Epoxy prep — concrete discoloration

[theapexdifference]

How perfect does the concrete need to be to ensure a strong bond? This floor was very greasy and filthy. It was ground with an rental dual head grinder, then hand ground with a 7" angle grinder (edges and missed areas).

It's been cleaned with a floor scrubber rental, degreased several times.

The attached photo is a representation of the slab. It's not a perfect uniform color and there's some splotchiness. Is this fine to coat?

The surface doesn't feel oily. I don't think I can conceivably get the surface entirely uniform.

 

[RivennHewn]

If it’s critical, it needs to be blasted.

Even then, no real guarantee that it’ll come out perfect.

Oil is a *****

 

[Shea]

The color of the floor is not a concern. It's not uncommon for concrete to be permanently stained darker when the actual oil is removed. What IS a concern is whether or not the areas that were oily will absorb or reject/bead water. The best way to check is to do water drop tests throughout the floor, particularly over the oily areas. If the concrete immediately turns darker and absorbs the water you should be fine. If the water sits or gets repelled, then more cleaning needs to be done.

 

[dcg9381]

Does acid etching address oil?

 

[theapexdifference]

The color of the floor is not a concern. It's not uncommon for concrete to be permanently stained darker when the actual oil is removed. What IS a concern is whether or not the areas that were oily will absorb or reject/bead water. The best way to check is to do water drop tests throughout the floor, particularly over the oily areas. If the concrete immediately turns darker and absorbs the water you should be fine. If the water sits or gets repelled, then more cleaning needs to be done.

That's good peace of mind. There's zero beading when water is applied.

Laying down an epoxy vapor barrier before the base coat as well, so I'm hoping this adds some more protection against any concrete imperfections.

 

[FJ4FUN]

Does acid etching address oil?

No, etching will not remove oil stains.
Also, best practice is to thoroughly degrease prior to grinding and do not use high pressure power washers. If staining exists after grinding and fails water droplet test i.e. water beads and does not readily absorb, clean/grind some more. Finally, to address any remaining concerns, use a high quality primer such as Wolverine Coatings' BondTite 1101 primer!