After building our frames, it's time to add the foam. I use 1/2" pink insulation foam. You might remember, I used 5/8" batten to build the frame... carpenters will know that wood is never the actual size listed - it's always slightly smaller. It matches up pretty close to the 1/2" foam. This stuff is sandwiched between two thin plastic films that you want to remove. It makes cutting much easier and I prefer that the glue I'm going to be using later adheres to the foam and not the plastic.
I carefully cut the foam so it fits tightly into my frame and then I drag out my plan and a marker. The first three boards I am going to make include tho river boards and one plain board. Using the precut edges as a guide, I draw out my river, including marking the 45-degree angles on the edges. You don't have to get this step perfect except at the edges where it meets the frame. If your river seems to have wandered off course, just redraw the offending part. We're going to cover all of this up later.
After I was satisfied with my drawing, I cut the river out of the board with a craft knife and angled the blade to produce a beveled edge. The t-square had nothing to do with this step. It was apparently upset that I left it out of the earlier stage when I trimmed the board to fit the frame and chose to leap into this shot. If you would prefer your river to have steep banks, you can leave them this way and skip down to the part where we glue them down. Keep the cut out scraps because we are going to use them on a later board.
The tools of the trade. Starting on the left, we have an x-acto knife, next a craft knife (which I used to cut the initial river shape), then a serrated knife, and finally a hot wire cutter. The hot wire cutter uses electricity to heat up a thin strand of metal wire that cuts through foam like butter. This particular model has an on/off switch on the handle which makes it safer to use because the wire cools almost instantly when you trigger it off.
The next step I want to do is give my riverbanks a more gentle slope (everywhere except near the edges - we want those to stay 45-degrees to match up with the battens). The serrated knife with it's long blade is ideal for this... except for the mess it makes! The hot wire cutter does a much cleaner job and it's the tool I use. I just thought I'd show the other option in case you don't have a hot wire cutter. They are kind of expensive and the knife will do an admirable job, but make sure you have a vacuum handy! Both of these tools should be used in a well ventilated room - you don't want to breathe in too much of this stuff. The knife puts particles everywhere while the hot wire cutter creates fumes as you carve through the foam.
Use a model to check the grade of your slopes to make sure they will be able to stand with out tipping over!
Finally, I use an x-acto knife to trim any remaining rough spots. If you really want to go to town on this, you can sand the foam with fine sand paper to get rid of any sharp edges (like the ridgeline behind the model above). This something again you'll want to do in a well ventilated area. I intend to take my boards outside and sand off the rough spots, but I skipped the step for this article because of the photography. You can always sand up the rough parts after you glue them down.
Speaking of gluing them down... I use woodglue, but I'm sure a dozen other adhesives would work just as well. You don't have to cover the entire surface. The wooden frame will protect the outside edges and for our river boards, we are going to be gluing some texture along the banks that will add more stability to the exposed edges. The glue will expand as you push it down against the wood.
Weight the foam down with books and leave them to dry overnight. In the next post, these things will start to look more like terrain and less like lumber!