A few newbie questions
Hi I am new to the forum and would like to know people opinion on the best size and thickness of blocks to use for a 25 feet dome. Also what size form for making the blocks at this thickness. I will be unsing the full bag of cement and making around 45 gallons at a time. Also I am adjusting to us gallons as everything on here is in us gallons. I am from the UK but I live in Cambodia and I am in the planning and buying equipment stage for my dome project.
@Joeboy, Welcome to the community of aircrete pioneers.
At the Domegaia workshops, blocks are made about 3.5 inches thick.
Here are some decent posts on the topic: Search: Brick size.
Here's another good post, showing a video of a dome about 25': Dome Layout.
3.5 inches thick is probably the minimum thickness for the structural integrity of a dome that size. The other dimensions can vary quite a bit. The smaller your blocks are the more work in cutting and setting (it adds up). The larger they are the more angular your dome will be. Something around 9 to 12 inches on either or both sides is a good starting point. A factor in determining block size is your form. Most folks lay some 2x4s on the ground and screw them together to make a slab form. 45 gallons equals 6 cubic feet, which will fill 18 square feet at 4" deep, or 24 square feet at 3" deep, or 21 square feet at 3.5" deep.
OK thats sounds good I kept going from 4 inch to 6 inch and back again in my thinking. 4 inch block is good by the sounds of it. It's very hot here all year round so insulation from cold is not an issue. It will save me a lot of cement doing it in 4 inch of course. I will go with a 3 feet x 6 foot x 4 inch form then I think that's about right. Also I am concerned about the form leaking around the joint at the bottom to the plastic any tips on this?
@joeboy Sounds like you're on the right track. One method is to allow the plastic to lap over the sides a few inches so that it turns up and creates a wall as you pour in the aircrete. Cut open trash bags work well especially for a 3' wide form. Does that make sense?
Yes sounds like a good plan. Also I may use the 3 foot blocks for the arch forms and half them for the dome build.
Your 25' dome will weigh 51,045 pounds soaking wet. A 6 inch thick block will be holding 8.85 pounds per square inch not accounting for the arch taking some load. No problem for aircrete.
At 4" thick:
Dome wet weight: 39489.5
Pounds/square inch: 10.33
My blocks tested over 167 psi before falure at 30 days. My scale would not go any higher so I don't know what the actual strength was.
I'm really not sure what the strength is at 24-48 hours, but you could test one.
I would say the secondary consideration for thickness is insulation value. You want to design an energy efficient house. That can be achieved with block thickness alone or with added interior insulation.
3 foot blocks for the arch forms and half them for the dome build
Right on. Totally.
@handydan What is your recipe? We have not been able to make successful aircrete yet and have tried many things form seventh generation to Sodium Lauryl Sulfate with sugar and gluten to try and make the bubbles last longer..... I would love to hear from you since it sounds like you have been successful in making aircrete. Thanks in advance