painting concrete

I plan to paint my garage floor tomorrow with a kit made by Rust-O-Leum. I painted it ten years ago with an epoxy paint, and I've scraped all that is loose enough to scrape. The kit includes a packet of concrete etch(citric acid). I don't remember using it when I painted the floor before. Is the concrete etch necessary where I'm painting over the old epoxy paint?
Butch

I can't imagine that the acid will etch epoxy paint. I also, painted my floor with the 2 part epoxy and I have zero flaking or loose. The stuff has with stood every thing I could throw at it for the last 20 years. No, don't etch, clean it and paint it. Or, contact the manufacturer of the paint and ask them.

running a sander over it will really help. Coatings need a clean surface with a profile ( " tooth if you will) to bond correctly. If what you have left is stuck from 10 years ago is still well adhered take advantage of that and overcoat it with the new. With epoxies, they can get so hard that the next coat won't adhere ( intercept delamination) so you should sand to open up that coating window - dull finish is the next coats best friend

The acid will do nothing to the existing coating. It is used when you are going over bare concrete to provide a profile for the first time the concrete is coated.

Been doing this coating stuff for over 20 years and have witnessed everything that can go wrong

I applied a Sherman Williams 2 part epoxy product on a 70 plus year old floor. It was a mess; dirty, greasy. cracked with multi coatings of paint. Spent much more time and money in prep than putting the actual coating down. Well worth the effort.

The prep is really important. Follow the MFR's instructions closely. Concrete is not the easiest material to get coatings to bond to. I did one of these for a customer, cleaned, etched an otherwise ideal slab, that no one had been doing mechanical work on, so their was no oil or other similar residue. I figured it would last for what it was, darned thing peeled up where the vehicle tires ride on it. I followed the instructions to the letter, it was a home depot material, I forget the name now.

I've also managed huge installations of real epoxy coatings onto concrete floors, in correctional facilities, the prep was just as important, but this material was more than likely never coming up, there's a big difference in commercial and residential coatings. The biggest issue with those large installations was getting the non-slip part of it just right, the state agency fussed about that until they got what was considered ideal. The prep on this was glass beading with a machine that was built to do floors, without it, the epoxy could delaminate from the substrate, (concrete)

If the slab is loaded with oils, stains of unknown nature, this could be short lived, but you did say it was coated previously, so the new material needs to bond to that or be compatible with it if it remains. Research it thoroughly before you buy the materials and do the work, it may not be feasible if it fails and comes up because it will not adhere.

The etch is important but cleaning the oil and dirt off first is probably more important. I would get some purple power or krud kutter and a power washer and thoroughly wash the floor first.

When you paint the floor if you use sprinkle flakes in it hold the container about 4' off the floor when you do it. It's easier to get more uniform. Then when it is dry follow with a clear coat.

Thanks for all the replies. I appreciate the advice, and I, too, was of the opinion that the etch wouldn't affect the old coating.