoming drybrush some texture) on the sides
6) Drybrush with a light tan color, being a bit heavier on the cliff edges and anywhere the angle of the hill changes.
7) A light dusting of matte spray.
It sounds like alot, but the individual steps are quite quick. Far longer is the amount of time it takes for the paint or glue to dry between steps. I am lucky enough to have a porch where I could leave the hills and come back to complete the steps at my leisure.
It would be much faster to just cut some insulation foam paint it and drybrush it, but I think it's worthwhile to spend the extra time to to make some hills that will better stand up to the rigors of the gaming table.