The short answer is no
A new coating needs to bond to clean, open concrete. Oil soaked into the slab and old paint or coatings that are already losing their grip will both stop that bond. Coating straight over them traps the problem underneath, and the new floor fails where the old problem was. The good news is that both can usually be dealt with. This post explains why coating over them fails and the steps that come first.
Why oil causes failures
LearnCoatings, in a video on why epoxy floors peel, lists contamination as one of the main causes. He shows an industrial floor so soaked in oil that the crew kept grinding and scarifying until it was clean, and says that if they had coated over it, the coating would not have lasted more than a week. Oil prevents the coating from wetting and gripping the concrete.
How water reveals oil
This Old House, in a segment with nearly 4 million views, sprays water on the slab and watches where it pulls away. Those spots get degreased before etching. It is a simple test anyone can do.
Step 1: remove surface oil and stains
DIY MAN, in a video with more than 880,000 views, tests a commercial oil stain remover on heavy garage stains. He found the general cleaning instructions only partly effective even after several rounds, but pouring the product directly on the stain at the depth the manufacturer recommends, letting it dry about 12 hours, sweeping and rinsing removed most of the staining. Rust spots and paint on the same floor did not come out.
Step 2: degrease and rinse
Lowe's and This Old House both scrub degreaser into stained areas, rinse and remove the water. Repeat for heavy stains until water no longer beads on the spot.
Step 3: grind through what remains
Even after cleaning, oil can remain deeper in the concrete. Grinding removes the top layer where most of it sits. Mike Day, whose garage video has nearly 1.9 million views, grinds as standard prep.
Why old paint usually has to go
Old paint or coating that is peeling, chalky or poorly bonded will take the new coating with it when it fails. Mike Day says grinding is the easiest way to remove old paint or an old epoxy coating before a new one goes down.
When coating over old epoxy can work
Greg's Garage, in a video with more than 66,000 views, recoats a floor he says he originally coated about 15 or 16 years earlier and that was still in good shape in most places. He cleaned it thoroughly, filled cracks, scuffed the whole floor with coarse sandpaper, wiped it with a thinner recommended by his coatings supplier, and rolled on a water-based epoxy that the supplier said could go over an existing coating. That approach depends on the old coating being well bonded.
How to tell if old paint is sound
Try scraping at an edge with a putty knife. If it lifts easily, it has to come off. If it is firmly bonded, ask your installer whether a recoat is possible for the system you want.
What happens if you skip these steps
The new coating may bubble, lift or peel over old stains and weak paint, often within months. LearnCoatings shows examples of exactly that.
FAQ: Will kitty litter remove oil?
It can absorb fresh spills but does not remove oil already soaked into the concrete.
FAQ: Do professionals always grind off old paint?
Most do, unless the existing coating is well bonded and compatible with the new system.
Rust, paint drips and other marks
Not every mark is oil. DIY MAN found rust spots and paint on his floor that the oil remover did not touch. Rust stains and paint drips usually come off during grinding. Tire marks often grind out as well. If a mark survives grinding, it is generally sealed under the primer, but anything that is still soft, flaky or oily should be removed first.
Sealers and curing compounds
An old clear sealer is easy to miss because it is invisible. It behaves like old paint: the new coating bonds to the sealer, not the concrete. The water test will show it. Tim Seay shows his crew adding weight and sand to a grinder to strip a heavily sealed floor, which shows how stubborn these products can be.
Mastic and adhesive residue
If the floor once had tile or carpet, adhesive residue may remain. It has to be removed completely, usually by grinding, because coatings will not bond to it reliably.
Planning ahead if you park on stains today
If you plan to coat in a few months, put a drip pan under any leaking vehicle now. Every week of fresh oil is more to remove later.
Budget for removal
Removing old coatings and deep stains adds labor. Ask contractors to price it as its own line so you can see what the removal costs separately from the new floor.
Get help with a stained floor
Austin Epoxy Flooring Pro removes stains and old coatings before installing new floors in Austin and Georgetown. Call (512) 325-5434, open 24 hours, 7 days a week.
Related pages
Related pages on our site: Existing paint, sealer or old coating questions; How to prepare a garage floor for epoxy; New coating over old concrete; Garage floor epoxy in Austin.
Call 512-325-5434 (open 24 hours, 7 days a week) or request a free estimate.
Sources
How to remove big oil stains from concrete with one product//It actually works! — DIY MAN (YouTube, 883,150 views as reported 2026-10-14)
Epoxy Floor Peeling? Here are the Reasons (and how to prevent it) — LearnCoatings - Epoxy Flooring Training (YouTube, 77,791 views as reported 2026-10-14)
How To Epoxy Coat Your Garage Floor | Must Watch For Diy'rs — Mike Day Concrete (Everything About Concrete) (YouTube, 1,892,569 views as reported 2026-10-14)
How to Apply a New Garage Floor Epoxy Coating Over Old Epoxy — Greg's Garage (YouTube, 66,307 views as reported 2026-10-14)
How to Epoxy Coat a Garage Floor | This Old House — This Old House (YouTube, 3,973,497 views as reported 2026-10-14)
PRO vs. DIY Epoxy Garage Floor Kits :: Whats the difference? — Tim Seay (@TimDCVA) (YouTube, 940,155 views as reported 2026-10-14)
How to Epoxy a Garage Floor — Lowe's Home Improvement (YouTube, 617,355 views as reported 2026-10-14)