How to Sand a Painted Concrete Floor for Recoating

In our Sanding vs. Grinding: Preparing Previously Painted Concrete guide, we established that if your floor passes the Cross-Hatch Adhesion Test, then the next step for recoating will be sanding.

Choosing to sand rather than grind saves you hundreds of pounds in equipment rental and diamond consumables. However, sanding in an industrial context isn't just a quick scuff - it is a much more deliberate process of creating a Mechanical Key. This ensures that your new paint will successfully bond to the previous coat and last just as long as if you had painted it on brand new concrete.

When to Commit to the Refresh

As we noted in the initial test, you only proceed with sanding if your duct tape came up clean.

• The Foundation: You are trusting the old paint to hold up the new paint. As long as it passed the test, your previous paint will still have a solid grip to the concrete.

• The Goal: You aren't trying to see bare concrete. You are simply removing the "top skin" of the previous coating to expose a fresh, porous surface.

Professional Tools

For professional results, a hand-sander won't suffice for larger areas. You need equipment that provides consistent downward pressure.

• The Industrial Floor Buffer (Rotary): The gold standard for "Refresh" projects. Use a drive plate equipped with 80-120 grit sandpaper or mesh discs.

• Orbital Sanders: Essential for the 20% of the floor the buffer can't reach, i.e. corners, near fixed machinery, pillars, etc. 

• Abrasive Choice: We recommend 80-grit. It is aggressive enough to bite into old epoxy, but fine enough that scratch marks won't show through your new finish.

Step-by-Step Guide

1. Cleaning

A common mistake is sanding a dirty floor. If there is leftover grease or workshop grime, the heat of the sanding disc will "smear" those contaminants into the scratches you’re creating.

To avoid this, you need to scrub the concrete down with a heavy-duty degreaser.

Once you have scrubbed the floor, rinse off the cleaner and let it dry before moving on. 

2. Sanding

Operate the buffer in slow, rhythmic passes. You are looking for a specific visual change. The floor should transform from its original gloss to a dull, white, and chalky appearance.

Tip: Keep a damp cloth in your pocket. Wipe a small section of your sanded area. If the original gloss reappears vividly when wet, you haven't gone deep enough. You need a permanent matte finish.

3. Dust Management

Sanding creates a fine powder. This powder acts as a bond-breaker if left on the floor.

• Vacuum: Use a high-CFM industrial vacuum. Sweeping only puts the dust into the air, where it will settle back onto your wet paint later.

• The Solvent Wipe: For the ultimate bond, do a final "tack-rag" wipe using a lint-free cloth and a solvent that is compatible with your new coating.

Advantages of Sanding

Because you haven't exposed the highly porous, bare concrete, you can apply your Everest Industrial Floor Paint directly to the sanded surface. The mechanical key you’ve created provides all the adhesion necessary.

You don't need to use a primer in this situation, saving money and time.

Avoiding the Patching Trap

We see many tradesmen try to spot-sand only the worn areas. As our main guide warns, this is a risk. Even if 80% of the floor looks good, the transition between "old gloss" and "sanded matte" can create visible ridges.

Conclusion

If you’re committed to the Refresh, sand the entire footprint. Uniform prep equals a uniform finish.

Sanding your previously painted concrete floor makes sure that your next coat of paint goes down just as strong as the previous coat. The extra work here saves you a lot of headache down the line.