Grinding not going well - advice needed (possibly urgent!)

[cookiemcsnax]

Hi all,
Grinding my garage to prep for epoxy. I started out yesterday with angle grinder + diamond cup, my dust shroud + vacuum proved utterly useless in collecting much of the dust, and I decided to rent a dual-disc Edco, which I've been using pretty much the whole of today. I've now made 7 passes over the floor (slow ones too), but there's still a bunch of darker spots. I'm rationalizing that these are just part of the concrete, but I know in all likelihood they're spots that haven't been ground properly yet.

I think the problem lies in the Edco being electric and thus having no balls (Sunbelt didn't have the 11-hp gas one, and I think the motor on this is 1.5 hp or whatever fits in a normal 15A circuit), but at this point I've spent 10 hours grinding and am wondering if I can get away with what I have.

This is somewhat urgent because if I need to grind more I need to make a decision whether to keep the Edco one more day.

Do I need to keep grinding? If I put down epoxy now, am I going to get hot tire liftup or is it just that it'll not last as long?

Some of the dark spots feel a bit smoother and like a little depression, which obviously is not good. Should I take the angle grinder and just grind these spots down? Or are they small enough that I don't have to worry about it?

Thanks for any advice!

Pictures:

 

[5Cent]

I had the same issue. Those are low lying areas. As you said, you have the following options:

1.) Use hand grinder and just touch up those areas.
2.) Use big electric grinder and continue to grind down until it's all the same level

Do you plan on doing an acid etch after the grinding? By looking at the pictures, it looks like you have atleast ruffed up the surface of the spots, just don't have it down to the same depth as the rest of the floor. It is completely up to you with what you want to do, but I am going to say it will be fine.

I used acid etching after I ground the floor to really open it up, then washed it, dried it then epoxied. It's still holding up great!

 

[cookiemcsnax]

I do have acid handy, because originally I was going to etch, so I could do that. I'm pretty sure my floor was sealed, because when I put water on it it didn't sink in immediately, but perhaps if I've gotten the spots already scuffed up a bit it's taken off some of the sealer and acid should still work. The concrete's about 30 years old, so no surprise there are some low spots.

Decided not to keep the grinder a second day, but I still have it until about 2 PM today so I could do a bit more grinding. There are some fairly big splotches there that I think I want to go over with the big grinder because it'll take a while with the angle (also much less dust).

 

[AlphaGarage]

If there is sealer there's a good chance the acid will not remove it. On a low spot the grinder may not have hit, and the sealer may not remove or penetrate it, so adhesion could be a problem.

If you have a hand held angle grinder try hitting those low spots before you acid etch.

 

[5Cent]

Here's a thread showing my floor....done with a 4.5" grinder....don't be afraid to get into those spots!

http://www.garagejournal.com/forum/showthread.php?t=23761&highlight=grinding

 

[FunfDreisig]

FWIW you can tell how deep these low spots are by laying a straight edge (e.g. a 4ft level) across them and then trying to push various thickness of paper, thin cardboard (e.g. a coke box), thin sheet metal, etc.. The truly **** would use an old valve adjustment feeler gauge.

The reason to measure them is that in order to completely remove the deepest low spot you would need to remove that thickness EVERYWHERE else. This might give you incentive to just rough them up a bit and leave them a little lower than the rest of the slab.

Funf Dreisig

 

[cookiemcsnax]

^^^ Yeah, that's why I went with the grinding only the spots, because I didn't want to lower the entire floor to the depth of the lowest spot.

Well, I went over the low spots with the handheld, or at least the big ones (some of the little ones I decided it wasn't worth worrying about). So now I have low spots that are ground, and it's noticeably rougher than the Edco was. However, hopefully I have enough IntegraFlex left after the expansion joints to fill in some of these, and if not perhaps the Bondtite/Liquatile are thick enough to cover them. (They're not that noticeable when standing, it's more that when you're kneeling on the floor you can clearly see the difference between the ground spots and the rest of the floor. I tried to feather the edges as much as possible so it's not clearly discernible gouges in the floor).

Anyone have an opinion on concrete patcher? I've got a tub of DAP Ready-Mixed Concrete Patch (crystalline silica, calcium carbonate, clay, ethylene glycol, vinyl acetate & formaldehyde). Fred, I know Wolverine doesn't recommend putting in siliconized patchers because the Bondtite won't bond as well, but I'm not sure if this qualifies. I'd rather use this than the Bondtite+sand because it's cheaper and also ready-mixed.

Also, since I've ground the spots, how much am I going to suffer if I don't acid etch? (Kinda itching to get the epoxy down, although I know that if I skimp on prep I'm going to regret it later).

 

[AlphaGarage]

If the floor's been ground and roughed up nicely you can proceed with putting down that prime, no need to acid etch.

The reason you want to avoid silicon is because silicon contamination often leads to "fish eyes" in epoxy coatings. These are visible round imperfections that look like, well... fish eyes.

Just spoke with a painting contractor who had some fish eyes pop up on a new floor. Couldn't figure out where they came from. After looking low and high he spotted an air conditioning duct on the ceiling, right over the fish eyes. Case closed.

 

[wifehatescar]

When you guys use a handheld to rough up the low spots to remove the dark spots, what kind of blade/stone to you recommend? And it is better with an angle grinder or a high speed rotary?

 

[Viper966]

im having the EXACT same problem right now, except i have a bunch more low spots...

im on day 2 of grinding with a hand held... really getting sick of it...

most of my low spots are about half the size of a penny... do i really need to get ALL Of them up or if i acid etch afterwards will i be ok with the epoxy not lifting?

im using an OCC kit with the 100% solids topcoat...

 

[v7guy]

I'm getting ready to do this and have been reading a lot about it. I would go ahead and use a handheld and make sure everything is roughed up even at the cost of a low spot. My thinking being that you want the best adhesion everywhere. How irritated would you be if a year from now you had a half dozen penny sized spots that lifted?
It ***** right now but in the long run you'll be happier you spent more time on prep.

 

[nate379]

Why are you guys even grinding the floor, is it really that rough?

Mine was nice and smooth so I just acid etched it.

 

[v7guy]

to clean off any sealer or prior coating mostly.

 

[Jaguar Fan]

im having the EXACT same problem right now, except i have a bunch more low spots...

im on day 2 of grinding with a hand held... really getting sick of it...

most of my low spots are about half the size of a penny... do i really need to get ALL Of them up or if i acid etch afterwards will i be ok with the epoxy not lifting?

im using an OCC kit with the 100% solids topcoat...

Can you post some pictures?

 

[Viper966]

ill post some pictures tommorow... i went out and hit up most of the fllor with teh hand grinder... its slow going but its coming out fine.... takes about 3-4 hours to do each 1/4 of my garage... dont know why i even bothered with the floor grinder, as ive pretty muuch already done the entire floor with a hand grinder

 

[5Cent]

ill post some pictures tommorow... i went out and hit up most of the fllor with teh hand grinder... its slow going but its coming out fine.... takes about 3-4 hours to do each 1/4 of my garage... dont know why i even bothered with the floor grinder, as ive pretty muuch already done the entire floor with a hand grinder

I completely agree. I could not justify renting one and wanted a closeup/personal relationship with the surface before I put down my epoxy. It takes a few days and the dust is absolutely crazy, but it's well worth it