I don't know but if I was doing a raised bed with the weight of the soil and all I would run rebar myself for added strength as it would be a lot cheaper and probably add a little more portland, you would hate to do all that work then have it crack "assuming there large raised beds".

I also would strongly consider just covering the cinder block, it would be quicker and just as cost effective/you wouldn't know the difference/would add structural support. I am no hypertufa expert, just know some things about concrete. Mabye the hypertufa experts can chime in.

18'X12"x4" ?
What is this: 18' long X 12" wide X 4" high?
I am in the same boat, but I want 8 feet Long X 4feet wide X 18 inches high. I am not sure if I should cover cinder blocks, but I need the height for carrots & asparagus. Rebar sounds good to me.

What would be the benift of making the hypertufa blocks?
Do you want them to be more natual looking - like rocks, do you think they will be cheaper? Do you have an idea about how lagre one would be. I think that it will work, if you have the time to mix and put into a mold. Mutlple molds would be the best appoach -
I think it may be harder to cover a cinder block, with tufa - you could only do one or two sides at a time.

Mike

Here is a link that might be useful: Garden Design Ideas

OK, the block would be 18 inches long, 12 inches high and 4 inches deep. It would take 16 blocks to make a long bed about 9 feet by 3 ft. I would connect them by pvc inserted into 2 holes on each side. I want it to look natural. Wood erodes, poured concrete too heavy and permanent. don't think i would need rebar as i don't believe it would need it??? yes looking into a mold and just taking my time... i am big on esthetics.

Have you worked with Hypertufa? Why do you think that Hypertufa will look natural? Certain Hypertufa recipes erode. You don't need pvc dowels just build your molds so the pieces will "key" together. You mention the weight of concrete, wait until you've lifted a few of your blocks. Post some pics showing your progress. Good luck!

have not worked with hypertufa but i love the idea; the keying is an idea. what recipes erode, what are good recipes...regarding pvc ... i just thought putting dowel holes a couple inches into the sides of the molds and using short pvc dowels to hold them in place was an easy solution? wont be starting project for a yr so am trying to as much info as possible. Thanks!!

You might want to try a little test project first, to get the general feel of the right consistency of the mix, whether you use hypertufa, papercrete, or some hybrid. Maybe try the recipe in " Papercrete Project photo " from about 2006 in this Forum. I have drawn and redrawn several projects, with sometimes big improvements just by the creative thought process, but also after "slapping some mud". It IS more fun to play with it, and you can make some small test blocks to see what works for you. It's much more like making French toast than making croissants!