prep - acid etch, diamond grind or leave as is?

[nomercy346]

Hi, everyone, new member here. I have been browsing the forums once in a while and already benefitted from the wealth of knowledge on here. Now it's time to actually register to ask a couple questions too

I'm currently helping my dad with his new garage project and the next step is putting in the epoxy floor coating. I'm not 100% sure on the prep work needed.

The garage sits on a new slab, so the concrete has a pretty smooth finish. Now I have spent countless hours on the web and on here, reading about floor prep etc.
Some people will tell you all you need is a porous (and clean, obviously)surface on the concrete. Others will tell you it has to be rough to some extent as well and you have to acid etch or diamond grind no matter what. (I know that is probably the safest route).

To test for porosity, I splashed some water on the slab and when I wipe it over the surface it instantly darkens and the water disappears. Not wiping it around it just darkens instantly but the water will pool up. No vehicles were driven on it yet, so no oil, tire marks etc.
The surface feels roughly like 4-600 grit sandpaper.

Is that enough to risk it and just clean it up and put the primer on (as I have been told by some people)? Or should we still acid etch or grind it. How rough does the surface need to be to have the epoxy securely binding to the concrete? Reason I ask is I'd rather keep the smooth surface we have. Wouldn't the sanding marks and rough texture still be visible in the coating afterwards?

 

[Shea]

You need to acid etch at the minimum. Grinding is the preferred method but not everyone can grind for a variety of reasons. New floors especially need to be prepped in one of these two methods because they are troweled smooth and can also have excess laitance on the surface that inhibits a good bond.

I suggest reading this article here that explains the difference between grinding and acid etching as well as why it has to be done.

 

[jaye944]

I just used a diamond floor grinder, and found if you are careful and take your time, grinding will be better that acid, or rather, do a more through job, you should leave major marks, and the epoxy should cover that.

I did acid, then grind, but that was for a different reason (see my links for why)