Stain help

[pierre]

Stain help & rustbullet

After spending many moons grinding with diamond cups, I got to the point where I'm ready to wash away the dust and finally paint one half of the garage. Everything is a uniform bright white after breaking through the top layer of glaze. Yay... thought I was home free.

As I was grinding I was testing random spots and it seemed to absorb water fine. Once I got the pressure washer out and did the area I got a surprise. There's trails most likely left by tires that didn't darken as much as surrounding areas. Water didn't bead up here and it did get slightly dark, but clearly not as much as the rest of the slab.

I hit it with a direct blast from the washer to the point I started getting fine spiderweb cracks. Straight muriatic acid (well, directly from the jug at whatever concentration it comes in) didn't do it either. Additional grinding didn't help. Chip away like 1/4" deep and fill? That will be a horrible mess, and whose to say how deep it goes? Risk it and paint (rustbullet) over? Sigh... disappointed and frustrated after all that work knowing it may still turn out bad.

 

[Jaguar Fan]

If it darkens - but not as much as surrounding areas -- it sounds OK. Primer should be able to penetrate. When you say "most likely left by tires" -- were you parking on the concrete AFTER grinding? Without, say, cardboard under the path of the tires?

You might try a stiff brush and some kitchen sink dishwashing soap. I wouldn't use any degreaser at this point, because many are petroleum based, causing water to bead even more.

I do not think there is any reason to "Chip away like 1/4" deep and fill".

Can you post a picture or two?

 

[pierre]

I've attached two files - one of what a dry ground area looks like, and one of wet concrete showing a spot. I bought the house (30+ years old) recently and have never parked in the garage. The previous owners did but of course that was all pre-grinding.

I came upon a post mentioning using lye to clean spots on concrete. Remembering I had some heavy duty oven cleaner that was lye based, I grabbed the can and went at it. Actually made reasonable progress with it - the tire trails have mostly disappeared and it's just random spots. I went ahead and started painting. If it does peel I'll deal with the deeper grinding and filling then.

Worked myself into a pickle. I painted the half closest to the driveway first. I need to finish grinding the other half then washing it down before painting but that means water will run onto the painted half. I probably should let it dry the full 72 hours before I get it wet.

Incidentally - what happens if you paint in sunlight? I just read the directions to say avoid doing it but I didn't have a choice if I wanted to meet the recoat window.