Posted on 01/07/2011 8:49:19 AM PST by RadiationRomeo
I am thinking about creating raised beds for my garden using boards made of glass fiber reinforced concrete. I've done the math and a board 12 foot long, 1 foot high and half inch thick would weigh about 60 pounds. I used a half inch thickness because this stuff is extremely strong. I would use tabs and slots in the side and end boards to attach them together without nails.
I know this is much more expensive than wood but I like the look much better. Also, a very important constraint is I need raised beds that will eventually be 3 feet tall so when I get older I can still garden. I'll just add more layers and tie them together using the same slot and tab method. Having something that will last forever is important to me.
I would construct the forms and do all the labor myself. Is this a overly crazy idea?
/johnny
Can you use regular woodworking tools to work the stuff? Skill saw, hand saw, nails/screws....Sounds like this stuff will be difficult and heavy to work.
If you are thinking about using them when older, then make them wide enough to sit on without discomfort. and strong enough to support being sat upon and stepped on.
Thank about putting a stain in the concrete when you mix it so it can be a better cosmetic for for your yard.
Plan ahead for what goes in the ‘boxes’ you build. Can you plant enough rows or specimens ALONG WITH ROOM TO STEP between specimens/rows in the size you specify. also space them far enough apart that you can maneuver your wheelbarrow between the boxes.
Draw a grid and make it real in your mind first.
Just some ideas.
This combination will grow great tomatoes. Paint the concret black and they will become a solar collector as well as a thermal storeage medium.
Instead of waiting for the beds to be too low to stoop for, why not build a four foot tall supporting structure and have the beds up off the ground in the first place ?
A nursery near Jeff City (north of here) does all its starter seedlings this way and saves on back pain.
If you’re talking about Hardie Plank or similary, that stuff’s pretty flexible, so my concern would be the outward pressure from the dirt deforming or causing failure of the retaining walls. I kind of like the idea, though - much cheaper than building a preformed stone or brick retaining wall.
Would love to hear how it turns out.
Colonel, USAFR
Also build in some holes so you can run ropes and or carriage bolts through them — to move them or secure treated lumber to them for some future purpose - maybe lattice or string bean poles. dunno.
plan ahead.
We have Certainteed’s brand of cement siding on our house. It is hard as a rock and takes a diamond saw to cut.
I am a ‘master’ gardener and I have used wooden beds for a long time. I may even write an e-book on the science of raised bed gardening. I have the bed spacing, crop rotation, etc down to a science.
I think I will be dieing the concrete barn red to maximize the heat reflection/heat absorption.
The concrete material is fairly expensive and I couldn’t afford to make all the beds tall right away. My garden is quite large. Also I would be adding compost over the years to increase the depth gradually.
I understand the beds on legs to get them to a nice heigth right away, but most crops need deeper ground. However, I do this in the passive solar green house for lettuce in the winter.
My biggest fear is that I will actualy need rather thicker boards that will double the cost. The outward pressure of the wet dirt needs to be considered.
To make seating easier I would either use a suitable chair or stick a boards between the beds to sit on. Oh, and the beds will be 4 feet x 12 feet. 3 feet is a nicer width but the material is so expensive that you need to maximize the crop per bed.
If were talking about Hardy Plank, then yes, you can. Although it would be best to use a different blade in your circular saw rather than a standard wood one. At least if you’re going to be cutting a lot.
I once worked with a construction manager, the carpenters were using circulars with the special blade, but then switch to something like powered siscors. But again, they were cutting a lot of plank.
bad news,
A) you concrete “boards” will not span 12’ without bowing and breaking.
B) when you are too old to bend down to garden, you will also be too old to build your beds higher. Build them to the final design height now (about 24” or the tops of plants will be hard to reach)
This stuff is not designed for this. Dirt would blow out these boxes and moisture will deteriorate the board. It’s different than regular concrete. Build your boxes from PT lumber, braced every four feet to prevent blowout. Remember, dirt is tremendously heavy. Keep it in mind when planning.
Look in the paper for people who offer to do concrete work. You may be surprised at how the costs compare, if you just made this out of concrete.
Concrete block salvaged from a build site gone bust should be cheap.
And you can spray the exterior face with a variety of colored concrete stains.
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Cheapest materials to make raised beds out of are discarded tractor tires or 55g plastic barrels (use a reciprocating saw to cut one end off, drill the other end full of holes, sink it into the ground til it’s the right height). The barrels can be procured from car washes, restaurants, or Craigslist for free or cheap.
As with jagusafr, I am imagining that you’re considering using HardiePlank material. This material is meant mostly for siding (vertical) applications, where the plank or sheet ends need to be covered. It is not impermeable.
Also, as an architect and engineer, I can categorically state that HardiePlank is not designed to be a structural-grade material. Keep in mind that in designing horizontal support, accommodation must be made for dead and live loads. In addition, temporary loads must be included in calculation. If you do research on construction websites, they will provide information on “roof-top gardens” which will indicate joist supports required as well as acceptable joist spacing. Also, they will show diagrams of recommended materials to use.
I have seen GLASS FIBER reinforced conrete that is quite thin that was used as an extremely long bench. It was way stronger than it looked. But if necessary I can use another thin board to tie the beds together at the midpoint using the slot method. The tie would be C shaped and just laid in the tabs. It would be replaced with an H shaped tie to connect a second layer.
I have a decade or so before I will be too old to make the beds higher. Not all the beds would be at the same finished height so those tall plants are reachable, and this would impact the crop rotation! oh well.
The two big questions are the general theory and the cost. Like a lot you I am somewhat OCD and a perfectly laid out bed system would be great.
The concrete sounds like too much work, effort and expense to me.
Check out Accoya Wood. It’s expensive but does have a warranty and is a safer alternative to traditional treated lumber.
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