Back in 2008 my backyard course was coming along nicely but I wanted a really big and steep climb of some sort. That is when I was turned on to this thread by a local TXRCRCA guy:
RCC THREAD
After a few failed experiments I went ahead and began construction on Mt. Yamada. The basic idea is to make a frame of some sort and cover it with burlap, grout & mortar. I tossed around the idea of wood frames, chicken wire and even started on a wooden base for something but it didn't turn out well. One day while I was in Walmart I walked by an archery target and a lightbulb went off in my head. After construction a friend pointed out you can usually find free styrofoam on craigslist ... live and learn I guess.
PARTS & SUPPLIES NEEDED
3 Archery targets
4 x 1/4" x 12" dowels (plastic hanges work too)
4-6 yards of burlap
12.5 lbs of mortar
12.5 lbs or sanded grout
3 cans of great stuff expanding foam
4-5 cans of Duplicolor bedliner (AutoZone)
4 cans of paint
Drop cloth
5 gallon bucket
TOOLS
Sawzall with loooong blades
Electric carving knife
1. I started by unwrapping the archery targets and notching them to fit together. The sawzall cuts a lot faster and deeper, but also makes 10 times the mess.
2. Once they fit together, I used the dowels to "pin" the pieces together while using the Great Stuff as a bonding agent. Normal adhesive (and paint) eats the blown foam (archery targets) so I really suggest using the Great Stuff as a glue.
3. Once the main pieces were glued together I went ahead and started shaping the rock. I used some of the cut off pieces to add to the base to help with the climbing.
4. Up next I did some testing with paint. I found that putting on a very light coat of low solvent primer was OK, but if the primer built up at all and got wet it would eat into the foam. Then, because I'm impatient, I went ahead and hit the whole thing with primer just to see what it would look like.
5. At this point I did a little testing and found the rock was going to be quite difficult to climb. Using what I had learned about the paint melting the foam I "burned in" some channels that are my track width to lessen the angles.
6. Once it all dried and was shaped the way I wanted, I started with the grout/mortar mixture. I used a 50/50 ratio of mix (about 5 lbs of each) and added water until it was pancake batter consistency. Next I cut some strips out of the burlap and after soaking them in the mix I laid them on the foam. I tried to make sure the strip was well covered with mix but not excessivly. I started on top and worked my way around to the sides and was pleasantly surprised at how well it stuck to everything. While the top part was drying I did the inside & underside of the tunnel, then worked back out and got a second layer on the top since it will see the most abuse.
7. After that had dried for about 24 hours, I decided to paint the grout with bedliner to help hold it together and seal it. The bedliner then got painted with a few different colors of paint (I'm still working on a good color).
8. Overall I'm very pleased. The top is 35" and it only weighs 56lbs.
