Tuesday, April 15, 2008

urbanite construction and raised beds

Our backyard used to be a parking lot, and there's still a lot of concrete back there. At a work party recently, we busted up another 10'x10' square. With that busted concrete, I built a retaining wall for the raised beds that also serves as a bench for the social area around the swing. I was really surprised how well it turned out.

urbanite wall at Mariposa Grove

I learned a few things while doing this, which hopefully I, or you, can use in future urbanite construction.

My wall is rather narrow, which is preferable for a host of reasons - aesthetic, space conserving - but it's only put together with dirt, no mortar or cob or nothin'. So while it feels really stable right now, I'm not sure about its longevity.

Besides just making it thicker, or using cob under the top layer, I think it could be made to be sturdier if I hadn't made it flat at each level. Here's an illustration of what I mean:
my thoughts on future urbanite walls with no mortar
If I was to do it again, I would make each level slant in toward the dirt, and only make the top pieces level. Or, if it was a stand-alone wall, I would make it lean in on itself, each cross section looking like a very shallow "V." Basically, as Kevin (one of my Grovers) pointed out, the cross section would be a modified (filled in) arch. This way it would better resist any lateral pressures.

Okay. So I mentioned that we made raised beds, but I didn't show any pictures yet. We used a basket-weaving technique with a lot of the trimmings from trees in our yard and on the street. Here's a couple of pictures.

a closeup of the woven bed made of plum branches
a close up.
and now, an overhead:
top down on the raised beds.

Bob van de Walle, one of the Grovers, keeps a blog where he also mentions the raised beds. His pics might give you another idea of what they look like (tho his are during construction).

He also mentions the sprouting of some of the stakes that we used to build the raised beds. This is a concern, but we're monitoring it to make sure it doesn't get out of hand.


Anonymous molfamily said...

Beautiful garden pictures. I volunteer at a school garden that has themes for their raised beds that I thought your readers might find fun. The name of the school garden is Woodward Gardens and it is located in Tigard, Oregon. http://www.betterlivingshow.org/WoodwardGardensraisedbeds.asp

7:35 PM  
Blogger aaron said...

Just an update on the wall construction:

Six months in, and the wall/bench has received normal use and has not needed any maintenance. I extended it slightly when we installed soaker hoses and replanted the bed. I still think the filled in arch construction is a good idea, but apparently the flat construction is fairly sturdy on its own.

3:20 PM  
Anonymous Anonymous said...

Israel asks:
I had the idea of replacing a rotting pressure treated retaining wall with urbanite. My wall is 30 foot long and betweeen 30 inches- 36 inches in height. Is that too high for dry lay urbanite? Do you have any aesthetic tips for this project? (Your wall looks nice.

2:00 PM  
Blogger aaron said...

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2:29 PM  
Blogger aaron said...

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2:41 PM  
Blogger aaron said...

My wall is probably about 18" high, 9" to 1 ft. wide, and the extended wall (not pictured) is a curved 8' length.

I think a 36" high retaining wall could be made out of urbanite, but would probably need to be quite a bit thicker (or use larger pieces than I had) to feel sturdy.

If I was building a higher retaining wall, I'd probably use the second method from the drawing above - laying the pieces so that they all slant toward the dirt. I'd also taper it slightly toward the top so that the wall basically leans against the dirt.

I think that how thick you end up building the wall, how much taper to the top, etc., really depends on what your source material is like. The concrete we broke up in the yard was poured in a pretty sloppy way, so the thicknesses varied considerably. This complicated the wall construction, so I really had to take my time in fitting it together like a jigsaw puzzle. I think that contributed to its aesthetic appearance (making it irregular in a nice way), but also made it take a lot longer.

I bet most urbanite is probably a bit more uniform than what we had.

Another piece of advice, get a hand-sledge that you can use to shape your urbanite as you work. Sometimes you'll want a piece of a certain size, and a sledge is handy for that.

As for aesthetic advice, well, just think about how a piece will look before you place it. I dug out the ground a few inches down before placing the first stones, and that helped me decide on a pleasing curving front before I started building.

As I worked through our pile, I picked out pieces that would look nice for the top of the bench. So I was sort of laying out the top in parallel as I built the foundation.

I also tried to make the front face relatively flat, by selecting good pieces, and using the sledge. The back of the wall just faces dirt, so I put small chips of urbanite in there. You can just throw the ugly chunks back there as fill/structural support. So the back is very rough but structurally fine, and nobody can see it anyway.

The most difficult part (given our very wonky thicknesses) was getting the top to be flat. I had to adjust the layer underneath the top layer quite a bit to get the oddly formed pieces to create a top layer where all the pieces were flush. Liberal use of high-clay-content dirt, as well as urbanite chips really helped at that point.

2:58 PM  

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