Grinding Concrete Question

[josephny]

I'm using a 7" hand angle grinder (Makita) and a Dewalt 7" cup (DW4775) on a 2400 sq-ft, 2 year old electric troweled floor in very good condition.

I wanted to get it smoother, cleaner and ready for densifier/sealer.

I asked Dewalt what the equivalent grit of this cup is, and this is their response:

"This model doesn't have a grit, this is meant to grind rough surfaces like thinset used to install tile. It will make the surface smooth but not provide any polishing of the surface."

I know very little about concrete grinding. I understand it will remove a coating on top of concrete (like thinset), but how could it not have an equivalent grit level?

When I brush my hand against the newly ground floor, it's nice and smooth. The cup is definitely grinding some concrete (I can confirm lots and lots of concrete dust being caught by the vacuum as well as escaping into the air).

I believe it is important to know what grit level I am at, for one reason, because the densifier/sealer has an optimal floor roughness level for application.

Thank you!

 

[Retroman]

Can't help on the grit but grinding 2,400 sf with a hand grinder is going to be a chore. Have you checked with any rental yards for a bigger machine? The walk behind grinders have different grit diamond inserts and it will be much flatter than using a 7" cup.

 

[bigjon]

If it’s used for removing coatings, etc. it’s probably somewhere between a 30# and 100#. They’re aggressive, but the concrete will still feel smooth to the touch. You’ll definitely ‘open the pores’ of your concrete.

 

[LegacyIndustrial]

Definitely NOT the tool you want to use for making the floor smoother. Your floor was probably ready to go as-is.

Polishing is done with resin-pads, in ascending order they make the floor smoother and smoother. You probably could start around 100 or 200. They go up to 2000 and can be purchased online. Over a large area however, you want a large tool 16-20” in width or your floor will look very uneven.






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[josephny]

Can't help on the grit but grinding 2,400 sf with a hand grinder is going to be a chore. Have you checked with any rental yards for a bigger machine? The walk behind grinders have different grit diamond inserts and it will be much flatter than using a 7" cup.

Yes, indeed. The work is done, and it took quite a long time. But the shop has been in use, so I had to move stuff out of one area at a time to get it done. Would have required renting a machine for a week.

 

[josephny]

If it’s used for removing coatings, etc. it’s probably somewhere between a 30# and 100#. They’re aggressive, but the concrete will still feel smooth to the touch. You’ll definitely ‘open the pores’ of your concrete.

Sounds like I didn't do any damage and can now move to a 100 grit resin pad, right?

 

[josephny]

Definitely NOT the tool you want to use for making the floor smoother. Your floor was probably ready to go as-is.

Polishing is done with resin-pads, in ascending order they make the floor smoother and smoother. You probably could start around 100 or 200. They go up to 2000 and can be purchased online. Over a large area however, you want a large tool 16-20” in width or your floor will look very uneven.

-----I see we all got sucked into a VERY OLD POST. LOL------


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The floor had stains and hardened drops of glue and epoxy and some cracks that I filled, so it needed a good smoothing.

Sounds like I can start now with 100 grit resin pads, move to 200, spray the densifier/sealer, then move higher if I want.

My understanding is that the higher I go, the more resistant the floor becomes to staining or absorbing whatever is spilled on it.

Not sure about the old post -- I just posted it this morning.

 

[LegacyIndustrial]

Joseph:
Yes, theoretically. However polished floors will still stain and can be damaged easily by salts or acids.

 

[Armorpoxy]

from what you desribed we would not recommend going to a resin yet. Normally polishing goes 40-80-120-200 metals-density- 200 hybrid- and up from there. Stain blocker as last step.

Legacy is correct a polished floor has very little resistance against stains and chemicals, hence why we don’t normally recommend for garages.