Why dry grinding does not work as a surface prep technique for urethane concrete countertop sealers

I’m often asked whether dry grinding the concrete can be used to prepare the concrete surface for Omega Concrete Countertop SealerTM. The answer is NO.

Dry grinding is not the same as wet grinding, even with the same grit. Dry grinding/polishing tends to burnish the concrete surface, making it too smooth for good sealer adhesion. This applies to any coating sealer, not just Omega.

Here’s Why You Can’t Dry Grind

The dry polishing process creates concrete cuttings which don’t get flushed away like they do with wet polishing. Because the powdery cuttings tend to remain under the polishing head longer, they break down and act as finer polishing media. This is why dry polishing is more effective than wet polishing when trying to polish concrete to a mirror shine, because the concrete cuttings themselves act as a finer polishing compound than the diamond pad that created them.

Additionally, the super-fine cuttings get forced into the open concrete surface pores, contaminating the surface, and that can cause adhesion failure.

These two characteristics are the major drawbacks of dry polishing, and why dry polishing is not permitted as suitable surface preparation for Omega (nor recommended for any urethane coating sealer).

Polishing Your Countertop | Grinding Surfaces

 

The following two videos show how variable your concrete can be depending solely on the surface preparation technique used. The first video also shows two possible surface preparation techniques for Omega, which can be used on freshly cast concrete or on concrete that has been dry ground.

Introduction and How to Wet Process:

The video shows:

  • Wet hand sanding with 400 grit wet/dry sandpaper, and a spray bottle with water. This will maintain a cream finish.
  • Wet diamond honing with 100 or 200 grit diamond pad on a random orbit sander, and a spray bottle with water. This will likely maintain a cream finish, unless your concrete is soft.

You can also use a traditional wet polisher to expose sand grains for a “salt and pepper” finish or to expose decorative aggregate, stopping at 200 grit (or a maximum of 400 grit).

If you can’t wet sand or hone as shown in the video below, use the muriatic acid etching method. The Omega instructions you receive after purchase contain full details of this method.

Please note that in all cases, the concrete must be cleaned with water and acetone after completing your chosen surface preparation technique. Again, the Omega instructions you receive after purchase contain full details.

Why Dry Grinding Does Not Work:

What to Do if You Already Dry Ground the Surface

The first video above shows two possible techniques you can use to fix a dry ground surface. Also please see this article about how to fix a dry ground surface.

Note that in some cases, wet sanding/honing by hand will change the appearance of the concrete. If you were trying to get a cream finish, you might sand it off and expose sand grains, resulting what I call and salt and pepper finish. If you acid stained or glazed, you will likely remove the coloring.

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