There are a few ways to remove paint from concrete. We all know what a time consuming headache removing paint can be. So I'm guessing the easiest and quickest method is what you're looking for.
It's not as bad as carpet glue and other adhesives, but still a pain. I wish I could give you one simple solution, but I haven't found one myself that works for all painted concrete surfaces. Before deciding which method to use, there are several factors to consider.
Stripping paint with a high power pressure washer is hands down the best method for exterior surfaces. You might get a little wet, but the equipment is easy to use and relatively inexpensive to rent. 4000-5000 psi will strip most coatings. It is strong enough to scar the concrete, so be careful not to make the stream to narrow. Fan it out at least 2 inches or so.
Unless it's a big warehouse or garage, power washing is out of the question. Let's take a look at options for interior floors.
A shotblast machine will strip concrete of most coatings as well as the surface of the concrete itself. It works like a sandblaster but shoots tiny metal beads that are recollected. Many of the beads get away so it is important to have a magnet to easily pick them up. A vacuum is attached for debris and dust collection which is essential indoors.
Besides paint removal, shotblasting is also good for creating a floor profile that is fitting for any future coatings and overlays. You must be careful and move along at a steady pace. It will dig a hole if you pause too long.
The big drawback to shotblasting is the difficulty in locating a machine and the cost of rental. By the time you rent the equipment and buy the bags of shot, you can easily be in it for over $500 a day. See the shotblasting video to get a better idea of the process.
High speed floor grinders with diamond wheels will remove any paint or coating from concrete. Depending on how thick the coating is, it may be fairly quick or it can be a lengthy process.
The key here is dust collection. Grinders can make a huge mess in a matter of seconds, so it's important to have a dust shroud and vacuum connected.
If you keep the grinder moving, you can avoid leaving gouges and scars while creating a smooth but porous surface.
Grinding is also better for soft coatings, glues, and adhesives that shotblasting won't remove.
Check out the removing paint from concrete with a grinder video for some more insight.
Using stripping agents to remove paint from concrete is still the most common method. There are several types of stripping agents and knowing the type of paint and even the brand will help to decide which one to use. You can contact the manufacturer of the paint (if you know it) for recommendations.
It would be great if there was a chemical that could just melt the paint away, but unfortunately you still have to do most of the work. Once the paint is softened and loose, you need to scrape it up.
The problem with most chemical strippers is toxicity. They can be very dangerous without good ventilation and harmful to the environment. Take all precautions including respirators, covering all your skin and eyes, and even turning off furnaces, boilers, and pilot lights.
There are some new, soy based products that will remove paint from concrete or any surface. These strippers are low odor, environmentally safe, and easy to use. They come in a gel form. Just spread the gel on, let it sit for while, and the paint will easily scrape right up. Watch this soy gel paint removal video to see how it's done. The key is to be patient and let the gel do the work, not you.
I've only been able to find the soy based products at contractor supply stores and online. They really do work and are completely safe. They say you can eat the stuff and it won't hurt you, but I'll just have to take their word for it. The nice thing about the gel is, when you scrape it up, you can move over to the next area and spread it again. You can do this two or three times unless there are multiple coats of paint to remove. So you don't have buy enough to cover the entire surface, just reuse it as you go.