Stilts for home needed

[MarkP]

Having mixed a lot of concrete by hand I gravitate towards a concrete truck. That requires increased planning and preparation though as well as rental of a concrete pumper and crew. For us small DIYers mixing by hand is often a necessity as we prep and pour each pillar individually.

[dobanion]

The question of truck vs on site comes down to volume (cubic yards) and time (how long do you need to place it). Also, additional consideration, for columns, the wet concrete is gonna need to be lifted to the top of the columns, or pumped.

Take a 10" column, that's 8' high. That's 4.36 cu/ft, or .16 cu/yd of concrete per column. That's not much, at all. You only need to be sure to get each column done, from start to finish, in one go. You don't want to fill it halfway, let the concrete set, then fill it to the top.

I'd suggest buying aggregate (crushed rock and sand) from Puna Rock or Yamada's, and having it delivered on site. Then buy Portland cement from Hilo, and store it on site, OUT OF THE RAIN. Rent a cement mixer. Now mix the aggregate, cement, and water in the mixer, in batches. Take the wet concrete in buckets up a ladder and drop it into the forms. Figure you can lift 50lbs up a ladder per trip, that's about a dozen trips up the ladder per column. Not too bad.

Don't try this approach for big concrete work, it will kill you. But for 600ish pounds of concrete per column, done one at a time, totally doable for a owner builder. I'd guess with two people you could knock out a column per hour without breaking your back.

As for the formwork and rebar and all that, take your time setting all that up, and making sure they are plumb and level. I'd put 4 sticks of gatorbar in each column, spaced equally.

I'm sure some will say just put the columns directly on top of the lava, but then in a big earthquake there's not anything really holding the column to lateral movement. By having footings sunk into holes in the lava, and rebar tying the footings to the columns, it's much more likely to stay put when things start shifting.

[Maggie]

This is fantastic information and makes me feel much more confident about this process. Mahalo for that! If you’re able, can you please explain the process with the rebar. Does it go in vertical? How would I keep it from all sinking as I went? Mahalo everyone... having a community who takes the time to share like this is one of the things I cherish abut Hawai’i : )

[kalakoa]

Rebar is sold in 20' lengths, I believe you would form one end into the footing and run it continuously through the blocks.

Concrete + pump isn't cheap ... but not having to worry if I got it right was totally worth it. Tie all the columns together with a slab while you're at it, instant workshop/parking space.

[Hawai'i Is Home]

Fantastic info...thank you everyone! I have only used 5-6 foot rebar but I should have realized it would be sold in longer lengths. I'm assuming there is some form of attachment that can be placed in the top of the concrete pillars as they dry, giving the foundation a place to attach to (8-10 feet up). I'm open for suggestions if you have any, mahalo!

[randomq]

Galvanized steel strapping is one option, sold at HD in 25' rolls.

When you pour your footings, consider adding an ufer ground. Better than copper rods in lava rock.

[kalakoa]

I would use something heavier than the strapping, either a long heavy tie plate (the ones hanging next to the rebar at HD) or some kind of post or column base, viz

https://www.strongtie.com/nonstandoffcol..._base/p/cb

Tie the lower part of the bracket to the rebar.

Some construction of exactly this sort just went up on Kilauea, across from/near the 76 station. Stack of hollow blocks, filled with concrete, big glue-lam beams across the top. The property slopes down, so the stilts put the apartments at eye level with the street.

Consider that large enough beams might require a crane or some kind of rigging.

[dobanion]

If you shoot for 9' columns, you could cut the 20' rebar sticks in half, giving you 10' lengths. Then when you pour the footing, and while the concrete is just starting to set up, simply stick the rebar straight down, 1' into the wet concrete, sticking up 9' out of the footings. After the footings set, put the sonotubes over the lengths of rebar. Use a little timber at the top of the sonotubes to hold the vertical rebar in position when you pour in the concrete for the columns. Simple.

Putting a slab on top makes it VERY difficult. This requires massive formwork to hold the slab in place at the top of the columns. This is for professionals only.

It MAY be possible to cast a slab on the ground and lift it into place afterwards, but I don't see the point in going through that. Put a shipping container or a wooden deck on top, much easier.

[kalakoa]

Putting a slab on top makes it VERY difficult.

I meant on the ground where it would be easy. For an upper floor, I would float some concrete over the corrugated steel decking used in commercial construction, avoid wood entirely.

[dobanion]

Oh ok, like a parking area/carport for the slab? Yeah, that'd work.

And yes, if you want to pay for the corrugated steel decking (not cheap, I have looked), that would be doable for the top part.