Hi everyone, 

I was wondering if someone could lend me their expertise on a pour gone wrong. We were attempting to have a floating concrete stair, which, I was told the execution of would be tricky as the entire thing is exposed. It was poured last week, and the results were disasterous. The texture was crumbly, (see pics), and the contractor attempted to fix it by honing the stairs, but this creates an undesirable terrazzo look we did not want. 

We are going to demo, and repour. The contractor is adament that the design mix on file, was not an issue, and it was just a bad batch of concrete. Should the concrete sub look into another design mix which we will have to get our eng to sign off on? Is anyone an expert on this? (see pics)

It's not the mix , it's the finisher 

When you say it's the finisher - just poor workmanship then? What can be done to provent this with the repour? 

Get a better finsiher.  That is what happens when people do things that is way over their head.

All I see wrong is technique. The finisher needs to do a much better job. Also a very small vibrator or tapping the forms might have helped get rid of some of your voids. Finishing concrete is a skill, not just hand a guy a trowel...

Thanks everyone. Our General Contractor might use another concrete sub based on our crappy results from the first go around. What questions should I be asking the concrete sub pre pour to make sure we don't have this happen again? I've asked for pictures, asking them to provide technical examples that they are capable of executing such a stair, but any other questions I should be asking would be helpful.

Just throwing this out there, Why cant you just sack it? It would save you a lot of money if its just cosmetic.

if its made of concrete and its fukt, it must be pump operator error!

Doesn't look like a mix issue. Small rock mixes usually finish well. This finisher did not use a pencil vibrator and the result is the rock you see. It really is unfortunate. Stairs... both formwork and finishing take a lot more work than people realize. Lots of these types of stairs are pre-cast on their side edges in a plant, and flown or hoisted into place. Site casting, as you now know can be hit and miss. Durlach Industries in Bradenton Florida are experts in precast stairs.

I've seen worse that have been repaired with grout or tiled, and then painted. Demolition job is going to the extreme.

Stairs/stepa are a Bit$h. Need to strip while green and rub/work the edges. Time consuming and costly. We try to up the bag mix to help out. Vibrating is tough because of the constant blow out from the face form. Lightly tapping on forms with a hammer will help with the honey combs on the surface.

I'd go with a 7 sack low gravel about 1,300 lbs and 1700 lbs of sand and pour on a 5-6" slump and get a pencil vibrator and these issues could be avoided .