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 October 19 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! 

[Andehh]

On 19/10/2025 at 16:11, saveasteading said:

What is the problem? Is it breaking up?

Yeah, that small semi circle area is sitting on insulation which the bastard screeders buried as they ran low in material. Builder missed it when he dig out and relaid the rest.

 

I'll chisel it out and reconcrete, but want to achieve a very smooth flush surface! 

[saveasteading]

Take out sone insulation so that the screed doesn't break up again. The heat loss difference will be minimal.

You could add some reinforcement. Either wire, or fibres.

[Andehh]

Thanks! How do I achieve such a perfectly flat/smooth surface though? Or am I over thinking it?

 

Do I need to do return after X hours etc for a final go over etc? 

[saveasteading]

3 hours ago, Andehh said:

do I achieve such a perfectly flat/smooth surface though? Or am I over thinking it?

You are looking at a tiny area so it is just a trowel job. Use a plasterer's float to smooth it. After an hour or so you can give it another smooth over.

If there are ripples then you can rub them off later.

Or as above, leave it low then use self levelling.

[Nickfromwales]

Does this get routinely driven on, or just foot traffic. 
 

Making this up in layers, with slc for eg, will not survive imo. Better off one section of concrete, anchored with horizontal fixings for purchase, and some small stainless / galv mesh. 
 

Small patches are the biggest pita. 

[Nickfromwales]

Could also do this with a resin. 

[Andehh]

Thanks all, have finished the job. Forgot to pull in any mesh in, but for a small job I'll keep my fingers crossed.

 

Not 100% happy with it, but it's one of those if I faff with it any more I risk making it worse... Only want it to last a year or so, as I'd like to tile the garage floor eventually... For now it's just trying to make it look tidy!

 

We shall see. 

[Andehh]

Will see how it is tomorrow, and give it a rub down to smooth it off. I think one side is a good few mm lower then the lip which I missed due to poor lighting. Only noticed it taking the damn photo, but 2 hours later I don't want to fiddle! 

Edited Sunday at 15:21 by Andehh

[saveasteading]

You'll walk past it without a glance after a while.