Oil-stained concrete needs a contamination assessment before a coating is chosen. Ask how the installer will clean affected areas, verify the prepared surface and handle contamination that remains. Grinding is a preparation method, but it should not be treated as a substitute for a documented cleaning and acceptance plan.
Map the stain before the garage is emptied
A photograph of the whole room can hide the important detail. Take a closer photograph of each stained parking spot, then a wider one showing where it sits. Include the space beneath a stored engine, compressor, mower or workbench if you can see it safely.
Tell the assessor what leaked if you know: engine oil, grease, a cleaning product, or an unidentified liquid. Record when it happened and what you used to clean it. “Dark patch beneath the mower; liquid unknown” is useful. Guessing a chemical name is not.
Your notes give the installer a starting map. They do not prove how far a contaminant entered the slab or whether the surface is acceptable for a particular product.
Cleaning and profiling answer different questions
Sika surface preparation guide calls for contaminants to be removed before a surface profile is created. It also explains that contamination that cannot be eliminated can require removal and replacement of affected concrete. That is why a proposal should describe cleaning and mechanical preparation as separate decisions.
Ask which cleaning method is intended for your condition, how residues and rinse water will be handled, and what must happen before coating starts. Then ask for the required surface profile for the chosen resin. The grinding and etching comparison explains preparation choices; a machine name alone does not establish that an oily surface is ready.
Questions that make a contamination allowance clear
- Which stained areas are included in the quoted cleaning scope?
- Does the price include more than one cleaning attempt if needed?
- Who decides that the prepared area is acceptable, and against which requirement?
- Is a representative test area or other verification specified?
- What happens if preparation exposes a larger affected area?
- Is replacement concrete an option, and how would it be priced?
- How does known contamination affect the offered warranty?
These questions help you distinguish a fixed inclusion from an open allowance. An installer may need to inspect or perform preparation before giving a final answer. Ask what is unknown now and when the decision will be made.
Do not create a new unknown while trying to help
Before the assessment, avoid experimenting with products the installer has not approved. Send the name of anything already used. Keep the label or a photograph of it. A cleaned-looking patch can still leave a question about product residue, so appearance should not be the only acceptance criterion.
If you want to do part of the cleaning yourself, agree on that scope in writing. Ask whether it changes the preparation price and whether the installer will still verify the surface. A vague instruction to “get it clean” gives neither side a clear handover.
Protect the floor from new spills once it has been prepared. Tell the installer about equipment that must remain in place and who is responsible for moving it. Do not plan to run a leaking vehicle through the room between preparation and coating.
Keep concealed conditions out of a false fixed price
Imagine two proposals for the same room. One includes removal of an old coating and a defined allowance for contaminated areas; the other lists only “grind and coat.” This is an editorial comparison, not a completed project. You cannot conclude which offer costs less until you know what happens when contamination is exposed.
Ask for a change-order rule: how additional work is measured, who approves it and whether the job pauses until you accept the price. Put that beside the cost comparison worksheet. The point is to prevent a disputed allowance, not to demand certainty about hidden concrete.
What to send with your first inquiry
Include floor dimensions, a stain map, the age of any old coating, known spill history, cleaning-product names and the date you need the garage back. A coating assessment should address the contamination before a decorative finish is selected.
Read the warranty questions for contamination-related exclusions, then open a project inquiry. If the source of a dark patch is unknown, say so. That uncertainty belongs in the scope.
References behind this guide
Technical limits apply to the named product or test. Confirm the current requirements for your proposed system.
