Here's the short version of my resume: 9 years as a facilities engineer handling epoxy and concrete repair projects for a mid-sized commercial property group. I've personally made—and documented—14 significant mistakes, totaling roughly $6,500 in wasted material and budget. That doesn't count the labor, the re-rented equipment, or the walk of shame across a jobsite after a very visible failure. Now I maintain our team's epoxy checklist so the next person doesn't repeat my errors.
This checklist has seven steps, from picking the right resin system—including the hard epoxy resin and the Hilti-type concrete epoxy cartridges—to the exact method for sanding epoxy resin when you're finally ready. If epoxy on concrete is new to you, run the list top to bottom. If you're experienced, use it as a sanity check. I do.
Fair warning: epoxy is forgiving right up until it isn't. Every step below has a scar attached.
The 7-Step Epoxy Checklist
Step 1: Pick the right epoxy system
Not all epoxy resin is the same. I know that sounds obvious. It's not obvious when you're standing in a supply aisle looking at eight buckets of identical-looking goo.
A hard epoxy resin that makes a beautiful cast bar top is the wrong choice for anchoring rebar into a concrete wall. Hilti's concrete epoxy—the HIT-RE 500 stuff that's all over structural jobsites—is formulated for drilled-in anchors and rebar dowels. A general-purpose casting resin is not. The technical data sheets show 20-30% lower bond strength when you pick the wrong product family. That's not a defective material; that's misuse.
What most people don't realize: the base resins in those cartridges and buckets come from large chemical manufacturers, and the same base resin can show up under a dozen brand names. Olin's D.E.R. and D.E.N. epoxy resin lines, for instance, are the backbone of countless formulations in coatings, adhesives, and laminates. But the base resin isn't the whole decision. The formulation and the hardener make the system.
So look at the full product label and check three things:
- ASTM C881 classification if it's for concrete bonding. According to ASTM C881 (astm.org), epoxy systems are sorted into types, grades, and classes—each matched to a specific application.
- Pot life and gel time at your actual working temperature, not the lab's.
- Sag rating if you're working overhead or vertical.
And here's something vendors won't tell you: datasheet cure times are lab numbers taken at 77°F. A real slab at 50°F cures at maybe half the speed. Plan around the jobsite, not the pretty chart in the PDF.
Step 2: Prepare the concrete like it's a chemistry experiment
People assume a clean-looking slab is ready for epoxy. What they don't see is the invisible barrier: curing compound from when the concrete was poured, old sealer, laitance, or dust trapped in micro-pores. Epoxy is only as good as the bond, and the bond is only as good as the surface.
I knew I should grind a garage floor before coating it back in March 2022. I looked at it and thought: “what are the odds?” The surface looked fine. The odds caught up with me when the coating delaminated in the first month—800 square feet, $1,800 in material, plus a grinder rental that should've been in the original bid. In my defense, I've only made that mistake once.
Minimum prep, no shortcuts:
- Mechanical grind or shot-blast to open the pores. Acid etching works for light-duty coatings but is a poor second place for anything structural.
- Vacuum thoroughly, then wipe with a solvent that leaves no residue.
- Do the overnight plastic-sheet test: tape a 2×2 ft piece of plastic to the concrete. If there's condensation under it in the morning, no epoxy goes down today.
That last one has caught 11 bad pours for us since 2024. It looks like paranoia; it acts like a miracle.
Step 3: Measure and mix like a chemist
“Mix 2 parts resin with 1 part hardener” should be easy. It's not easy when you're rushing, when the pump has been sitting on the canister for six months, or when you're eyeballing it. I've been guilty of all three.
Hard epoxy resin isn't paint. You can't stir until it “looks right.” An off-ratio batch won't cure hard; it cures soft, chalky, and permanently sticky. Then when you sand, the paper gums up instantly. That's not a sanding problem. That's a chemistry problem you created during mixing.
My specific failure: I anchored a stainless steel handrail with a batch of concrete epoxy mixed by eye. It passed the hand test. It failed the torque test—by a couple of millimeters of movement. I had to cut the anchor out, drill a new hole, and explain why there were two holes. The lesson: weigh your resin and hardener if the product allows it, or use fresh calibrated pumps. Mix for a full three minutes, scraping the bottom and sides. When you think you're done, mix one more minute.
Step 4: Respect pot life and gel time
Every epoxy has a window between mixing and hardening. For cartridge systems like Hilti's concrete epoxy, that's often 20-30 minutes at room temperature. Past that window, the material in the mixing nozzle is cooked and gets laid down as a lumpy mess.
Here's the thing: larger batches generate more heat, and heat accelerates cure. A 4-gallon pail will kick off faster than a quart of the same product. Mix only what you can apply in about half of the stated pot life. And if you pause mid-cartridge past the gel time, swap the mixing nozzle. Reusing a set nozzle is a quiet way to ruin an otherwise fine installation.
Step 5: Wait for full cure, not “dry enough”
The epoxy is dry to the touch in six hours. It looks done. A small voice says: how much longer could it possibly need?
For most systems, full cure—the point at which the material reaches structural properties and becomes genuinely sandable—takes 3 to 7 days. Some formulations get there sooner; none get there in six hours. Check the cure schedule on the datasheet, adjust for your temperature, and count actual days.
Field test: press your thumbnail into a scrap or an unnoticeable edge. If you can dent it, it isn't ready. Not even close.
Step 6: How to sand epoxy resin
From the outside, sanding epoxy resin looks exactly like sanding wood. The reality: epoxy is harder than wood, softer than metal, and very good at melting into sandpaper when it's under-cured or mis-formulated.
Method I use now:
- Verify cure first. Dent test, not vibes.
- Start with 80-grit to knock down drips and the glossy skin. Light-to-moderate pressure; let the grit do the work.
- Step up through 120 to 220 if you'll coat or paint over it. Each grit removes the scratches from the one before. Don't skip.
- For a clear, glossy finish, wet-sand from 400 to 600, then 1000+. Water as lubricant, on a block or sanding sponge so you don't create divots.
- Sand in a circular motion. Don't lean into it.
- Wear an N95 or better. Epoxy dust is a respiratory irritant, and “I didn't know” doesn't help your lungs.
The mistake that cost me an afternoon: I hand-sanded a tabletop pour for four hours. The paper kept clogging; the surface stayed dull. I told myself it just needed more work. At hour four, I finally pressed a thumbnail into the edge and it dented. The resin was under-cured because I'd skimped on hardener. I ground it all down and started over. The fix was never more sanding. It was patience and a proper ratio.
Step 7: Test before you trust it
Before anyone leans a ladder on that repair or rolls a pallet jack across that floor, verify. For coatings, do the thumbnail test and check for glossy soft spots. For anchors, do a torque or pull test per the product spec. We've caught 17 installs in the past 18 months that would've failed in the field. Every one of them looked fine from a meter away.
Notes from the burn pile
Two final things, and neither is about technique.
The first is about cost. A colleague once bought a bucket of unlabeled “generic epoxy” to save 30%. No datasheet, no batch number, no cure chart. It failed. The real cost wasn't the savings he lost; it was removal, replacement, downtime, and the client asking whether he could be trusted with the next job. I've learned to ask what's not included before asking what the price is.
The vendor who hands you the data sheet before you ask—who lists cure times, limitations, storage requirements—is the one who ends up being cheaper.
The second is about sourcing. When I can't verify the chemistry inside a finished product, I look up the base resin manufacturer on the data sheet. Olin is one of the companies that publishes technical data openly for its D.E.R. and D.E.N. epoxy resin lines, which makes it easier to trace what's actually in the bucket. Traceability isn't bureaucracy. It's how you avoid a $2,000 surprise.
That's the whole list. Seven steps and a few scars. I'd rather you learn from my mistakes than repeat them.