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Grinding vs. Shot Blasting: How We Prep Before Epoxy Floor Coatings

In this article, we'll explain why our team at STRONGHOLD FLOORS utilizes mechanical diamond grinding for most concrete surface preparation. We'll also discuss the downfalls of utilizing shot blasting.
The bottom of a diamond grinder.

One of the defining factors in professionally applied garage floor coatings is the surface preparation. While DIY kits are often applied after just broom cleaning or acid etching the concrete, professional coatings are generally applied after mechanically diamond grinding or shot blasting the concrete surface (see: Concrete Surface Profiles Explained). So which surface preparation process do we use and why?

An example of unprepared concrete with massive damages.

Most of the time, we diamond grind

For most garage and commercial projects, we utilize mechanical diamond grinding for our surface preparation. 

What do we mean by grinding the floor?

Mechanical diamond grinding involves running a multi-head, rotating, walk-behind machine with diamond tooling affixed to the heads across the entire concrete floor surface. The diamonds exposed in the tooling grind away the cream layer, remove loose concrete, and leave a uniform scratch pattern with open pores which coatings can adhere to.

Why mechanically diamond grind the concrete?

  • Diamond grinding does not cause the micro fracturing in the top of the concrete floor, so it’s less destructive to the topmost remaining surface of the concrete. The micro fractures can decrease the coatings bond strength. (ASTM D7234-05 - Pull off Adhesion Strength of Coatings on Concrete).
  • Diamond grinding does not leave corn rows (blasting row lines) which can be visually apparent in the finished, decorate floor coating. If normal decorative systems are being applied, the shot blasted floor must also be mechanically diamond ground anyway to achieve a level surface prior to coating.
  • Unless applying epoxy mortar systems, our coatings don’t require the concrete surface profile (CSP) created by shot blasting.
  • If we are removing existing coatings, our diamond grinders can remove the coatings faster and with less mess than with shot blasting.
  • Our shot blaster cannot get as close to the wall as our grinders.
  • Shot blasting is noisier and creates more cleanup than grinding with our attached dust vacuums.
  • If shot blasting, we often apply additional primer and body coatings, which drives up the price of the installed system without any benefit to the customer.

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What about shot blasting?

There are some circumstances where we utilize shot blasting for surface preparation. We'll typically use this method when:

  • We need remove a greater amount of a contaminated concrete surface. Often, the surface has had years of exposure to petroleum products or animal fats (cooking oils and grease).
  • The floor coating system we are applying requires a CSP of 3 or higher. The most common reason being we are installing an epoxy mortar or urethane mortar system – typical in food services and commercial kitchens.
Learn More about Surface Preparation

To learn more about surface preparation for floor coatings, please see:

Diamond grinding a garage floor before applying the epoxy coatings.The author, Mike Mincemoyer, is the founder and President of STRONGHOLD FLOORS.  Mike attended training by HTC and SASE, manufacturers of some of the diamond grinders and shot blasters used by installation teams of STRONGHOLD FLOORS.