[N0tT00Handy]

Need a bit of guidance here,

I have tough yard and my contractors are going to pour concrete over some large boulders and filled in the remaining area with parts of other boulders (6in to 1 foot). They are planning on using rebar but not much else. I have read this is not optimal but they are pretty deep into the project now - thoughts? Should I ask them to use extra rebar? Adjust the concrete mix so it is more liquid? Wet the rocks jut in advance of the pour so the concrete binds better. Any help you can provide is genuinely appreciated, a bit outside my comfort zone here.

 

[stadry]

this isn't how 'pre-placed aggregate' is defined,,, this is, impo, a cheap *** attempt to duck some rqd work,,, what is the desired result - slab on grade ? paved ramp ?
no matter what you want, its a plan for uncontrolled random cracking &, in the right location, extremely susceptible to degradation from freeze/thaw

 

[dj3]

There are a few questions:
- Who's doing the work? Lic concrete contractor?
- Forming must stop wet concrete from oozing down the rocks, how are they going to do that?
- Forming with 2x4s may not be enough.
- Placing rebars has to follow a schedule, from your picture 1/2" rebars every 12" in both directions.
- Future cracks might be inevitable, if you don't prepare a better pad for the slab. More 3/4" crushed rock (not just 6" -12") could help.

 

[joed]

Adjust the concrete mix so it is more liquid?

Definitely not. It will make the concrete weaker. Good vibration to fill all the spaces is what you want.

 

[Drachenfire]

Based on the picture, what the contractor is proposing is only saving him time (and material for which he is probably charging you for anyway) and wasting your money.

If you live in a zone subject to frost heave, in all probability the concrete will crack.

A concrete pour is a to hefty an investment to risk failure by going cheap.

Do it right the first time.

 

[N0tT00Handy]

@Drachenfire - Thanks, We live in Southern California so we get frost rarely but it does happen. What would be you suggestion on how to best resolve?
@joed - Thanks, I had read somewhere they can adjust the concrete before pouring it to modify the viscosity so it fills in spaces better. What is your suggestion on vibrations?
@dj3 - Yes, Lic. contractor but feels like they should have more experience in this realm. They still have some framing to finish, I think they are going to bring in a bit more fill dirt and use foam to prevent the oozing. Rebar we are good on, the supplies are off to the side (not pictured) sounds like one way or another the rocks are a necessity.
@stadry - Level, concrete slab with steps leading up to it Going to put a 7 x 7 hot tub in lower left corner where fence line is - filled weight will be around 5000 lb. the rest will just be slab for patio chairs, etc. Live in SoCal so freeze than while feasible is not super common, any thoughts on how to best remedy the situation?

 

[joed]

Your contractor should have one of these. It vibrates and makes the concrete flow into all the cracks and crevices.

 

[Old Thomas]

Concrete should be as uniform in thickness as possible. Where it thins out over a boulder it won’t hold up. A vibrator is for consolidating concrete and getting air out. It is not for transporting or flowing concrete, as that will cause the mix to segregate.