How Concrete Is Ground and Prepped for a Coating

How concrete is ground and prepped for a floor coating: grinding versus acid etching, step by step, with what each method leaves behind for the coating to grip.

Prep decides whether a coating lasts

Every installer in the most-viewed garage coating videos says some version of the same thing: the coating is only as good as the surface under it. Preparation opens the concrete so the coating can grip it, removes anything that would block the bond, and fixes damage that would show through. There are two main ways to open the surface: diamond grinding and acid etching. This post walks through both, step by step.

Why the surface has to be opened

LearnCoatings explains that a coating needs both a mechanical bond and a chemical bond to the concrete. Epoxy Flooring Co, in a video with more than 120,000 views, says the same and adds that the best results come from combining the two. A smooth, sealed or dirty slab gives the coating nothing to hold on to mechanically, so it relies on chemistry alone.

Step 1: empty and inspect the garage

Lowe's Home Improvement, in a how-to with more than 600,000 views, starts by removing everything that touches the floor and inspecting the concrete for cracks, oil stains and other imperfections. This is also when to check for a sealer. This Old House, in its widely viewed segment, sprays water on the floor: where it soaks in, the concrete is open; where it beads or pulls away, a sealer or contamination is present.

Step 2: degrease problem areas

Oil and grease have to come off before any opening method. This Old House spot-degreases areas where water pulled away. Lowe's scrubs degreaser into stained areas, rinses and squeegees the water out, repeating for heavy stains.

Method A: acid etching, step by step

For acid etching, Lowe's pre-wets the floor, applies the acid solution from its kit with a plastic watering can, scrubs it in, keeps the floor damp, leaves it for at least 15 minutes, then rinses thoroughly and lets the floor dry for 24 to 48 hours. This Old House uses a plastic watering can because acid reacts with metal, and vacuums the gritty residue after rinsing. Gloves, eye protection and rubber boots are worn throughout.

What etching leaves behind

Epoxy Flooring Co etched one section of a garage side by side with a ground section. He says the acid wash cleaned the surface but left far less profile than grinding, and he points out acid residue that has to be rinsed two or three times, sometimes with scrubbing, or the coating may peel later. He allows about three days for rinsing and drying when he etches.

Method B: diamond grinding, step by step

Grinding uses a machine with diamond tooling to remove the top layer of concrete. Everyday Home Repairs, in a video with more than 300,000 views, explains that a dust shroud and a shop vacuum with a fine-particle or HEPA filter and a bag are essential to keep dust under control and maintain suction. Mike Day grinds with a diamond tool connected to a vacuum and notes that a diamond brush on a rented floor buffer is another way to prep.

What grinding leaves behind

Epoxy Flooring Co says his ground section was clean, exposed fresh concrete and removed most stains in one pass, and that he could coat it the same day. Everyday Home Repairs prefers grinding because it keeps the slab dry instead of soaking it with water during degreasing and etching.

Step 3: repair cracks and pits

After opening the surface, cracks and pits are filled. Mike Day fixes cracks and divots with a patch material and grinds the repairs smooth. Our post on fixing cracks and spalls covers this in more detail.

Step 4: remove all dust

Mike Day vacuums and then wipes the floor with denatured alcohol to pick up remaining dust. Lowe's re-cleans just before coating so the floor is dust-free.

Step 5: prime

A primer goes on first. Mike Day says his primer prepares the concrete and blocks moisture that might come up through the slab. LearnCoatings notes that primers penetrate, capture micro dust and seal the surface to reduce bubbles.

Which method should you choose?

Grinding gives a stronger mechanical profile and keeps the slab dry. Etching is more accessible for DIY and needs careful rinsing and drying. Epoxy Flooring Co suggests that a capable homeowner rent a grinder for a better result in less time.

Safety notes for both methods

Acid needs eye, skin and foot protection. Grinding needs dust control and hearing protection. Follow equipment and product instructions.

FAQ: Does a new slab need prep?

Yes. New slabs often have a smooth surface layer or a cure-and-seal product that has to be removed.

FAQ: Can I just pressure wash?

Pressure washing cleans but does not create the profile a coating needs.

Shot blasting: a third option

Some crews use a shot blaster instead of, or along with, a grinder. Leggari Products, in a winter garage project, has the main floor shot blasted and the edges ground by hand to get past the smooth top layer, which the installer calls the cream, and create a porous profile. Leggari's training video describes a floor shot blasted to make it really porous before a thin seal coat.

Edges and corners

Large grinders cannot reach tight to walls. Everyday Home Repairs notes that a small 4.5-inch angle grinder with a shroud is useful for tighter spaces even when you rent a large floor grinder. Edges that are skipped are a common place for coatings to lift.

See how we prep your floor

Austin Epoxy Flooring Pro grinds and preps floors in Austin and Georgetown. Call (512) 325-5434, open 24 hours, 7 days a week.

Source note: Steps and times are as shown in the credited videos for their specific products. Follow your product's instructions.

Need an epoxy-floor evaluation?
Call 512-325-5434 (open 24 hours, 7 days a week) or request a free estimate.

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