There's basically five ways you can prep your garage floor for an epoxy coating.
I'll show you how to prepare your concrete floor using each method and I'll tell you which one I think is the best way to prep concrete for epoxy coatings.
Lightly grinding the concrete, in my opinion, is the best method to prepare concrete for an epoxy coating. (Like in both the pictures above)
Using a 7" or 5" hand grinder or a walk behind floor grinder with diamond grinding attachments will clean and profile the concrete at the same time. (Using attached vacuums of course)
An epoxy coating needs a "rough" surface to adhere to properly. We call that "surface profile" for those of us in the coating business.
Your concrete floor needs a surface profile of about 80 grit sandpaper so the epoxy coating will have something to bond to. Otherwise there's a very good chance it'll peel off in places.
Grinding the concrete is one of the best (and quickest) ways to achieve the proper surface profile. It's also a great way to remove existing paint or sealers on your floor.
An added benefit of grinding the concrete is it keeps the concrete dry so you can coat the floor with epoxy the same day. (Unlike washing, etching & rinsing where you have to let the concrete "dry out" for 24 - 48 hours before coating it.
The video below shows us grinding a garage floor to prep it for a new epoxy coating.
The hand grinders and walk behind grinder can be rented at most tool rental centers if you need one.
Learn how to install an epoxy flake garage floor coating from me. I made a video training course that teaches you step by step how to professionally install an epoxy coating to your garage floor.
The Diamabrush concrete prep tool was made specifically for cleaning concrete floors and concrete prep for epoxy coatings.
It'll mechanically etch and prepare bare concrete similar to the way grinding does. It also keeps the concrete "dry" so you can begin your epoxy coating the same day as the prep.
The Diamabrush attachment comes in two sizes. One can be used on a hand grinder and the other on a 17" floor buffer for faster prep time.
Check out the video below to see it in action.
Shot blasting a concrete floor for prep before an epoxy coating is the preferred method by a lot of professional epoxy coating contractors.
A shot blaster will remove coatings, sealers, paint and profile the concrete all in one pass. Compared to grinding, it leaves behind very little dust as it prepares the concrete for epoxy.
Some Pro's consider it a better prep tool than a floor grinder. The trouble is finding one to use. Most tool rental stores don't have this machine to rent.
If you do have access to one, you may want to consider this method over grinding to prep your floor for an epoxy coating.
See the video below that shows how a shot blaster prep's concrete before a coating is applied.
Using a concrete etching & cleaning solution like Eco-Etch Pro is another way to prep concrete for an epoxy coating.
I know some of you may not be able to use methods 1, 2, or 3 so I'm including this method although I don't personally use it or recommend it.
This method of prep will clean and etch the concrete but it does (or doesn't do) a couple things I don't like.
WHAT IT DOES DO: Etching your concrete with this product will clean it and give you somewhat of a surface profile (but not enough in my opinion) to really give the epoxy something to bond to long term.
WHAT IT DOESN'T DO: Etching with this doesn't keep the concrete DRY. Epoxy coatings don't like moisture. You'll have to let your floor dry for at least a couple days if not more.
Concrete soaks up water like a sponge. Even though the surface looks dry, inside it's capillaries there could still be moisture. As that moisture evaporates, it tries to escape out through the surface as a vapor.
When the pressure of the moisture vapor rising up through the concrete exceeds the "bonding" strength of the epoxy, the epoxy starts to bubble and peel off the surface.
When is the concrete completely "dry" after washing, etching, and rinsing? It's hard to say really. Temperature and humidity both effect the drying conditions.
Here's a good article on why acid etching isn't recommended for prep before an epoxy coating.
PRO TIP: All the epoxy flooring contractors I know, including myself, don't ever use this method of prep before we install an epoxy coating for our customers.
Etching concrete doesn't profile (roughen) the surface enough to create a good bond. Especially under a vehicle's tires. Use this method at your own risk.
In my professional opinion, I would tell you no. But there may be a solution if you can't etch or grind.
Epoxy2U.com has a concrete primer called Crazy Bond. It's a concrete primer and prep system all in one.
It bonds to virtually any surface, including smooth troweled concrete, sealed concrete, and painted concrete.
They made it for areas where prep and grinding is not allowed like Pharmaceutical plants and commercial kitchens. But you can use it on your garage floor if none of the above methods are possible.
It's also good to use if you have oil spills on your concrete floor. Although I would clean as much oil off the surface with their oil cleaner as possible before coating.
You would clean the concrete the best you can (scrape and vacuum up any dirt & debris), then apply this coating before doing your epoxy flake coating.
Use this method for concrete prep only if none of the other methods of prep are possible.
If you do use Crazy Bond as a primer/prep method, I would use Epoxy2U.com's epoxy coating system to finish your floor also.