Grinding a garage floor versus acid etching is a topic of much discussion when it comes to preparing concrete for an epoxy coating. Also known as profiling, it sometimes comes to the surprise of a homeowner when he or she finds out that you just can’t paint over the concrete to get the floor they want. Typical questions asked are “Why do I need to grind my concrete?”, “Which method is better?” or “Can’t I just acid etch it?” With these questions in mind, let’s look at why concrete has to be prepared in this manner and which method may be best for you to achieve the results that you want – grinding or acid etching?
Epoxy needs to bond mechanically to concrete in order for it to adhere properly. The problem however is that concrete in a garage is always finished to provide a smooth and even surface. This process reduces the porosity, thus requiring the surface to be profiled to expose the pores so that the epoxy coating can bond to it. If not, the epoxy will fail. Typically, this profiling is done by either grinding the surface or by acid etching to expose these pores.
Contrary to what some DIY installers believe, new concrete or concrete from a newly built home still needs to be profiled. Though it is fresh and clean without any stains, it still needs the pores of the newly troweled concrete to be opened up in order for the epoxy to bond to it.
Which profiling method is best?
When it comes to profiling concrete for an epoxy flooring, the best method is to mechanically grind the surface. The reason for this is that the profile of the surface can be controlled and the outcome will almost always provide the desired texture that you want. Depending on the manufacturer, concrete needs a texture anywhere from 60 to 120 grit sandpaper for the epoxy to adhere to. Grinding will also remove excess laitance (crumbly, powdery substance on the surface) that acid etching doesn’t always remove.
Epoxy contractors who stand behind their work will always grind the concrete knowing that their floors will not fail due to insufficient profiling.
The problem with grinding your garage floor, however, is that it’s not always feasible for the average homeowner to do so. There is the question of where to rent the equipment, how to control the dust, gouging of the surface due to inexperience, and finally cost. Sometimes it’s just not in the budget. This is why acid etching is still a popular practice. If done properly, acid etching can provide a satisfactory surface for the epoxy to adhere to.
Since acid etching is fairly easy to do, it provides an attractive alternative to grinding for many homeowners and depending on the process used, it can be downright cheap in terms of cost. The problem is that the uniformity of the etching cannot be controlled as well as grinding the concrete. If multiple areas of the surface are not tested for porosity and texture, then you run the chance of having areas of your coating fail.
Note: If you have a sealer or coating on the concrete, acid etching will not work. You will have to grind the floor to remove it.
If you are going to hire a contractor to install an epoxy coating in your garage, make sure that they mechanically grind the concrete. Any contractor that wants to acid etch is just cutting corners to reduce costs and should be suspect of providing a good quality floor. If this is a DIY job and you are fairly confident with your abilities, you can rent the proper grinding equipment necessary for the job for around $100 a day depending on your area. In most cases you should be able to grind a two or three car garage in less than a day. There is also the option of hiring someone to do it for you.
If you are installing the epoxy coating yourself and grinding is not in the budget or you are not comfortable with it, then acid etching is your answer. There are many commercially available products other than muriatic acid available that can etch your floor safely and are biodegradable at the same time.
Remember, acid etching will not remove dirt and oil from your concrete floor. It still needs to be cleaned first.
Whichever method you decide to use, if not done properly, your coating is destined to failure. Whether grinding or acid etching, it is imperative that you do it correctly and check your floor for the proper texture. There is nothing worse than spending the time to apply a nice epoxy coating only to have it fail due to the improper profiling of your concrete. If you take the time to do it correctly, you will be rewarded with a coating that will last for years.
Note: Shot blasting is another form of mechanically profiling your concrete that is widely acceptable to grinding and is used professionally by many installers. Due to the cost of renting these machines and the experience required to shot blast effectively, we did not discuss this option here.