New finish over old

[Jack T.]

After putting up with a terrible garage floor in the house we moved into 1-1/2 years ago, I'm planning to take care of it once warm weather is here to stay. I suspect the existing finish was regular floor paint, judging from how it's completely lifted where hot tires have run on it. And that would be in keeping with the quality of some of the other 'improvements' done around here. The rest of it looks ok, just old and stained. The garage is 28 x 25.

I'd prefer to use a good two-part epoxy system, but I don't want to have to completely remove the existing paint on the entire floor. Will it be enough to rough up the existing paint, or does epoxy have to go on bare concrete? And will it make a difference depending on if the existing paint is latex or oil-based? If the epoxy won't work, I'd rather save the time and money and just topcoat with a better grade of paint.

I've been searching this forum and other sites for a similar problem but haven't come across a definitive answer. I'm hoping someone here has it. Thanks for any advice you can provide.

 

[AlphaGarage]

Jack:

Actually your search has resulted in the definitive answer, and that is that there is none. No manufacturer is able to test their coating for compatibility with all other coatings, so it's difficult to predict with certainty that there will be good adhesion. Even if there is good adhesion between the old coating and the new one, it's impossible to say that the existing coating will continue to adhere to the substrate.

Now, that being said, if the remaining coating hasn't exhibited any recent lifting, that is pieces of paint flaking off, and it's only wearing down, you could get lucky. Pick a few areas, take a knife and score the paint, then stick down pieces of duct tape over the scratches and yank them off, if no paint comes up there's a good chance the remaining paint won't be lifting off after an over coat. Rough up the entire floor with 60 grit paper, clean well, and take a shot. Just understand that you're traveling in uncharted waters and if the coating fails you're on your own.

But the best way to approach your floor would be to remove the all existing coatings. There are a couple of ways to do that, mechanically and chemically, with mechanically being the most reliable method. If you choose mechanical removal there are two main methods, grinding or shot blasting, of the two shot blasting is probably the choice to go with. About the only downside is finding the shot blast machine, tool rental yards like USRentals and Sunbelt Rentals the first place to look, some Lowes and Home Depot rent them also. Look for an 8” or 9” one that works with whatever power supply you have, a couple of the more popular models are the Blastrac 1-8DEZ or the 1-9DEZ. Prices are all over the place, from $100 to $300 for the same set-up.

Fact is these aren't that well known of outside of pro contractor circles, and they're usually sitting around in the rental yard on weekends. So if you find one, and plan on doing a weekend job, try bargain on the rate.



As with any piece of gear you're unfamiliar with, try it out in an inconspicuous area first.

If you can’t source a shot blaster, a floor grinder is the next choice. They’re usually cheaper to rent, and easier to find, and sometime they even produce better results. There are several types of grinders and grinding medium so ask the rental center for the best set-up to handle your floor.

Either way - grinding or shot blasting - neither are that costly or difficult considering the other material and time resources required.

There really isn't a "better paint" option, paints just can not handle the task.

 

[Jack T.]

Hey, thanks much for the response and detailed info. I'm especially encouraged that you did not say "epoxy will definitely not work over existing paint". Since the areas where we pull our cars in is already down to bare concrete, I should at least be getting the best bond where it's really needed.

There is a rental store five minutes away, so I planned on going to them to see what they have. I appreciate the insight into the different types of equipment. I remember using a Tennant grinder at the steel mill to get grease off the floor of the machine shop 40 years ago.

Jack

Jack:

Actually your search has resulted in the definitive answer, and that is that there is none. No manufacturer is able to test their coating for compatibility with all other coatings, so it's difficult to predict with certainty that there will be good adhesion. Even if there is good adhesion between the old coating and the new one, it's impossible to say that the existing coating will continue to adhere to the substrate.

Now, that being said, if the remaining coating hasn't exhibited any recent lifting, that is pieces of paint flaking off, and it's only wearing down, you could get lucky. Pick a few areas, take a knife and score the paint, then stick down pieces of duct tape over the scratches and yank them off, if no paint comes up there's a good chance the remaining paint won't be lifting off after an over coat. Rough up the entire floor with 60 grit paper, clean well, and take a shot. Just understand that you're traveling in uncharted waters and if the coating fails you're on your own.

 

[thegarageguy]

I'm especially encouraged that you did not say "epoxy will definitely not work over existing paint".

Jack

Hey Jack, understand that "paint" just lays on top of your surface. Epoxies (with a proper prepped concrete) penetrate and chemically and mechanically bond.

So in essence epoxies will not work over "paint"

In life we learn that taking shortcut usually ends with problems along the way. This is a perfect example of this. If you are going to rent a machine, do the whole damn floor. Properly prep your floor and coat it by manufacturers specs. Any shortcut inbetween will cause failure. Do it once, do it right and enjoy.

 

[krooser]

You can use an orbital sander to remove the old floor coating. I rented one when I was prepping my floor for my epoxy. I had to remove all the fiber mesh particles that were on the surface. The sander worked remarkably well... I only used a couple 80 grit sanding discs to do the 30X36' area.

 

[nissan_crawler]

I would remove it all. If you put epoxy over it, and it starts peeling up again, you have twice the mess and cost.

 

[WolverineCoatings]

Hey Jack, understand that "paint" just lays on top of your surface. Epoxies (with a proper prepped concrete) penetrate and chemically and mechanically bond.

Epoxies DO NOT chemically bond to concrete unless they are grafted to do so. Very few of us (manufacturers) actually make products that will do this. Our BondTite 1101 Primer is chemically grafted to form a physical bond like other epoxies but will also chemically bond to the concrete. Our LiquaTile 1184 will NOT chemically bond to concrete but will chemically bond to the BondTite 1101 primer.

A chemical bond is MUCH stronger than a physical bond and when you combine chemical bonding and physical bonding you get the best bond possible.

I would guess that less than 5% of products you will get your hands on are modified to chemically bond to concrete.