building dome - help!

[timmarhy]

folks i just started building my dome and it's turned into a nightmare. i built the whole thing only to have it collapse.
the refactory mortor i have is sh!thouse and doesn't seem to dry hard or stick to anything. i mixed it 50% with normal cement and sand and that seems to have improved things but i'm still not confident in this lastest arch. the problem is got to the point of putting in the key stone and it only went in about 1/2 way.
now should take out the key stone and cut it some more or will it do it's job here it is?
my other question is, is there a prefered method of pulling out the supports once the mortor is dry?
and finally, just how much mortor should each block need on it? the stuff is setting so fast on the block i can't even pour it down the cracks.
http://i43.tinypic.com/501heq.jpg

[jasoni789]

Re: building dome - help!

Your dome has no dome. It is flat in the middle. Look at basic phyisics of stone masonry, the flatter the arch the stronger the foundations/footings holding the arch have to be. I'm no expert but the shape of the arch you have chosen is not a constant arch(it appears flat in the middle) and the arch needs a bigger arch(or the circumference of a smaller circle to follow). I hope that I have made sense. If not read up on how the stone masons used to build arches in old stone churches and bridges. Once you read about the physics of a stone arch, it should be reasonably easy to build.

[brokencookie]

Re: building dome - help!

Jason is right - your arch is so flat that it has very little chance of succeeding.

[the stuff is setting so fast on the block i can't even pour it down the cracks.

Are you soaking your bricks before mortaring ? It sounds like your bricks are just sucking the water right out of your mortar. This gives you a cold joint which is almost sure to be weak.

Not to rain on your parade, but you probably need to go back to basics. Have you downloaded the free Pompei plans ? They contain a wealth of information and tips that can save you valuable time and effort.

Good Luck
Keep posting and we'll try to help out. The more pictures and information you give us, the better the feedback will be.


Bruce

[wlively]

Re: building dome - help!

Don't mix in regular cement and sand, it is made to use straight.

[Dutchoven]

Re: building dome - help!

Tim
My suggestions are such...
1. move the walls in a bit so that their base rests flat on your floor bricks...there will be a tremendous amount of thrust acting on them even with cladding(which you will need)
2. Hang a chain on a piece of plywood at your desired span and arch height and then attempt to completely enclose that curve in the center of the bricks comprising the arch...that will give you a chance of keeping the flatter arch vault without necessarily compromising stability
3. check out this website about arches vaults and domes Auroville Earth Institute is a research, design and developing agency for vaulted structures, construction of various Vaults, Arches, Domes (VAD).
Good luck and all the best!
Dutch