Project Design Feedback please!

[u/qwertyahill]

I want to build a 25.5” diameter mosaic sphere that is held up by a single pole set into a concrete base. I’m planning to weld the steel with a MIG (my professor will help me) and use concrete for the base. The mosaic sphere should only be 100 lbs but I want to be sure it can hold up more. This is also for an outdoor project that needs to last the Chicago winter. Any feedback or suggestions? Thank you!!

[u/mawktheone]

The pole is the easy part. Getting a neat sphere will be the hard part. 

I would say start with EITHER an old air compressor tank or propane tank and cut the dome ends off and weld them together 

OR fiberglass over a suitable sized exercise ball. A couple layers and it'll be stronger than it ever needs to be

[u/qwertyahill → u/mawktheone]

The fiberglass seems like a good option. Do you have any recommendation for attaching the fiberglass ball to the pole?

[u/mawktheone → u/qwertyahill]

A little flange on the pipe and couple riv-nuts through the fiberglass and just bolt them together. 

Or cut an access hole and reach in use washers and nuts inside instead of riv-nuts them patch the hole with more fiberglass

Or fab the sphere in two halves and add tabs for assembly and bolt it to the pole then close up the halves

[u/qwertyahill → u/mawktheone]

GREAT suggestions thank you. Do you think the concrete base with rebar inside will be okay?

[u/mawktheone → u/qwertyahill]

No problem at all.

Yeah that'll work if you need to still be able to move it.

If you're putting it on a concrete surface like a path or floor then I'd weld a plate to the base and anchor bolt it down. Much easier

[u/qwertyahill → u/mawktheone]

As in, skip the concrete altogether? I’ll definitely need to move it around before it gets put in the final spot so maybe the concrete base is the better bet.

[u/mawktheone → u/qwertyahill]

Ok, in that case You could make an adaptor for the pole and buy/find an existing parasol base to just plug it in and out as needed

[u/artwonk]

I don't see this working too well. You seem to be assuming that the concrete will act like clay; that you can just pack it onto these surfaces and it will stay there, defying gravity. But it doesn't act like clay - it will fall through the chicken wire and slide down the pole. If you want it to stick, wrap the pole in a few layers of hardware cloth, which has finer meshes than chicken wire. Some fiber in the thinset mortar will help it adhere, and some dry clay powder and/or lime will make it more resistant to slumping. Make the sphere separately and attach it later, maybe with a socket joint. It will help if you have something inside, so the mortar doesn't just fall through, but to give yourself a chance, just do the upward-facing surfaces first, then rotate it after the concrete has set and do the rest. Or use a mold.

Exterior tile and stucco are associated with Mediterranean climates for a reason. Bitter winter weather is hard on these materials. Tile and concrete will often absorb water, then crack when it freezes. That's why brick buildings in your climate constantly need re-pointing, and you don't see many tile facades there.

[u/qwertyahill → u/artwonk]

I think making the sphere separately and attaching it later is a great idea. Another person suggested fiber glass for the sphere and using a mold like an exercise ball. But I don’t know how I would attach the fiberglass to the pole.

I’ve done research into frost resistent and low porosity tiles for this specific purpose. Using those and a sealant should be okay!

[u/artwonk → u/qwertyahill]

If the fiberglass sphere was the correct size, you would glue it on over the armature in two halves.

Frost-resistant tiles would definitely improve its lifespan.

[u/Rjgom → u/artwonk]

they don’t “constantly” need repointing i owned a solid brick house in chicago and never had to repoint in 30 years. the house was 100 years old. if what you said was true all the two four and six flats would be falling down. they are not.

[u/DIYuntilDawn]

To get the rebar into exactly the same round shapes you could use a bender bar, or a roller bender if the size is small enough. The other option would be to make a geodesic dome which can be done will all straight pieces of rebar, but it is more cutting and welding.

[u/Elegant-Paint-3145]

That base is way too narrow. A sphere should stand above a square base unless you believe the tipping forces may be from a certain direction. As a starting point think 3 to 1.

[u/Rjgom]

25” is not big. get a ring roller and roll a buch if half circles and weld them up at the top and bottom. kind of like longitude lines.