Need help with block angles

  • I plan to build a 1500 sq ft dome(s) and what I would like to do is make forms for each row of blocks as the build goes up. I need the angles to build the forms and not have to worry about cutting each block. Does anyone have the math or geometrical formulas for a 20ft dome? Since I will building more than 1 dome I think this would help in speeding up the build process. Any thoughts on this? I can understand any level of math and not All you folks have a good day.

  • Major Contributor

    To me the effort of casting each block individually would be more time consuming than trimming each to fit perfectly.. Each block should be a trapezoid also, the method for finding amount of angle for the trapezoid is beyond me lol. Here’s what your looking for :)


    A=block angle
    C= circumference
    W= dimension of block perpendicular to angle in question, don’t forget to account for mortar width. This dimension should be at the point of intersection of C (if your using the outside dimension for C the widest point is W, inside the thinnest point is W)

    Nothing has to be an exact fit but this should get you very close!
    Good luck :)

  • Thanks kimo, the angle of the trapezoid is what I am looking for. My plan is to build a form which will make about 50 blocks at a time but I need the angles first in order to build the forms. I could prolly get away with building a form for every other row because there is not much variance from one row to the next. Maybe every other row but that is yet to be determined. I want to start a strait up block on first row to make a 1/2 sphere exactly, So I will have to have my swivel almost or at ground level. I am going to do some math and some dry experiments with the swivel pole, angle square ad a laser level and see what I come up with. I will keep you posted. Sorry for over analyzing this but I am an Engineer, it's what we do. lol thanks again my friend.

  • @kimo said in Need help with block angles:


    It would be nice if you can record somebody trimming some blocks to see how that process goes. Thanks for all your help Kimo!

  • Major Contributor

    I forgot to mention but sounds like you know, all angles will change as you develop distance from the equator
    I had the same mindset when I was planning my project. I have a background in engineering and almost thought my way into not starting the project. I eventually just went for it and I tried cast in place, preformed blocks, then just resigned to pouring a slab and cutting blocks out of it.. Cast in place is problematic because the form has to almost be water tight to work.
    The method I was using for precasting led to more work in removing the blocks than it was worth. Im very cheap and decided to cast multiple blocks with adjacent sides, one block would come out just fine, the next would crack and be rubbish.. I’m certain there is a much better way of precasting than I came up with my cheap method lol.

    If one of my kids is around this weekend I will have them take a quick video of the block trimming process.. It will show what a max budget of $20 a week looks like after a couple months :)

  • I want to try to figure something out, it is just me and the wife doing the work, and we are both hitting 60 so we need to work smarter not harder, Im not going to spare no expense on the forms and if this works out OK i will surely share it with everyone. Got to get my water well drilled first but just planning ahead. I have to build a 1500ft2 due to HOA laws, they are pretty laxed and don't even need a building permit. But i will on the septic. Anyway so I digress.. I will keep all interested informed.

  • Major Contributor

    Your 1500 Sq ft minumum requirement might be for the minimum of the whole house, including garage. You could build 2 or 3 joined domes that fullfill the 1500 requirement. I am looking for land know and got into that with the covenants of some of them. Good luck.

  • Major Contributor

    @algares here's a quick video of me trimming a block, sorry about the moldy lens and my misspeaking and mumbling lol..

    Youtube Video

  • @kimo thank you so much! you are amazing!

  • @Joe I will have to build 5 domes (20ft dia) that would be just over 314 ft2 ea. HOA's do not count garage area as living area.

  • Major Contributor

    @ach2oman Check your covenants. An enclosed garage attached to the building should be counted as living area. At least it does where I live.

  • Major Contributor

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