How to achieve ultra smooth concrete?

[Andehh]

When we had our garage floor done, the sub contracted bastards hid an insulation panel under the surface, likely as they ran out of material.

 

Our builder came back 2 years later to rectify, and his team achieved a brilliant finish. The only issue is there is about 1sqft they missed, it's probably not worth me getting the builder out, so I'd like to cut this chunk out and reconcrete it myself. 

 

I've mixed plenty of concrete in my time, but achieving such a smooth finish I'm unsure of.... 

 

Pics attached, I filled a chunk with silicone just to stop water getting in.  Other pic is what the builder achieved, and I painted over it. 

 

Any recommendations?? 

[SteamyTea]

We have been discussing this here.

 

 

Hoping to find answers as well.

[Conor]

Where is the water coming from?

 

If you're going to cut out and relay, I'd fisning the new surface 5-10mm lower, then come back a week later with a bag of self leveller.

Edited Sunday at 12:33 by Conor

[nod]

Which ever you decide to do Use a rotating sponge float It will bring the fat to the surface and come up like glass 

[Andehh]

Thanks all, sorry the water bit is just dripping from the car!

 

Nod - are you able to link to the sort of thing you suggest? cheaper the better with it being such a small area!!!

[saveasteading]

What is the problem? Is it breaking up?

[Andehh]

It was originally but builder dug it out, a miss communication with their team meant they didn't go far enough... So I need to just take out a bit extra. Rest has been down about 8 months without issue!

 

You can see the sort of semi circle which is causing the problems!