Well at first I was thinking of do an epoxy paint job, but now I am just considering trying to clean the garage concrete first and see if it looks better from there. The concrete does seem to have a mild shine so I am guessing it's sealed, any good ideas on how to maybe clean the old oil stains that have been set in for some time now. Maybe degreaser? wd-40 I have read? any ideas would be great.
Hiya Streets...
Oil stained concrete can be really hard to clean completely. Degreasers work better than acids, but does so by re-liquefying the oils, that may remove the heaviest deposits from the surface...Unfortunately, when re-liquefied, these oils are often driven deeper into the concrete making a permanent, indelible stains.
Perhaps a better, more efficient means to remove superficial stains is to create a "slurry" mixture of TSP & water (mix only enough water to create a trowel-able paste), apply to affected areas and allow to set for several hours. Then rinse, and re-rinse entire surface with clean water.
Without knowing the history of your floor, I'm gonna assume the sheen you see on your floor is actually the remnants of concrete hardeners applied at the time your garage floor was installed. These hardeners keeps the moisture in the concrete longer allowing for a harder cure. They also prevent, or minimize, concrete spalling - and as a secondary benefit, reduces the amount of dusting (that is rampant in unsealed concrete).
Compositionally, these hardeners are not all that different than some sealers you buy at hardware or paint stores to seal patios, sidewalks, etc. to create a degree of moisture resistance, or to control moisture penetration. Since these sealers are applied after the concrete has cured, they are not an integral part of the concrete as "hardeners" are. These hardeners will prevent
some penetration of oils, etc., but as mentioned earlier, that's not their main purpose.
When attempting to paint concrete floors, it is absolutely necessary to remove these hardeners prior to painting - and that is a standard recommendation by every paint & coating manufacturer. This is where muriatic acid comes in. Muriatic acid is the cheapest and easiest way to etch a concrete floor (other means of removing hardeners is shot-blast, diamond sanding, scarifying - and requires equipment most homeowners don't really want to get involved with). Because it is a relatively strong acid, and because an improper etch is also fairly easy to achieve, follow manufacturer's explicit instructions of the application and neutralization of this acid mix very carefully (we can get into what a proper etch is later if you really want more info). What etching does, though, is multi-fold...(1) etching removes concrete hardeners, (2) acid-etching neutralizes the surface alkalinity, and (3) etching "profiles" slick concrete for a better mechanical bond of subsequently applied coatings. What etching also does is makes your concrete way more porous than it was right before etching - in other words, you may have cleaned a surface of concrete by using muriatic acid, but you've created a surface far more susceptible to staining now than ever before. Plus, depending on how large the area is, if acid is used to remove oil stains (which as mentioned before, is not all that effective anyway), it will also remove the hardeners, which returns concrete to a more natural state, which means that uncontrollable dusting thing again...
OK, I realize I have just completed 5 paragraphs to set you up for this answer. Don't use muriatic acid to clean oil spots - TSP works better. If you're gonna use muriatic acid, do so only to prep the floor for painting...and if you're gonna etch the floor for painting, make sure you do it properly and completely. Good luck.
