Grinding concrete slab- worth trying?

[cwr]

Hi folks

I have a concrete floor for a garage that was poured late last year, it unfortunately had some rain on it before it was set so the top surface is not great. Probably be quite dusty when I finally get a roof over it and it eventually gets a chance to dry out. 

I'm wondering if it's worth trying to grind back, my local hire place has this sort of machine:

Is this the right approach to improving it? Or something else? Or maybe I'm over thinking it for a garage and should just live with it.

Thanks

[Nickfromwales]

Mat the force be with you, as grinding concrete with that wonderful looking machine, is a bastard of a job. Check how many 'teeth' you'll go through before taking the leap.

[Roger440]

You want one with diamond discs. That looks like one with the "scabbling blocks". Useless for what you need.

 

The ones with diamond discs seem rather hard to hire.

 

How big an area. I did a double garage sized area of very rough tamped concrete with a Hilti hand held one. Bloody hard work mind!

[Nickfromwales]

1 hour ago, Roger440 said:

You want one with diamond discs. That looks like one with the "scabbling blocks". Useless for what you need.

 

The ones with diamond discs seem rather hard to hire.

 

How big an area. I did a double garage sized area of very rough tamped concrete with a Hilti hand held one. Bloody hard work mind!

Arms like a fiddler crab afterwards?  

[cwr]

They also have this, which has 250mm dia diamond disc.

 

 

It's a big enough area, about 70m2. I wouldn't fancy going at it with anything handheld!

[saveasteading]

10 hours ago, cwr said:

the top surface is not great

What are you finishing the floor with?

Are the levels generally OK apart from ridges and raindrop marks?

How soft is the top? Can you scratch it?

[JohnMo]

I had some high spots on our concrete slab, used a diamond disc and a hoover attachment/guard attachment on an angle grinder. Used a Henry hoover which survived. Worked well enough, but time consuming. You will still need a face mask.

[cwr]

On 07/02/2026 at 08:53, saveasteading said:

What are you finishing the floor with?

Are the levels generally OK apart from ridges and raindrop marks?

How soft is the top? Can you scratch it?

 

Finishing not yet confirmed,  tho will likely be some form of sealer/paint.

 

It's probably +/-5 or 6mm from nominal. 

 

I can scratch in about 1mm.

[saveasteading]

1 hour ago, cwr said:

probably +/-5 or 6mm from nominal. 

That's quite good.

More important is local variations. The industry way is remarkably and sensibly lo-tech, with a 3m straight-edge. Any completely straight timber will do. Lay it down (not levelled) and measure any gap whether at ends or middle. Then lean on the ends and rock it, and repeat. Any and all directions.

3mm or less is a pass and a few scattered  failures may be OK too.  I bet your floor passes.

[jack]

On 07/02/2026 at 08:10, cwr said:

They also have this, which has 250mm dia diamond disc.

 

 

It's a big enough area, about 70m2. I wouldn't fancy going at it with anything handheld!

 

Don't underestimate the potential costs of using one of these. The wear charges on diamond discs is eye-watering.

 

When we did our spalled garage floor (about 45 m²) with something like this a few years ago, I think the wear charge would have been hundreds of quid on top of the hire (we got it through my wife's family's plant hire company, so thankfully we didn't have to cover it).

 

Admittedly the slab had been there for several years, so under the spalling the concrete was very hard, and I had to take quite a lot off to get it even roughly flat, but just be aware of the potential costs.

An alternative would be to scrabble with something like your first machine to remove anything loose, then a primer to stabilise, followed by a thin layer of epoxy floor covering to smooth over any residual roughness.